We have shown that hypoxia reduces plasma insulin, which correlates with corticotropin-releasing hormone (CRH) receptor 1 (CRHR1) in rats, but the mechanism remains unclear. Here, we report that hypobaric hypoxia at an altitude of 5,000 m for 8 h enhances rat plasma CRH, corticosterone, and glucose levels, whereas the plasma insulin and pancreatic ATP/ADP ratio is reduced. In islets cultured under normoxia, CRH stimulated insulin release in a glucose- and CRH-level–dependent manner by activating CRHR1 and thus the cAMP-dependent protein kinase pathway and calcium influx through L-type channels. In islets cultured under hypoxia, however, the insulinotropic effect of CRH was inactivated due to reduced ATP and cAMP and coincident loss of intracellular calcium oscillations. Serum and glucocorticoid-inducible kinase 1 (SGK1) also played an inhibitory role. In human volunteers rapidly ascended to 3,860 m, plasma CRH and glucose levels increased without a detectable change in plasma insulin. By contrast, volunteers with acute mountain sickness (AMS) exhibited a marked decrease in HOMA insulin sensitivity (HOMA-IS) and enhanced plasma CRH. In conclusion, hypoxia may attenuate the CRH-insulinotropic effect by reducing cellular ATP/ADP ratio, cAMP and calcium influx, and upregulated SGK1. Hypoxia may not affect HOMA-IS in healthy volunteers but reduces it in AMS volunteers.

To enjoy social activities, millions of people travel to high altitudes every year. High-altitude hypoxia often induces dysfunction and illness, particularly acute mountain sickness (AMS) (1). During the construction of the Qinghai-Tibet railway (at altitudes of 3,000–5,000 m) in China, >100,000 construction workers were involved, and 51% of them developed AMS (2). Moreover, since the railway began service, >10 million travelers have visited the Tibet region in 2012, of whom 31% developed AMS despite traveling with an oxygen supply on the train (3). Increasing evidence in both humans and animals suggests that exposure to either high-altitude or hypobaric hypoxia influences plasma insulin levels and glucose homeostasis, depending on the oxygen level and duration of exposure (49). We previously showed that subacute hypoxia at an altitude of 5,000 m for 5 days reduces plasma insulin in rats, and this effect is blocked by a corticotropin-releasing hormone (CRH) receptor 1 (CRHR1) antagonist in vivo (10). However, the underlying mechanisms have not been clearly addressed.

Insulin, the unique hypoglycemic hormone, plays a crucial role in maintaining glucose sensing in pancreatic β-cells and regulating glucose uptake in a variety of tissues and cells during health and disease (11,12). Apart from glucose, many neural and endocrine hormones regulate pancreatic insulin release (13). In particular, CRH is the key regulator of the hypothalamic-pituitary-adrenal (HPA) axis; is activated by a variety of stressors, including hypoxia; and mediates a variety of neural and endocrine response to stress (14). Studies have shown that CRHR1 exists in human, mouse, and rat islets (15,16) and that CRH enhances calcium influx (17), increases insulin content, and elevates insulin secretion in a glucose-dependent manner in cultured islets (15,16,18). Furthermore, CRH modulates development, proliferation, and antiapoptosis in islets (15,16,19). These findings suggest that CRH and CRHR1 play significant roles in regulating insulin release under normal conditions. We previously showed that hypobaric hypoxia results in upregulated CRH in the paraventricular nucleus and corticosterone (CORT) in the plasma of rats (20,21), which was associated with reduced plasma insulin (reversed by a CRHR1 antagonist) and glucose levels in vivo (10).

In the current study, we address the mechanisms by which CRHR1 mediates insulin secretion and glucose homeostasis during hypoxia. To achieve this goal, we completed comparative studies on rats under hypobaric hypoxia and on humans following a rapid ascent to the Tibetan plateau. Under hypoxia, the cell metabolic state switches from aerobic metabolism toward anaerobic glycolysis, which may lead to reduced ATP production and plasma insulin levels (10). In the present article, the data suggest that a fall in the ATP/ADP ratio and loss of cAMP signaling capacity during hypoxia attenuate voltage-gated calcium influx and, thus, inactivate insulinotropic action of CRH.

Animals

Male Sprague-Dawley rats weighing 200–220 g were purchased from the Laboratory Animal Center of Zhejiang Province, China (certification no. SCXK2008-0033), and maintained in a 12-h light/dark cycle (lights on at 0600 h) at 20 ± 2°C with food and water ad libitum. Rats were adapted for 1 week before experiments. All animal experiments were approved by the Animal Care and Use Committee of the School of Medicine, Zhejiang University.

Islet Isolation

Pancreatic islets were isolated by collagenase digestion from rats as previously described (22). Intact islets were cultured in RPMI 1640 medium (containing 8.3 mmol/L glucose) supplemented with 10% FBS, 10 mmol/L HEPES, and penicillin/streptomycin (Invitrogen, Carlsbad, CA) at 37°C under 5% CO2 and 21% O2 for overnight recovery before experiments.

Human Hypoxia Exposure

Sixty-seven healthy male volunteers (18–23 years old) were recruited in Chengdu, China, at 540 m altitude, as basal lowland control subjects. They were informed about the objectives of the study and agreed to the experimental protocols. All studies were approved by the Ethics Committee of the Third Military Medical University. The volunteers’ oxygen saturation (SpO2) was determined with a finger pulse oximeter. Fasting blood samples were collected at 0700–0800 h before breakfast in Chengdu. Each day, starting 2 days before the flight to Rikaze, China, at 3,860 m altitude, volunteers were given a Rhodiola capsule (Z10980020, Tibet Nuodikang Medicine, Lhasa, China) to improve endurance and resistance to hypoxia. On the third morning at Rikaze, SpO2 was measured, and fasting blood samples were collected again. The AMS score was obtained using the Lake Louise Score ≥3 (23). Plasma was obtained by centrifugation as soon as possible and stored at −80°C until use.

Hypoxia Exposure of Animals and Isolated Islets

The rats in the hypoxia group were placed in a hypobaric chamber (FLYDWC-50-IIC; AVIC Guizhou Fenglei Aviation Armament Co., Ltd., Guizhou, China) and exposed to hypoxia of 2,000 m altitude (79.97 kPa, equivalent to 16.0% O2 at sea level) or 5,000 m altitude (54.02 kPa, 10.8% O2). The chamber was opened daily for 30 min to clean and replenish food and water during the 5 days of exposure. The normoxia group was placed in an identical chamber at sea level (100.08 kPa, 20.9% O2). Rats received intraperitoneal injections of the CRHR1 antagonist cp-154,526 (30 mg/kg) (donated by Pfizer, Groton, CT), the glucocorticoid receptor (GR)-specific antagonist RU486 (50 mg/kg) (Tocris, Bristol, U.K.), or vehicle 30 min before exposure. After exposure, rats were killed by decapitation at 1300–1400 h, and trunk blood was collected. Plasma was obtained by centrifugation and stored at −80°C. The liver and pancreas were immediately removed, frozen in liquid nitrogen, and stored at −80°C until use. Isolated islets in the hypoxia group were incubated in 5% CO2 and various O2 conditions delivered by the hypoxia chamber (ProOx model P110 and ProCO2 model P120 systems; BioSpherix, Lacona, NY) (24).

Insulin Secretion

Size-matched islets were washed and preincubated for 1 h in RPMI 1640 medium containing 2.8 mmol/L glucose, 10 mmol/L HEPES, and 0.1% BSA. Ten islets per well were then incubated in testing RPMI 1640 medium containing 10 mmol/L HEPES and 0.1% BSA with the indicated glucose and drugs under hypoxia or normoxia. At the end of the experiments, the testing medium was collected for insulin measurement using a rat insulin enzyme immunosorbent assay kit (Mercodia, Uppsala, Sweden), whereas islets were placed in lysis buffer for quantitative PCR (qPCR) assay.

Calcium Imaging

Islets were washed and loaded with 5 μmol/L Fluo-4 AM (Molecular Probes, Eugene, OR) in Krebs-Ringer bicarbonate HEPES buffer comprising (in mmol/L) 129 NaCl, 4.7 KCl, 1.2 KH2PO4, 5.0 NaHCO3, 2.0 CaCl2, 1.2 MgSO4, 10 HEPES, and 0.1% BSA at pH 7.4 containing 5.6 mmol/L glucose for 1 h at 37°C. Calcium-free conditions were achieved by use of calcium-free Krebs-Ringer bicarbonate HEPES buffer containing 2 mmol/L EGTA. Intact islets were immobilized with a wide-bore glass suction pipette under a Nikon TE2000 inverted microscope with a Yokogawa spinning disk confocal system (PerkinElmer, Wellesley, MA). Calcium images were captured at 3-s intervals and three different depths with 488-nm excitation and 505–530-nm emission. At the end of each experiment, 0.5 mmol/L tolbutamide, a KATP channel inhibitor (Sigma, St. Louis, MO), was added to present the functional β-cells (25). As a rule, cells in islets were defined as β-cells if fluorescence signals were markedly increased in response to tolbutamide. The change of fluorescence intensity (ΔF) was calculated as a percentage of the basal level (F0, background subtracted), and frequency was calculated as events per minute. Methods for assays of plasma hormones and metabolism (glucose, lactate, pyruvate, ATP, ADP, and AMP), drug treatment, cAMP assay, qPCR, immunofluorescence staining, and Rhodiola rosea treatment are described in the Supplementary Data.

Statistical Analysis

All data are presented as mean ± SD and were analyzed using Student unpaired two-tailed t test and one-way ANOVA with Tukey post hoc test (GraphPad Prism 6 software). The paired t test was used in calcium imaging and human data analyses. P < 0.05 was considered significant.

Acute Hypobaric Hypoxia Affects Insulin and Glucose Levels in Rat Plasma Through CRHR1

To investigate the effect of hypoxic stress on plasma glucose, insulin, CRH, and CORT, rats were exposed to hypoxia of 2,000 or 5,000 m altitude for 8 h. Hypoxia of 5,000 m but not of 2,000 m decreased plasma insulin and increased plasma glucose, CRH, CORT, and HOMA insulin sensitivity (HOMA-IS) (Fig. 1A–E). All changes were reversed by treatment with a CRHR1 antagonist (cp-154,526) (Fig. 1A–E). Therefore, after activation of the HPA axis, CRHR1 is likely involved in the regulation of insulin release and glucose metabolism under acute hypoxia.

Figure 1

CRHR1 is involved in the regulation of rat plasma insulin and glucose under hypoxia of 5,000 m altitude for 8 h. Hypoxia of 5,000 m significantly decreased plasma insulin (A) and increased plasma glucose (B) and HOMA-IS (C); these effects were blocked by pretreatment with a CRHR1 antagonist. CRHR1 antagonist administration reversed the hypoxia-induced high CRH (D) and high CORT (E) levels in plasma. n = 7 in each group. *P < 0.05, ***P < 0.001 vs. control group; #P < 0.05, ##P < 0.01, ###P < 0.001 vs. cp group. cp, cp-154,526.

Figure 1

CRHR1 is involved in the regulation of rat plasma insulin and glucose under hypoxia of 5,000 m altitude for 8 h. Hypoxia of 5,000 m significantly decreased plasma insulin (A) and increased plasma glucose (B) and HOMA-IS (C); these effects were blocked by pretreatment with a CRHR1 antagonist. CRHR1 antagonist administration reversed the hypoxia-induced high CRH (D) and high CORT (E) levels in plasma. n = 7 in each group. *P < 0.05, ***P < 0.001 vs. control group; #P < 0.05, ##P < 0.01, ###P < 0.001 vs. cp group. cp, cp-154,526.

Acute or Subacute Hypobaric Hypoxia Reduces ATP Level in Rat Pancreas

To determine how hypobaric hypoxia influences ATP homeostasis in the pancreas, the lactate/pyruvate, ATP/ADP, and ATP/AMP ratios were assessed in both the pancreas and the liver of rats under 5,000 m hypoxia. After 8 h of hypoxia, rat pancreas exhibited an elevated lactate/pyruvate ratio, lowered ATP/ADP ratio, and elevated AMP/ATP ratio (Fig. 2A, C, and E). The lactate/pyruvate ratio was also elevated in the liver (Fig. 2B) but without detectable falls in the ATP/ADP or AMP/ATP ratio (Fig. 2D and F). However, after subacute hypoxia for 5 days, the lactate/pyruvate ratio was not changed (Fig. 2A and B), even though the ATP/ADP ratio decreased and AMP/ATP ratio increased in both pancreas and liver (Fig. 2C–F). These changes indicate that acute or subacute hypoxia switches glucose metabolism to anaerobic glycolysis and thus reduces ATP production in the pancreas.

Figure 2

Metabolic changes of rat pancreas and liver after 5,000 m hypoxia for 8 h or 5 days. Hypoxia for 8 h increased the lactate/pyruvate ratio in pancreas (A) and liver (B) and decreased the ATP/ADP ratio in pancreas (C), whereas 5 days of hypoxia reduced the ATP/ADP ratio in both pancreas (C) and liver (D). The AMP/ATP ratio in pancreas (E) was increased with 8 h or 5 days of hypoxia, and AMP/ATP in liver (F) was elevated only with 5 days of hypoxia. n = 7 in each group. *P < 0.05, **P < 0.01 vs. each control group. C, control; H, hypoxia.

Figure 2

Metabolic changes of rat pancreas and liver after 5,000 m hypoxia for 8 h or 5 days. Hypoxia for 8 h increased the lactate/pyruvate ratio in pancreas (A) and liver (B) and decreased the ATP/ADP ratio in pancreas (C), whereas 5 days of hypoxia reduced the ATP/ADP ratio in both pancreas (C) and liver (D). The AMP/ATP ratio in pancreas (E) was increased with 8 h or 5 days of hypoxia, and AMP/ATP in liver (F) was elevated only with 5 days of hypoxia. n = 7 in each group. *P < 0.05, **P < 0.01 vs. each control group. C, control; H, hypoxia.

CRH Stimulates and Hypoxia Suppresses Insulin Release

To investigate the insulinotropic action of CRH and the effects of hypoxia on this process, isolated islets were exposed to hypoxia and rotenone, an inhibitor of mitochondrial respiratory chain complex I. Treatment of islets with CRH (10 pmol/L–10 nmol/L) for 1 h induced dose-dependent increases in insulin secretion at 5.6 or 11.1 mmol/L glucose but not at 2.8 mmol/L glucose (Fig. 3A). The CRH-induced maximum magnitude of insulin at 11.1 mmol/L glucose (1.7-fold) was larger than at 5.6 mmol/L glucose (1.4-fold) (Fig. 3A). The insulinotropic action of CRH was persistently shown after 1, 12, and 24 h incubation at 5.6 mmol/L glucose, and this augmentation was completely abolished by pretreatment with 1 μmol/L cp-154,526, a CRHR1 antagonist (Fig. 3B). This CRH-insulinotropic action was blocked by cAMP-dependent protein kinase (PKA) inhibitors (H89 and Rp-8-Br-cAMPs, 10 μmol/L) but not by inhibitors of protein kinase C (Go 6983, 10 μmol/L) or phospholipase C (U-73122, 10 μmol/L) (Fig. 3C). Moreover, this insulinotropic effect of CRH depended on extracellular calcium and was blocked by an L-type calcium channel inhibitor (nifedipine, 10 μmol/L) (Fig. 3C).

Figure 3

Hypoxia and ATP deficiency inactivates the insulinotropic action of CRH in isolated rat islets. CRH augmented insulin secretion at 5.6 and 11.1 mmol/L glucose but not at 2.8 mmol/L for 1 h. The CRH-induced maximum magnitude of insulin was at 1.7-fold at 11.1 mmol/L glucose and 1.4-fold at 5.6 mmol/L glucose (A). CRH persistently enhanced insulin secretion at 5.6 mmol/L glucose at 1, 12, and 24 h, and this was blocked by pretreatment with cp-154,526 (cp) (B). The insulinotropic action of CRH was blocked by PKA inhibitors (10 μmol/L H89 and Rp-8-Br-cAMPs [Rp-cAMP]), an L-type calcium channel inhibitor (10 μmol/L nifedipine), and in calcium-free solution (2 mmol/L EGTA) at 5.6 mmol/L glucose; this effect was not changed by inhibitors of protein kinase C (Go 6983) and phospholipase C (U-73122) (C). Hypoxia (5% or 1% O2) abolished the insulinotropic action of CRH on 24-h insulin secretion at 5.6 mmol/L glucose (D). CRH 1 nmol/L stimulated insulin secretion with 0.1 nmol/L rotenone, but this effect did not occur with 1 or 10 nmol/L rotenone at 5.6 mmol/L glucose. Linear regression analysis showed a correlation between rotenone concentration and insulin secretion at three doses of CRH (each slope is shown in the inset) (E). Crhr1 mRNA expression was high in islets under hypoxia (5% O2) but not under rotenone (1 nmol/L)-induced ATP-deficient conditions (F). n = 3–4 in each group. *P < 0.05, **P < 0.01 vs. each control group; $P < 0.05, $$P < 0.01, $$$P < 0.001 vs. vehicle treatment group; #P < 0.05, ##P < 0.01, ###P < 0.001.

Figure 3

Hypoxia and ATP deficiency inactivates the insulinotropic action of CRH in isolated rat islets. CRH augmented insulin secretion at 5.6 and 11.1 mmol/L glucose but not at 2.8 mmol/L for 1 h. The CRH-induced maximum magnitude of insulin was at 1.7-fold at 11.1 mmol/L glucose and 1.4-fold at 5.6 mmol/L glucose (A). CRH persistently enhanced insulin secretion at 5.6 mmol/L glucose at 1, 12, and 24 h, and this was blocked by pretreatment with cp-154,526 (cp) (B). The insulinotropic action of CRH was blocked by PKA inhibitors (10 μmol/L H89 and Rp-8-Br-cAMPs [Rp-cAMP]), an L-type calcium channel inhibitor (10 μmol/L nifedipine), and in calcium-free solution (2 mmol/L EGTA) at 5.6 mmol/L glucose; this effect was not changed by inhibitors of protein kinase C (Go 6983) and phospholipase C (U-73122) (C). Hypoxia (5% or 1% O2) abolished the insulinotropic action of CRH on 24-h insulin secretion at 5.6 mmol/L glucose (D). CRH 1 nmol/L stimulated insulin secretion with 0.1 nmol/L rotenone, but this effect did not occur with 1 or 10 nmol/L rotenone at 5.6 mmol/L glucose. Linear regression analysis showed a correlation between rotenone concentration and insulin secretion at three doses of CRH (each slope is shown in the inset) (E). Crhr1 mRNA expression was high in islets under hypoxia (5% O2) but not under rotenone (1 nmol/L)-induced ATP-deficient conditions (F). n = 3–4 in each group. *P < 0.05, **P < 0.01 vs. each control group; $P < 0.05, $$P < 0.01, $$$P < 0.001 vs. vehicle treatment group; #P < 0.05, ##P < 0.01, ###P < 0.001.

Hypoxia reduced the CRH-insulinotropic action in a manner that was inversely related to O2 supply. Under 5% O2, CRH (0.01–1 nmol/L) failed to stimulate insulin secretion at 5.6 mmol/L glucose (Fig. 3D), whereas 1% O2 not only suppressed the insulinotropic action of CRH, but also reduced basal insulin secretion (Fig. 3D). To mimic the inhibition of oxidative phosphorylation and ATP production in the absence of hypoxia, rotenone was used to inhibit complex I of the mitochondrial electron transport chain in islets. Rotenone treatment (0.1–10 nmol/L) gradually inhibited insulin secretion. Rotenone (0.1 nmol/L) suppressed the augmentation of insulin release by 0.1 nmol/L CRH, whereas 1 or 10 nmol/L rotenone completely abolished 1 nmol/L CRH-stimulated insulin release (Fig. 3E).

Of note, qPCR results indicated an increase in Crhr1 mRNA in islets under 5% O2 hypoxia but not under 1 nmol/L rotenone-induced ATP deficiency (Fig. 3F). These findings indicate that although hypoxia increases Crhr1 expression (Fig. 3F), the insulinotropic action of CRH was attenuated by hypoxia due to insufficient supplies of O2 and ATP.

CRH-Insulinotropic Effect Is Inactivated by Gradually Reducing cAMP, ATP, and Calcium Influx in Islets

To determine the requirement for ATP as a substrate for the CRHR1-activated insulin release pathway, the cAMP level, ATP/ADP ratio, and calcium oscillations in islets were assessed. CRH (0.1–1 nmol/L) significantly enhanced the accumulation of cAMP in normoxia, and 1 nmol/L CRH increased the cAMP levels at 0.1 or 1 nmol/L rotenone, whereas the basal cAMP levels were decreased and not stimulated by CRH at 10 nmol/L rotenone (Fig. 4A). Furthermore, 1 nmol/L CRH markedly elevated the ATP/ADP ratio under normoxia. This elevation was abolished by pretreatment with 10 nmol/L rotenone (Fig. 4B), which increased the AMP/ATP ratio in a concentration-dependent manner (0.1–10 nmol/L) (Fig. 4D). Moreover, 1 and 10 nmol/L rotenone suppressed the basal ATP/ADP ratio (Fig. 4B), and the CRH-induced increases in ATP/ADP ratio were blocked by the CRHR1 antagonist with and without 1 nmol/L rotenone (Fig. 4C).

Figure 4

Low cAMP and calcium oscillations suppress the insulinotropic action of CRH under the ATP-deficient condition. The CRH-induced high cAMP level (A) and ATP/ADP ratio (B) were attenuated or abolished by rotenone pretreatment. The CRH-induced increase of the ATP/ADP ratio was blocked by the CRHR1 antagonist with or without 1 nmol/L rotenone (C). The AMP/ATP ratio was elevated by rotenone pretreatment (D). CRH increased the calcium oscillatory frequency of β-cells in the normal condition, and this increase was abolished by cp-154,526 or Rp-8-Br-cAMPs (E). However, CRH did not increase the calcium oscillatory frequency in β-cells under the ATP-deficient condition (FH). Calcium signaling patterns of single β-cells under the CRH challenge in normal (F), ATP-deficient (G and H), and calcium-free conditions (I). In AD, n = 3–4 per group. *P < 0.05, **P < 0.01, ***P < 0.001 vs. each control group; $P < 0.05 vs. vehicle treatment group; #P < 0.05, ##P < 0.01 vs. cp-154,526 group. In E, n = 30–40 β-cells from more than five islets in five rats. &&&P < 0.001 vs. control group. TOL, tolbutamide.

Figure 4

Low cAMP and calcium oscillations suppress the insulinotropic action of CRH under the ATP-deficient condition. The CRH-induced high cAMP level (A) and ATP/ADP ratio (B) were attenuated or abolished by rotenone pretreatment. The CRH-induced increase of the ATP/ADP ratio was blocked by the CRHR1 antagonist with or without 1 nmol/L rotenone (C). The AMP/ATP ratio was elevated by rotenone pretreatment (D). CRH increased the calcium oscillatory frequency of β-cells in the normal condition, and this increase was abolished by cp-154,526 or Rp-8-Br-cAMPs (E). However, CRH did not increase the calcium oscillatory frequency in β-cells under the ATP-deficient condition (FH). Calcium signaling patterns of single β-cells under the CRH challenge in normal (F), ATP-deficient (G and H), and calcium-free conditions (I). In AD, n = 3–4 per group. *P < 0.05, **P < 0.01, ***P < 0.001 vs. each control group; $P < 0.05 vs. vehicle treatment group; #P < 0.05, ##P < 0.01 vs. cp-154,526 group. In E, n = 30–40 β-cells from more than five islets in five rats. &&&P < 0.001 vs. control group. TOL, tolbutamide.

CRH 1 nmol/L markedly increased the frequency of calcium oscillations in identified β-cells (Fig. 4E and F), and this increase was reversed by pretreatment with the CRHR1 antagonist (1 μmol/L) and the PKA inhibitor (10 μmol/L Rp-8-Br-cAMPs) (Fig. 4E). In calcium-free conditions, calcium oscillations were not induced by 1 nmol/L CRH or 1 μmol/L forskolin (Fig. 4I). In the rotenone-induced ATP-deficient condition, the frequency of calcium oscillations was unaltered by CRH (Fig. 4E and G) but was still increased by forskolin (Fig. 4E and H). These findings strongly suggest that a deficiency of ATP and reduced ATP/ADP ratio limit cAMP production and thus lead to defective calcium oscillations in islets in a manner that may contribute to the inactivation of the CRH-insulinotropic action.

Hypoxia Inhibits Insulin Release by Both Reducing ATP and Increasing CORT in Islets

To examine the effects of glucocorticoid and intracellular ATP on insulin secretion under hypoxia, insulin secretion and GR target gene mRNA levels were assessed in isolated rat islets. Dexamethasone (DEX) concentration dependently decreased insulin secretion under normoxia and 5% O2 and severely inhibited it under 1% O2 (Fig. 5A). Reduction of insulin release correlated with increased DEX and rotenone (ATP reduction) concentration (Fig. 5B). DEX elevated serum and glucocorticoid-inducible kinase 1 (Sgk1) mRNA and inhibited Glut2 and Crhr1 mRNA expression under normoxia (Fig. 5C). These changes were not affected by ATP deficiency (1 nmol/L rotenone) or hypoxia (5% O2) despite that hypoxia increased the Crhr1 mRNA level (Fig. 5C). These data suggest that both hypoxia-stimulated glucocorticoid release and a reduced ATP supply inhibit insulin release from pancreatic islets.

Figure 5

DEX inhibits insulin secretion under normoxic, hypoxic, and ATP-deficient conditions in isolated rat islets. DEX inhibited 24-h insulin secretion under normoxia (21% O2) and hypoxia (5% and 1% O2) (A). Inhibition of insulin release by DEX was negatively correlated with ATP level (0.1–10 nmol/L rotenone) (B). DEX elevated Sgk1 mRNA and inhibited Glut2 and Crhr1 mRNA expression under normoxia, and these changes were not affected by ATP deficiency (1 nmol/L rotenone) or hypoxia (5% O2) (C). Hypoxia induced Crhr1 mRNA expression. n = 3–4 in each group. *P < 0.05, **P < 0.01, ***P < 0.001 vs. each control group; $P < 0.05, $$$P < 0.001 vs. vehicle treatment group.

Figure 5

DEX inhibits insulin secretion under normoxic, hypoxic, and ATP-deficient conditions in isolated rat islets. DEX inhibited 24-h insulin secretion under normoxia (21% O2) and hypoxia (5% and 1% O2) (A). Inhibition of insulin release by DEX was negatively correlated with ATP level (0.1–10 nmol/L rotenone) (B). DEX elevated Sgk1 mRNA and inhibited Glut2 and Crhr1 mRNA expression under normoxia, and these changes were not affected by ATP deficiency (1 nmol/L rotenone) or hypoxia (5% O2) (C). Hypoxia induced Crhr1 mRNA expression. n = 3–4 in each group. *P < 0.05, **P < 0.01, ***P < 0.001 vs. each control group; $P < 0.05, $$$P < 0.001 vs. vehicle treatment group.

GR Mediates Inhibition of Insulin Release Under Hypobaric Hypoxia

To test the role of glucocorticoid in insulin secretion and glucose homeostasis under hypoxia in vivo, a GR antagonist (RU486) was used in rats under hypoxia of 5,000 m altitude for 8 h. RU486 pretreatment reversed the hypoxia-induced hyperglycemia and low plasma insulin (Fig. 6A). Immunofluorescence also showed a higher SGK1 signal in the nuclei of islet β-cells under hypoxia. The proportion of SGK1-positive β-cells increased under hypoxia, and this was blocked by RU486 (Fig. 6B and C). These data suggest that hypoxia-evoked increases of SGK1 contribute to the inhibitory role of GR in insulin release in pancreatic islets.

Figure 6

GR mediates hypoxia-induced plasma insulin reduction. GR antagonist RU486 administration reversed the increased glucose and decreased insulin in rat plasma induced by hypoxia (5,000 m, 8 h) (A). Immunofluorescence of SGK1 (red), insulin (green), and nuclei (DAPI blue) showed a high SGK1 signal (B) and an elevated percentage of SGK1-positive cells (C) in pancreatic islets under hypoxia; these increases were reversed by RU486. In A, n = 7–8 rats in each group. In B and C, n = 15–20 islets from five to seven rat pancreata. Scale bar = 100 μm; dotted line, islet region. *P < 0.05, **P < 0.01, ***P < 0.001 vs. control group; ##P < 0.01, ###P < 0.001 vs. hypoxia group.

Figure 6

GR mediates hypoxia-induced plasma insulin reduction. GR antagonist RU486 administration reversed the increased glucose and decreased insulin in rat plasma induced by hypoxia (5,000 m, 8 h) (A). Immunofluorescence of SGK1 (red), insulin (green), and nuclei (DAPI blue) showed a high SGK1 signal (B) and an elevated percentage of SGK1-positive cells (C) in pancreatic islets under hypoxia; these increases were reversed by RU486. In A, n = 7–8 rats in each group. In B and C, n = 15–20 islets from five to seven rat pancreata. Scale bar = 100 μm; dotted line, islet region. *P < 0.05, **P < 0.01, ***P < 0.001 vs. control group; ##P < 0.01, ###P < 0.001 vs. hypoxia group.

High-Altitude Hypoxia Affects Human Plasma Insulin and Glucose Homeostasis

To determine the regulatory effect of high-altitude hypoxia on circulating hormones and plasma glucose in humans, 67 volunteers rapidly ascended to 3,860 m altitude in Rikaze and stayed for 2 days. On the morning of day 3, plasma glucose, insulin, CRH, and cortisol levels were analyzed. High-altitude hypoxia induced a dramatic decrease in SpO2 and increase in plasma CRH (Fig. 7A and D) but exerted no detectable effect on plasma insulin (Fig. 7B). Despite unaffected plasma insulin levels, plasma glucose was significantly elevated relative to control (Fig. 7C). Further analysis showed that plasma glucose increased in volunteers with AMS (12 of 67) but not in those without AMS (55 of 67) (Fig. 7F). HOMA-IS declined only in AMS volunteers (Fig. 7G), who had a higher plasma CRH compared with those without AMS (Fig. 7D and H). Plasma cortisol was decreased under hypoxia in all volunteers (Fig. 7E).

Figure 7

High-altitude hypoxia results in changes of insulin and glucose homeostasis, and these are correlated with AMS in humans. Compared with low altitude (540 m), high altitude (3,860 m) decreased SpO2 (A) and caused no change in plasma insulin (B), increased plasma glucose (C) and CRH (D), and decreased plasma cortisol (E). Plasma glucose was elevated in volunteers with AMS (F), whereas their HOMA-IS was reduced (G). The increase in plasma CRH was significantly higher in volunteers with AMS than in those without (H). n = 67 (12 with AMS, 55 without). *P < 0.05, **P < 0.01, ***P < 0.001 vs. low altitude; $P < 0.05 AMS vs. no AMS.

Figure 7

High-altitude hypoxia results in changes of insulin and glucose homeostasis, and these are correlated with AMS in humans. Compared with low altitude (540 m), high altitude (3,860 m) decreased SpO2 (A) and caused no change in plasma insulin (B), increased plasma glucose (C) and CRH (D), and decreased plasma cortisol (E). Plasma glucose was elevated in volunteers with AMS (F), whereas their HOMA-IS was reduced (G). The increase in plasma CRH was significantly higher in volunteers with AMS than in those without (H). n = 67 (12 with AMS, 55 without). *P < 0.05, **P < 0.01, ***P < 0.001 vs. low altitude; $P < 0.05 AMS vs. no AMS.

We addressed a different regulatory effect of CRH and glucocorticoids on hypoxia-reduced insulin levels. Under hypoxia, CRH-stimulated insulin release was abolished due to hypoxia-reduced cellular ATP and cAMP levels, and a consequent inhibition of calcium influx in isolated rat islets, despite that hypoxia-activated CORT, still inhibited insulin release (Fig. 8). In humans, rapid ascent to high altitude acutely elevated plasma glucose without altering plasma insulin. Furthermore, AMS volunteers exhibited reduced HOMA-IS and higher plasma CRH compared with non-AMS volunteers.

Figure 8

Proposed inhibitory regulation of insulin release by hypoxia-activated CRH and CORT. Hypoxia switches from aerobic to anaerobic glycolysis, resulting in low ATP/ADP and high AMP/ATP ratios, which inhibit cAMP production and calcium oscillations in rat islets. This consequently inactivates the insulinotropic role of CRH, although CRHR1 is triggered by upregulated plasma CRH. Meanwhile, hypoxia-stimulated plasma CORT inhibits insulin secretion through upregulated Sgk1 mRNA; Crhr1 mRNA is also inhibited by CORT.

Figure 8

Proposed inhibitory regulation of insulin release by hypoxia-activated CRH and CORT. Hypoxia switches from aerobic to anaerobic glycolysis, resulting in low ATP/ADP and high AMP/ATP ratios, which inhibit cAMP production and calcium oscillations in rat islets. This consequently inactivates the insulinotropic role of CRH, although CRHR1 is triggered by upregulated plasma CRH. Meanwhile, hypoxia-stimulated plasma CORT inhibits insulin secretion through upregulated Sgk1 mRNA; Crhr1 mRNA is also inhibited by CORT.

CRH, a critical stress peptide, plays a key role in regulating the HPA axis and adjustments in neural, endocrine, metabolic, and glucose homeostasis to various stressors, including hypoxia (14,20,26,27). Consistent with our previous study (10), we show that acute hypobaric hypoxia induces marked increases in plasma CRH, which mediates reduced insulin and increased glucose in rat plasma (Fig. 1). Insulin, the hypoglycemic hormone, is only secreted from pancreatic islet β-cells and is mainly regulated by glucose and neuroendocrine inputs (11,13). There have been reports that CRHR1 is expressed in human, mouse, and rat islets (15,16), which upon activation by CRH, increases calcium influx (17) and stimulates insulin secretion in a glucose-dependent manner (15,16,18). The current study demonstrates a 24-h persistent insulinotropic role of CRH under normoxia, depending on both glucose and CRHR1 signaling pathways, namely PKA and L-type calcium channel-mediated calcium influx (Fig. 3A–C). However, under hypoxia, this effect of CRH was inactivated (Fig. 3D) despite Crhr1 mRNA being upregulated in islets (Fig. 3F). These findings suggest that the insulinotropic effect of CRH depends on sufficient O2 supply, and this view is supported by previous reports of attenuated glucose-stimulated insulin secretion with stable basal insulin levels under hypoxia of 6.7% (28) and 3% O2 (29).

It is well documented that decreased O2 supply switches cell respiration from aerobic metabolism toward anaerobic glycolysis. Consistent with this view, ATP production was deficient in rat pancreas under 5,000 m hypoxia (Fig. 2C). Islet β-cells express low levels of lactate dehydrogenase (30); thus, islets may have a lower capacity for anaerobic glycolysis and ATP production. The ATP/ADP ratio of islet β-cells, therefore, may decrease more dramatically than that of pancreas under hypoxia. ATP is not only an energy molecule but also an important signaling molecule in islet β-cells, controlling insulin secretion. Under physiological conditions, insulin secretion is tightly correlated with the ATP/ADP ratio in islet β-cells, although it is still controversial whether increased ATP or decreased ADP contributes to the alteration of ATP/ADP ratio upon glucose stimulation (31,32). Other nutrients, including amino acids and free fatty acids, also have the capacity to modify the ATP/ADP ratio and insulin secretion (11). Therefore, islets may be more sensitive to ATP deficiency under hypoxia than other cells. Here, rotenone-induced ATP deficiency abolished the stimulatory role of CRH on insulin secretion (Fig. 3E), as did 5% O2 (Fig. 3D). Under normoxia, CRH increased cAMP production by stimulating G-protein binding to CRHR1 and thus activating adenylate cyclase (AC), but cAMP production was lowered (not enhanced) when islets were deficient in ATP (Fig. 4A). This reduction in cAMP likely contributes to the suppression of CRHR1 signaling and might result from a low ATP/ADP ratio under hypoxia and consequent reductions in substrate supply for AC-dependent cAMP production. Hypoxia or ATP deficiency also induced an increased AMP/ATP ratio (Figs. 2E and 4D), resulting in inhibited AC activity throughbinding to the intracellular P site (33,34). Otherwise, a low ATP/ADP ratio under ATP deficiency (Fig. 4B and C) might limit the CRHR1 signaling pathway by gating of KATP channels, closure of L-type calcium channels, reduction of calcium oscillations (Fig. 4E), and consequent reductions in insulin secretion (Fig. 3E). We conclude, therefore, that the insulinotropic role of CRH is inactivated by a fall in ATP production under hypoxia, consequent reductions in the cAMP level and ATP/ADP ratio, and, thus, inhibition of calcium oscillations in islets (Fig. 8). Consequently, high plasma CRH during hypoxia may not exert the expected insulinotropic effects.

Acute (Fig. 1) or subacute (10,26) hypoxia increases not only plasma CRH but also CORT through activation of the HPA axis, raising the possibility that hypoxia-stimulated CORT is important in insulin regulation. Glucocorticoids coordinate various stress responses and glucose homeostasis (35,36), and DEX is known to inhibit insulin secretion in isolated islets (37,38). We found the same inhibitory effect of DEX on insulin secretion in cultured islets (Fig. 5A and B) associated with upregulated Sgk1 and downregulated Glut2 and Crhr1 mRNA expression under ATP-deficient or hypoxic conditions (Fig. 5C). These data suggest that CORT, activated by hypoxia, may initiate a discrete inhibitory pathway from CRH and correlate with the O2 and ATP supply. The current in vivo study shows that acute hypoxia-induced high CORT indeed contributes to the low plasma insulin and high plasma glucose mediated by GR (Fig. 6A) through high SGK1 expression in islets (Fig. 6B and C).

In humans, high-altitude hypoxia exposure for 2 days significantly reduced SpO2 (Fig. 7A) and increased plasma CRH (Fig. 7D). To reduce the responsiveness to hypoxia, all volunteers took a Rhodiola capsule (extracted from R. rosea), a traditional Chinese herb to improve resistance to AMS. Of note, R. rosea can reduce hypoxia-induced high plasma CRH and CORT in rats (Supplementary Fig. 1). Consistent with the antistress effect in previous reports (3941), R. rosea may thus contribute to low plasma cortisol at high altitude (Fig. 7E). In the current study, cortisol remained low, but high plasma CRH levels were still evoked by hypoxia in human volunteers. Under these conditions, the raised plasma CRH level fails to stimulate insulin release during high-altitude hypoxia. These results greatly support the conclusion derived from animal experiments that hypoxia increases CRH and inactivates its insulinotropic role by inhibiting the CRHR1 signaling pathway.

In the current study, acute hypoxia (5,000 m, 8 h) induced low plasma insulin, high plasma glucose, and increased insulin sensitivity in rats (Fig. 1A–C). Other studies individually showed a gradual decrease in insulin level of rats during acute hypoxia for 1–4 days (6) or hyperglycemia in mice less than 1 day of hypoxia (7). We found that the CRH-induced high CORT mainly decreased insulin release and elevated blood glucose. High CORT directly elevates blood glucose through decreased glycogen synthesis and glucose uptake in muscle (35). In liver, the current study shows that a high anaerobic glycolysis rate and glycogen storage maintain stable liver ATP production and support hyperglycemia under acute hypoxia (Fig. 2D). After 5 days of hypoxia, low insulin modulated by CRHR1 still occurs in rats. However, decreased blood glucose is not affected by CRHR1 (10). Low insulin level and hypoglycemia also occur in mice after 4 weeks of hypoxia (8) and likely result from adaptations to hypoxia that consequently reduce the anaerobic glycolysis rate and ATP/ADP ratio in liver (Fig. 2D), despite that hepatic glycogen is sufficient and CORT remains high (10). Therefore, CRHR1 regulation of blood glucose likely depends on high hepatic metabolism. In man, 3,860 m hypoxia for 2 days only increased plasma glucose and affected insulin sensitivity in the AMS group (Fig. 7C and G) in association with low cortisol (Fig. 7E) induced by R. rosea. Other studies have reported high cortisol, glycemia, and insulin levels in man in the first 1–2 days of exposure to 4,300 m hypoxia without any drugs (4,5). The sustained hyperglycemia with different insulin and cortisol levels in acute hypoxia may imply that blood glucose is regulated by greater integration of systems, including, for example, the autonomic nervous system. In short, a greater increase of CRH in the AMS group may activate the sympathetic nervous system (42) and induce hyperglycemia (43). Furthermore, 5–10 days of adaptation to hypoxia returns hyperglycemia to basal levels in healthy people (5). Moreover chronic hypoxic exposure reduces fasting insulin and improves insulin resistance in type 2 diabetic patients (4446) and decreases the insulin dosage in type 1 diabetic patients (47,48). Of note, lower insulin levels or reduced insulin signaling is beneficial for health and longevity (49,50). It is therefore tempting to speculate that fast travel to high altitude may benefit both healthy people and diabetic patients in terms of glucose-insulin metabolic control.

In conclusion, we propose a dynamic modulation of a CRH-insulinotropic role in pancreatic islets, which depends on CRH, glucose levels, and O2 availability. Under normoxia, the CRH-insulinotropic role increases with raised glucose levels but is inactivated under hypoxia due to reductions in ATP, cAMP, and calcium influx into islets, even though plasma CRH and islet Crhr1 are upregulated. Additionally, hypoxia-stimulated CORT inhibits insulin release through activated SGK1 and in an O2- and ATP-dependent manner. Consistent with these findings, rapid ascent to high altitude does not affect HOMA-IS in healthy volunteers but reduces HOMA-IS in AMS volunteers who usually exhibit high plasma CRH.

Acknowledgments. The authors thank Iain C. Bruce (Department of Physiology, School of Medicine, Zhejiang University) for editing the manuscript and all the volunteers for participating in the study.

Funding. This work was supported by grants from the Ministry of Science and Technology of the People's Republic of Chinahttp://dx.doi.org/10.13039/501100002855, the National Basic Research Program of China (973 Program no. 2012CB518200 and no. 2006CB504100), the National Natural Science Foundation of Chinahttp://dx.doi.org/10.13039/501100001809 (no. 31171145 and no. 30871221), and a Wellcome Trust Programme Grant (081195) to A.M.E.

Duality of Interest. No conflicts of interest relevant to this article were reported.

Author Contributions. K.H. contributed to the experimental research, data analysis, and writing and editing of the manuscript. F.-P.K. and J.-W.T. contributed to the experimental research. Y.-Q.G. and J.C. contributed to the collection of human plasma samples. A.M.E. contributed to the design of the nucleotide and the measurement of AMPK and the writing and editing of the manuscript. S.L.L. contributed to the writing and editing of the manuscript. X.-Q.C. and J.-Z.D. contributed to the study design, data analysis, and writing and editing of the manuscript. X.-Q.C. and J.-Z.D. are the guarantors of this work and, as such, had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

1.
Basnyat
B
,
Murdoch
DR
.
High-altitude illness
.
Lancet
2003
;
361
:
1967
1974
[PubMed]
2.
Wu
TY
,
Ding
SQ
,
Liu
JL
, et al
.
Who should not go high: chronic disease and work at altitude during construction of the Qinghai-Tibet railroad
.
High Alt Med Biol
2007
;
8
:
88
107
[PubMed]
3.
Wu
TY
,
Ding
SQ
,
Zhang
SL
, et al
.
Altitude illness in Qinghai–Tibet railroad passengers
.
High Alt Med Biol
2010
;
11
:
189
198
[PubMed]
4.
Larsen
JJ
,
Hansen
JM
,
Olsen
NV
,
Galbo
H
,
Dela
F
.
The effect of altitude hypoxia on glucose homeostasis in men
.
J Physiol
1997
;
504
:
241
249
[PubMed]
5.
Barnholt
KE
,
Hoffman
AR
,
Rock
PB
, et al
.
Endocrine responses to acute and chronic high-altitude exposure (4,300 meters): modulating effects of caloric restriction
.
Am J Physiol Endocrinol Metab
2006
;
290
:
E1078
E1088
[PubMed]
6.
Simler
N
,
Grosfeld
A
,
Peinnequin
A
,
Guerre-Millo
M
,
Bigard
AX
.
Leptin receptor-deficient obese Zucker rats reduce their food intake in response to hypobaric hypoxia
.
Am J Physiol Endocrinol Metab
2006
;
290
:
E591
E597
[PubMed]
7.
Lee
EJ
,
Alonso
LC
,
Stefanovski
D
, et al
.
Time-dependent changes in glucose and insulin regulation during intermittent hypoxia and continuous hypoxia
.
Eur J Appl Physiol
2013
;
113
:
467
478
[PubMed]
8.
Gamboa
JL
,
Garcia-Cazarin
ML
,
Andrade
FH
.
Chronic hypoxia increases insulin-stimulated glucose uptake in mouse soleus muscle
.
Am J Physiol Regul Integr Comp Physiol
2011
;
300
:
R85
R91
[PubMed]
9.
Chintamaneni
K
,
Bruder
ED
,
Raff
H
.
Effects of age on ACTH, corticosterone, glucose, insulin, and mRNA levels during intermittent hypoxia in the neonatal rat
.
Am J Physiol Regul Integr Comp Physiol
2013
;
304
:
R782
R789
[PubMed]
10.
Chen
XQ
,
Dong
J
,
Niu
CY
,
Fan
JM
,
Du
JZ
.
Effects of hypoxia on glucose, insulin, glucagon, and modulation by corticotropin-releasing factor receptor type 1 in the rat
.
Endocrinology
2007
;
148
:
3271
3278
[PubMed]
11.
Prentki
M
,
Matschinsky
FM
,
Madiraju
SR
.
Metabolic signaling in fuel-induced insulin secretion
.
Cell Metab
2013
;
18
:
162
185
[PubMed]
12.
White
MF
.
Insulin signaling in health and disease
.
Science
2003
;
302
:
1710
1711
[PubMed]
13.
Chandra
R
,
Liddle
RA
.
Neural and hormonal regulation of pancreatic secretion
.
Curr Opin Gastroenterol
2009
;
25
:
441
446
[PubMed]
14.
Bale
TL
,
Vale
WW
.
CRF and CRF receptors: role in stress responsivity and other behaviors
.
Annu Rev Pharmacol Toxicol
2004
;
44
:
525
557
[PubMed]
15.
Huising
MO
,
van der Meulen
T
,
Vaughan
JM
, et al
.
CRFR1 is expressed on pancreatic beta cells, promotes beta cell proliferation, and potentiates insulin secretion in a glucose-dependent manner
.
Proc Natl Acad Sci U S A
2010
;
107
:
912
917
[PubMed]
16.
Schmid
J
,
Ludwig
B
,
Schally
AV
, et al
.
Modulation of pancreatic islets-stress axis by hypothalamic releasing hormones and 11beta-hydroxysteroid dehydrogenase
.
Proc Natl Acad Sci U S A
2011
;
108
:
13722
13727
[PubMed]
17.
Kanno
T
,
Suga
S
,
Nakano
K
,
Kamimura
N
,
Wakui
M
.
Corticotropin-releasing factor modulation of Ca2+ influx in rat pancreatic beta-cells
.
Diabetes
1999
;
48
:
1741
1746
[PubMed]
18.
O’Carroll
AM
,
Howell
GM
,
Roberts
EM
,
Lolait
SJ
.
Vasopressin potentiates corticotropin-releasing hormone-induced insulin release from mouse pancreatic beta-cells
.
J Endocrinol
2008
;
197
:
231
239
[PubMed]
19.
Jeong
KH
,
Sakihara
S
,
Widmaier
EP
,
Majzoub
JA
.
Impaired leptin expression and abnormal response to fasting in corticotropin-releasing hormone-deficient mice
.
Endocrinology
2004
;
145
:
3174
3181
[PubMed]
20.
Wang
X
,
Meng
FS
,
Liu
ZY
, et al
.
Gestational hypoxia induces sex-differential methylation of Crhr1 linked to anxiety-like behavior
.
Mol Neurobiol
2013
;
48
:
544
555
[PubMed]
21.
Xu
JF
,
Chen
XQ
,
Du
JZ
,
Wang
TY
.
CRF receptor type 1 mediates continual hypoxia-induced CRF peptide and CRF mRNA expression increase in hypothalamic PVN of rats
.
Peptides
2005
;
26
:
639
646
[PubMed]
22.
Sutton
R
,
Peters
M
,
McShane
P
,
Gray
DW
,
Morris
PJ
.
Isolation of rat pancreatic islets by ductal injection of collagenase
.
Transplantation
1986
;
42
:
689
691
[PubMed]
23.
Roach RC, Bärtsch P, Oelz O, Hackett PH; Lake Louise AMS Scoring Consensus Committee. The Lake Louise acute mountain sickness scoring system. In Hypoxia and Mountain Medicine. Sutton JR, Houston CS, Coates G, Eds. Burlington, VT, Charles S. Houston, 1993, p. 272–274
24.
Zhao
Y
,
Ren
JL
,
Wang
MY
, et al
.
Codon 104 variation of p53 gene provides adaptive apoptotic responses to extreme environments in mammals of the Tibet plateau
.
Proc Natl Acad Sci U S A
2013
;
110
:
20639
20644
[PubMed]
25.
Quesada
I
,
Nadal
A
,
Soria
B
.
Different effects of tolbutamide and diazoxide in alpha, beta-, and delta-cells within intact islets of Langerhans
.
Diabetes
1999
;
48
:
2390
2397
[PubMed]
26.
Chen
XQ
,
Kong
FP
,
Zhao
Y
,
Du
JZ
.
High-altitude hypoxia induces disorders of the brain-endocrine-immune network through activation of corticotropin-releasing factor and its type-1 receptors
.
Zhongguo Ying Yong Sheng Li Xue Za Zhi
2012
;
28
:
481
487
[PubMed]
27.
Carlin
KM
,
Vale
WW
,
Bale
TL
.
Vital functions of corticotropin-releasing factor (CRF) pathways in maintenance and regulation of energy homeostasis
.
Proc Natl Acad Sci U S A
2006
;
103
:
3462
3467
[PubMed]
28.
Dionne
KE
,
Colton
CK
,
Yarmush
ML
.
Effect of hypoxia on insulin secretion by isolated rat and canine islets of Langerhans
.
Diabetes
1993
;
42
:
12
21
[PubMed]
29.
Hyder
A
,
Laue
C
,
Schrezenmeir
J
.
Metabolic aspects of neonatal rat islet hypoxia tolerance
.
Transpl Int
2010
;
23
:
80
89
[PubMed]
30.
Sekine
N
,
Cirulli
V
,
Regazzi
R
, et al
.
Low lactate dehydrogenase and high mitochondrial glycerol phosphate dehydrogenase in pancreatic beta-cells. Potential role in nutrient sensing
.
J Biol Chem
1994
;
269
:
4895
4902
[PubMed]
31.
Doliba
NM
,
Wehrli
SL
,
Vatamaniuk
MZ
, et al
.
Metabolic and ionic coupling factors in amino acid-stimulated insulin release in pancreatic beta-HC9 cells
.
Am J Physiol Endocrinol Metab
2007
;
292
:
E1507
E1519
[PubMed]
32.
Tanaka
T
,
Nagashima
K
,
Inagaki
N
, et al
.
Glucose-stimulated single pancreatic islets sustain increased cytosolic ATP levels during initial Ca2+ influx and subsequent Ca2+ oscillations
.
J Biol Chem
2014
;
289
:
2205
2216
[PubMed]
33.
Johnson
RA
,
Shoshani
I
.
Kinetics of “P”-site-mediated inhibition of adenylyl cyclase and the requirements for substrate
.
J Biol Chem
1990
;
265
:
11595
11600
[PubMed]
34.
Hardie
DG
.
Metformin-acting through cyclic AMP as well as AMP?
Cell Metab
2013
;
17
:
313
314
[PubMed]
35.
Vegiopoulos
A
,
Herzig
S
.
Glucocorticoids, metabolism and metabolic diseases
.
Mol Cell Endocrinol
2007
;
275
:
43
61
[PubMed]
36.
Kainuma
E
,
Watanabe
M
,
Tomiyama-Miyaji
C
, et al
.
Association of glucocorticoid with stress-induced modulation of body temperature, blood glucose and innate immunity
.
Psychoneuroendocrinology
2009
;
34
:
1459
1468
[PubMed]
37.
Lambillotte
C
,
Gilon
P
,
Henquin
JC
.
Direct glucocorticoid inhibition of insulin secretion. An in vitro study of dexamethasone effects in mouse islets
.
J Clin Invest
1997
;
99
:
414
423
[PubMed]
38.
Ullrich
S
,
Berchtold
S
,
Ranta
F
, et al
.
Serum- and glucocorticoid-inducible kinase 1 (SGK1) mediates glucocorticoid-induced inhibition of insulin secretion
.
Diabetes
2005
;
54
:
1090
1099
[PubMed]
39.
Panossian
A
,
Wikman
G
,
Sarris
J
.
Rosenroot (Rhodiola rosea): traditional use, chemical composition, pharmacology and clinical efficacy
.
Phytomedicine
2010
;
17
:
481
493
[PubMed]
40.
Panossian
A
,
Hambardzumyan
M
,
Hovhanissyan
A
,
Wikman
G
.
The adaptogens rhodiola and schizandra modify the response to immobilization stress in rabbits by suppressing the increase of phosphorylated stress-activated protein kinase, nitric oxide and cortisol
.
Drug Target Insights
2007
;
2
:
39
54
[PubMed]
41.
Olsson
EM
,
von Schéele
B
,
Panossian
AG
.
A randomised, double-blind, placebo-controlled, parallel-group study of the standardised extract shr-5 of the roots of Rhodiola rosea in the treatment of subjects with stress-related fatigue
.
Planta Med
2009
;
75
:
105
112
[PubMed]
42.
Nijsen
MJ
,
Croiset
G
,
Stam
R
, et al
.
The role of the CRH type 1 receptor in autonomic responses to corticotropin- releasing hormone in the rat
.
Neuropsychopharmacology
2000
;
22
:
388
399
[PubMed]
43.
Kalsbeek
A
,
Bruinstroop
E
,
Yi
CX
,
Klieverik
LP
,
La Fleur
SE
,
Fliers
E
.
Hypothalamic control of energy metabolism via the autonomic nervous system
.
Ann N Y Acad Sci
2010
;
1212
:
114
129
[PubMed]
44.
Schobersberger
W
,
Leichtfried
V
,
Mueck-Weymann
M
,
Humpeler
E
.
Austrian Moderate Altitude Studies (AMAS): benefits of exposure to moderate altitudes (1,500-2,500 m)
.
Sleep Breath
2010
;
14
:
201
207
[PubMed]
45.
Schobersberger
W
,
Schmid
P
,
Lechleitner
M
, et al
.
Austrian Moderate Altitude Study 2000 (AMAS 2000). The effects of moderate altitude (1,700 m) on cardiovascular and metabolic variables in patients with metabolic syndrome
.
Eur J Appl Physiol
2003
;
88
:
506
514
[PubMed]
46.
de Mol
P
,
Fokkert
MJ
,
de Vries
ST
, et al
.
Metabolic effects of high altitude trekking in patients with type 2 diabetes
.
Diabetes Care
2012
;
35
:
2018
2020
[PubMed]
47.
de Mol
P
,
de Vries
ST
,
de Koning
EJ
,
Gans
RO
,
Tack
CJ
,
Bilo
HJ
.
Increased insulin requirements during exercise at very high altitude in type 1 diabetes
.
Diabetes Care
2011
;
34
:
591
595
[PubMed]
48.
Moore
K
,
Vizzard
N
,
Coleman
C
,
McMahon
J
,
Hayes
R
,
Thompson
CJ
.
Extreme altitude mountaineering and type 1 diabetes; the Diabetes Federation of Ireland Kilimanjaro Expedition
.
Diabet Med
2001
;
18
:
749
755
[PubMed]
49.
Blüher
M
,
Kahn
BB
,
Kahn
CR
.
Extended longevity in mice lacking the insulin receptor in adipose tissue
.
Science
2003
;
299
:
572
574
[PubMed]
50.
Taguchi
A
,
Wartschow
LM
,
White
MF
.
Brain IRS2 signaling coordinates life span and nutrient homeostasis
.
Science
2007
;
317
:
369
372
[PubMed]

Supplementary data