This study tested whether ATP-dependent K+ channels (KATP channels) are an important mechanism of functional coronary hyperemia in conscious, instrument-implanted diabetic dogs. Data were collected at rest and during exercise before and after induction of diabetes with alloxan monohydrate (40–60 mg/kg intravenously). KATP channels were inhibited with glibenclamide (1 mg/kg intravenously). In nondiabetic dogs, arterial plasma glucose concentration increased from 4.8 ± 0.3 to 21.5 ± 2.2 mmol/l 1 week after alloxan injection. In nondiabetic dogs, exercise increased myocardial oxygen consumption (MVo2) 3.4-fold, myocardial O2 delivery 3.0-fold, and heart rate 2.4-fold. Coronary venous Po2 decreased from 19.9 ± 0.8 mmHg at rest to 14.8 ± 0.8 mmHg during exercise. Diabetes significantly reduced myocardial O2 delivery and lowered coronary venous Po2 from 16.3 ± 0.6 mmHg at rest to 13.1 ± 0.9 mmHg during exercise. Glibenclamide did not alter the slope of the coronary venous Po2 versus MVo2 relationship in nondiabetic dogs. In diabetic dogs, however, glibenclamide further reduced myocardial O2 delivery; coronary venous Po2 fell to 9.0 ± 1.0 mmHg during exercise, and the slope of the coronary venous PO2 versus MVo2 relationship steepened. These findings indicate that KATP channels contribute to local metabolic coronary vasodilation in alloxan-induced diabetic dogs.

Numerous investigations have focused on the role of ATP-dependent K+ (KATP) channels in coronary blood flow regulation (114). These studies indicate that KATP channels are important in regulating coronary vascular resistance under baseline conditions (310), during hypoxic coronary vasodilation (11,12), and during reactive coronary hyperemia (1,4, 13). However, it does not appear that KATP channels are required to increase coronary blood flow when myocardial metabolism is increased (35,7, 8).

Recently, Kersten et al. (14) found that diabetes enhanced KATP channel-mediated coronary vasodilation of coronary arterioles, suggesting that KATP channels are important in local metabolic coronary vasodilation in diabetes. Supporting this notion are the results of Shimoni et al. (15) showing that the half-maximal inhibitory concentration (IC50) for ATP-dependent inhibition of KATP channels was approximately twofold higher for channels from diabetic rat hearts. If there is an increase of KATP channel activity in diabetes, then oral hypoglycemic agents such as glibenclamide (Glyburide or Diabeta), which are KATP channel antagonists, could seriously impair control of coronary blood flow, especially when myocardial oxygen demand is elevated. Despite this fact, no study has examined whether KATP channels contribute to metabolic coronary vasodilation in an intact diabetic model. Furthermore, characterizing mechanisms that regulate coronary vascular tone is particularly important since coronary flow reserve (1619), functional coronary hyperemia (18), and the balance between coronary blood flow and myocardial metabolism (20) are impaired in diabetic subjects.

Accordingly, this study was designed to determine whether KATP channels contribute to local metabolic coronary vasodilation in diabetic subjects. Experiments were conducted at rest and during graded treadmill exercise, with and without KATP channel blockade (glibenclamide, 1 mg/kg i.v.) (7,8), in chronically instrument-implanted dogs before and after induction of diabetes with alloxan monohydrate (40–60 mg/kg i.v.) (21).

Surgical preparation.

This investigation was approved by the Institutional Animal Care and Use Committee and was conducted in accordance with the Guide for the Care and Use of Laboratory Animals (National Institutes of Health publ. no. 85-23, revised 1996). Experiments were performed on six adult mongrel dogs of either sex (weighing 25–30 kg) taught to run on a motorized treadmill. Preanesthesia (acepromazine 0.03 mg/kg intramuscularly) was administered 30 min before induction of anesthesia with thiopental sodium (5 mg/kg i.v.). After endotracheal intubation, a surgical plane of anesthesia was maintained by mechanical ventilation with 1–3% isoflurane gas with supplemental oxygen. Using sterile technique, a left lateral thoracotomy was performed in the fifth intercostal space. A custom-made, coextruded polyurethane catheter (Putnam Plastics, Dayville, CT) was implanted in the descending thoracic aorta to measure aortic blood pressure and obtain arterial blood samples (8,22). A second polyurethane catheter was placed in the coronary sinus via a purse-string suture in the right atrial appendage for coronary venous blood sampling. The circumflex coronary artery was dissected free, and a flow transducer was placed around the artery. To avoid ventricular tissue injury, no devices were implanted in the myocardium and no surgical stitches were placed in the ventricles. A chest tube was placed to evacuate the pneumothorax, and the chest was closed in layers. The catheters and the flow transducer wire were tunneled subcutaneously and exteriorized between the scapulae. The incision was infiltrated with 2.5% bupivacaine, and buprenorphine (Buprenex) (0.3 mg intramuscularly) was administered to minimize postoperative pain. Amoxicillin (Clavamox; 6.25 mg/lb) and aspirin (81 mg) were administered twice a day for 10 days after surgery. A nylon jacket (Alice King Chatham, Hawthorne, CA) was placed on the animals to protect the catheters and the flow transducer wire. A elastomeric balloon pump (Access Technologies, Skokie, IL) was connected to the coronary sinus catheter so that heparinized saline (5 units/ml) could be continuously infused at 2 ml/h. The aortic catheter was flushed daily and filled with heparinized saline (5,000 units/ml). The animals were allowed at least 7 days for recovery before the experiments were conducted.

Pressure and flow measurements.

A coextruded polyurethane catheter was implanted in the aorta so that a high-fidelity catheter-tipped pressure transducer (Mikro-tip 3F; Millar Instruments, Houston, TX) could be inserted through it at the time of the experiment to measure aortic blood pressure (23). This pressure transducer was introduced into the polyurethane aortic catheter through a hemostatic control valve (Tuohy-Borst; Mallinckrodt Medical, Hazelwood, MO), which allowed arterial blood samples to be drawn while maintaining a fluid-tight seal around the catheter.

Phasic and mean coronary blood flow were continuously measured throughout the experimental protocol with an ultrasonic, perivascular flow transducer (Transonic Systems, Ithaca, NY). After experiments were completed, the animals were killed with sodium pentobarbital, and the circumflex perfusion territory was dyed with Evans blue. The weight of the dyed tissue was used to calculate coronary blood flow per gram of perfused myocardium.

Blood sampling.

Arterial and coronary venous blood samples were collected simultaneously in heparinized syringes that were immediately sealed and placed on ice. The samples were analyzed in duplicate for pH, Pco2, Po2, hematocrit, and oxygen content with an automatic blood gas analyzer (Synthesis 30) and CO-oximeter (model 682) system (Instrumentation Laboratories, Lexington, MA). Plasma glucose and lactate concentrations were measured with a Radiometer analyzer (model EML105; Radiometer, Bronshoj, Denmark). Myocardial oxygen consumption (MVo2) (μl O2 · min−1 · g−1) was calculated by multiplying coronary blood flow per gram of perfused tissue by the coronary arteriovenous difference in oxygen content. Lactate uptake (μmol · min−1 · g−1) was calculated by multiplying coronary plasma flow per gram of perfused tissue by the coronary arteriovenous difference in plasma lactate concentration.

Experimental protocol.

The hypothesis that KATP channels are an important mechanism of functional coronary hyperemia in diabetes was tested at rest and during graded treadmill exercise with and without the KATP channel inhibitor glibenclamide. Each animal served as its own control. The dose of glibenclamide (1 mg/kg i.v.) used in this investigation has been used in previous studies (7, 8,24) and was found to effectively block the vasodilating action of the KATP channel opener cromakalim (25). After an overnight fast, coronary blood flow, aortic pressure, and heart rate were continuously measured while the dogs were resting in a sling and then during three levels of treadmill exercise: 1) 2 mph, 0% grade; 2) 3 mph, 5% grade; and 3) 4 mph, 10% grade. The animals exercised at similar levels (i.e., speed and percent grade) before and after alloxan treatment. Arterial and coronary venous blood samples were collected when hemodynamic variables were stable at each exercise level. Each exercise period was ∼2 min in duration, and the animals were allowed to rest sufficiently between each level for hemodynamic variables to return to baseline.

After nondiabetic control experiments were conducted, alloxan monohydrate (40–60 mg/kg) was administered intravenously over 1 min to induce diabetes (21). Alloxan was prepared as a 5% solution in citrate buffer (pH 4.0–4.5). The dogs were fasted at least 12 h before the injection of alloxan and were then fed immediately. A dog was considered diabetic if its plasma glucose concentration was >11 mmol/l. The experimental protocol described above was repeated in the diabetic animals at least 7 days after the alloxan injection with and without glibenclamide. In addition, three experiments were also conducted at rest and during exercise with glibenclamide in nondiabetic dogs to confirm the previous findings that KATP channels are not required for exercise-induced coronary vasodilation (35,7,8).

Assessing the relationship between coronary blood flow and myocardial metabolism.

Changes in myocardial oxygen supply must be evaluated in relation to MVo2, the primary determinant of coronary blood flow. Thus, the present data were analyzed by plotting changes in myocardial oxygen delivery and coronary venous Po2 directly with changes in MVo2. Coronary venous Po2 is a sensitive index of tissue oxygenation, and the plot of coronary venous Po2 versus MVo2 is a sensitive way to determine whether the relationship between coronary blood flow and myocardial metabolism has been altered. On this plot, a vasodilator influence will either shift the regression line upward or make the slope less negative. A vasoconstrictor influence will shift the regression line downward or make the slope more negative. Influences on baseline flow will shift the relationship in a parallel manner, whereas an intervention that affects only exercise vasodilation will change the slope. Importantly, by plotting coronary response variables as a function of MVo2, these plots account for any drug-induced changes in heart rate, blood pressure, or contractility that may significantly affect myocardial oxygen demand. Many studies have used this approach to analyze mechanisms of coronary blood flow control (35,8,20, 22,24).

Statistical analyses.

Data are presented as means ± SE. Hemodynamic variables were recorded with a Hewlett Packard 7758A recorder and analyzed with a Sonometrics Sonolab 3.1.4 data acquisition system. Statistical testing was directed to detect overall treatment effects, i.e., diabetes-control versus diabetes-glibenclamide. A repeated-measures ANOVA was used to test for differences between coronary and systemic hemodynamic variables at rest and during exercise. When significance was found with ANOVA (P < 0.05), a Student-Newman-Keul’s multiple comparison test was performed. Linear regression analysis was used to compare the slopes of response variables (oxygen delivery and coronary venous Po2) plotted versus MVo2.

Hemodynamic, blood gas, and metabolic variables at rest and during exercise are given in Table 1. Average blood urea nitrogen and creatinine levels after 1 week of alloxan treatment were 34.5 ± 11.9 and 1.75 ± 0.60 mg/dl, respectively. (Reference values for dogs range from 7 to 27 mg/dl for blood urea nitrogen and from 0.5 to 1.8 mg/dl for creatinine.) Body weight was reduced from 28.7 ± 3 to 27.5 ± 3 kg after alloxan treatment. Average arterial plasma glucose concentration increased from 4.8 ± 0.3 mmol/l in nondiabetic control dogs to 21.5 ± 2.2 mmol/l ∼1 week after alloxan injection. Glibenclamide did not significantly alter the arterial plasma glucose concentration in the alloxan-treated dogs. In the nondiabetic control dogs, exercise significantly increased MVo2 3.4-fold, myocardial oxygen delivery 3.0-fold, and heart rate 2.4-fold (Table 1). Coronary venous Po2 decreased from 19.9 ± 0.8 mmHg at rest to 14.8 ± 0.8 mmHg at the highest level of exercise. Diabetes significantly reduced the exercise-induced increase in myocardial oxygen delivery to 2.5-fold and lowered the coronary venous Po2 to 16.3 ± 0.8 mmHg at rest and to 13.3 ± 0.8 mmHg during exercise.

Blockade of KATP channels with glibenclamide in the diabetic dogs tended to lower coronary blood flow (Fig. 1A) and MVo2 (Fig. 1B) at rest and during exercise. KATP channel blockade decreased myocardial oxygen delivery at the highest level of exercise (Fig. 1C) and significantly reduced coronary venous Po2 to 14.3 ± 0.7 mmHg at rest and to 9.4 ± 0.9 mmHg at the highest level of exercise (Fig. 1D).

The relationship between myocardial oxygen delivery and MVo2 is shown in Fig. 2. Glibenclamide treatment significantly decreased the slope of this relationship (P = 0.03), indicating that KATP channels are important to functional exercise coronary hyperemia in alloxan-induced diabetes. Because of the normally high oxygen extraction by the left ventricle (8,22,24), the data points and regression lines lie extremely close to the line of 100% oxygen extraction (oxygen consumed = oxygen delivery) illustrated in Fig. 2. Thus, significant differences in oxygen delivery at a given MVo2 are hard to visualize. The difference between these data points and the line of 100% oxygen extraction represents the oxygen extraction reserve of the myocardium, which is shown in Fig. 3. Glibenclamide significantly reduced the percent myocardial oxygen reserve at rest and at each level of exercise, indicating that KATP channel blockade impaired the balance between oxygen delivery and consumption and forced the heart to use more of its limited oxygen extraction reserve.

A more sensitive index of the relationship between coronary blood flow and myocardial metabolism is shown in the plot of coronary venous Po2 versus MVo2 (Fig. 4) (4,5,8,20,22, 24). KATP channel blockade with glibenclamide made the slope of this relationship more negative (P = 0.01), indicating that KATP channels contribute to local metabolic coronary vasodilation in experimental diabetes.

Additional experiments (n = 3) were also conducted to confirm earlier findings of the effects of KATP channel blockade on coronary blood flow control during exercise. Results from these experiments, plus a replotting of the data from Richmond et al. (8), are shown in Fig. 5. Consistent with previous studies (3,8), KATP channel blockade with glibenclamide in the normal (control) dogs resulted in a significant parallel shift downward in the relationship between coronary venous Po2 and MVo2 (P < 0.0001). However, the slope of this relationship did not become more negative (P = 0.66), indicating that KATP channels are not required for exercise-induced coronary vasodilation in normal, nondiabetic dogs.

The present study is the first to examine whether KATP channels contribute to local metabolic coronary vasodilation during exercise in experimental diabetes. Relative to diabetes alone, KATP channel blockade with glibenclamide significantly reduced myocardial oxygen delivery at the highest level of exercise (Fig. 1C) and reduced the slope of the relationship between myocardial oxygen delivery and MVo2 (Fig. 2), thereby decreasing the oxygen reserve of the myocardium (Fig. 3). In addition, glibenclamide made the slope of the relationship between coronary venous Po2 and MVo2 more negative (Fig. 4). These findings indicate that KATP channels are an important mechanism of functional coronary hyperemia in experimental diabetes.

KATP channels, coronary blood flow control, and diabetes.

Whether KATP channels contribute to functional coronary hyperemia in diabetic subjects has not been previously investigated. This hypothesis was examined in the present study by relating changes in myocardial oxygen delivery and coronary venous Po2 directly with changes in MVo2. Thus, changes in myocardial oxygen supply are related directly to changes in myocardial oxygen demand. When KATP channels were inhibited in the diabetic dogs with glibenclamide, the slope of the coronary venous Po2 vs. MVo2 relationship (Fig. 4) was steepened, i.e., became more negative. This finding indicates that KATP channels normally contribute to local metabolic coronary vasodilation in the diabetic animals. In addition, glibenclamide significantly decreased the slope of the relationship between myocardial oxygen delivery and MVo2 (Fig. 2). In other words, the oxygen delivery to the myocardium was impaired by glibenclamide as MVo2 was increased during exercise. It should be appreciated that the slope of this relationship can only decrease to a limited extent, since the myocardial oxygen extraction is so high at rest (>80% in the diabetic group). Because KATP channel blockade limited the delivery of oxygen to the myocardium, the heart was forced to use more of its limited extraction reserve to meet the metabolic requirements of the tissue. This fact is also evidenced by the reduction in the oxygen reserve of the myocardium (Fig. 3).

The present findings that KATP channels contribute to local metabolic coronary vasodilation in alloxan-induced diabetic dogs are supported by the earlier findings of Kersten et al. (14), who found that the coronary vasodilatory response of coronary arterioles (<100 μm) to the KATP channel agonist aprikalim was significantly enhanced in alloxan-induced diabetic dogs relative to euglycemic (control) dogs. The coronary arteriolar response to aprikalim was also enhanced in nondiabetic hyperglycemic dogs, suggesting that high circulating glucose levels may be responsible for the increase in KATP channel activity. The results of Shimoni et al. (15), showing that the IC50 for ATP-dependent inhibition of KATP channels was approximately twofold higher for channels from diabetic rat hearts, also support the present findings. Further studies are needed to determine whether hyperglycemia per se is responsible for the apparent increase in KATP channel activity detected in this investigation.

It should be acknowledged that glibenclamide also has nonspecific effects on other coronary vasodilator mechanisms that may have contributed to the present findings. Most notably, glibenclamide also significantly attenuates adenosine-mediated coronary vasodilation (2,4,5,11,13, 24,25). Adenosine does not contribute to local metabolic coronary vasodilation during exercise in nondiabetic animals (22), and furthermore, adenosine-induced coronary vasodilation is attenuated in diabetic animals (21, 2628). Therefore, it is unlikely that glibenclamide-induced attenuation of adenosine vasodilation was directly responsible for the findings of this study. However, our laboratory recently reported that the balance between coronary blood flow and myocardial metabolism is significantly impaired at rest and during exercise in alloxan-induced diabetic dogs (20). Data from the present study support this finding (Table 1). This imbalance could lead to a compensatory increase in cardiac adenosine release, in which case the present treatment with glibenclamide would have blunted vasodilation of both KATP channels and adenosine. Either way, this study has demonstrated that sulfonylurea treatment with glibenclamide significantly attenuates functional coronary hyperemia in diabetic dogs.

Previous investigations have examined the role of KATP channels in modulating coronary vascular resistance in nondiabetic animals. The consensus of these studies is that KATP channels contribute to control of resting coronary blood flow (310) but are not required for coronary hyperemia during increases in MVo2 (35,7,8). Data from control (nondiabetic) animals studied in this investigation support these conclusions. At rest, glibenclamide decreased resting coronary flow and venous Po2 (Fig. 5). During exercise, glibenclamide did not compromise coronary vasodilation in these animals, since the KATP channel blockade resulted in a parallel shift of the coronary venous Po2 versus MVo2 relationship but did not significantly alter the slope (Fig. 5).

Alloxan-induced diabetes.

The present experiments were conducted in alloxan-induced diabetic animals whose fasting plasma glucose concentration averaged ∼20 mmol/l (360 mg/dl). Acute glibenclamide administration did not significantly reduce the arterial plasma glucose concentration (Table 1), indicating that an increase in the release of insulin from the pancreas was not a confounding effect of glibenclamide treatment in this study. This effect is most likely due to the fact that alloxan destroys the islets of Langerhans in pancreas, and thus insulin release could not be significantly altered (29). The animals were not treated with insulin and thus represent a model of poorly controlled type 1 diabetes, i.e., chronic hypoinsulinemia and hyperglycemia. Whether KATP channels contribute to exercise-induced coronary vasodilation in type 2 (insulin-resistant) diabetes merits future investigation.

Clinical implications.

Sulfonylurea-derivative drugs such as glibenclamide have been used for many years to increase insulin release in patients with non-insulin-dependent diabetes. However, studies showing that blockade of KATP channels increases coronary vascular resistance in experimental nondiabetic animals (310) has led to an unresolved debate as to whether sulfonylurea drugs should be used in patients with diabetes, especially those with ischemic heart disease (30,31). In earlier studies designed to examine the effect of diabetes on coronary flow reserve, some patients had received oral hypoglycemic therapy (18, 32). Because the drug was withheld on the day of the investigation, its effect on coronary flow control was not determined. However, other investigations have reported a significant decrease in forearm vascular blood flow (33) and in calf reactive hyperemia (34) in nondiabetic humans after oral glibenclamide treatment.

It is also important to point out that KATP channels have different properties in different tissues. The IC50 for glibenclamide is ∼4 nmol/l in pancreatic β-cells and ∼27 nmol/l in cardiac myocytes (35,36). Its lower potency in cardiac myocytes suggests that glibenclamide could possibly affect pancreatic insulin release without influencing coronary vasomotor tone at clinically administered doses. However, the fact that oral glibenclamide reduced peripheral blood flow control in nondiabetic patients argues against this hypothesis (33,34). To date, no study has directly examined whether oral hypoglycemic drugs significantly impair coronary vasodilation in diabetic humans.

Conclusion.

This study is the first to show that KATP channels contribute to local metabolic coronary vasodilation in experimental diabetic animals. This finding is important because it is well established that KATP channels are not required for functional coronary hyperemia in normal (nondiabetic) animals (35,7,8). Future clinical studies are needed to determine whether oral hypoglycemic therapy with agents such as glibenclamide compromises coronary vasodilation in patients with diabetes.

FIG. 1.

Average results of coronary blood flow (A), MVo2 (B), oxygen delivery (C), and coronary venous Po2 (D) at rest and during exercise in diabetic dogs with and without glibenclamide treatment. Blockade of KATP channels tended to lower coronary blood flow and MVo2 at rest and during exercise. Glibenclamide significantly reduced oxygen delivery at the highest level of exercise and reduced coronary venous Po2 at each condition. *P < 0.05 vs. diabetes, same condition.

FIG. 1.

Average results of coronary blood flow (A), MVo2 (B), oxygen delivery (C), and coronary venous Po2 (D) at rest and during exercise in diabetic dogs with and without glibenclamide treatment. Blockade of KATP channels tended to lower coronary blood flow and MVo2 at rest and during exercise. Glibenclamide significantly reduced oxygen delivery at the highest level of exercise and reduced coronary venous Po2 at each condition. *P < 0.05 vs. diabetes, same condition.

FIG. 2.

The relationship between myocardial oxygen delivery and MVo2 in diabetic dogs with and without glibenclamide treatment. Glibenclamide significantly decreased the slope of this relationship, indicating that KATP channels contribute to exercise-induced coronary vasodilation in alloxan-induced diabetic dogs. The point at which the oxygen delivery equals the oxygen consumed (i.e., 100% extraction) is represented by the dash-dot-dash line.

FIG. 2.

The relationship between myocardial oxygen delivery and MVo2 in diabetic dogs with and without glibenclamide treatment. Glibenclamide significantly decreased the slope of this relationship, indicating that KATP channels contribute to exercise-induced coronary vasodilation in alloxan-induced diabetic dogs. The point at which the oxygen delivery equals the oxygen consumed (i.e., 100% extraction) is represented by the dash-dot-dash line.

FIG. 3.

Average percent oxygen reserve in diabetic dogs with and without glibenclamide treatment. Glibenclamide significantly reduced the myocardial oxygen reserve at rest and during exercise, indicating that KATP channel blockade impaired the balance between coronary blood flow and myocardial metabolism, which forced the heart to use its limited oxygen extraction reserve. *P < 0.05 vs. diabetes, same condition.

FIG. 3.

Average percent oxygen reserve in diabetic dogs with and without glibenclamide treatment. Glibenclamide significantly reduced the myocardial oxygen reserve at rest and during exercise, indicating that KATP channel blockade impaired the balance between coronary blood flow and myocardial metabolism, which forced the heart to use its limited oxygen extraction reserve. *P < 0.05 vs. diabetes, same condition.

FIG. 4.

Relationship between coronary venous Po2 and MVo2 in diabetic dogs with and without glibenclamide treatment. Glibenclamide made the slope of this relationship more negative, indicating that KATP channels contribute to local metabolic coronary vasodilation in alloxan-induced diabetic dogs.

FIG. 4.

Relationship between coronary venous Po2 and MVo2 in diabetic dogs with and without glibenclamide treatment. Glibenclamide made the slope of this relationship more negative, indicating that KATP channels contribute to local metabolic coronary vasodilation in alloxan-induced diabetic dogs.

FIG. 5.

Relationship between coronary venous Po2 and MVo2 in nondiabetic (control) dogs with and without glibenclamide treatment. Glibenclamide did not alter the slope but did produce a significant parallel shift downward in this relationship, indicating that KATP channels are not required for local metabolic coronary vasodilation in normal (nondiabetic) dogs. In addition, a replotting of the average data from Richmond et al. (8) demonstrates that our results are consistent with earlier studies.

FIG. 5.

Relationship between coronary venous Po2 and MVo2 in nondiabetic (control) dogs with and without glibenclamide treatment. Glibenclamide did not alter the slope but did produce a significant parallel shift downward in this relationship, indicating that KATP channels are not required for local metabolic coronary vasodilation in normal (nondiabetic) dogs. In addition, a replotting of the average data from Richmond et al. (8) demonstrates that our results are consistent with earlier studies.

TABLE 1

Hemodynamic, blood gas, and metabolic variables at rest and during graded treadmill exercise

nRestExercise
Level 1Level 2Level 3
Coronary blood flow (ml · min−1 · g−1     
 Control 0.59 ± 0.04 1.01 ± 0.05 1.25 ± 0.09 1.65 ± 0.16 
 Diabetes 0.55 ± 0.06 0.69 ± 0.09* 0.94 ± 0.14* 1.19 ± 0.17* 
 Diabetes + glibenclamide 0.48 ± 0.03 0.65 ± 0.06* 0.83 ± 0.06* 1.05 ± 0.11* 
Myocardial oxygen delivery (μl O2 · min−1 · g−1     
 Control 105 ± 6 198 ± 9 239 ± 14 316 ± 27 
 Diabetes 94 ± 10 130 ± 19* 178 ± 27* 236 ± 35* 
 Diabetes + glibenclamide 80 ± 7 116 ± 14* 144 ± 14* 193 ± 25* 
Myocardial O2 consumption (μl O2 · min−1 · g−1     
 Control 80 ± 4 169 ± 7 205 ± 11 272 ± 22 
 Diabetes 78 ± 7 114 ± 18* 156 ± 24 211 ± 34* 
 Diabetes + glibenclamide 69 ± 6 106 ± 13* 134 ± 14* 180 ± 26* 
Mean aortic pressure (mmHg)      
 Control 106 ± 4 114 ± 5 112 ± 7 119 ± 4 
 Diabetes 105 ± 5 110 ± 5 113 ± 2 116 ± 3 
 Diabetes + glibenclamide 115 ± 6 120 ± 5 122 ± 3 123 ± 3 
Heart rate (beats/min)      
 Control 98 ± 7 155 ± 11 183 ± 9 236 ± 19 
 Diabetes  95 ± 13 134 ± 13 172 ± 10 206 ± 8 
 Diabetes + glibenclamide 81 ± 12* 114 ± 9* 153 ± 16* 187 ± 18* 
Arterial pH      
 Control 7.42 ± 0.01 7.44 ± 0.01 7.46 ± 0.02 7.45 ± 0.02 
 Diabetes 7.42 ± 0.02 7.43 ± 0.03 7.42 ± 0.02 7.43 ± 0.02 
 Diabetes + glibenclamide 7.40 ± 0.02 7.43 ± 0.02 7.43 ± 0.03 7.44 ± 0.02 
Coronary venous pH      
 Control 7.38 ± 0.01 7.41 ± 0.02 7.40 ± 0.02 7.39 ± 0.02 
 Diabetes 7.37 ± 0.02 7.39 ± 0.03 7.39 ± 0.02 7.39 ± 0.03 
 Diabetes + glibenclamide 7.37 ± 0.02 7.39 ± 0.02 7.40 ± 0.02 7.39 ± 0.02 
Arterial Po2 (mmHg)      
 Control 87 ± 2 99 ± 4 94 ± 3 84 ± 4 
 Diabetes 86 ± 2 93 ± 3 88 ± 4 86 ± 3 
 Diabetes + glibenclamide 87 ± 3 89 ± 3* 90 ± 4 85 ± 4 
Coronary venous Po2 (mmHg) 
 Control 19.9 ± 0.8 15.1 ± 0.8 15.0 ± 0.6 14.8 ± 0.8 
 Diabetes 16.3 ± 0.8 13.7 ± 0.8 13.3 ± 0.7 13.3 ± 0.8 
 Diabetes + glibenclamide 14.3 ± 0.7* 10.6 ± 0.7* 9.4 ± 0.9* 9.4 ± 0.9* 
Arterial Pco2 (mmHg) 
 Control 34 ± 1 28 ± 2 28 ± 1 28 ± 2 
 Diabetes 30 ± 1 27 ± 2 27 ± 1 26 ± 2 
 Diabetes + glibenclamide 30 ± 2 28 ± 2 27 ± 2 27 ± 2 
Coronary venous Pco2 (mmHg)      
 Control 47 ± 2 44 ± 2 43 ± 2 43 ± 2 
 Diabetes 45 ± 3 42 ± 3 41 ± 2 40 ± 2 
 Diabetes + glibenclamide 44 ± 3 42 ± 2 41 ± 2 42 ± 2 
Hematocrit (%)      
 Control 38 ± 2 40 ± 2 40 ± 2 42 ± 3 
 Diabetes 40 ± 1 40 ± 2 41 ± 1 42 ± 3 
 Diabetes + glibenclamide 36 ± 1 39 ± 2 39 ± 2 41 ± 2 
Arterial oxygen content (ml O2/dl blood)      
 Control 17.9 ± 0.7 19.7 ± 0.9 19.5 ± 0.9 19.7 ± 1.1 
 Diabetes 17.8 ± 0.6 19.1 ± 0.9 18.6 ± 0.4 19.1 ± 0.8 
 Diabetes + glibenclamide 16.8 ± 0.6 17.7 ± 0.9 17.1 ± 0.6 18.2 ± 0.8 
Coronary venous oxygen content (ml O2/dl blood)      
 Control 4.3 ± 0.3 2.8 ± 0.2 2.7 ± 0.2 2.7 ± 0.2 
 Diabetes 2.8 ± 0.2 2.5 ± 0.3 2.3 ± 0.3 2.3 ± 0.4 
 Diabetes + glibenclamide  2.3 ± 0.2* 1.5 ± 0.2* 1.3 ± 0.2* 1.3 ± 0.3* 
Arterial plasma glucose concentration (mmol/l)      
 Control 4.8 ± 0.3 4.6 ± 0.2 4.6 ± 0.3 5.2 ± 0.3 
 Diabetes 21.5 ± 2.2* 20.5 ± 2.4* 21.3 ± 2.3* 21.8 ± 1.9* 
 Diabetes + glibenclamide 19.9 ± 2.5* 20.1 ± 2.5* 19.5 ± 2.5* 20.8 ± 2.7* 
Myocardial lactate uptake (μmol · min−1 · g−1
 Control 0.08 ± 0.03 0.21 ± 0.08 0.42 ± 0.14 0.77 ± 0.32 
 Diabetes 0.01 ± 0.01 0.03 ± 0.02 0.06 ± 0.03 −0.04 ± 0.04* 
 Diabetes + glibenclamide 0.01 ± 0.01 0.06 ± 0.02 0.08 ± 0.02 0.05 ± 0.05* 
nRestExercise
Level 1Level 2Level 3
Coronary blood flow (ml · min−1 · g−1     
 Control 0.59 ± 0.04 1.01 ± 0.05 1.25 ± 0.09 1.65 ± 0.16 
 Diabetes 0.55 ± 0.06 0.69 ± 0.09* 0.94 ± 0.14* 1.19 ± 0.17* 
 Diabetes + glibenclamide 0.48 ± 0.03 0.65 ± 0.06* 0.83 ± 0.06* 1.05 ± 0.11* 
Myocardial oxygen delivery (μl O2 · min−1 · g−1     
 Control 105 ± 6 198 ± 9 239 ± 14 316 ± 27 
 Diabetes 94 ± 10 130 ± 19* 178 ± 27* 236 ± 35* 
 Diabetes + glibenclamide 80 ± 7 116 ± 14* 144 ± 14* 193 ± 25* 
Myocardial O2 consumption (μl O2 · min−1 · g−1     
 Control 80 ± 4 169 ± 7 205 ± 11 272 ± 22 
 Diabetes 78 ± 7 114 ± 18* 156 ± 24 211 ± 34* 
 Diabetes + glibenclamide 69 ± 6 106 ± 13* 134 ± 14* 180 ± 26* 
Mean aortic pressure (mmHg)      
 Control 106 ± 4 114 ± 5 112 ± 7 119 ± 4 
 Diabetes 105 ± 5 110 ± 5 113 ± 2 116 ± 3 
 Diabetes + glibenclamide 115 ± 6 120 ± 5 122 ± 3 123 ± 3 
Heart rate (beats/min)      
 Control 98 ± 7 155 ± 11 183 ± 9 236 ± 19 
 Diabetes  95 ± 13 134 ± 13 172 ± 10 206 ± 8 
 Diabetes + glibenclamide 81 ± 12* 114 ± 9* 153 ± 16* 187 ± 18* 
Arterial pH      
 Control 7.42 ± 0.01 7.44 ± 0.01 7.46 ± 0.02 7.45 ± 0.02 
 Diabetes 7.42 ± 0.02 7.43 ± 0.03 7.42 ± 0.02 7.43 ± 0.02 
 Diabetes + glibenclamide 7.40 ± 0.02 7.43 ± 0.02 7.43 ± 0.03 7.44 ± 0.02 
Coronary venous pH      
 Control 7.38 ± 0.01 7.41 ± 0.02 7.40 ± 0.02 7.39 ± 0.02 
 Diabetes 7.37 ± 0.02 7.39 ± 0.03 7.39 ± 0.02 7.39 ± 0.03 
 Diabetes + glibenclamide 7.37 ± 0.02 7.39 ± 0.02 7.40 ± 0.02 7.39 ± 0.02 
Arterial Po2 (mmHg)      
 Control 87 ± 2 99 ± 4 94 ± 3 84 ± 4 
 Diabetes 86 ± 2 93 ± 3 88 ± 4 86 ± 3 
 Diabetes + glibenclamide 87 ± 3 89 ± 3* 90 ± 4 85 ± 4 
Coronary venous Po2 (mmHg) 
 Control 19.9 ± 0.8 15.1 ± 0.8 15.0 ± 0.6 14.8 ± 0.8 
 Diabetes 16.3 ± 0.8 13.7 ± 0.8 13.3 ± 0.7 13.3 ± 0.8 
 Diabetes + glibenclamide 14.3 ± 0.7* 10.6 ± 0.7* 9.4 ± 0.9* 9.4 ± 0.9* 
Arterial Pco2 (mmHg) 
 Control 34 ± 1 28 ± 2 28 ± 1 28 ± 2 
 Diabetes 30 ± 1 27 ± 2 27 ± 1 26 ± 2 
 Diabetes + glibenclamide 30 ± 2 28 ± 2 27 ± 2 27 ± 2 
Coronary venous Pco2 (mmHg)      
 Control 47 ± 2 44 ± 2 43 ± 2 43 ± 2 
 Diabetes 45 ± 3 42 ± 3 41 ± 2 40 ± 2 
 Diabetes + glibenclamide 44 ± 3 42 ± 2 41 ± 2 42 ± 2 
Hematocrit (%)      
 Control 38 ± 2 40 ± 2 40 ± 2 42 ± 3 
 Diabetes 40 ± 1 40 ± 2 41 ± 1 42 ± 3 
 Diabetes + glibenclamide 36 ± 1 39 ± 2 39 ± 2 41 ± 2 
Arterial oxygen content (ml O2/dl blood)      
 Control 17.9 ± 0.7 19.7 ± 0.9 19.5 ± 0.9 19.7 ± 1.1 
 Diabetes 17.8 ± 0.6 19.1 ± 0.9 18.6 ± 0.4 19.1 ± 0.8 
 Diabetes + glibenclamide 16.8 ± 0.6 17.7 ± 0.9 17.1 ± 0.6 18.2 ± 0.8 
Coronary venous oxygen content (ml O2/dl blood)      
 Control 4.3 ± 0.3 2.8 ± 0.2 2.7 ± 0.2 2.7 ± 0.2 
 Diabetes 2.8 ± 0.2 2.5 ± 0.3 2.3 ± 0.3 2.3 ± 0.4 
 Diabetes + glibenclamide  2.3 ± 0.2* 1.5 ± 0.2* 1.3 ± 0.2* 1.3 ± 0.3* 
Arterial plasma glucose concentration (mmol/l)      
 Control 4.8 ± 0.3 4.6 ± 0.2 4.6 ± 0.3 5.2 ± 0.3 
 Diabetes 21.5 ± 2.2* 20.5 ± 2.4* 21.3 ± 2.3* 21.8 ± 1.9* 
 Diabetes + glibenclamide 19.9 ± 2.5* 20.1 ± 2.5* 19.5 ± 2.5* 20.8 ± 2.7* 
Myocardial lactate uptake (μmol · min−1 · g−1
 Control 0.08 ± 0.03 0.21 ± 0.08 0.42 ± 0.14 0.77 ± 0.32 
 Diabetes 0.01 ± 0.01 0.03 ± 0.02 0.06 ± 0.03 −0.04 ± 0.04* 
 Diabetes + glibenclamide 0.01 ± 0.01 0.06 ± 0.02 0.08 ± 0.02 0.05 ± 0.05* 

Data are means ± SE.

*

P < 0.05 vs. diabetes, same condition;

P < 0.05 vs. control, same condition.

This study was supported by a Career Development Award to J.D.T. from the American Diabetes Association.

The authors wish to thank Arthur G. Williams, Jr., and Abraham Heymann for expert technical assistance.

1.
Aversano T, Ouyang P, Silverman H: Blockade of the ATP-sensitive potassium channel modulates reactive hyperemia in the canine coronary circulation.
Circ Res
69
:
618
–622,
1991
2.
Belloni FL, Hintze TH: Glibenclamide attenuates adenosine-induced bradycardia and coronary vasodilation.
Am J Physiol Heart Circ Physiol
261
:
H720
– H727,
1991
3.
Duncker DJ, Van Zon NS, Altman JD, Pavek TJ, Bache RJ: Role of K+ATP channels in coronary vasodilation during exercise.
Circulation
88
:
1245
–1253,
1993
4.
Duncker DJ, Van Zon NS, Pavek TJ, Herrlinger SK, Bache RJ: Endogenous adenosine mediates coronary vasodilation during exercise after K+ATP channel blockade.
J Clin Invest
95
:
285
–295,
1995
5.
Duncker DJ, Van Zon NA, Ishibashi Y, Bache RJ: Role of K+ATP channels and adenosine in the regulation of coronary blood flow during exercise with normal and restricted coronary blood flow.
J Clin Invest
97
:
996
– 1009,
1996
6.
Imamura Y, Tomoike H, Narishige T, Takahashi T, Kasuya H, Takeshita A: Glibenclamide decreases basal coronary blood flow in anesthetized dogs.
Am J Physiol Heart Circ Physiol
263
:
H399
–H404,
1992
7.
Richmond KN, Tune JD, Gorman MW, Feigl EO: Role of K+ATP channels in local metabolic coronary vasodilation.
Am J Physiol Heart Circ Physiol
277
:
H2115
–H2123,
1999
8.
Richmond KN, Tune JD, Gorman MW, Feigl EO: Role of K+ATP channels and adenosine in control of coronary blood flow during exercise.
J Appl Physiol
89
:
529
–536,
2000
9.
Samaha FF, Heineman FW, Ince C, Fleming J, Balaban RS: ATP-sensitive potassium channel is essential to maintain basal coronary vascular tone in vivo.
Am J Physiol Cell Physiol
262
:
C1220
–C1227,
1992
10.
Standen NB, Quayle JM, Davies NW, Brayden JE, Huang Y, Nelson MT: Hyperpolarizing vasodilators activate ATP-sensitive potassium channels in arterial smooth muscle.
Science
245
:
177
–180,
1989
11.
Daut J, Maier-Rudolph W, Beckerath NV, Mehrke G, Gunther K, Goedel-Meinen L: Hypoxic dilation of coronary arteries is mediated by ATP-sensitive potassium channels.
Science
247
:
1341
–1344,
1990
12.
Nakhostine N, Lamontagne D: Contribution of prostaglandins in hypoxia-induced vasodilatation in isolated rabbit hearts: relation to adenosine and KATP channels.
Pflügers Arch
428
:
526
–532,
1994
13.
Clayton FC, Hess TA, Smith MA, Grover GJ: Coronary reactive hyperemia and adenosine-induced vasodilation are mediated paritally by a glyburide-sensitive mechanism.
Pharmacology
44
:
92
–100,
1992
14.
Kersten JR, Brooks LA, Dellsperger KC: Impaired microvascular response to graded coronary occlusion in diabetic and hyperglycemic dogs.
Am J Physiol Heart Circ Physiol
268
:
H1667
–H1674,
1995
15.
Shimoni Y, Light PE, French RJ: Altered ATP sensitivity of ATP-dependent K+ channels in diabetic rat hearts.
Am J Physiol Endocrinol Metab
275
:
E568
–E576,
1998
16.
Meyer C, Schwaiger M: Myocardial blood flow and glucose metabolism in diabetes mellitus.
Am J Cardiol
80 (Suppl. 3A)
:
94A
–101A,
1997
17.
Nitenberg A, Valensi P, Sachs R, Dali M, Aptecar E, Attali J-R: Impairment of coronary vascular reserve and Ach-induced coronary vasodilation in diabetic patients with angiographically normal coronary arteries and normal left ventricular systolic function.
Diabetes
42
:
1017
–1025,
1993
18.
Nahser PJ, Brown RE, Oskarsson H, Winniford MD, Rossen JD: Maximal coronary flow reserve and metabolic coronary vasodilation in patients with diabetes mellitus.
Circulation
91
:
635
–640,
1995
19.
Pikänen O-P, Nuutila P, Raitakari OT, Rö nnemaa T, Koskinen PJ, Iida H, Lehtimäki TJ, Laine HK, Takala T, Viikari JSA, Knuuti J: Coronary flow reserve is reduced in young men with IDDM.
Diabetes
47
:
248
–254,
1998
20.
Tune JD, Yeh C, Setty S, Zong P, Downey HF: Coronary blood flow control is impaired at rest and during exercise in conscious diabetic dogs.
Basic Res Cardiol.
In press
21.
Zhao G, Zhang X, Smith CJ, Xu X, Ochoa M, Greenhouse D, Vogel T, Curran C, Hintze TH: Reduced coronary NO production in conscious dogs after the development of alloxan-induced diabetes.
Am J Physiol Heart Circ Physiol
277
:
H268
–H278,
1999
22.
Tune JD, Richmond KN, Gorman MW, Feigl EO: Adenosine is not responsible for local metabolic control of coronary blood flow in exercising dogs.
Am J Physiol Heart Circ Physiol
278
:
H74
–H84,
2000
23.
Fanton JW, Lott LE, Lott KA, Reister C, White CD, Latham RD: A method for repeated high-fidelity micromanometer measurements of intracardiac pressures.
J Invest Surg
9
:
67
–173,
1995
24.
Tune JD, Richmond KN, Gorman MW, Feigl EO: K+ATP channels, nitric oxide, and adenosine are not required for local metabolic coronary vasodilation.
Am J Physiol Heart Circ Physiol
280
:
H868
–H875,
2001
25.
Stepp DW, Kroll K, Feigl EO: K+ATP channels and adenosine are not necessary for coronary autoregulation.
Am J Physiol Heart Circ Physiol
273
:
H1299
–H1308,
1997
26.
Downing SE, Lee JC, Weinstein EM: Coronary dilator actions of adenosine and CO2 in experimental diabetes.
Am J Physiol Heart Circ Physiol
243
:
H252
–H258,
1982
27.
Downing SE, Chen V: Dissociation of adenosine from metabolic regulation of coronary flow in the lamb.
Am J Physiol Heart Circ Physiol
251
:
H40
–H46,
1986
28.
Koltai MZ, Wagner M, Pogatsa G: Altered hyperemic response of the coronary arterial bed in alloxan-diabetes.
Experientia
39
:
738
–740,
1983
29.
Rerup CC: Drugs producing diabetes through damage of the insulin secreting cells.
Pharmacol Rev
22
:
485
–518,
1970
30.
Schotborgh CE, Wilde AAM: Sulfonylurea derivatives in cardiovascular research and in cardiovascular patients.
Cariovasc Res
34
:
73
–80,
1997
31.
Hofmann D, Opie LH: Potassium channel blockade and acute myocardial infarction: implications for management of the non-insulin requiring diabetic patient.
Eur Heart J
14
:
1585
–1589,
1993
32.
Yokoyama I, Momomura S-I, Ohtake T, Yonekura K, Nishikawa J, Sasaki Y, Omata M: Reduced myocardial flow reserve in non-insulin dependent diabetes mellitus.
J Am Coll Cardiol
30
:
1472
–1477,
1997
33.
Bijlstra PJ, Lutterman JA, Russell FGM, Thien T, Smits P: Interaction of sulphonylurea derivatives with vascular ATP sensitive channels in humans.
Diabetologia
39
:
1083
–1090,
1996
34.
Kosmas EN, Levy RD, Hussain SNA: Acute effects of glyburide on the regulation of peripheral blood flow in normal humans.
Eur J Pharmacol
274
:
193
–199,
1995
35.
Gribble FM, Tucker SJ, Seino S, Ashcroft FM: Tissue specificity of sulfonylureas: studies on cloned cardiac and β-cell KATP channels.
Diabetes
47
:
1412
–1418,
1998
36.
Geisen K, Vegh A, Krause E, Papp JP: Cardiovascular effects of conventional sulfonylureas and glimepiride.
Horm Metab Res
28
:
496
–507,
1996

Address correspondence and reprint requests to Johnathan D. Tune, Department of Integrative Physiology, University of North Texas Health Science Center, 3500 Camp Bowie Blvd., Fort Worth, TX 76107. E-mail: jtune@hsc.unt.edu.

Received for publication 4 September 2001 and accepted in revised form 4 January 2002.

KATP channels, ATP-dependent K+ channels; MVo2, myocardial oxygen consumption.