Hypoglycemia reduces sympathoadrenal responses to subsequent hypoglycemic bouts by an unknown mechanism. To assess whether such hypoglycemia-associated autonomic failure is due to actual brain damage, male Sprague-Dawley rats underwent 1-h bouts of insulin-induced (5 U/kg i.v.) hypoglycemia (1.6-2.8 mmol/l) 1 or 3 times on alternate days. Rats remained alert and were rescued with intravenous glucose at 60-80 min. Plasma epinephrine and corticosterone responses were significantly reduced during the second and third bouts. Brains from these rats were processed by the terminal transferase-mediated deoxyuridine triphosphate-biotin nick end-labeling (TUNEL) procedure as an index of apoptotic cell death at 24, 48, or 96 h after their first bout. At 48 h, but not 24 h, TUNEL+ cells were consistently seen only in the arcuate nucleus (arcuate hypothalamic nucleus [ARC]). Hypoglycemic rats had 188% more apoptotic ARC cells (1 bout 39+/-5; 3 bouts 37+/-4) than euglycemic controls (13+/-3;P = 0.001). In situ hybridization for neuropeptide Y (NPY) and proopiomelanocortin (POMC) mRNA was performed in sections of ARC containing maximal numbers of apoptotic cells as well as in other fresh frozen brains. After 1 bout, NPY (0.041+/-0.003) and POMC (0.119+/-0.022) mRNA were decreased, respectively, by 52 and 55% vs. controls (NPY 0.076+/-0.007; POMC 0.222+/-0.020; P = 0.01). NPY (0.029+/-0.002) but not POMC (0.093+/-0.013) fell 29% further after a third bout. NPY (r = -0.721; P = 0.001) and POMC (r = -0.756; P = 0.001) mRNA levels correlated negatively with the number of apoptotic ARC cells in the same sections. Thus, non-coma hypoglycemia produces apparent apoptotic cell death with reduced NPY and POMC expression selectively in the ARC. This may contribute to the reduced counterregulatory response following repeated bouts of hypoglycemia.
Presumed apoptosis and reduced arcuate nucleus neuropeptide Y and pro-opiomelanocortin mRNA in non-coma hypoglycemia.
N C Tkacs, A A Dunn-Meynell, B E Levin; Presumed apoptosis and reduced arcuate nucleus neuropeptide Y and pro-opiomelanocortin mRNA in non-coma hypoglycemia.. Diabetes 1 May 2000; 49 (5): 820–826. https://doi.org/10.2337/diabetes.49.5.820
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