385-P: Blocking the Nicotinic Receptors of the Parasympathetic Nervous System Prevents Severe Hypoglycemia-Induced Fatal Cardiac Arrhythmias in Rats

Abstract

In response to hypoglycemia, excessive stimulation of the parasympathetic nervous system (PNS) may induce bradycardia and fatal heart block. Since signaling via nicotinic receptors mediates the PNS response, it was hypothesized that these receptors may mediate hypoglycemia-induced cardiac arrhythmias. To test this hypothesis, mecamylamine (a nicotinic receptor antagonist; 7.5 mg/kg, n = 17) or saline (control; n = 20) was infused intravenously in Sprague Dawley rats during insulin-induced (0.2mU/kg/min) severe hypoglycemic (10-15 mg/dl) clamps for 3 hours with electrocardiogram recordings. Compared to controls, mecamylamine-treated rats required a 3-fold higher glucose infusion rate during severe hypoglycemia, consistent with lower peak epinephrine levels (5698±557 vs. 2418±396 pg/ml; p < 0.001). In control rats, hypoglycemia led to 2nd degree heart block (1.8±1.7/min), 3rd degree heart block (32%), and mortality (25%). However, mecamylamine treatment completely prevented 2nd and 3rd degree heart block resulting in 100% survival (*p < 0.05). In summary, blocking nicotinic receptors prevents cardiac arrhythmias and mortality during severe hypoglycemia. Clinically, targeting the parasympathetic nervous system could be a logical approach to prevent sudden death in people with insulin-treated diabetes at risk for hypoglycemia. Disclosure C.M. Reno: None. J. Bayles: None. Y. Huang: None. M.B. Oxspring: None. S. Fisher: None. Funding National Institutes of Health; National Institute of Diabetes and Digestive and Kidney Diseases; JDRF