Project Summary/Abstract Hypoglycemia as a complication in the treatment of diabetes is associated with up to 10% of all deaths in type 1 diabetes. Altered autonomic function in diabetes and recurrent hypoglycemia can increase cardiovascular mortality. Hypoglycemia induced mortality is hypothesized to occur through two separate mechanisms: 1) acute hypoglycemia mediated cardiac arrhythmias and 2) recurrent hypoglycemia induced changes in autonomic function that increase risk of major cardiovascular events such as myocardial infarction (MI). Preliminary results revealed that 1) rats with type 1 diabetes have increased mortality associated with increased parasympathetic tone, and 2) recurrent hypoglycemia increases damage from an MI. Aim 1 will utilize in vivo studies in rats and transgenic mice to test blockade of the parasympathetic nervous system and target downstream pathways through the cardiac ryanodine receptor to reduce hypoglycemia-induced cardiac arrhythmias. Additionally, ex vivo heart perfusions will be used to test the involvement of parasympathetic nervous system mediated arrhythmias via the ryanodine receptor. Aim 2 will address the mechanisms of how recurrent hypoglycemia predisposes to worse outcome from a subsequent MI by utilizing in vivo rats and transgenic mice. Rodents will undergo an experimentally induced myocardial infarction after 3 days of recurrent hypoglycemia. The role of the parasympathetic nervous system and ryanodine receptors will be tested by pharmacological blockade and genetic disruption (transgenic mice), respectively. Overall, it is expected that the increased parasympathetic tone in type 1 diabetes mediates fatal cardiac arrhythmias during acute severe hypoglycemia, and recurrent hypoglycemia increases parasympathetic tone leading to increased damage from a subsequent MI. Additionally, mechanistic studies will reveal that ryanodine receptors are the downstream mediators of both arrhythmias and damage from an MI. Results from both studies have clinical implications for improving targeting strategies to prevent cardiovascular mortality associated with hypoglycemia in people with diabetes.