Hypoglycemia, Cardiovascular Autonomic Function and Type 2 Diabetes Mellitus

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DESCRIPTION (provided by applicant): Control of blood glucose is the cornerstone of diabetes management because glycemic control decreases the incidence and progression of diabetic complications. The implementation of rigorous regimens to control blood glucose levels in patients with diabetes mellitus has led to an increased incidence of severe iatrogenic hypoglycemic events. Unfortunately, hypoglycemia itself impairs the ability of individuals to respond appropriately to subsequent hypoglycemia - a disorder known as hypoglycemia associated autonomic failure, thus increasing the predisposition to severe hypoglycemia and its consequences. Recently an increase in mortality was observed in the highly-intensive treatment limb (targeting HbA1c values of <6%) of a multi-center clinical trial of individuals with type 2 diabetes at high risk for cardiovascular disease events. In addition, a multi-center study i the intensive care setting, demonstrated increased mortality in hyperglycemic patients randomized to highly intensive glycemic control. While the cause of the mortality in these studies could not be directly attributed to hypoglycemia, the studies raise concerns about potential indirect consequences of hypoglycemia. Because there is evidence that cardiovascular autonomic impairment is associated with, and may cause, increased mortality in diabetic and post-myocardial infarct populations, we hypothesized that antecedent hypoglycemia may impair cardiovascular autonomic function. In preliminary studies, we showed that antecedent hypoglycemia resulted in significant decreases in: (i) cardiac vagal baroreflex sensitivity (ii) th sympathetic response to a transient pharmacologically induced hypotensive stress and (iii) the sympathetic response to graded simulated orthostatic stress using lower body negative pressure. We also showed that hypoglycemia increases circulating aldosterone and interleukin-6 (IL-6) levels. Aldosterone and IL-6 are proinflammatory, cause vascular injury and are implicated in the pathophysiology of cardiovascular disease. Furthermore, both aldosterone and IL-6 attenuate autonomic function. In this proposal, we wish to extend these studies to individuals with type 2 diabetes. The specific aims of the proposal are (1) to determine the effects of antecedent hypoglycemia on cardiovagal baroreflex and sympathetic cardiovascular function in euglycemic subjects; (2) to determine the effects of hypoglycemia on cardiovagal baroreflex function during hypoglycemia; (3) to determine the effects of hypoglycemia on aldosterone and IL-6 levels during hypoglycemia; and to determine the role of the mineralocorticoid receptor in mediating the autonomic changes. Thus, the broad long term objectives are (1) to understand the autonomic cardiovascular consequences of hypoglycemia in individuals with diabetes; (2) to determine the mechanisms involved; (3) to develop treatments to ameliorate any adverse consequences; and (4) thereby allow for safe and effective rigorous glycemic control.