Sympathetic Nerve Activity During Hypoglycemia and Exercise

The body has defensive responses to correct low blood sugar (hypoglycemia). A vital component of this response is release of glucagon and activation of the sympathetic nervous system, which provides the means for raising blood glucose levels towards normal. We can measure circulating hormones indicating the level of these responses, but additionally, sympathetic nervous system responses can be measured directly. We can measure the sympathetic nerve activity that controls blood flow to muscles (MSNA) and blood flow and sweating to skin (SSNA). The purpose of this study is to determine if either hypoglycemia or exercise cause differential responses in muscle and skin sympathetic nerve activity. We would also like to determine what the sympathetic response is to cycling exercise with insulin and normal blood sugar. Therefore, we would like to test the sympathetic responses to insulin with normal blood glucose, hypoglycemia, and during exercise bouts and normal blood glucose, with or without insulin.