Specific Aim 3: To determine the mechanism by which certain PIs increase hepatic glucose production; an infusion of somatostatin during the fasting state and hyperinsulinemic state will be used to suppress the effects of glucagon. Subjects will undergo a randomized, double-blind, placebo-controlled trial of a single dose of PI or placebo on insulin sensitivity using the euglycemic hyperinsulinemic clamp. Somatostatin, glucagon, and growth hormone will be infused before and during the clamp study. Hepatic glucose production, glycogenolysis, and gluconeogenesis will be assessed using stable isotope tracer techniques. Results will be compared to PIs acutely given in the absence of somatostatin, as stated in Specific Aim 2.