Effects of Insulin and Growth Hormone on the Flux Kates of Plasma Glucose and Plasma Free Fatty Acids in Man

The mechanisms of hypoglycemia and hypolipacidemia due to insulin and growth hormone were investigated in human volunteers. 6-14C-glucose and 1-14C-palmitic acid were infused simultaneously at a constant rate into healthy adults. Plasma glucose and free fatty acid concentrations and specific activities were measured. The data so obtained were used to compute the inflow and outflow rates of plasma glucose and plasma FFA, with equations derived from a model of a single open pool system. Insulin at a dose below 0.05 U/kg body weight caused hypoglycemia by decreasing the inflow of glucose; at higher doses it caused hypoglycemia by both decreasing the rate of inflow and increasing the rate of outflow. When the subjects were pretreated with 5 mg of growth hormone, insulin action on flux rates was diminished, probably by both inflow and outflow mechanisms. Insulin caused hypolipacidemia by decreasing inflow; the dose for maximal effect was much less than that for maximal hypoglycemic effect, and growth ...