These studies were done to clarify the actions of human growth hormone (HGH) during the two hours after concentrations were increased. These effects cannot be attributed to generation of somatomedin. Mean systemic levels of HGH were increased to 92.6 ng. per milliliter by the intravenous infusion of 4 mg. of HGH over thirty minutes. During the first hour, mean plasma glucose and free fatty acid (FFA) concentrations decreased by 9.5 ± 1.9 per cent and 21.2 ± 3.6 per cent, respectively. After two hours, FFA concentrations rose to 145 per cent of basal.
An identical preparation of HGH was then perfused across forearm tissues at mean forearm venous concentrations of 28.4 ± 1.5 ng. per milliliter or 200.3 ± 7.9 ng. per milliliter. Glucose uptake was acutely decreased (by 30 per cent) by both doses of HGH; neither dose had significant effects upon lipolysis. Therefore, neither physiologic nor supraphysiologic concentrations of HGH had an insulin-like effect upon peripheral muscle or adipose tissue. Small increases in peripheral HGH concentrations had virtually identical effects upon enhancement of potassium uptake and reduction of glucose uptake across muscle as mean concentrations ten times higher.