Effect of Very Small Concentrations of Insulin on Forearm Metabolism. Persistence of Its Action on Potassium and Free Fatty Acids without Its Effect on Glucose.

When insulin is infused into a brachial artery of normal men at a constant rate of 100 uU per minute per kg of body weight, there appears rapidly evidence of increased glucose uptake by forearm muscles and by forearm adipose tissue, a shift from net potassium loss to potassium uptake by muscle, increased K uptake by adipose tissue, and marked decrease in release of free fatty acids (FFA) by forearm adipose tissue (1, 2). When insulin is infused at the same rate into a brachial artery of patients with active acromegaly, into normal men in whom endogenous growth hormone activity has been increased by a 3-day fast, or into normal men simultaneously with human growth hormone (HGH) in the same syringe, there is evidence of less than the normal response to insulin with respect to glucose uptake by forearm muscles and by forearm adipose tissue (3-7). In every instance, however, the response with respect to FFA release was at least as great as that occurring in normal men to whom only insulin was exhibited. Interpretation of the combined effect of HGH and insulin on K uptake is com-