Acute cortisol excess results in unimpaired insulin action on lipolysis and branched chain amino acids, but not on glucose kinetics and C-peptide concentrations in man.

To assess whether acute cortisol excess impairs insulin action on lipolysis, plasma amino acids, endogenous insulin secretion, and glucose kinetics, nine normal subjects were studied after acute cortisol excess (80 mg hydrocortisone by mouth) and after placebo. Insulin sensitivity was assessed 6 hours after hydrocortisone using the glucose clamp technique (insulin infusion of 20 mU/m2 X minute for 120 minutes, plasma insulin levels of approximately equal to 50 mU/L). Hyperinsulinemia suppressed plasma free fatty acids (FFA) similarly by 75 and 76%, respectively. Most plasma amino acid concentrations were increased after hydrocortisone; however, the insulin-induced decrease of branched chain amino acids, serine, threonine, and tyrosine was unimpaired after hydrocortisone. Plasma C-peptide concentrations were less suppressed during hyperinsulinemia after hydrocortisone than after placebo (by 0.15 +/- 0.03 v 0.25 +/- 0.02 nmol/L, P less than 0.01), suggesting diminished insulin-induced suppression of insulin secretion. The glucose infusion rates required to maintain euglycemia were 35% lower (P less than 0.01) after hydrocortisone due to decreased insulin effects on metabolic clearance rate of glucose and diminished suppression of hepatic glucose production (0.4 +/- 0.1 v -0.1 +/- 0.1 mg/kg X minute, p less than 0.05, 3-3H-glucose infusion method). The data demonstrate that acute elevation of plasma cortisol to levels near those observed in severe stress results in insulin resistance of peripheral and hepatic glucose metabolism but in unimpaired insulin effects on plasma FFA and branched chain amino acids, suggesting that cortisol's lipolytic and proteolytic effects are antagonized by elevated plasma insulin levels.