Suppression of cortisol secretion by human growth hormone

The adrenocortical responses to the daily administration of 10 mg human GH (hGH) for 4-6 days were compared in 12 patients with Cushing's disease, 2 patients with cortisol-secreting adrenal cortical adenoma, and 4 healthy subjects. The administration of hGH resulted in a significant mean percent decrease in urinary 17-hydroxycorticosteroids [17OHCS; 30 +/- 7.8 (SE)], cortisol secretion rate (32 +/- 5.5), plasma 17OHCS (31 +/- 5.1), and urinary 17-ketosteroids (46 +/- 6.0) in the patients with Cushing's disease. In contrast, it did not significantly decrease urinary or plasma 17OHCS or the cortisol secretion rate in the other groups of subjects similarly studied. Treatment with hGH did not impair the adrenocortical response to exogenous ACTH, but it decreased the response to metyrapone in all subjects tested. In one of the healthy subjects who had exhibited diminished response to metyrapone on hGH, measurement of plasma ACTH levels demonstrated a lower rise after the administration of the drug. Treatment with hGH did not alter the peripheral metabolism of cortisol, as measured by cortisol turnover rates. We conclude that hGH inhibits ACTH release and that this effect is maximally demonstrated in patients with increased hypothalamic-pituitary-adrenal function.