Effect of Metyrapone on Secretion of Growth Hormone in Man

One and a half g of metyrapone provoked a marked decrease of plasma cortisol and a conspicuous increase of both plasma 11-DOCS and HGH. Two out of 5 normal subjects showed increased responses of blood glucose and plasma insulin to this drug. Furthermore, the present study was performed to elucidate whether or not this HGH response was related to a negative feedback mechanism through which metyrapone stimulated ACTH release. When hydrocortisone hemisuccinate was infused simultaneously at a rate of 4 mg/hr with metyrapone administration, plasma cortisol showed no significant decrease. However, plasma HGH was significantly more increased than that in subjects given lactose capsules (control), though the response of plasma HGH was slightly lower than that in metyrapone alone. Also, plasma HGH response to metyrapone following dexamethasone premedication (4 mg) was significantly increased. On the other hand, this response of plasma HGH to metyrapone was suppressed by glucose infusion. These data may suggest that the mechanism of HGH response to metyrapone not only is independent of a negative feedback of plasma cortisol, but is dependent upon the direct effects on the pituitary and/or the hypothalamus as a nonspecific stimulus. Metyrapone is as useful a diagnostic tool for testing HGH secretory capacity as for testing ACTH reserve.