Simultaneous determinations of plasma ACTH and GH levels after an oral metyrapone.

Abstract

The levels of plasma ACTH and GH were simultaneously measured in normal subjects every 30 min for 4 nr after an oral administration of metyrapone, either 1.0g or 1.5g. Both doses of metyrapone caused a significant decrease in plasma cortisol levels 90min later, when the mean values of plasma cortisol levels were not significantly different between both groups. An administration of 1.0g of metyrapone raised plasma ACTH levels in 2 out of 6 subjects within 90min, while an increase in plasma GH levels of 5.0ng/ml above the base line levels was observed in 2 subjects. In one of the subjects in whom the levels of plasma GH increased, plasma GH peak was preceded by that of plasma ACTH, but no rise in plasma ACTH levels was observed in another subject. When 1.5g of metyrapone was given, plasma ACTH levels increased in all 6 subjects. The response of plasma ACTH was quite different in each individual and there appeared one or two peaks within 240 min. The mean value of plasma ACTH was 69±17 pg/ml at 0 time and increased to 165±18 pg/ml at 60min (p<0.01 vs 0 time). An increment in plasma GH levels was observed in 5 out of 6 subjects. The mean peak value was reached at 90min and the difference between the values at 0 and 90 min was significant. There was also no correlation between the secretion of ACTH and that of GH. These results may indicate that a higher dose of metyrapone causes both ACTH and GH secretions within a short period not by a negative feedback mechanism of cortisol but presumably by acting directly on the pituitary and/or on the hypothalamus as a nonspecific stimulus.