Interactions between Spontaneous and Provoked Cortisol Secretory Episodes in Man

Abstract

This study describes the interactions between cortisol peaks due to spontaneous episodic release and peaks provoked by external stimuli. Successive and equidistant transitory rises of similar amplitude and duration were produced either by muscular exercise (30 min, 75% VO_2max) or by injecting ACTH_1-24 (Synacthen: 250 ng) before and after the midday mealrelated peak. ACTH_1-24 was also injected during sleep before the nocturnal sequence of the major secretory episodes. In all instances, cortisol levels had reverted to basal levels when the second stimulus was applied. ACTH-induced cortisol peaks depressed the subsequent mealrelated peaks, the exercise-induced peaks, and the spontaneous secretory episodes at the end of the night, and thus had a strong depressor capacity. When exercise was the prior stimulus, the subsequent meal-related peaks were depressed, but the response to later exercise was not affected. Meal-related peaks and the spontaneous diurnal or nocturnal peaks did not depress the subsequent secretory episodes. These quantitatively comparable cortisol episodes were preceded by ACTH rises whose amplitude and duration were not identical: spontaneous and meal-related ACTH peaks were smaller than the provoked one; exerciseinduced ACTH peaks were of longer duration than those after ACTH_1-24 injection. The different depressor capacities of similar sized cortisol episodes and the lack of proportionality between spontaneous and provoked ACTH and cortisol peaks suggest that there are separate adrenocortical activation channels, which depend on the origin of the stimulation.