Circadian and seasonal changes in ACTH-induced effects in healthy young men

The effects of the ACTH 1-17 analogue (100 micrograms i.m.) as a function both of time of day (7.00, 14.00 and 21.00 h) and season (winter versus summer) were determined on a set of physiological variables: urinary 17-hydroxycorticosteroids, oral temperature, grip strength (right and left hands), peak expiratory flow and self - rated fatigue. Six young healthy males took part in the study in January-February 1980 and June-July 1981. They were synchronized with a diurnal activity from 7.00 to midnight and a nocturnal rest. Urine was collected every 3 to 4 hours, at fixed clock hours over 72 h (winter) and 48 h (summer). There was a one week interval between each ACTH test or placebo control. Variables were measured according to the same schedule. 24 h urinary 17-OHCS excretion was maximum for ACTH injected at 7.00 in winter and 14.00 in summer, and the minimum occurred after ACTH given at 21.00. The highest peak of urinary 17-OHCS was found after ACTH at 7.00 both in winter and in summer. It is likely that the maximal stimulation of glucocorticoid secretion occurs when ACTH is administered around the beginning of the activity span. Both in winter and summer the injection of ACTH at 7.00 was followed by the greatest decrease in self-rated fatigue (24 h mean) and the largest increase (24 h mean) both in grip strength and peak expiratory flow (bronchial patency) in comparison with other times of ACTH administration (14.00 and 21.00 h).