A study of the short-time variation and interrelationship of plasma hormone levels reflecting pituitary, adrenocortical and testicular function in fertile men.

Using radioimmunoassay method, we have estimated the levels of cortisol (C), pregnenolone (delta 5P), 17-hydroxypregnenolone (17-OH-delta 5P), dehydroepiandrosterone (DHEA), 17-hydroxyprogesterone (17-OH-P), androstenedione (A), testosterone (T) and dihydrotestosterone (DHT) in peripheral plasma samples collected at short-time (15 min) intervals from 10 fertile men, during two 4-h periods (06.00 to 10.00 and 18.00 to 22.00). In addition, the levels of biologically active luteinizing hormone (LH) were measured by an in vitro bioassay method in 9 of the subjects. The levels of all steroids studied exhibited diurnal variation with higher levels during the morning and lower levels during the evening period. The cortisol and the delta 5-steroid levels also exhibited individual short-term episodic spikes during the 2 periods. No short-term variation was observed in the levels of 17-OH-P, A, T and DHT. Statistically significant correlations were found between the levels of C and those of the delta 5-steroids and A in most of the subjects. No correlation was found between the above steroid levels and those of 17-OH-P, T and DHT. Also the LH levels exhibited episodic spikes of 60 to 90 min duration, but no diurnal variation. When the LH levels were related to those of T found in the same samples or in samples withdrawn 15 to 810 min afterwards, a significant positive correlation was found on repeated occasions in 5 of the 9 subjects. No systematic negative correlation was found when the T levels were related to those of LH in the same sequential fashion. Whereas the positive correlations found between LH and T levels in some of the subjects might suggest that physiological changes in peripheral LH levels are instrumental in regulating T-secretion, the rather consistent lack of significant negative correlation between T and LH levels seems to favour the view that the release of LH is not modulated by peripheral testosterone levels alone.