RESPONSE OF PERIPHERAL SERUM SEX STEROIDS AND SOME OF THEIR PRECURSORS TO A SINGLE INJECTION OF hCG IN ADULT MEN

Nine healthy men were given a single intramuscular injection of 5000 iu of human chorionic gonadotrophin (hCG). Peripheral blood samples were serially collected up to 7 days after the injection, and the sera were analysed for hCG and eight steroids hCG reached a maximum, 130·13 (SEM) iu/l, at 8 h and declined thereafter with a half-life of about 24 h. Testosterone and 17-hydroxyprogester-one were elevated at 2 h, to 132·11% and 169·32%, respectively, when compared with the 0 h levels. It is to be observed, however, that in saline injected control men (n= 6) an early increase in serum testosterone was also observed. When compared with the saline-injected controls, the first significant elevation in testosterone was obtained not earlier than at 12 h, and the maximum was seen at 96 h (239·23% of controls). Correspondingly, the first significant elevation of 17-hydroxyprogesterone was seen at 8 h and the maximum at 36 h (296·44%) after the hCG injection. The maximum concentration of serum oestradiol was also found at 36 h (230·15%). The patterns of response in serum levels of androstenedione, and, to a lesser extent, in those of 5α-dihydrotestosterone, were similar to those of testosterone. Progesterone levels decreased during days 3–7 after the hCG injection, and no clear changes were seen in the peripheral serum concentrations of pregnenolone and androsterone. The -24 and -12 h control samples displayed a diurnal rhythmicity for progesterone, androstenedione, testosterone and androsterone; the 08.00 h levels being significantly higher than those at 20.00 h. Our results show that, in the adult, human testicular androgen biosynthesis responds relatively slowly to additional gonadotrophic stimulation. The late peak of peripheral serum testosterone level after the hCG injection and the stimulatory sequence of its precursor steroids suggest that the side chain cleavage of C₂₁ steroids, beyond 17 α-hydroxylation, may be a critical step in the human testicular androgen response to this gonadotrophin. The clear increase in serum oestradiol during the hCG stimulation points out the potential importance of endogenous oestrogens in testicular endocrine function.