Serum levels of testicular and adrenal steroids after dexamethasone adn HCG-administration in the laboratory-maintained Rhesus monkey.

Abstract

ABSTRACT In order to evaluate the endocrine testicular and adrenal function of rhesus monkeys in vivo, and to compare this with the human situation, the effect of dexamethasone (Dxm), HCG and combined Dxm/HCG administration on the steroid levels was investigated in 8 adult male rhesus monkeys in November/December (= season of high testicular activity). Serum levels of cortisol, testosterone (T), androstenedione (A), 17-hydroxyprogesterone (17-OHP), oestradiol (Oe2), dehydroepiandrosterone (DHA) and its sulphate (DHA-S) were measured radioimmunologically. Basal T and DHA serum levels were similar to those found in man, whilst A levels amounted to 1/10 and DHA-S to 1/30 of human values. Oe2 and 17-OHP levels were higher than in man. T and A levels were not suppressed by Dxm and very high degrees of stimulation were reached after HCG. The HCG-induced increment in T was smaller under Dxm/HCG than under HCG alone. 17-OHP levels were reduced to 25% of basal levels under Dxm, but the incremental response to Dxm/HCG was the same as that without Dxm. DHA and DHA-S were 60 and 75% lower under Dxm, and the increment in DHA after Dxm/HCG was less than that after HCG. DHA-S did not respond to HCG. In conclusion, several important differences in basal steroid levels and in the response to dynamic testing were found in the rhesus monkey, as compared to man. The adrenal contributes 75% to circulating 17-OHP levels, and 60 and 75% respectively to DHA and DHA-S levels. A is produced solely by the testis in the rhesus monkey. As compared to man, the rhesus monkey testis in vivo synthesises T via both the Δ4 and Δ5 pathways. The Δ5 pathway appears to be dependent on adrenal steroid precursors.