Stimulation of Testosterone Production in Vivo and in Vitro in the Male Rhesus Monkey Fetus in Late Gestation

Abstract

To assess intrauterine fetal testicular function, the carotid or femoral vessels of rhesus monkey fetuses, 129-145 days gestational age, were catheterized following hysterotomy of the mother. The fetus was returned to the uterus, the catheters were exteriorized through the mother''s vagina and the pregnancy was allowed to continue. In this chronic preparation, basal levels of testosterone (measured with an RIA [radioimmunoassay] with 65% crossreactivity with 5.alpha.-dihydrotestosterone) in male fetal serum were 0.85 .+-. 0.29 (SD) ng/ml. Administration of a 10 or 100 IU intra-arterial bolus of hCG [human chorionic gonadotropin] into the fetal circulation stimulated an increase in fetal serum testosterone levels of 70 and 630%, respectively. Other fetuses were challenged with bolus infusions of 10 and 50 .mu.g of synthetic gonadotropin releasing hormone (GnRH). The lower dose caused an increase in serum testosterone concentrations in only 1 of 4 fetuses, while the higher dose resulted in a positive response in all 3 experiments performed. With this dose, the mean increase in circulating testosterone concentration after 1 h was 105%. In vitro, specific binding of iodinated hCG was demonstrated in testicular homogenates from Rhesus fetuses near term and hCG stimulated testosterone biosynthesis in testicular minces. Maximal stimulation was achieved at hCG concentrations between 5 and 50 ng/ml. The testes of fetal rhesus monkeys during late gestation were capable of androgen biosynthesis and bound and responded to gonadotropin stimulation. The pituitary-gonadal axis in the fetal male monkey was capable of responding to GnRH stimulation at this stage of gestation.