Treatment of Pregnant Rhesus Macaques With Testosterone Propionate: Observations on Its Fate in The Fetus1

Castrated male primates, unlike castrated male rodents, respond to exogenous estrogen by releasing gonadotropin. Although this disparity is unexplained, it may occur because the amount of testicular androgen secreted during a critical period for sexual differentiation is not sufficient to completely androgenize the anlagen of the central nervous system (CNS) in male primates. Therefore, male primates might be incompletely masculinized, and if fetal males were exposed to additional androgen during sexual development, they would no longer display the positive feedback to estrogen that usually characterizes females. Besides the development of mechanisms mediating the release of gonadotropins, questions about relationships between adult male sexual behaviors and the intensity of the androgen stimulus upon developing neural structures are of interest. We tested some of these possibilities by injecting androgen into 8 pregnant rhesus macaques from Days 40 through 50 of gestation, and we compared serum levels of testosterone (T), dihydrotestosterone (DHT), and androstenedione (Δ4) in the fetal circulation with that of 5 untreated control males. Fetal sera (both male and female) from treated pregnancies did not contain significantly greater quantities of T and DHT than sera of intact control males from untreated mothers. The maternal sera, however, contained large amounts of T (125.05 ± 27.40 [SEM] ng/ml, n=8) and significant elevations of DHT and Δ4 after treatment. The concentrations of Δ4 in the fetal circulation were significantly elevated (p<0.01) in treated fetuses compared to intact control males, probably due to the actions of the 17 β-hydroxysteroid dehydrogenases in the placenta, the fetus, or both. In an independent study, 3 males whose mothers received a similar treatment, viz. 25 mg testosterone propionate (TP) per day from 40 to 49 days of gestation and beyond, were subjected to an estrogen challenge to test for “positive feedback” on luteinizing hormone (LH) release. LH levels in the systemic circulation were quantified and the results compared to 5 control males (adult) given a comparable estrogen challenge. In neither intact controls nor intact androgenized males (A♂) did EB treatment produce surges of LH in sera taken from the systemic circulation, whereas the same treatment in long-term castrated males produced an LH surge 48 h after treatment. The A♂ and the controls were castrated and EB was injected on Days 1, 8, 16, and 23 after castration in Ad and on Days I and 21 in control males. LH surges generally occurred within 48 h after the estrogen treatment. Thus, although mothers may be treated with large quantities of androgen, small quantities of T reach the fetus; hence, the procedure is not an appropriate test of the masculinizing action of T on the male CNS. The high levels of Δ4 formed in the intact fetal male and after TP treatment of the mother may exert developmental effects.