Androgen Secretion by the Fetal and Neonatal Rhesus Monkey¹

The capacity of the gonad to produce androgens was studied in the fetal rhesus monkey. At approximately days 45 and 60 of fetal life the testes converted 14C-pregnenolone to testosterone (T) and androstenedione (Δ) in vitro. By days 45, 60 and 80 of fetal life, the ovary is relatively quiescent with regard to its ability to synthesize T and Δ from pregnenolone. Measurement of T and Δ in pools of umbilical artery plasma (UAP) and gonads of the monkey at 100, 125 and 150 days of gestation showed more T in plasma from male compared to female fetuses. Δ Concentrations did not differ with fetal sex. Similarly, greater quantities of T were found in the systemic plasma of mothers with male fetuses. During the neonatal period, androgens in the plasma were high on days 1 or 2 but diminished to low levels with time. Fetal testicular tissue contained large quantities of T that fell to low or undetectable amounts in the neonatal period. Ovarian or adrenal tissue contained Δ but no T. These data demonstrate that the fetal testis of the rhesus monkey synthesizes and releases T into the fetal circulation, while the ovary is relatively quiescent in this regard. The significance of these observations is discussed. (Endocrinology87: 680, 1970)