The androgens in the guinea-pig foetus throughout the embryonic development.

Testosterone (T) and dihydrotestosterone (DHT) content and concentration were measured by radioimmunoassay in plasma, gonads, adrenals, and sexual ducts of 235 male and 214 female guinea-pig foetuses at various stages of gestation after gonadal and adrenal differentiation occurred. In the male foetus, a sharp increase in the content and concentration of T and, to a lesser degree of DHT, is observed in the testis, the plasma and the ducts at the time of sexual differentiation between days 28 and 36. Thereafter androgen concentrations in these tissues decrease and rise again after day 52. In the female foetus, levels of T and DHT in the ovary are low throughout foetal life and do not account for the relatively high concentrations found in the plasma; in sexual ducts, T concentrations decrease at the time of differentiation. DHT levels are low at every stage. In both sexes, T and DHT are present in the adrenal. No sexual dimorphism is observed in the evolution of T and DHT adrenal content and concentration.