Testosterone, dihydrotestosterone and estradiol-17β levels in maternal and fetal plasma and in fetal testes in the rat

Abstract

In Sherman rats testosterone, dihydrotestosterone (DHT) and estradiol-17 beta levels were measured in maternal and fetal plasma of both sexes during the last 5 days of gestation and in the fetal testes from day 14.5 of pregnancy using celite microcolumn chromatography and radioimmunoassay. All the plasma testosterone concentrations in males were at least 4 times higher than in their female littermates. In male fetuses, levels of plasma testosterone were maximum on day 18.5 (mean = 1.42 ng/ml) and declined thereafter (mean = 0.85 ng/ml on day 21.5). In female fetuses and in mothers, levels were consistently very low (mean less than 0.2 ng/ml). Plasma DHT titers in fetal plasma of the two sexes and in maternal plasma were consistently minute. Plasma estradiol-17 beta levels in fetuses did not differ between sexes; they were higher than maternal levels; there was a prepartum increase both in fetuses and their mothers. Testicular testosterone content became detectable on day 15.5, increased to reach a peak on day 18.5 (mean = 2.3 ng/testis) and remained at this plateau throughout the end of gestation. Intratesticular DHT and estradiol-17 beta were in minute concentrations. From these data we conclude that, in fetal rat, (1) DHT in genital tract is entirely formed in situ during masculinization, (2) among the three plasma steroids assayed, only testosterone can play a determining role in sexual differentiation.