The influence of fetal adrenals on the androgen levels during brain differentiation in human subjects and rats.

Measurements of plasma total and free testosterone (T) levels in human subjects from fetal to postpubertal life showed about twofold higher total T and 15-fold higher free T levels in female fetuses than in female adults. The ratios between the sexes were only moderate in fetal life. Between the 17th and 31st week of pregnancy the ratios (male:female) of total T were found to be 6.6 in week 17, 1.5 in week 22, 2.3 in week 28 and 1.2 in week 31 of pregnancy compared to 16.2 in adulthood. The corresponding ratios of free T were calculated to be 5.6 in week 17, 1.4 in week 22, 0.9 in week 28 and 0.7 in week 31 of pregnancy compared to 34 in adulthood. In amniotic fluids, we measured even an overlapping of T values between the two sexes. The reason for the observed striking difference of T levels between the sexes in fetal and postpubertal life may be the high adrenal activity and secretion rate in fetal life during brain differentiation. In rats, the contribution of adrenals to plasma T levels is only moderate and much smaller than in human beings. As measured in adult female rats, the portion was found to be about 20% only, contrary to about 60% in women. The main sources of T in female rats appear to be the gonads. The mainly gonadal secretion may be the reason that exposure of pregnant rats to stress diminished the T levels in male fetuses, but did not significantly elevate the T levels in females.(ABSTRACT TRUNCATED AT 250 WORDS)