Maternal testosterone and sexual differentiation of the male guinea-pig foetus

The part of foetal testosterone originating from the mother was explored in the guinea-pig at the time of sexual duct differentiation on day 32 of gestation. Using constant intravenous infusion of tritiated testosterone in the maternal compartment, total radioactivity (RA) and radioactive testosterone ([3H] T) and dihydrotestosterone ([3H] DHT) were measured in the maternal plasma, whole foetus and various foetal tissues, including the genital tract and gonads, brain and liver. After [3H] T was infused to the mother, significant amounts of total RA were found in foetuses of both sexes. The two metabolites isolated from the whole foetus contributed in various amounts to the RA present: 8% for [3H] DHT and 2 to 3% for [3H] T; no significant differences in the amounts of foetal T derived from maternal T (around 5 pg/g) were found between male and female foetuses. The brain, liver and genital tract and gonads concentrated more RA than the whole foetus, but only the male genital tract and gonads concentrated more RA than maternal plasma. Only DHT was isolated from the brain and liver of both sexes (8 to 10% of the RA found), but neither of the two hormones was found in the genital tract and gonads of either male or females foetuses. The results indicated that maternal testosterone and its metabolite, DHT, were not directly involved in the differentiation of sexual ducts in the male guinea-pig foetus.