Secretion of the androgens in the male guinea-pig during the perinatal period.

Plasma and testicular testosterone, androstenedione and dihydrotestosterone concentrations have been estimated by radioimmunoassay in the male foetus and newborn guinea-pigs between day 62 of pregnancy to day 12 of post-natal life. The prenatal period is characterized by low plasma androgen levels and high testosterone and androstenedione testicular content. After birth there is a peak of plasma testosterone concentration on day 3 concomitant with a release of testicular androgens; no similar increase of androstenedione or DHT is observed in plasmaa. This peak in plasma testosterone is testis dependent because it disappears after castration; it is also light dependent at birth. The investigations on testosterone and androstenedione peripheral metabolism have shown that day 3 after parturition is a "critical period" in the evolution of the metabolic clearance rate, the production rate and the conversion rate of these two androgens. The neonatal increase in plasm testosterone may be accounted for by the variations in these metabolic parameters and may have an influence upon certain sexual target organs, especially upon the vas deferens, the androgens content of which increases during the same "critical period".