Control of testicular steroidogenesis in foetal rat: effect of decapitation on testosterone and plasma luteinizing hormone-like activity

These studies were designed to investigate the regulation of testicular testosterone and the role of the hypophysis during the last 5 days of gestation in the rat. Plasma LH-like activity was measured by bioassay and testosterone by radioimmunoassay. In both sexes, plasma LH-like activity levels were low on days 17.5 and 18.5 (less than 0.10-0.26 ng/ml) and rose on day 19.5 (0.10-1.25 ng/ml). Thereafter the levels increased considerably and were significantly higher in females than in males: on day 21.5 they reached 0.44-2.42 ng/ml in males and 2.20-3.96 ng/ml in females. Plasma levels of testosterone were significantly higher in males than in females and were maximal on day 18.5 in males. Testicular content of testosterone reached maximum values on day 18.5 and remained constant thereafter. Foetal decapitation clearly reduced testicular production of testosterone and plasma LH-like activity only after day 19.5. A residual gonadotrophic activity was detected at all stages in decapitated foetuses from both sexes (less than 0.10-0.46 ng/ml). These results suggest that pituitary LH secretion and pituitary-testicular interrelationships are essentially established between day 19.5 and 20.5, and that the ageing testis becomes more dependent on gonadotrophic stimulation. The existence of an extrapituitary LH-like activity might indicate the presence of placental gonadotrophins.