Control of estrogen synthesis in the testis of the infant rat by FSH and androgen

The experiments studied the ability of androgens to stimulate in vivo the production of estradiol by the testes of the 12-day-old rat as well as interactions between FSH and androgens in this regard. The content of testosterone and estradiol in the testes was measured by RIA of methanolic extracts which were purified on columns of Sephadex LH-20. It was found that androstenedione, testosterone and 19-hydroxytestosterone were able to stimulate estradiol formation in the testes; the response was optimal 3 h after s.c. injection. The stimulatory effect was absent after injection of 5 alpha-reduced androgens. It was concluded that the ability of a single injection of androgen to increase the content of estradiol in the testes was due to provision of additional substrate for aromatization by the Sertoli and/or Leydig cells. Priming of rats for 2 days with testosterone (60 microgram/g bw daily) resulted in a reduction of concentration of LH and FSH in plasma and was associated with an inhibition of the estradiol response to a subsequent injection of testosterone. If priming with testosterone was followed by an injection of FSH, more estradiol was formed than when the FSH injection was preceded by an oil or dihydrotestosterone priming regimen. It was concluded that the inhibition of testosterone-induced aromatization noted after testosterone priming was due to low gonadotropin secretion rather than a direct effect on the testis and that priming of the infant rat with androgen enhanced the response to FSH because such treatment provided additional substrate for aromatization.