Effects of in vivo Gonadotropin Treatment on Estrogen Levels in the Testis of the Immature Rat1

The effect of FSH injection on the concentration of estradiol in the testis of the immature rat was evaluated. Estradiol levels in testes were measured by RIA of methanolic extracts first sub-jected to Sephadex LH-20 chromatography. In 12-day-old rats i.p. injection of NIH-FSH-S11 caused an increase of estradiol concentration in the testes. The response was greatest 6 h after treatment and a dose-response relationship was observed between 2 5-200 pg FSH/rat. Similar treatment with 25 pg NIH-LH-S21 was without effect on the concentration of estradiol in the testes, thus the FSH effect was not attributable to LH contamination. Treatment of 9-day-old rat pups for 3 days with FSH (25pg, 2 times/day) caused an increase in testis estradiol to 205 ± 13 pg/g tissue and did not affect the estrogen response to a subsequent single injection of FSH (50 pg) administered at 12 days of age. Similar experiments utilizing older rats yielded quite different results. Injection of 100 pg oFSH into 18-day-old animals caused the concentration of estrogen in the testes to increase from 42 ± 4 pg/g to 83 ± 19 pg/g tissue, a significantly smaller change than that encountered in the younger animal. Chronic treatment with FSH (50 pg, 2 times/day) begin-ning at 15 days of age did not increase the concentration of estradiol in the testes, nor did it influence the stimulatory effect of 100 pg FSH administered at 18 days of age. These results show that oFSH is capable of increasing the amount of estrogen in the testes of the 12-day-old rat, but that this capability is markedly reduced by 18 days of age. Because hCG is known to stimulate testicular aromatization, it is suggested that in the young rat aromatization is a function of both Sertoli and Leydig cells; as the animal ages a greater proportion of the aromatizing capability may reside in the interestitial tissue