Mechanisms Involved in the Ability of Human Chorionic Gonadotropin to Increase the Responsiveness of the Infant Rat’s Testis to Follicle-Stimulating Hormone

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Abstract
Pretreatment of 9-day-old rats for 3 days with human chorionic gonadotropin (hCG) increased the amount of estradiol secreted by the testis in response to in vivo or in vitro stimulation with FSH. Potential mechanisms for this sensitizing effect were studied by treating infant rats with a variety of agents and then using radioimmunoassay to determine testicular estradiol secretion. Substitution of 3 days priming with estradiol for hCG did not enhance subsequent in vitro responsiveness to FSH. S.c. capsules of 1,4,6-androstatriene-3,17-dione (ATD) blocked stimulation of testicular aromatization in vivo by hCG or FSH. ATD capsules alone, or when combined with the antiestrogen tamoxifen, were not able to alter the ability of hCG pretreatment to increase responsiveness to in vitro FSH. Estradiol evidently was not involved in the sensitization caused by hCG in this model system. When gonadal tissue from 12-day-old rats was incubated in the presence or absence of 0.6 .mu.M testosterone and various concentrations of FSH, more estradiol was secreted by testes in the containing testosterone. The amount secreted was not different from that noted after hCG priming. Priming of 9-day-old rats for 3 days with the nonaromatizable androgen 5.alpha.-dihydrotestosterone did not influence the amount of estradiol secreted in response to FSH. Evidently hCG augments the testicular aromatization response of infant rats to FSH by providing additional substrate for these reactions.