Gonadotropin Secretion in Cryptorchid and Castrate Rams and the Acute Effects of Exogenous Steroid Treatment1

Abstract

Gonadotropin secretion in cryptorchid and castrate rams and the acute effects of exogenous steroid treatment on gonadotropin secretion were determined. Rams made cryptorchid at 6 wk of age had increased serum levels of luteinizing hormone (LH) and follicle stimulating hormone (FSH) when determined at 9 mo. of age. These levels approached those of the castrate animal; yet serum levels of testosterone (T) were unchanged. Even though mean serum LH concentrations were elevated 6- to 8-fold over those of intact ram levels, a temporal relationship between this hormone and T was observed similar to that reported in the intact ram. I.m. injections of dihydrotestosterone had no effect on circulating levels of LH or FSH in either cryptorchid or castrate rams, whereas T effectively reduced these gonadotropins in castrate but not in cryptorchid rams. Only estradiol-17.beta. (E2) was effective in both cryptorchid and castrate rams. Estradiol was a potent inhibitor of LH secretion; its effect on FSH levels was less dramatic. Testicular products other than E2 may be important in the regulation of FSH production and/or release. Importantly, the inhibition of LH secretion lasted less than 12 h, whereas the negative effects of E2 on FSH secretion lasted 72 to 144 h. T is not the single factor responsible for regulation of LH and FSH secretion in male sheep. Estradiol may be an important regulator of gonadotropin secretion, but 5.alpha.-reduction plays no apparent role in this process.