Endocrine profiles of the testicular functions in the stallion

The present studies were designed to elucidate the property of estrogen and inhibin and to establish on the endocrine profiles of testicular functions in the stallion. The kinds of estrogens secreted from stallion testes were identified with estradiol-17beta and estrone by a gas chromatography mass spectormetric method. A simple defatting method for a RIA of estradiol-17beta was set up by a distribution using acetonitorile and n-hexan. RIA for immunoreactive inhibin and an ELISA for inhibin pro-alpha C on the stallion were validated to base on a bovine RIA and a human ELISA system, respectively. Inhibin alpha-, beta A- and beta B - subunit were localized in both Sertoli cells and Leydig cells in the testiculer tissue. Seasonal changes in plasma concentrations of irinhibin, testosterone, estradiol, FSH and LH showed the highest values in equine breeding season. A single injection of hCG made peripheral concentrations of all testicular hormones increase, and this effect was much more clear in the non-breeding than the breeding season. By the treatment of anabolic steroid, plasma concentrations of inhibin, testosterone and LH remarkably decreased, but FSH levels did not significantly change. The testis weights decreased after treatment of anabolic steroid, and their histology showed suppression of spermatogenesis and disappearance of Leydig cells. Localization of inhibin alpha - subunit and steroidogenesis enzymes in the interstitial cells were not detected, but inhibin alpha - subunit in the Sertoli cells was clearly observed. These results show changes in the endocrine functions of pituitary-testicular axis in relation to the testicular activity and these endocrine parameters indicate to be useful for the evaluation of reproductive functions in the stallion.