Ram hypothalamic - pituitary - gonadal - interactions. Effects of castration and cryptorchidism

Abstract

Abstract. The changes in hypothalamic LRH content, serum levels of LH, FSH and testosterone, and pituitary gonadotrophin contents were systematically compared in three experiments with rams. The first experiment was designed to identify specific endocrine changes at 15, 30 or 180 days after castration; the second, the influence of injections of testosterone (2 × 30 mg/day) for 15 days in castrated rams and the third, the effects of surgical cryptorchidism. The rapid decrease in plasma testosterone levels after castration (P < 0.05) was associated with an increase in plasma gonadotrophins (P < 0.01). By 2 weeks post-castration, hypothalamic LRH content was significantly reduced. This reduction (∼ 60% of intact controls) remained unchanged at 30 and 180 days after castration. In the second experiment the post-castration rise of plasma gonadotrophins was entirely prevented by testosterone administration and no difference was observed in hypothalamic LRH content of intact control and testosterone treated castrate rams. In the third experiment cryptorchidism induced a significant increase in plasma gonadotrophins which was intermediate between those of intact and castrate rams. Pituitary gonadotrophin content increased in cryptorchid rams without a concomitant change in hypothalamic LRH content. The data show that: 1) the mode of regulation of pituitary gonadotrophin concentration differs from that observed in the rat, 2) factors other than testosterone are implicated in the regulation of gonadotrophin secretion and synthesis and, 3) testosterone supplementation was able to maintain a normal hypothalamic LRH content.