Hypothalamic, pituitary and gonadal hormone production in relation to nutrition in the male hyrax (Procavia capensis)

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Abstract
The effects of different planes of nutrition on spermatogenesis and androgenesis in [P. capensis] males during the mating season were studied, and whether there were associated changes in anterior pituitary and hypothalamic hormone secretion was investigated. Testicular weight, seminiferous tubule diameter and plasma testosterone concentration were all significantly lower in hyrax fed a low-plane diet than in hyrax on a high plane of nutrition. Plasma and pituitary LH [luteinizing hormone] were also lower in the former group although not significantly. Hypothalamic LH-RH [luteinizing hormone-releasing hormone] and plasma cortisol levels did not differ in the 2 groups. The results of the parameters studied were intermediate for the animals on a low plane of nutrition between those for hyrax fed a high-plane diet and sexually quiescent animals. The nutritional effects on reproduction were probably primarily due to alterations in the secretion of LH-RH. Although LH-RH is undetectable in the circulation, an inverse relation was previously observed between hypothalamic LH-RH content and plasma LH concentration, such a correlation appears true for these results. Sexually quiescent hyrax had high hypothalamic LH-RH levels and low plasma LH. The higher mean hypothalamic LH-RH in low-plane hyrax compared with high-plane animals therefore implies a decrease in release of the hormone. As with LH, the difference was not statistically significant.

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