Does growth hormone treatment of stallions during the non-breeding season increase testis sensitivity to luteinizing hormone or pituitary sensitivity to GnRH?

摘要

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) appear to play a role in gonadal function in various species. Cochran et al. [1] reported that administration of recombinant equine GH increased the number of small follicles on the ovaries of the cyclic mare. Similar treatment of seasonally anovulatory mares resulted in a similar increase in number of small follicles [2], but did not result in follicles big enough to ovulate. However, the combined treatment of seasonally anovulatory mares with GH and a sub-threshold daily GnRH analog treatment [3] resulted in follicular growth to a size that could be induced to ovulate with human chorionic gonadotropin (hCG) [4]. One explanation for this latter observation was that GH treatment potentiated the ovary of the seasonally anovulatory mares such that they responded to much lower gonadotropin concentrations than they normally would, perhaps via increasing the number of gonadotropin receptors on the ovary. The present experiment was designed to test the hypothesis that similar GH treatment during the non-breeding season would enhance the testosterone response of the stallion testis to exogenous LH.