HCG stimulation of testicular LHRH-like activity

It is well established that the administration of high doses of luteinizing hormone (LH) or human chorionic gonadotropin (HCG) to animals can impair gonadal function in both the male and female. These effects can be duplicated by the administration of LH releasing hormone (LHRH) or its agonists to intact animals, including man. Somewhat surprisingly, recent results have demonstrated that similar impairment of gonadal function by LHRH and its agonists can be achieved in the absence of the pituitary (for review see ref. 7), and the demonstration of specific, high-affinity binding sites for LHRH and its agonists on ovarian luteal cells and on testicular Leydig cells, could mean that LHRH-like factors are involved in the local regulation of the gonads. A further intriguing finding is the striking similarity between the direct, inhibitory effects of LHRH and LH/HCG on the gonads; for example, both treatments reduce LH receptor numbers and the steroidogenic responsiveness of rat Leydig cells. We now offer a possible explanation for this similarity by demonstrating that HCG treatment stimulates the testicular production of a biologically active LHRH-like factor, suggesting that the inhibitory actions of HCG on the Leydig cell may be mediated by the local production of this factor.