The role of follicle stimulating hormone in testicular function of the mature rhesus monkey

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Abstract
In the rat, while FSH [follicle stimulating hormone, follitropin] necessary for the initiation of spermatogenesis, this hormone does not appear to be involved in the maintenance of spermatogenesis in the mature animals. Since the role of FSH has not been conclusively established in primate species, including humans, a study based on the neutralization of FSH by passive immunization with specific FSH antibodies was initiated in adult male rhesus monkeys. Prior to the actual study an antiserum pool was generated from 4 monkeys actively immunized with highly purified ovine FSH. In this FSH antiserum there was no evidence for the existence of LH [lutropin] antibodies, and the capacity of the antiserum to neutralize rhesus FSH was demonstrated by bioassay. Because of marked circannual variations in testicular functions passive immunization with FSH-antiserum was performed during the period of full testicular development in 4 other monkeys. FSH antiserum was injected for 106 days (i.e., a period covering the full duration of the total spermatogenetic process twice). Four further monkeys serving as controls were injected with normal rhesus serum for the same period. Testicular volume and histology, anti-FSH-titer, seminal parameters, serum testosterone and LH were monitored at regular intervals. In the passively immunized animals the testicular volume decreased by 50%, sperm counts decreased below control counts, histology revealed reduction of the tubular diameter by 40%, derangement of spermatogenesis and, on instances, tubuli with Sertoli cells only. Leydig cells appeared histologically normal, although testosterone levels in the passively immunized monkeys tended to be lower than in control animals. Values were not significantly different at the end of the observation period. In contrast to the rat FSH plays a specific role in the maintenance of spermatogenesis in the mature rhesus monkey.