Hormonal Basis of Reproductive Defects in Athymic Mice: Reduced Gonadotropins and Testosterone in Males1

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Abstract
We wished to determine if congenitally athymic nude male mice have the same reduction in circulating concentrations of gonadotropins and gonadal steroids observed in their female counterparts when compared to their normal heterozygous littermates. We therefore quantitated pituitary and circulating concentrations of gonadotropins and circulating levels of testosterone in 102 congenitally athymic mice and 101 of their heterozygous littermates ranging in age from 1 to 120 days. Although the developmental patterns observed for both circulating luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were similar to those previously observed in rats and mice, the athymic mice had significantly reduced concentrations of both pituitary and serum LH and FSH in comparison to the heterozygotes. In general, the reduced secretion of gonadotropins was most marked prior to sexual maturation but persisted in adult athymic males. Circulating concentrations of testosterone were also markedly reduced in the adult athymic males. Histologically, the number of Leydig cells appeared reduced in testes from 20-day-old athymic mice. However, no differences could be detected in testes from 40-day-old animals, and spermatogenesis appeared normal. Thus, unlike athymic females, athymic male mice appear to have normal reproductive capacity despite these hormonal abnormalities.