The effects of thymus-derived peptides on hypothalamic LRF and pituitary gonadotropin content in prepubertal congenitally athymic nude mice and their normal heterozygous littermates.

Congenitally athymic nude mice have recognized reproductive defects, accompanied by decreased pituitary gonadotropin and hypothalamic LRF concentrations at 3 weeks of age, compared to their normal heterozygous littermates. To determine if these hormonal changes are due to decreased secretion of thymic peptides, we measured pituitary concentrations of LH and FSH and hypothalamic LRF content at 21 days of age in 122 congenitally athymic nude (nu/nu) mice and in 190 heterozygous (nu/+) littermates administered daily injections of a crude thymic extract, semipurified thymosin fraction 5, or a synthetic thymic protein preparation. All animals receiving crude thymic protein extract, and some receiving either thymosin or synthetic thymic factor, had reduced levels of hypothalamic LRF. The changes in concentrations of gonadotropins were more variable. All mice receiving crude thymic extract (with reduced hypothalamic LRF content) appeared to have increased pituitary concentrations of LH, FSH, or both when compared to control animals, although statistical significance was not achieved in all groups. A similar but less marked trend toward increased pituitary gonadotropins was also noted in mice receiving thymic factor. These preliminary results suggest that thymus-derived peptides can affect hypothalamic-pituitary function and support our hypothesis that thymic hormones may play a role in programming the hypothalamic-pituitary axis in the prepubertal period in rodents.