Regulation of serum gonadotropins by photoperiod and testicular hormone in the Syrian hamster.

Male hamsters were maintained on long (14L:10D) or short (10L:14D) photoperiods. The serum concentrations of LH and FSH were reduced in the animals kept on the short photoperiod, and these animals had atrophied testes and sex accessories. Serum gonadotropin concentrations increased following castration in both long and short photoperiods, but gonadotropin secretion was inhibited by much smaller doses of testosterone in the males maintained on the short photoperiod as compared to males kept on a long photoperiod. The levels of testosterone required to suppress serum gonadotropin levels in castrated animals corresponded reasonably well with the serum androgen levels observed in intact males, suggesting that serum androgen is a major regulator of gonadotropin secretion in the male hamster.