Daily rhythms of follicle-stimulating hormone in adult anestrous and prepubertal female Turkish hamsters (Mesocricetus brandti).

We tested the hypothesis that daily FSH surges are correlated with the anestrous condition in adult Turkish hamsters. Blood samples were collected from anestrous hamsters on short (12L:12D) and long photoperiods (16L:8D) by cardiac puncture. Both photoperiod-induced anestrous (PIA) and spontaneously anestrous adult Turkish hamsters had a daily rhythm of FSH secretion with maximum hormone concentrations occurring late in the afternoon. We also hypothesized that daily FSH and progesterone surges are correlated with the reproductive response to short photoperiod in prepubertal female Turkish hamsters. Prepubertal hamsters reared on 16L:8D were sampled at 13, 15, 17, 19, and 21 days of age. Only at 19 days was a rhythm of FSH present. Prepubertal female hamsters reared on 12L:12D were sampled at 30, 35, 55, 75, 95, and 115 days of age or until estrous cycles were established. Those hamsters that delayed puberty in response to this short photoperiod had a daily rhythm of FSH and progesterone secretion. Conversely, no daily rhythms were observed in female hamsters that failed to respond to the inhibitory photoperiod with a delay in puberty. These results indicate that the daily rhythm of FSH secretion in the female Turkish hamster is correlated with reproductively inhibited physiological states.