Prolactin or dopamine mediates the induction of puberty by long days in female ferrets.

The role of PRL in sexual maturation of female ferrets was examined in these studies. Longitudinal profiles of PRL secretion were obtained by thrice weekly blood sampling of intact female ferrets undergoing photoperiod-stimulated development as well as age-matched control females which remained in nonstimulatory short days. Two additional groups of intact females, one in each photocycle, were treated with the dopamine agonist drug bromocriptine throughout the study. The relationship between developmental changes in PRL secretion and the critical pubertal decrease in the efficacy of estradiol (E2) inhibitory feedback on LH secretion was studied by using additional groups of females which were ovariectomized and treated with E2 implants (OVX + E2). These latter females were housed in either long or short day photoperiods; some were treated with bromocriptine, the remainder were treated with the vehicle only. Results of this study revealed that PRL secretion in ferrets does not change acutely with an abrupt increase in day length. After 4 weeks of exposure to long days, however, a marked increase in PRL secretion occurred. This increased secretion of PRL was contemporaneous with the onset of pubertal ovarian activity in intact females and with the escape of LH from the negative feedback of E2 in OVX + E2-treated females. The further observation that pharmacological blockade of the long day-induced rise in PRL secretion also prevented the pubertal onset of ovarian activity suggested that PRL may play a critical role in the induction of puberty in this species. The mechanism by which bromocriptine prevented puberty induction was illustrated in the OVX + E2-treated ferrets in stimulatory photoperiod. The drug treatment prevented the pubertal decrease in the efficacy of E2 negative feedback on LH. These studies suggest an important interaction between the dopamine-PRL system and the GnRH-LH system in the regulation of sexual maturation of female ferrets.