Balance between opposite effects of short day stimulation and testicular steroid feedback inhibition on pituitary pulsatile LH release in male mink, Mustela vison

Abstract

This study explores changes in pituitary pulsatile Luteinizing Hormone (LH) secretion in intact and castrated male mink, either previously photogonadostimulated by short day treatment (LD 4:20), or maintained in a state of sexual quiescence by long day treatment (LD 20:4). Artificial photoperiodic treatment of intact mink significantly increases plasma LH level and pulse frequency, following transfer from inhibiting long-to stimulating short-days. This photoperiodic control mimics two important phases of the annual reproductive cycle: seasonal maximum gonadal activity and sexual quiescence. Furthermore, pulsatile secretion of LH is investigated 48 hours after castration. When mink castrated during long day treatment are compared against control intact mink, no change in their low LH secretion parameters are observed. This result indicates that gonadal steroids on long days are not suppressing LH secretion, which is controlled by photoperiodic inhibition alone. When mink are castrated at the onset of short day induced gonadal growth, mean plasma LH level and amplitude of LH pulses are increased over that found in stimulated intact mink. This result indicates that, during the phase of resumption of gonadal activity on short days, testicular steroid feedback partially controls the pituitary activity.