Differential Photoperiodic Control of Seasonal Variations in Pulsatile Luteinizing Hormone Release in Long-Day (Ferret) and Short-Day (Mink) Mammals

Abstract

The aim of this study was to elucidate the pituitary adjustments implicated in photoperiodic control of reproduction in two mammalian species, the ferret and the mink. In the ferret, which displays renewed testicular activity when the days lengthen, we observed a stimulation of the pulsatile liberation of luteinizing hormone (LH) reflecting the pulsatile activity of the gonadotropin-releasing hormone (GnRH) system when daylight was equal to or in excess of LD 8:16. This photoperiod coincides precisely with the phase of photosensitivity known to be essential for gonadal stimulation in this species. In the mink, which displays renewed testicular activity when the days shorten, pituitary stimulation was activated when daylight was reduced to LD 11:13, and gonadal stimulation occurred only when daylight was further reduced to LD 10:14. In addition to requiring different photoperiodic stimuli to trigger the seasonal reproductive process, the two species display variations in the "timing" of pituitary control of renewed gonadal activity.