Sex Difference in the Effect of Mating on the Pulsatile Secretion of Luteinizing Hormone in a Reflex Ovulator, the Ferret*

Sex differences in the pulsatile secretion of LH were examined in male and female ferrets after mating. Female ferrets which were either gonadally intact and in estrus or gonadectomized and maintained on a pulsed regimen of daily estradiol (E2) injections exhibited a prolonged rise in plasma LH, characterized by an elevation in mean LH levels and an increase in the number of LH pulses after receiving an intromission from a stud male. By contrast, no such increase in LH secretion occurred in males which achieved an intromission with a female, regardless of whether they were gonadally intact and in breeding condition or gonadectomized and given pulsed estrogen. In fact, intact breeding males which achieved an intromission had significantly fewer LH pulses 1-5 h later than unmated males bled serially over the same time period. This decrease in LH pulse frequency was followed by a significant rise in mean plasma levels of androgen 5-12 h later. When a sexually dimorphic LH response to intromission was observed in gonadectomized E2-treated ferrets, we asked whether this could reflect a sex difference in pituitary responsiveness to the endogenous release of GnRH. Thus, plasma LH levels were measured in gonadectomized and gonadectomized E2-treated ferrets for 2 h after iv injection of GnRH. In the absence of gonadal steroids, ferrets exhibited a sex-specific difference in LH responsiveness to GnRH; however, no sex difference was apparent under the influence of E2. These findings demonstrate that ferrets' sexually dimorphic LH responses to intromission probably reflect a sex difference in the processing of somatosensory inputs from the genitalia or in the neural control of GnRH release into the pituitary portal vessels.