Endocrine correlates of mating-induced reductions in estrous behaviour in an induced ovulator, the ferret

Experiments were conducted to assess the time course of behavioral and endocrine changes which occur in female ferrets as they switch from estrus to the pseudopregnant state. Significant reductions in females' acceptance of neck gripping by a stimulus male (receptivity) and in their latency to approach a stimulus male in an L-maze (proceptivity) were first observed 3 days after receipt of an intromission; no such changes occurred in other females which were only neck gripped by stimulus males during the initial test session. Corpora lutea were later found only in the ovaries of females which received intromissions, confirming that ovulation had occurred in these animals. Plasma concentrations of prostaglandin E1, prostaglandin F2 alpha, and the 13,14-dihydro 15-keto metabolite of prostaglandin F2 alpha (PGFM) were unchanged in female ferrets for 4-5 days after receipt of an intromission. By contrast, plasma concentrations of progesterone were significantly elevated beginning 5 days after, whereas plasma estradiol was significantly reduced beginning 4 days after receipt of an intromission. Daily sc administration of the progesterone receptor antagonist. RU 38486, significantly retarded the lengthening in females' approach latencies to a stimulus male, suggesting that postcoital elevations in circulating progesterone normally contribute to the expected decline in proceptive responsiveness. By contrast, postcoital reductions in acceptance quotients occurred at equivalent rates in females treated with RU 38486 versus vehicle, leading us to infer that postcoital reductions in estrogenic stimulation may cause this decline in ferrets' receptive responsiveness.