Effects of paced and non-paced mating stimulation on plasma progesterone, 3 alpha-diol and corticosterone

In the female rat, gonadal and adrenal progestins and androgens modulate sexual receptivity and in turn, their levels increase in response to mating stimulation. Paced mating, in which the female controls the timing of sexual contacts with the male, is particularly effective at eliciting acute increases in progesterone (P) and 5 alpha-Androstane-3 alpha, 17 beta-diol (3 alpha-Diol). Interestingly, restraint stress produces comparable increases in P and 3 alpha-Diol levels, as well as increases in corticosterone (CORT) levels. In this study, we explored the possibility that paced mating would be associated with increased CORT, in conjunction with mating-induced increases in P and 3 alpha-Diol. Ovariectomized rats primed with estradiol benzoate (10 micrograms in oil SC) and P (0.5 mg in oil s.c.) received a single ejaculatory series from males in paced or non-paced mating tests. Fifteen minutes post-mating rats were exposed to CO2 and rapidly decapitated for the collection of trunk blood and determination of P, 3 alpha-Diol and CORT via radioimmunoassay. As expected, P and 3 alpha-Diol concentrations were significantly elevated in serum obtained from animals allowed to pace their sexual contacts with males compared to those which did not pace their contacts. Importantly, although all mated animals had CORT levels between 10-20 micrograms/dl, there were no differences between paced and non-paced conditions. This suggests that the acute rises in P and 3 alpha-Diol in response to paced mating are not due to paced mating being more stressful than non-paced mating.