Effects of prostaglandin F2 alpha on sexual behavior and ovarian function in female garter snakes (Thamnophis sirtalis parietalis).

Sexual behavior, plasma steroid hormone levels, and ovarian growth of female red-sided garter snakes (Thamnophis sirtalis parietalis) treated with prostaglandin F2 alpha (PGF2 alpha; 0.5-5.0 micrograms/g BW) were observed. The largest dose of PGF2 alpha significantly inhibited receptivity (mating) within 0.5 h of treatment and resulted in a significant decrease in sexual attractively 24 h later. These changes precisely parallel those seen in females that have mated. Lower doses of PGF2 alpha significantly increased the latency of females to mate by 3-fold in both the laboratory and the field. In contrast to the inhibitory effects of PGF2 alpha on sexual behavior, females injected with PG had levels of steroid hormones (progesterone, testosterone, 17 beta-estradiol, and corticosterone) similar to those in unmated controls 24 h after treatment, while females that had mated 24 h previously had significantly elevated plasma levels of 17 beta-estradiol. There was no significant difference in the incidence of vitellogenesis 6-8 weeks later among unmated females, unmated females treated with PG, and mated females. These results suggest that complex neuroendocrine responses occur after mating. One response may involve mating-induced release of PGs and suppression of sexual behavior, while a second independent response may involve a PG-independent mechanism that influences ovarian function. These findings are interpreted within the context of the garter snake's reproductive physiology and ecology.