Estrogen and progesterone protect against the inhibitory effects of restraint stress
The effects of restraint stress on lordosis behavior were examined in ovariectomized (ovx), hormone-primed rats and in proestrous rats. In the first experiment progesterone (P) dose-dependently reduced the female rat's response to restraint. Ovx rats were primed with 10 μg estradiol benzoate (EB) followed 48 hr later with various doses of progesterone or sesame seed oil (oil). At 5 min after restraint, rats that were given oil or 2.5, 5.0, or 10 μg progesterone and restrained for 5 min showed a decline in lordosis behavior. By 10 min after restraint lordosis had increased; however at no time did the lordosis to mount (L/M) ratios (number of lordosis responses by the female divided by the number of mounts by the male) of rats given 25 μg or higher doses of progesterone decline. In the second experiment EB also acted dose-dependently to decrease the lordosis-inhibiting effects of restraint stress. Ovx rats were hormonally primed with various doses of EB followed 48 hr later with 250 μg P. An additional group received 50 μg EB and oil. The lordosis behavior of restrained rats given 0.5, 1.0, or 2.5 μg EB was reduced 5 min after restraint. This reduction in lordosis behavior lasted for 5 min, but by 10 min, L/M ratios had increased. In the third experiment, physiological levels of hormones protected against a stress-induced decline in lordosis behavior. Proestrous rats showed no decline in lordosis after 5 to 60 min of restraint. In the final experiment, after intraperitoneal treatment with ketanserin tartrate (ketanserin), 5 min of restraint reduced lordosis behavior of proestrous rats. Every rat given 1.0 mg/kg ketanserin and restrained for 5 min showed a decline in lordosis behavior by 5 min after restraint. With 0.50 or 0.75 mg/kg ketanserin, L/M ratios of proestrous rats were not reduced by 5 min of restraint. In conclusion these data are consistent with the suggestions that estrogen and progesterone contribute to facilitation of lordosis behavior and that 5-HT2A/2C receptors may attenuate the disruptive effects of stress.