Occurrence of pregnancy despite spontaneous ovulation suppression by intracerebroventricular infusion of substance P in rats.

Substance P (SP) infusion into the third cerebral ventricle and intraperitoneal injection of pentobarbital block spontaneous ovulation in female rats. This paper presents a study on the effect of SP intracerebroventricular infusion on the occurrence of copulation-induced ovulation. Spontaneous ovulation in female rats was blocked either by SP infusion into the third cerebral ventricle or by intraperitoneal injection of pentobarbital on the day of proestrus. Female rats infused with 20 nmol of SP in 10 microliter and then left with fertile males on the night of proestrus were found to be pregnant in 90% of cases, similarly as in the control group (86%). The lowest percentage of pregnancies was found in the group of animals injected with pentobarbital (69%). The obtained results suggest that reflex ovulation in female rats induced by copulation cannot be blocked by SP i. c. v. administration nor by i. p. pentobarbital, and suggest a different neural mechanism responsible for spontaneous and copulation-induced reflex ovulation.