Effect of Coitus on Chlorpromazine Inhibition of Ovulation in the Rat1

Abstract

Varying levels of chlorpromazine were injected subcutaneously into mature non-parous rats between 1230 and 12:45 PM on the day of proestrus. Females injected with chlorpromazine at the doses used in these experiments showed no overt signs of tranquilization and could not be distinguished from control females on a behavioral basis. No ovulations occurred in females not exposed to males following a dose of 0.8 mg of chlorpromazine, but at 0.4 mg some females ovulated. It was observed that about half the blocked females exposed overnight to males copulated and that significantly more (p .blocked females exposed overnight to males ovulated than did similarly blocked females not exposed to males. In an attempt to determine whether it was the presence of the male during the "critical period" for LH [luteinizing hormone] release or copulation that was responsible for overcoming the inhibition of ovulation, groups of females treated with 0.4 mg of chlorpromazine were exposed to males from 2:00 to 6:00 PM or from 8:00 to 12:00 PM on the day of proestrus. A significant (p < .01) increase in number of females ovulating occurred when males were present from 8:00 to 12:00 PM, while the presence of the male from 2:00 to 6:00 PM had no effect on ovulation. Additional groups of females blocked with 0.4 mg of chlorpromazine were exposed from 8:00 to 12:00 PM to males that would copulate ("fresh males") or males that would not copulate ("spent males"). The presence of spent males had no effect on ovulation, while the presence of the fresh males again caused a significnt increase (p < .01) in number of females ovulating. It was concluded on the basis of these data that copulation, presumably acting through the central nervous system, caused ovulation to occur in rats which had been blocked with chlorpromazine. It is believed that the stimulus of coitus triggered the release of luteinizing hormone from the adenohypophysis.