Effect of acute ovariectomy on mating in the cyclic rat.

Abstract

drops from a maximum at pro-oestrus to a minimum on the morning of oestrus (Schwartz & Bartosik, 1962; Schwartz, 1964), by which time ovulation and vaginal cornification have occurred. A great deal of evidence suggests that these changes are due to a cyclic increase in ovarian secretion (see Schwartz, 1964). In a recent investigation of the timing of this ovarian secretion it was demonstrated that ovariectomy at 16.00 hours on the day before pro-oestrus, but not at 10.00 hours on the morning of pro-oestrus, blocked vaginal cornification; however, it was necessary to perform the ovariectomy at 10.00 hours on the day before pro-oestrus in order to block the uterine weight change and the lh discharge (Schwartz, 1964). The present study investigated the time at which ovariectomy would block the mating response. Virgin female rats, running 4or 5-day cycles and kept under previously described conditions (Schwartz & Bartosik, 1962; Schwartz, 1964), were ovariectomized or sham-ovariectomized between 10.00 and 11.00 hours on the morning of pro-oestrus, or between 16.00 and 17\m=.\00hours the previous afternoon (the last day of di-oestrus). Each female was paired with a male after 16.00 hours on the afternoon ofpro-oestrus. The followingmorning (oestrus) the bottom of the cage was inspected for vaginal plugs, and the vaginal smear was examined for cornified cells and sperm. All but four of the sham-operated rats were laparotomized on this day in order to check for uterine swelling; all shams were then followed at least for 8 days and inspected for implantation sites, or were permitted to go to term. The ovariectomized rats were followed for at least 7 days to make sure that vaginal cornification did not recur and then were autopsied; uterine weight was measured as an additional criterion of completeness of ovariectomy. The data are presented in Table 1. Of the sham controls, fewer than 100% showed vaginal cornification at oestrus, in contrast to unmated sham-operated or untreated controls (Schwartz & Bartosik, 1962; Schwartz, 1964). Since all five of the non-cornified sham controls became pregnant and/or had ovulated at oestrus, it is apparent that they were in the proper stage of the cycle. Of the two sham-operated rats in