NORMAL AND DELAYED PSEUDOPREGNANCY IN THE RAT

Abstract

In rats bearing a transplanted immature ovary under the kidney capsule, the in situ ovaries were removed at estrus. In spite of this operation the sequence of vaginal estrous cycles was uninterrupted. Removal of the in situ ovaries on the morning after copulation was followed by 1 normal vaginal estrous cycle. After this experimental cycle, during which no corpora lutea were present, a normal pseudopregnancy was observed. Prolongation of this cycle by postponing removal of the in situ ovaries resulted in the observation that the pseudopregnancy did not occur when the experimental cycle lasted 7 or more days. It is concluded that copulation triggers off a period of LTH (luteinizing hormone) secretion lasting about 8 days and which is independent of the presence of corpora lutea. This period may account for the greater part of the LTH secreted during a normal pseudopregnancy. The copulation stimulus had no direct influence on follicle maturation and subsequent spontaneous ovulation, i.e. FSH (follicle stimulating hormone) and LH secretion. A single administration of reserpine also induced a prolonged period of LTH secretion. In contrast, the suckling stimulus did not induce prolonged LTH secretion in the absence of corpora lutea. The estrous cycle induced by a single administration of ergocornine methanesulphonate during pseudopregnancy was found to be followed by another pseudopregnancy of normal length, in about half the number of cases.