Summary

Abstract

With respect to the ovarian status and the estrous cycle as expressed by the vaginal cytology, it was emphasized that there is only a rough correspondence between the vaginal stages and the days of the cycle. The 4-day cycle tends to be the most frequent, with the 5-day cycle a normal variant. Spontaneous persistent vaginal estrus (SPE), an acyclic state occurring in older adult rats, reflects the presence in the ovaries of large vesicular follicles failing to luteinize and, hence, the absence of corpora lutea once the condition becomes well established. Pseudocyclic fluctuations in the vaginal smear during SPE resemble those in ovariectomized rats treated chronically with estrogen.