Alterations in rat vaginal histology by exogenous gonadotrophins

Changes in vaginal epithelium are known to occur during the normal oestrous or menstrual cycle and in ovariectomised animals in response to various ho rmones. However, vaginal changes due to exogenous gonadotrophins superimpos ed on the normal hormonal milieu as occurs in in vitro fertilisation progra mmes have not previously been demonstrated. Female rats were hyperstimulate d with follicle stimulating hormone and human chorionic gonadotrophin prior to mating. Control mated animals were not injected. Vaginal tissue was col lected at 4.5, 5.5 and 6.5 d after mating. Tissue was processed for light m icroscopy. Hyperstimulation by the exogenous gonadotrophins caused mucifica tion, a decrease in the number of epithelial layers and an increase in the thickness of the epithelium on d 4.5 of pregnancy. The mitotic index of the epithelial cells was depressed in the hyperstimulated rats with respect to control animals. Exposure to high levels of oestradiol and an altered prog esterone: oestradiol ratio appear to have caused the changes in the vaginal epithelium.