A New Method To Evaluate The Gestational Age Of Rat

Objective To predict the gestational age of rats precisely via observing vaginal smears of female rats in stages of estrous cycle and mating according to the observation.Methods1) To study the estrous cycle of female rats, vaginal smears of eight intact rats were collected at08:00,12:00,16:00,20:00everyday for20days. The smears were investigated under microscopy. Three kinds of cells were counted respectively, and the results were compared to evaluate the time for which different stages of the estrous cycle were lasting.2) To predict the gestational age of rats,32intact female SD rats were divided into two groups randomly (16in each group) and mated with male rats. Female rats in group A were mated with male rats spontaneously, and the day on which vaginal plugs were observed was defined as the day1of the gestational age. Female rats in group B were mated with male rats when the vaginal smear revealed that the female rat was in estrus. Gestation was diagnosed if sperms were found in the vaginal smear, and gestational age was ascended to18hours after estrus. On the day16of gestation, the pregnant rats were sacrificed, and the development of the fetuses were compared between the two groups. The data were analyzed by SPSS16.0. Results1) The characteristics of estrous cycle of female rat. Proestrus was characterized by dominant nucleated epithelial cells in the vaginal smear, which was lasting17-21hours,19hours in average. Estrus was defined as dominant keratinized epithelial cells appeared in the vaginal smear, and was lasting10-15hours,12hours in average. Metestrus was characterized by the co-presenting of nucleated epithelial cells, keratinized epithelial cells and dominant white blood cells in the smear, and was lasting10-14hours,12hours in average. Diestrus was characterized by mainly white blood cell, and was lasting60-72hours,66hours in average. The female rat estrous cycle was totally102-115hours,109hours in average. The appearance rates of three kinds of cell in four stages were significant different (P<0.05).2) The prediction of rat gestational age. The conception rate, conception speed and numbers of fetuses were not significant different bewteen two experimental groups. The difference of development of fetuses in group A was more obvious in contrast to group B.Conclusion Vaginal smears of female rat can be used to determine the different stages in estrous cycle, which can be used to predict the gestational age of rats precisely.