UTERINE HISTOLOGY OF THE DASYURID MARSUPIAL, ANTECHINUS-STUARTII - RELATIONSHIP WITH DIFFERENTIATION OF THE EMBRYO

Uterine samples from Antechinus stuartii on days 1, 4, 6, 8, 11, 13, 1 5, 18, 21 and 23 after ovulation were examined histologically. Animals were pregnant, nonpregnant and unmated, or nonpregnant and mated but found to have only unfertilized eggs on autopsy. The histological para meters used were thickness of the myometrium, endometrial stroma, and endometrial epithelium, and density of uterine stromal glands and of l ymphocytes at the endometrial basal lamina. Overall, the fluctuation p atterns of these parameters were superficially similar between pregnan t and nonpregnant animals (mated or unmated). However, statistically s ignificant differences were detected between pregnant and unmated nonp regnant animals in every parameter examined at nearly every time point except day 13. Comparison of these results with known data on embryon ic stages, corpus luteum development and plasma progesterone concentra tions revealed that the gravid uterus underwent histological changes c o-incident with changes in both progesterone concentration and develop mental delay or embryonic arrest. It was concluded that the uterus med iates progesterone-driven changes in embryonic developmental rate. Alt hough determination of number of lymphocytes provided inconclusive evi dence of cellular immunity against embryos, the possibility that embry onic signalling to the uterus occurs is discussed.