Histological differences between gravid and non-gravid uteri in the dasyurid marsupial, Sminthopsis macroura (Spencer).

Uterine samples from pregnant Sminthopsis macroura representing the first 10 days of its 11 day gestation period and samples from non-pregnant animals were compared histologically and examined for differences in the following characteristics: thickness of the endometrial stroma, luminal epithelium, myometrium and glandular epithelium, and the density of stromal glands and number of lymphocytes at the endometrial basal lamina. A highly significant difference between gravid and non-gravid uteri with respect to thickness of the endometrial epithelium was found on day 3, when lineage divergence occurs between the pluriblast and trophoblast. The endometrial stroma was significantly thicker in pregnant animals on day 8, when the epiblast differentiates into ectoderm, endoderm and mesoderm. Other differences between gravid and non-gravid uteri were detected in myometrial thickness on days 1 and 5. Taken together, these results indicate that despite similar endocrinological profiles of pregnant and non-pregnant marsupials, there are subtle, but significant, differences in uterine histology. The observed concordance between histological differences and differentiative events in embryogenesis is considered is indicative of embryo-maternal signalling.