HISTOLOGICAL DIFFERENCES BETWEEN GRAVID AND NONGRAVID UTERI IN THE DASYURID MARSUPIAL, SMINTHOPSIS-MACROURA (SPENCER)

Uterine samples from pregnant Sminthopsis macroura representing the fi rst 10 days of its II day gestation period and samples from non-pregna nt animals were compared histologically and examined for differences i n the following characteristics: thickness of the endometrial stroma, luminal epithelium, myometrium and glandular epithelium, and the densi ty of stromal glands and number of lymphocytes at the endometrial basa l lamina. A highly significant difference between,gravid and non-gravi d uteri with respect to thickness of the endometrial epithelium was fo und on day 3, when lineage divergence occurs between the pluriblast an d trophoblast. The endometrial stroma was significantly thicker in pre gnant animals on day 8, when the epiblast differentiates into ectoderm , endoderm and mesoderm. Other differences between gravid and non-grav id uteri were detected in myometrial thickness on days I and 5. Taken together, these results indicate that despite similar endocrinological profiles of pregnant and non-pregnant marsupials, there are subtle, b ut significant, differences in uterine histology. The observed concord ance between histological differences and differentiative events in em bryogenesis is considered as indicative of embryo-maternal signalling.