MORPHOLOGICAL-CHARACTERISTICS OF PREIMPLANTATION STAGE ENDOMETRIUM IN THE RHESUS-MONKEY

The morphological characteristics of endometrium on day 6 after ovulation of conception (group 1) and non-fecund, menstrual (group 2) cycles have been studied in the rhesus monkey (n = 30). A conception cycle was distinguished by the presence of a developmentally normal, age-stage-synchronized embryo. Thus, 78% of the mated cycles (n = 18) yielding synchronous embryos (12 zona-encased and two zona-free blastocysts) were used for this study. On day 6 after ovulation, no significant changes in the serum concentrations of oestrogen and progesterone were seen in conception cycles (n = 14) compared with the non-mated, normal ovulatory cycles (n = 12). Morphometric analyses revealed that on day 6 of gestation (n = 8), endometrium differed from the corresponding non-mated luteal phase (n = 7) with significant increases in epithelial mitosis (P < 0.01), height of glandular epithelium (P < 0.05), volume ratio of gland cell to gland (P < 0.03), degree of pseudostratification (P < 0.02), and higher frequency of supranuclear, adluminal accumulation of vacuoles in gland cells (P < 0.05). The degree of stromal oedema was higher (P < 0.02) in fecund cycles but there was no change in venular diameter. In a separate set of experiments, estimates of tissue vascular response revealed a higher (P < 0.02) endometrial extravascular albumin space on the same day of gestation; there were no differences, however, in endometrial blood volume, or in the number of von Willebrand antigen-positive capillaries and small vessels between the two groups (group 1, n = 6; group 2, n = 5). The overall results of the present study together with our earlier reports support the hypothesis that differential changes occur in luteal phase endometrium functionalis in the presence of preimplantation stage blastocyst in the rhesus monkey.