Abstract
Old World monkeys display physiological responses to steroid hormones that are similar
to those of women. In this review, we describe cyclic morphological changes that take
place within the uterus of Old World primates during the menstrual cycle. In primates,
estrogen stimulates endometrial growth in the follicular phase of the menstrual cycle.
Progesterone secreted in the luteal phase acts to induce secretory differentiation,
which is required for successful embryo implantation. During the differentiation process,
endometrial estrogen receptor-1 (ESR-1) is suppressed, and reduced staining for ESR-1
is a definitive marker of the onset of uterine receptivity. Downregulation of ESR-1
is topographically limited to the functionalis (upper) zones of the endometrium, the
zones in which embryo implantation occurs, indicating that zone-specific factors play
a role in the differentiation process. Future genomic and proteomic studies are expected
to reveal additional markers for diagnosing endometrial receptivity. Due to the distinct
zonal response of the endometrium to ovarian steroids, accurate histological characterization
will remain necessary to interpret novel targets in the assessment of fertility.
Keywords
menstrual cycle - histology - endometrium - secretory differentiation - progesterone