Patterns of estrogen and progesterone receptors in rhesus monkey endometrium during secretory phase of normal menstrual cycle and preimplantation stages of gestation

Abstract

Using validated methods, estradiol receptor (ER) and progesterone receptor (PgR) levels have been estimated in endometria collected in secretory phase of normal menstrual cycle and preimplantation stages of gestation from rhesus monkeys ( Macaca mulatta). Endometrial PgR in both cytoplasmic and nuclear compartments decreased significantly ( P < 0.001) from day 2 to day 6 post-ovulation in both groups, but in fertile cycle, absolute levels of nuclear PgR remained significantly higher ( P < 0.05) on days 4, 5 and 6 of gestation, ER concentrations, both total ( P < 0.02), as well as cytoplasmic ( P < 0.01) declined significantly in secretory phase of normal menstrual cycle while nuclear ER levels remained unchanged. In the preimplantation period, ER patterns remained unvarying on days 2–6 of gestation in both cytoplasmic and nuclear compartments; their levels in nuclear fraction were significantly higher from day 3 onwards while, total cytoplasmic ER concentrations were higher from day 4 of gestation compared with the values obtained for secretory phase tissues from normal ovulatory cycles. No changes were, however, detected in apparent equilibrium dissociation constants ( K d ) for the sex steroid receptors in endometria obtained from fertile and non-fertile cycles. It has been suggested that in prenidatory stage rhesus monkey endometrium elevated concentrations of nuclear ER and PgR possibly indicate higher degree of nuclear occupancy required for endometrial differentiation permitting blastocyst implantation.