[Cyclic changes in steroid hormone concentration and steroid hormone receptor in the human endometrium]

The levels of endometrial estradiol (E2), blood E2 and endometrial estradiol receptor (E2R), and the concentration ratio of blood E2 to endometrial E2 began a gradual increase in the early proliferative phase, forming peaks in the late proliferative phase. The levels of endometrial progesterone (P), blood P and endometrial progesterone receptor (PR), on the other hand, rose to peaks in the early or mid secretory phase. The concentration ratio of P rose to a peak in the late proliferative phase. The nuclear DNA histogram showed a rightward deviation from hyper 2n to hyper 4n in the late proliferative phase, and returned leftwards in the late secretory phase. The above results suggest the following correlation among them. The increase in blood E2 first increases endometrial E2R and then intensifies the concentrating ability of E2 to elevate endometrial E2, accelerating nuclear DNA synthesis. The increase in endometrial PR is more influenced by endometrial E2 than blood P. This together with blood P increases endometrial P. Nuclear DNA synthesis, however, seemed inhibited. Hence, E2R and PR were considered to play a significant role in the mechanism that may be defined as the concentrating ability of E2 and P in the endometrium.