Alterations in tight junctions of human endometrial epithelial cells during normal menstrual cycle--freeze-fracture electron microscopic study.

The structural change in the tight junction between human endometrial epithelial cells during the normal menstrual cycle was observed by means of freeze-fracture replica electron microscopy. Tight junctions between epithelial cells of the endometrial basal layer showed no alterations in structure during the menstrual cycle, while those between epithelial cells of the functional layer exhibited remarkable changes synchronized with the menstrual cycle; in the early proliferative phase, the tight junctions were composed of strands running mainly parallel to the luminal surface and the depth of the junctions from the luminal surface was 0.57 +/- 0.04 micron (Mean +/- S.E.), whereas in the late proliferative phase the junction formed a prominent network of strands 0.80 +/- 0.04 micron deep. In the early secretory phase, the junctions developed mostly as a complex network, and the depth was 0.96 +/- 0.04 micron. In the late secretory phase, the network consisting of the junctions looked disorderly and the depth of the junctions was reduced to 0.71 +/- 0.04 micron. As a conclusion, it was suggested that the tight junction in the human endometrial epithelium tended to develop or diminish according to the phase of the menstrual cycle.