Effects of ovarian hormones on cell membranes in the rat uterus. II. Freeze-fracture studies on tight junctions of the lateral plasma membrane of the luminal epithelium.

Freeze-fracture techniques have been used to study tight junctions on the lateral plasma membrane of cells of the luminal epithelium of the rat uterus under various hormonal regimes. Tight junctions from ovariectomized control rats extended some 0.5 micron down the lateral membrane and the junctional strands often formed a network of closely packed, circular compartments. Following treatment of rats with estrogen for 3 days the tight junctional region still extended 0.5 micron down the lateral membrane, but the strands ran more parallel to the apical surface. They did not enclose circular compartments. After treatment with progesterone, either alone or with estrogen in such a way as to condition the ovariectomized uterus for implantation, a third pattern of junctional organization emerged. In these animals the junctional region extended 1.1 micron down the lateral membrane and the strands frequently crosslinked, enclosing compartments of varying and irregular size and shape. Our observations suggest that ovarian hormones could regulate the contents of the uterine lumen by altering the structure and extent of the tight junctions which connect the epithelial cells enclosing the lumen.