Effects of ovarian hormones on cell membranes in the rat uterus. I. Freeze fracture studies of the apical membrane of the liminal epithelium.

Freeze fracture techniques have been used to study the apical membrane of cells of the luminal epithelium of the rat uterus under various hormonal regimes. In the ovariectomized but otherwise untreated rat, intramembranous particles (IMPs) occur at a density of 1395 +/- 122 per micron 2; they appeared spherical and uniformly distributed. After 3 days treatment with estrogen, no change in appearance or density was found, but 3 days of progesterone treatment produced a significant increase in IMP density to 1622 +/- 104. Treatment with progesterone, with an additional dose of estrogen on day 3, is known to produce an epithelium receptive to the implanting blastocyst. In these conditions, the IMP density rose to 3818 +/- 337: rod-shaped particles and aggregations of IMPs were seen, and some particle arrays resembling gap junctions, in addition to the isolated spherical particles.