Microtubule and plasmalemmal reorganization: acute response to estrogen.

The acute ultrastructural effects of estrogen in endometrial epithelial cells were investigated by transmission electron microscopy (TEM), with special reference to the microtubule (MT) apparatus and the luminal surface. Ovariectomized rats anesthetized with pentobarbitol sodium were injected intravenously with estradiol-17 beta (E2 beta), 0.5 micrograms/100 g body wt. At intervals from approximately 30 s to 30 min thereafter, 70-80 nm cross sections of a uterine horn were prepared for TEM. In placebo controls, cytoplasmic MT were conspicuous in length and number, whereas only a minimal population of short microvilli (MV) was evident. In contrast, the specimens subjected to E2 beta for only 35 s showed a significant decrease in MT number and length, with virtually complete depletion of these organelles by approximately 80 s. Concomitantly, the luminal MV exhibited striking enhancement in length and density. Thereafter, these rapid and reciprocal alterations of MT and MV underwent inversion. Thus MT structures began to reappear within 2 min, increasing progressively so that by 30 min their numbers were again substantial, although lengths remained diminished. During the same interval, the initial surge of luminal MV gradually subsided, to near-control appearance by 30 min. These coordinate, reciprocal, and biphasic responses are consistent with biochemical evidences of abrupt membrane perturbation associated with interception of estrogen at its cellular targets. The resultant modification of the intracellular environment may contribute to limited reorganization of cellular architecture and propagation of the hormonal signal.