Effect of estriol on the structure and organization of collagen in the lamina propria of the immature rat uterus.

Estradiol produces both hypertrophic and hyperplastic changes in the uterus, and these changes are associated with alterations in the structure of collagen in the lamina propria. Estriol induces only hypertrophic responses in the immature rat uterus; its effects on collagen structure were characterized in this study. Light micrographs of Masson's trichrome-stained sections revealed that the intensity of the collagen stain in the lamina propria of the rat uterus was profoundly reduced, relative to that in controls, 4 h after estriol (40 micrograms/kg) administration. These changes were not evident 24 h after estriol administration. In control uteri, transmission electron micrographs revealed that the collagen fibers surrounding stromal cells formed dense collections of bundles that were seen throughout the extracellular matrix, whereas in tissues exposed to estriol 4 h earlier, large regions of the extracellular spaces were devoid of collagen bundles. The 4-h changes in collagen were eliminated when animals were pretreated with actinomycin D (8 mg/kg) or cycloheximide (4 mg/kg). Dense collections of collagen bundles were present in tissues 24 h after estriol treatment, and their appearance was not altered by actinomycin D or cycloheximide treatment. Alterations in collagen 4 h after hormone administration appeared to be estrogen-specific since dexamethasone (600 micrograms/kg) and dihydrotestosterone (400 micrograms/kg) had no effect. These data provide evidence that the changes in collagen structure in the uterus are associated with events that function during the hypertrophic growth responses induced by estrogens.

The effect of estradiol on collagen structure and organization in the immature rat uterus.

An examination of collagen ultrastructure in the lamina propria of the immature ovariectomized rat uterus revealed that a single injection of estradiol (40 micrograms/kg) produced a biphasic effect on collagen structure and organization. In saline-treated animals (controls) dense populations of collagen bundles were seen throughout the extracellular matrix (EX). Cross-sections of these bundles suggested that the bundles run parallel to the long axis of the uterus and thin filaments seemed to form cross-links between collagen fibers. In contrast, large clear spaces, collagen fragments, and loosely packed bundles of collagen were observed in the EX of animals injected with estradiol 24 hr earlier. In a time course study (0, 1, 2, 4, 24, and 48 hr), estradiol treatment altered collagen structure and organization 1 hr following administration. Collagen bundles did not appear to be as densely packed as in control tissues and large clear spaces were evident in the EX. Two hours following estrogen administration, collagen fibers appeared to be fragmented and seemed to be separating from the plasma membrane of stromal cells. Four hours following estrogen administration, large clear spaces occupied most of the EX in the lamina propria. Collagen fragments were diffusely distributed throughout the EX and small cross-sectional patches of collagen bundles were present. In 48-hr-treated animals, collagen bundles reappeared and were often closely associated with the plasma membrane of stromal cells. The collagen was not as abundant as in control animals. An overview of the cellular organization of the lamina propria revealed that stromal cells in control tissues were more densely packed than in estradiol-treated tissues (4, 24, and 48 hr) and the stromal cell size appeared to increase in hormone-treated tissues. These responses provide a good model system to study the role of estradiol in the control of collagen structure and organization in the uterus.