Hormonal Basis for Collagen Bundle Generation in Uterine Stroma: Extracellular Studies of Uterus11

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Abstract
A study was carried out concerning the deposition and maintenance of a densely collagenous stroma in the rat endometrium. The experiments were begun immediately following parturition, at which time the endometrium is essentially free of thick collagen bundles. The reported findings are from the uteri of rats which were castrated on the day of parturition and then given daily injections of either estradiol-17β or progesterone and from the uteri of rats which suckled 14 young from the time of parturition until autopsy or weaning. The presence of endogenous or exogenous estrogen appears to be necessary for the deposition and maintenance of a densely collagenous stroma in the rat endometrium. Exogenous estradiol-17β given daily to castrated rats was associated with the appearance of thick, multifibrillated collagen fibers throughout most of the endometrial stroma by 10 days postpartum. In contrast, 3 weeks or more were required for a similarly collagenous stroma to be developed in the uteri of intact rats receiving only the endogenous estrogens produced by their ovaries during their normal estrous cycles. Progesterone is not required for the deposition or maintenance of a collagenous endometrial stroma. As long as suckling was continued, no new collagen bundles appeared in the endometrial stroma of the mother's uterus. However, shortly after weaning this stroma became increasingly fibrous. By 3 weeks following weaning, coarse collagen bundles permeated almost the entire endometrial stroma and appeared to be the dominant components in microscopic sections of such uteri stained with aniline blue. The relationship of these findings to the inhibition of estrous cycles during suckling and to the resumption of estrous cycles following weaning is discussed.