Progesterone control of fibronectin secretion in guinea pig endometrium

Immunohistochemistry with a polyclonal antibody raised against human plasma fibronectin (Fn) was used to determine the localization of Fn in endometrial sections of guinea pig uteri isolated at the first, fourth, sixth, or tenth day of the estrous cycle. Immunoreactive Fn was constantly visualized in the endometrial stroma but absent from the epithelial layer. Fn was detected in the uterine lumen on the first or fourth day of the estrous cycle and was absent from the other sections. To determine the origin of this luminal Fn the ability of subcultured endometrial cells to produce Fn was tested, and the hormonal regulation of Fn secretion was studied. Cells were treated by estradiol alone or in association with progesterone, progesterone alone, or untreated. Whatever the hormonal treatment, stromal cells constantly secreted immunoreactive Fn into the culture medium. In the same way, the amount of Fn synthesized and basally secreted by epithelial cells was not affected by any hormonal treatments. However, Fn was found in the apical secretions of the untreated or estradiol-treated epithelial cells but was undetectable in the apical compartment when the epithelial cells were treated by progesterone alone or in association with estradiol. These results indicate that Fn is constitutively secreted by stromal cells and that subcultured epithelial cells of guinea pig endometrium secrete Fn from both their basal and apical membrane domains. However, the apical secretion of Fn is specifically suppressed by progesterone.