Histochemical Examination of the Vaginal Epithelium of Sows at Various Stages of the Estrus Cycle

The aim of this study was to histochemically determine the substrates which have a bearing on the carbohydrate metabolism of the vaginal mucosa. Ten multiparous sows of the German Landrace breed were used. Samples were taken from the vagina with a biopsy device throughout the estrus cycle. Increased concentrations of glycoproteins and glycogen occur between proestrus and metestrus. Glycogen in the pig does not reach to vaginal lumen. It is most likely used for the biosynthesis of glycoproteins in deeper layers of the epithelium. Consequently, the drop in pH observed in the vaginal lumen during estrus must result from secretion of acidic glycoproteins by epithelial cells, rather than from the breakdown of glycogen to lactic acid. During proestrus and estrus, the superficial cell-layer of the epithelium secretes mucus. Mucus secretion plays an important role during estrus by supporting phagocytic activity of the neutrophilic granulocytes, and therefore the self-cleaning effect of the vagina. The lamina propria demonstrates cyclical changes as well: fibrocytes in the lamina propria contain increased amounts of cytoplasmic RNA during proestrus and estrus, indicating increased protein synthesis. The protein involved here is most likely a compound of hyaluronic acid-containing proteolycans, which are deposited in the interfibrous substance. RNA determined histochemically in the fibrocytes of the lamina propria is a reliable criterion for diagnosis of proestrus and estrus.