Collagen Distribution in the Mouse Endometrium during Decidualization

The distribution of collagen and reticular fibers was studied in the endometrium of virgin and pregnant mice. The collagen and reticular fibers were examined in picrosirius-stained sections observed in a polarizing microscope and in silver-impregnated sections. Picrosirius-stained sections of animals in estrus, diestrus and on the 2nd day of pregnancy had fine greenish fibers distributed irregularly in the endometrium and thicker red fibers concentrated near the myometrium. Argyrophyl fibers in virgin mice were scarce and irregularly distributed. On the 4th day of pregnancy very few fibers were observed in the endometrium. On the 5th, 6th and 7th days of pregnancy long greenish fibers were found surrounding decidual cells. A network of argyrophyl fibers was observed in the silver-impregnated decidua. It is suggested that new fibers are produced by decidual cells.