Effects of Estrogen and Progesterone on the Development of the Mammary Gland and the Associated Blood Vessels in Ovariectomized Mice

Abstract

Effects of estrogen and progesterone on the first abdomino-inguinal mammary gland and the associated blood vessels in ovariectomized mice were investigated morphometrically, and light and electron microscopically. Although there were no significant differences in the area of the fat pad of the mammary gland among the experimental groups, the area of the mammary parenchyma and diameters of the blood vessels supplying the mammary gland, i.e., A. et V. circumflexa ilium profunda and A. et V. epigastrica caudalis superficialis, reached the maximal value in ovariectomized mice treated with estradiol (E) + progesterone (P). Similarly, the blood capillaries around buds and ducts of the mammary gland were most densely distributed in E+P treated mice. In the adipose tissues of the mammary stroma in intact mice, fat cells were of multilocular type in the peripheral regions around the main vessel, and of unilocular type in the other part. In E and E+P treated mice, however, fat cells were mostly of unilocular type. These findings suggest that the formation of mammary fat tissues may occur in advance of that of the mammary parenchyma. By TEM, epithelial cells of the mammary parenchyma contained a large number of mitochondria and ribosomes, well-developed Golgi apparatus and rER, and large lipid droplets. Endothelial cells of blood capillaries displayed numerous pinocytotic vesicles, longer marginal folds and microvillous processes. Each organelle in these two cell types increased in number or developed to a greater degree in E+P treated mice than the other experimental groups. These observations prove the development of the mammary gland and associated blood vessels induced by the administration of E+P in ovariectomized mice, and indicate the close participation of ovarian steroid hormones in the development of the mammary parenchyma and vasculature. © 1992, JAPANESE SOCIETY OF VETERINARY SCIENCE. All rights reserved.