Apical Vesicles in the Rat Uterine Epithelium During Early Pregnancy: A Morphometric Study

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Abstract
A class of electron-transparent vesicles, 130-450 nm in diameter, located in the apical cytoplasm of rat uterine epithelial cells was examined morphometrically in normal and colchicine-treated rats in early pregnancy and in ovariectomized rats treated with ovarian hormones. The vesicles were present in cells from days 3-7 of pregnancy with the largest number on day 5. They appeared in ovariectomized rats in response to progesterone alone, but the number increased when progesterone was preceded by estrogen. Estrogen alone had no effect. The appearance of the vesicles coincided with the preattachment or preimplantation period; i.e., when blastocysts were free in the uterine lumen but not yet implanted. Colchicine treatment (1 and 3 mg/kg, i.p.) of rats on day 5 of pregnancy caused a decrease in the fractional volume of the apical vesicles in the apical cytoplasm. The drug-treated rats showed apical vesicles distributed throughout the cytoplasma from apex to base of the cells, while in untreated rats the vesicles were restricted to the apical halves. The structure and distribution of the Golgi complex was also affected by the drug. Normally the Golgi complex is restricted to the apical halves of the cells, but it appeared in both apical and basal halves of the cells and showed shorter cisternae with fewer stacks in colchicine (1 mg/kg) treated cells. Apical vesicles were frequently associated with the dispersed dictyosomes. In addition to these alterations, colchicine (3 mg/kg) frequently caused the rearrangement of the Golgi complex into a ring-type configuration which appeared in both the apical and basal parts of the cells. Again, apical vesicles appeared adjacent to the altered Golgi complex. The present quantitative data thus confirm earlier observations that the number of apical vesicles is correlated with the peak of endocytotic activity and that the apical vesicles are formed in the Golgi complex and move to the surface to replace plasma membrane taken into the cells by endocytosis.

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