Mouse uterine glandular epithelium during the lactationally delayed implantation period and after estradiol induction of implantation was investigated using light and electron microscopy. During the delayed implantation period the lumen of this simple tubular gland is narrowed. The glandular epithelial cells have a well developed Golgi complex lateral to the nucleus, and numerous cisternae of smooth and rough endoplasmic reticula (RER) and many electron lucent apical vesicles of sizes up to 0.2 μm in diameter near the luminal border. The basal region contains lipid droplets and dispersed, irregular cisternae of RER. Twenty-four hours after the administration of 17β-estradiol the glandular lumina become dilated but the luminal content does not stain with azure B. Ultrastructurally the glandular cells are not remarkably different from those seen during the delay period. However, by 48 hours after estradiol administration the glandular lumina are not only dilated but filled with material which stains intensely with azure B and is ultrastructurally dense and homogeneous. The apical region of the glandular cells contains granules up to 0.4 μm in diameter composed of electron dense material similar in density to that seen in the glandular lumen. In addition, the Golgi complex has assumed a position apical to the nucleus, and the basal RER has an increased number and more orderly arrangement of cisternae.
The changes seen in the uterine glands after the induction of implantation during the delay period are apparently indicative of increased secretory activity of the glandular epithelia. However, the contribution of the glands to the changes in uterine fluid composition has yet to be established.