Electron Microscopy of Milk Secretion in the Mammary Gland of the C3H/Crgl Mouse. III. Cytomorphology of the Involuting Gland2

Abstract

The cytologic changes occurring during involution of the mouse mammary gland were studied by light and electron microscopy in tissue samples taken up to 15 days after the cessation of suckling. By light microscopy there was a marked decrease in the amount of epithelial tissue in the mammary glands, accompanied by a corresponding increase of stromal adipose tissue. By electron microscopy most of the epithelial cells of the alveoli and small ducts showed an intracellular accumulation of fat and protein droplets, vacuolization, the appearance of several types of intracellular inclusions, and the disappearance of portions of the ergastoplasmic and Golgi sacs. By the 5th day these changes culminated in cytolysis of the epithelial cells with the release of free nuclei, mitochondria, fat droplets, and other structures into the alveolar and ductal spaces bounded by intact basement membranes. By the 15th day after the termination of suckling, the process was complete, and remaining epithelial structures consisted mostly of small ducts lined by intact epithelial cells.