Histochemistry and Electron Microscopy of Iron-Containing Granules, Lysosomes, and Lipofuscin in Mouse Mammary Glands2

Abstract

The mammary epithelium of virgin CBA mice contained ferritin-like granules and had acid phosphatase activity. The ferritin and acid phosphatase activity were in bodies considered to be lysosomes. In mammary tissue of mice over 20 weeks of age, the number of lysosomes increased quite rapidly and remained relatively high. Heavy deposits of iron-rich pigment, which characterized the fully involuted mammary epithelium of multiparous mice, were represented by heterogeneous groups of enlarged dense bodies composed of aggregates of ferritin-like grains, granular and membranous areas, and large round or oval bodies. They were iron-, acid phosphatase-, and periodic acid-Schiff-positive, acid fast, and contained insoluble lipides. They were defined as lipofuscin from both histochemical and ultrastructural characteristics. Mammary lipofuscin in parous mice was deposited, irrespective of the age of the animals and of the number of pregnancies. Structural association with lysosomes and the demonstration of acid phosphatase in certain portions led to the conclusion that lipofuscin accumulated in relation to lysosomes. The possible role of lysosomal iron as a catalyst for lipofuscin formation is discussed.