抄録
An electron microscopic observation was made on the hyperplastic nodules in the mammary glands of mice. The animals were derived from three inbred strains (C3H/HeMs, SL, and A/Jax), 2 groups of hybrids (F1 hybrid of the A/Jax×AKR cross, and F4 hybrid of the A/Jax×BALB/c cross), and 3 colonies of non-inbred mice (Swiss, na2, and dd/s). A total of 9 animals were used, consisting of one female mammary tumor-bearing mouse from each of these 8 different sources and one tumor-free female SL mouse. Animals, either parous or estrogen-treated in the past, had a various incidence of mammary tumor, from extremely high to very low. All the nodules taken from these 9 mice invariably showed the virus-like particles of Type B (Bernhard), The particles were round or oval in shape, approximately 1000Å in diameter, and had an eccentrically located dense nucleoid. They were distributed extracellularly. Membrane-bounded proliferation of the particles was recognized at the tips of the microvilli or at the apical plasma membrane. Some nodules derived from mice of A/Jax strain and (A/Jax×AKR)F1 hybrid had the intracytoplasmic Type A particles as well as the extracellular Type B particles. The possibility was considered that practically all hyperplastic nodules harbor the Type B particles irrespective of the mouse strains.
Besides the presence of the virus-like particles, the ultrastructure of the nodules retained all the characteristics of the glandular epithelium. The secretory mechanism was similar to that in the normal lactating glands. The fat droplets were released by a pinching-off mechanism and the protein particles through an opening at the cell surface.
