Electron Microscopy of Induced Secretion in Organ Cultures of Mammary Tissue of the C3H/Crgl Mouse2

Prelactating mammary tissue from C3H/Crgl mice, 12 to 14 days pregnant, was maintained in organ culture in chemically defined medium 199 with added hormones. Aldosterone (1 µg/ml) plus insulin (5 µg/ml) was added to both control and experimental cultures. In addition, ovine mammotropin (1, 2, or 4 µg/ml), bovine somatotropin (2 or 6 µg/ml), and ovine mammotropin plus bovine somatotropin (1 + 1 and 4 + 4 µg/ml) were added to the experimental cultures. By light microscopy 1 cultures receiving either one or both adenohypophysial hormones showed distension of alveoli with secretion and the appearance of fat droplets in the apexes of the cells. By electron microscopy, cultures receiving the pituitary hormones showed increased membranous ergastoplasm, enlarged Golgi apparatus, enhanced formation of protein droplets, and accumulation of protein and fat droplets in cell apex and alveolar lumen. Virus-like particles, although common in both the control and experimental cultures, were most numerous in those cultures receiving one or both adenohypophysial hormones. The extra cellular (B) particles sometimes formed large, crystalline-appearing aggregates, unlike anything previously reported in normal C3H mammary gland.