Effects of intraductal prolactin on some aspects of the ultrastructure and biochemistry of mammary tissue in the pseudopregnant rabbit.

Abstract

SUMMARY A study of the ultrastructure of the secretory epithelial cells of the mammary gland was carried out in virgin oestrous rabbits, pseudopregnant rabbits and pseudopregnant rabbits injected with prolactin to induce lactogenesis. Ultrastructural modifications of the mammary epithelial cells, from inactivity to active secretion after an intraductal injection of prolactin, are described. The changes produced after prolactin injection were characterized by a progressive increase in endoplasmic reticulum and in ribosomes in the cytoplasm. This was evident after 12–24 h. By the 2nd or 3rd day after hormone administration the cells had differentiated into active secretory epithelium. These cells were characterized by large numbers of ribosomes in the cytoplasm; an extensive development of rough endoplasmic reticulum; development of cisternae from the enlarging rough endoplasmic reticulum; hypertrophy of the Golgi apparatus and smooth endoplasmic reticulum; and the presence of protein granules in the vacuoles which were particularly abundant in the cytoplasm near the duct lumen. The presence of lipid droplets in the cells was less indicative of an active secretory state since they were also observed in mammary tissue from pseudopregnant rabbits. Biochemical investigation of the response of pseudopregnant mammary tissue to intraductal prolactin showed no significant rapid effects on either casein-like protein or lactose biosynthesis, but increases in both substances were observed on the 3rd day after hormone administration.