Cytological effects of hormones and plasma on bovine mammary tissue in vitro.

Abstract

Mammary explants from two heifers pretreated with oestradiol and progesterone were cultured for 96 h with various combinations of hormones and calf plasma to identify the complement causing mammary tissue development in vitro in the cow. Initial tissue histology, determined by quantitative morphological analysis, was maintained by incubation with insulin, cortisol, oestrogen and progesterone; enlarged lumina were observed after treatment with insulin and cortisol. Lactogenesis was induced in vitro by insulin, cortisol and prolactin, enhanced by adding oestrogen and progesterone at the doses used here and further stimulated by the addition of plasma. The most highly developed mammary alveoli were characterized by an increased luminal area with lipid and stainable secretion, epithelia with large lipid droplets in the apical cytoplasm and a limited stromal area. In a second experiment, samples of plasma were collected from two cows, successfully induced to lactate, on days 6, 15, 17, 19 and 21 after treatment with oestradiol and progesterone. Mammary gland explants from five heifers pretreated with oestradiol and progesterone in vivo were cultured with insulin and cortisol plus these plasma samples (30%, v/v) to test for changes in lactogenic activity. All plasma samples were found equally beneficial in promoting tissue differentiation. These experiments show that low concentrations of ovarian steroids synergize with prolactin at the level of the mammary epitherlium and suggest that other plasma components aid the development of bovine mammary epithelium in vitro.