Effect of polypeptide hormones on stimulation of casein secretion by mouse mammary epithelial cells grown on floating collagen gels.

The in vitro effects of protein hormones on the stimulation of casein secretion by mouse mammary epithelial cells were studied. Mouse mammary glands were enzymatically dissociated and used immediately or were stored frozen and thawed just before use. Cells were cultured on floating collagen gels in the presence of insulin, cortisol and a pituitary or placental polypeptide hormone. Casein, released into the medium, was assayed by a radioimmunoassay against one of the components of mouse casein. Mammary cells released casein into the medium in the presence of as little as 10 ng of ovine prolactin per ml of medium. Human growth hormone stimulated the casein secretion to the same extent as prolactin. Human placental lactogen, ovine and bovine growth hormones were less stimulatory. Luteinizing hormone, follicle-stimulating hormone and thyroid-stimulating hormone had no effect on the stimulation of casein secretion.