Normal mammary cells in long term culture. I. development of hormone-dependent functional monolayer cultures and assay of alpha-lactalbumin production.

Mammary cells from normal tissue of virginal, pregnant, and lactating rats have been adapted to long term monolayer culture in plastic culture dishes with retention of hormone-responsive functional activity. The addition of PRL, insulin, and corticosterone resulted in an increase in the proportion of epithelial cells. the development of intracellular lipid droplets, and the ordered aggregations of these cells. In the presence of these hormones, the milk protein, alpha-lactalbumin (a-LA), was secreted into the growth medium at rates of 20-100 ng/mg cellular protein . 24 h. A double antibody RIA for a-LA capable of measuring 0.1 ng a-LA/100 microliter growth medium was developed in our laboratory for these studies. Both intracellular and extracellular a-LA fell below detectability within 2-3 weeks after hormone withdrawal. Intracellular a-LA accounted for less than 3% of the total a-LA accumulated in each culture in 24 h. the production rate of cells continuously given hormones increased 4- to 7-fold over a period of several months in culture, and their output was greater than 100-fold above that of cells not given hormones. These cells were obtained by overnight digestion and dispersion of tissue using selected batches of collagenase in the presence of 5% fetal calf serum. Plating densities of at least 3 X 10(4) cells/cm2 in Minimum Essential Medium supplemented with 14% fetal calf serum were required for optimal functional activity. Despite several months without added hormones, these cultures can retain their hormone responsiveness, since subsequent hormone addition resulted in detectable a-LA production beginning within 7-14 days. Our studies demonstrate for the first time that normal mammary cells can be maintained in a functional hormone-responsive state for extended periods in primary cell culture. These long term cell cultures provide a system with which the effects of these and other hormones on milk production and cell differentiation can be assessed under conditions which minimize the influence of the prior in vivo hormonal millieu. (Endocrinology 108: 573, 1981)