HORMONAL INDUCTION OF ALPHA-LACTALBUMIN AND BETA-LACTOGLOBULIN IN CULTURED MAMMARY EXPLANTS FROM PREGNANT PIGS

Mammary tissue from pigs on days 60, 80, 90, 100 and 100 + (days 106-1 11.) of pregnancy has been cultured in vitro as explants. The total ac cumulation in tissue and culture medium of the whey proteins alpha-lac talbumin and beta-lactoglobulin has been measured using specific radio immunoassays. The control, uncultured tissue showed progressive morpho logical development from sparse, non-secretory epithelial tissue on da y 60 to full lobulo-alveolar development with some accumulated secreti on from day 100. In uncultured explants beta-lactoglobulin could be de tected consistently from day 90 (13 +/- 12 ng/mu g DNA, n = 4) and alp ha-lactalbumin from day 100 (1.3 +/- 0 5 ng/mu g DNB, n = 11). At all stages of pregnancy, both whey proteins increased markedly during the period of culture (up to 7 d). Stimulation of alpha-lactalbumin appear ed to be primarily under prolactin control. Prolactin increased alpha- lactalbumin accumulation to a similar extent alone, or in the presence of insulin and/or corticosterone. The response to prolactin was dose- dependent over the range 0.4-20 nM (10-500 ng/ml). Porcine prolactin w as more potent than ovine prolactin. There was no effect of porcine gr owth hormone and no synergism detected between prolactin and tri-iodot hyronine. By contrast, no specific hormonal requirements were establis hed for accumulation of beta-lactoglobulin, which appeared to increase in vitro if tissue remained viable in various combinations of insulin , corticosterone and prolactin. It was not stimulated by growth hormon e. There was some indication of a prolactin-sensitive component in lon ger term cultures after day 4.