Effect of prolactin on in vitro expression of the bovine mammary immunoglobulin G(1) receptor

Explants of mammary tissue from cows in late pregnancy were incubated for 72 h in serum-free, hormonally defined media to investigate the regulation of the bovine mammary IgG(1) receptor. Treatments included incubation in basal medium alone, basal medium plus estradiol-17 beta, basal medium plus prolactin, or basal medium plus estradiol-17 beta and prolactin. alpha-lactalbumin production was measured by radioimmunoassay in culture supernatants collected at 24, 48, and 72 h. Explants were examined immunohistochemically for expression of the IgG(1) receptor at 24, 48, and 72 h. alpha-lactalbumin concentrations increased, and IgG(1) receptor expression decreased, by 72 h wither-plants cultured in the medium containing prolactin. Results suggest that, in addition-to its positive lactogenic effect, prolactin decreases expression of the bovine mammary IgG(1) receptor.