Regulation of the immunoglobulin G(1) receptor: effect of prolactin on in vivo expression of the bovine mammary immunoglobulin G(1) receptor

Induction of colostrogenesis in non-pregnant cows was used to evaluate the relationship between prolactin (PRL) and mammary immunoglobulin G(1) (IgG(1 )) receptor expression. Six of eleven non-pregnant, non-lactating Holstein cattle responded to a standard lactation induction protocol by development of elevated IgG(1) concentrations in mammary secretions. In order to increa se the diversity in PRL concentrations, two of the six cattle were treated with bromocriptine, and two others were treated with recombinant bovine PRL . Serum alpha-lactalbumin, serum PRL and mammary secretion IgG(1) concentra tions were measured throughout the experiment. Biopsies of mammary tissue w ere collected after induction of lactation, and after treatments to alter s erum PRL. Immunohistochemistry was used to evaluate IgG(1) receptor express ion. Administration of recombinant bovine (rbPRL) was associated with incre ased lactogenic activity, decreased secretion IgG(1) concentrations, and de creased IgG(1) receptor expression. Decreased serum PRL, due to bromocripti ne, was associated with decreased lactogenic activity and maintenance of Ig G(1) receptor expression. Results of this experiment are consistent with an effect of PRL in decreasing the expression of the bovine mammary IgG(1) re ceptor at the onset of lactogenesis.