Regulation of the immunoglobulin G1 receptor:: effect of prolactin on in vivo expression of the bovine mammary immunoglobulin G1 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 increase 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) concentrations were measured throughout the experiment. Biopsies of mammary tissue were collected after induction of lactation, and after treatments to alter serum PRL. Immunohistochemistry was used to evaluate IgG(1) receptor expression. Administration of recombinant bovine (rbPRL) was associated with increased lactogenic activity, decreased secretion IgG(1) concentrations, and decreased IgG(1) receptor expression. Decreased serum PRL, due to bromocriptine, was associated with decreased lactogenic activity and maintenance of IgG(1) receptor expression. Results of this experiment are consistent with an effect of PRL in decreasing the expression of the bovine mammary IgG(1) receptor at the onset of lactogenesis.