Prolactin (gene name PRL) is a secreted neuroendocrine pituitary hormone that acts primarily on the mammary gland to promote lactation, but has pleiotropic effects in both males and females. Its primary function is to promote and maintain lactation during pregnancy and suckling. In addition, prolactin plays an immunoregulatory role by stimulating the activities of ornithine decarboxylase and protein kinase C, which are important for the proliferation, differentiation, and function of lymphocytes. Rat prolactin shares 77% ~ 90% a.a. sequence identity with human and murine prolactin. Recombinant rat prolactin is a 22.6kDa globular protein containing 197 amino acid residues.