Prolactin (also known as mammotrophin, luterotropic hormone, and lutetropin) is a neuroendocrine hormone secreted by the pituitary gland. Its primary function is to promote and maintain lactation during pregnancy and suckling. In addition, Prolactin plays an immune-regulatory 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 is a 22.5 kDa globular protein containing 198 amino acid residues.