Purity >95% as determined by SDS-PAGE. Prolactin (PRL) is a hormone that is produced and secreted by the pituitary gland. PRL acts in an endocrine, paracrine, and autocrine manner. The prolactin receptor (PRLR) is expressed on many cell types, including cells of the reproductive organs, central nervous system, and breast cancer. PRL signal transduction occurs via JAK kinase signaling pathways. The primary function of PRL is to regulate lactation, but PRL also plays functional roles in the immune system and during cell growth, apoptosis, and differentiation.