Hypothalamic–pituitary–prolactin axis Hypothalamic–pituitary–prolactin axis The hypothalamic–pituitary–prolactin axis (HPP axis), also known as the hypothalamic–pituitary–mammary axis or hypothalamic–pituitary–breast axis, is a hypothalamic–pituitary axis which includes the secretion of prolactin (PRL; luteotropin) from the lactotrophs of the pituitary gland into the circulation and the subsequent action of prolactin on tissues such as, particularly, the mammary glands or breasts. It is involved in lobuloalveolar maturation of the mammary glands during pregnancy and the induction and maintenance of lactation following parturition. Hormones that control the secretion of prolactin from the pituitary gland include dopamine ("prolactin-inhibiting factor", or "PIF"), estradiol, progesterone, thyrotropin-releasing hormone (TRH), and vasoactive intestinal
Pituitary adenylate cyclase-activating peptide Pituitary adenylate cyclase-activating peptide Pituitary adenylate cyclase-activating polypeptide also known as PACAP is a protein that in humans is encoded by the "ADCYAP1" gene. PACAP is similar to vasoactive intestinal peptide. One of its effects is to stimulate enterochromaffin-like cells. It binds to vasoactive intestinal peptide receptor and to the PACAP receptor. This gene encodes adenylate cyclase-activating polypeptide 1. Mediated by adenylate cyclase-activating polypeptide 1 receptors, this polypeptide stimulates adenylate cyclase and subsequently increases the cAMP level in target cells. Adenylate cyclase-activating polypeptide 1 not only is a hypophysiotropic hormone (i.e. a substance that induces activity in the hypophysis) but