Posterior Pituitary Hormones

The pituitary gland is composed of two functionally unique lobes known as the anterior and posterior pituitary. The primary purpose of the posterior lobe of the pituitary, also known as the neurohypophysis, is to act as a conduit whereby hormones made within the hypothalamus can be secreted directly into the peripheral circulation. The major hormones of the posterior pituitary are oxytocin (OT) and vasopressin (AVP). These two related neuropeptides are made by neurons in the paraventricular and supraoptic nucleus of the hypothalamus. They are structurally similar and are transcribed in opposite directions off the same chromosomal region where their genes are arranged in a tail-to-tail fashion. OT and AVP are phylogenetically ancient hormones and are conserved through evolution. Moreover, they operate by binding a distinct family of G protein-coupled receptors. Activation of the OT receptor induces changes in intracellular calcium to cause myometrial contraction necessary for parturition, whereas activation of AVP receptors (V1aR, V1bR, and V2R) is responsible for the effects of AVP on the regulation of blood pressure and water balance, both of which are essential for homeostasis. OT and AVP receptors are also found in brain, where OT and AVP regulate a number of behaviors as well as autonomic responses.