Hormones, Posterior Pituitary Hormones

Abstract

Oxytocin and vasopressin are cyclic peptide hormones primarily synthesized in the human hypothalamus and stored in the posterior pituitary. These nonapeptide amides, along with at least 14 other variants found in lower vertebrates and invertebrates, contain cysteine residues at positions 1 and 6, forming a disulfide bridged ring, along with a tripeptide C‐terminal extension. The hormones are stored in neurosecretory granules with their respective carrier proteins, the neurophysins, prior to release into the bloodstream. Oxytocin promotes milk ejection and uterine contraction; human arginine vasopressin promotes water retention and exerts a pressor effect. Both hormones or their analogues are used clinically and both are being intensively studied for additional physiological effects. These include nurturing behavior in women and penile erection in men for oxytocin, and memory consolidation for arginine vasopressin and analogues. Receptors, including some receptor subtypes, have been cloned for both hormones. Oxytocin and V 1 receptors function through the GP/1 phospholipase C complex, whereas V 2 receptors activate adenosine monophosphatase (AMP). Selective peptide and nonpeptide, ie, peptidomimetic, analogues are being developed that should offer improved therapeutic utility.