The neurohypophysis

Vasopressin (VP) and oxytocin (OT), the neurohypophysial hormones of mammals, are generally seen as being involved only in water balance and in parturition and lactation, respectively. In this review, new aspects of their physiology and pathophysiology are explored. Although VP is generally thought of as the antidiuretic hormone (ADH), it also is a highly potent vasoactive peptide. The physiology of VP, both as ADH and as a pressor peptide, is reviewed, and recent evidence suggesting that VP has a role in the maintenance of blood pressure and possibly in the pathogenesis of hypertension is presented. Clinical aspects of diabetes insipidus and of the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) are reviewed. The importance of identifying cases of SIADH secondary to other pathologies and in which the control of VP secretion is normal is stressed. To distinguish these cases of pseudo-SIADH from those in which the VP secretion control mechanisms respond abnormally, the term SAADH, or syndrome of appropriate secretion of vasopressin, is proposed. The role of OT in lactation and parturition is reviewed. Recent evidence suggesting that the fetus may, at least in part, be responsible for the initiation of labor is presented.