Chapter 169 - Renal Effects of Neurohypophyseal Peptides

Abstract

The neurohypophyseal hormones vasopressin (VP) and oxytocin (OT) are nonapeptides consisting of a 6-amino-acid ring with a cysteine to cysteine bridge, and a 3-amino-acid tail. Some form of these nonapeptides has existed throughout the evolutionary species from amphibia and reptiles to birds and mammals, and in all species their most prominent physiological function is participation in the maintenance of water homeostasis. Because the most important homeostatic function of VP is the maintenance of normal body water stores, the renal effects of VP that serve to accomplish this function can best be appreciated and understood within the context of the overall mechanisms that regulate body fluid homeostasis. The maintenance of normal water balance in humans is achieved principally through an integration of thirst, VP secretion, and renal responsiveness to VP. Despite large variations in water intake, the osmolality of body fluids in healthy individuals is maintained within a relatively narrow range. To maintain plasma osmolality at such a constant level, VP secretion must vary in response to relatively small changes in plasma osmolality, which is achieved through the activation of the osmoreceptors located in the anterior hypothalamus. Although nonosmotic secretion of VP is not involved with normal body fluid homeostasis, such secretion is of importance because the renal effects of VP are the same regardless of the stimulus that caused the secretion of the hormone, leading to potential disturbances in water homeostasis from inappropriate degrees of antidiuresis.