Chapter 1: A role for centrally-released vasopressin in brain ion and volume regulation: a hypothesis

Abstract

Vasopressin is synthesized and released within the central nervous system (CNS). It may then act locally on adjacent target cells or on more distant intracerebral sites following distribution through brain extracellular fluid (ECF) and/or cerebrospinal fluid (CSF). Systemically released vasopressin increases body water and electrolyte content. Vasopressin functions in an analogous way in the CNS, to increase brain water and electrolyte content. This chapter presents results of two series of experiments consistent with this hypothesis; one uses an in vivo rat model developed in this laboratory; the other employs cultured glial cells. Brain tissue and plasma are normally in osmotic equilibrium, and brain volume depends on the number of osmotically active solutes in the nervous tissue. In vivo model allows evaluating mechanisms of brain volume regulation in terms of a four-compartment model of fluid and electrolyte exchange among blood plasma, brain ECF, brain intracellular fluid (ICF) and CSF. The model includes two features unique to the regulation of volume in the CNS. These are: (1) secretion of ECF from plasma, based on the activity of Na + - pumps located at the blood–brain barrier; and (2) bulk flow of ECF between brain and CSF.