Aspects of neural and hormonal control of water and sodium balance.

This article reviews some aspects of neural and hormonal control of water and sodium balance. The maintenance of extracellular fluid volume and osmolarity depends on the coordinated action of multiple mechanisms of water and sodium intake and excretion. Different technics for manipulation of the central nervous system, i.e., withdrawing of nervous structures, electrolytic lesion, electrical stimulation and chemical stimulation, have allowed the identification of some brain areas, neural circuits and neurotransmitters that participate in the mechanisms of control of water and sodium intake and excretion. The signals for thirst and actions of angiotension II, cholinergic agents and atrial natriuretic factor upon drinking are discussed. Three possible types of effector mechanism for centrally induced natriuresis are discussed: 1) renal innervation; 2) secretion of a substance by the brain which causes natriuresis through direct or indirect action (antidiuretic hormone and active sodium transport inhibition); 3) CNS control of the secretion of a hormonal substance produced at another site (mineralocorticoid and atrial natriuretic factor). These mechanisms are not mutually exclusive.