Neuroendocrine Regulation of Hydromineral Homeostasis

Since the crucial evolutionary change from an aqueous to a terrestrial environment, all living organisms address the primordial task of equilibrating the ingestion/production of water and electrolytes (primarily sodium) with their excretion. In mammals, the final route for the excretion of these elements is mainly through the kidneys, which can eliminate concentrated or diluted urine according to the requirements. Despite their primary role in homeostasis, the kidneys are not able to recover water and solutes lost through other systems. Therefore, the selective stimulation or inhibition of motivational and locomotor behavior becomes essential to initiate the search and acquisition of water and/or sodium from the environment. Indeed, imbalances affecting the osmolality and volume of body fluids are dramatic challenges to the maintenance of hydromineral homeostasis. In addition to behavioral changes, which are integrated in the central nervous system, most of the systemic responses recruited to restore hydroelectrolytic balance are accomplished by coordinated actions of the cardiovascular, autonomic and endocrine systems, which determine the appropriate renal responses. The activation of sequential and redundant mechanisms (involving local and systemic factors) produces accurate and self-limited effector responses. From a physiological point of view, understanding the mechanisms underlying water and sodium balance is intriguing and of great interest for the biomedical sciences. Therefore, the present review will address the biophysical, evolutionary and historical perspectives concerning the integrative neuroendocrine control of hydromineral balance, focusing on the major neural and endocrine systems implicated in the control of water and sodium balance.