MULTIFACTORIAL CONTROL OF WATER AND SALINE INTAKE - ROLE OF ALPHA(2)-ADRENOCEPTORS

Water and saline intake is controlled by several mechanisms activated during dehydration. Some mechanisms, such as the production of angiote nsin II and unloading of cardiovascular receptors, activate both behav iors, while others, such as the increase in blood osmolality or sodium concentration, activate water, but inhibit saline intake. Aldosterone probably activates only saline intake. Clonidine, an alpha(2)-adrener gic agonist, inhibits water and saline intake induced by these mechani sms. One model to describe the interactions between these multiple mec hanisms is a wire-block diagram, where the brain circuit that controls each intake is represented by a summing point of its respective inhib iting and activating factors. The alpha(2)-adrenoceptors constitute an inhibitory factor common to both summing points.