Central effect of agents which alter sodium transport on water drinking in the rat

The central effect of ouabain (OUA), ethacrynic acid (EA) and diphenylhydantoin (DPH) on water drinking was studied in rats. OUA and EA inhibit cellular Na efflux, increasing intracellular (IC) Na content, while DPH inhibits cellular Na influx lowering IC sodium content. The animals were injected into the third ventricle (3V), fourth ventricle (4V), lateral ventricle (LV), or lateral hypothalamus (LH). Ouabain (50 pg) and EA (50 ng) when injected into the 3V or LV significantly decreased the water intake induced by 24 hr water deprivation. No effect was observed after injections in other loci, thus supporting the hypothesis that sensors could be located in the circumventricular organs, in an area without the blood brain barrier. DPH (270 ng) injected into the 3V or LV significantly enhanced water intake in rats deprived of water for 14 hr, but it did not increase water intake in water-repleted rats. DPH also enhanced water intake induced by cellular-dehydration (2 M NaCl IP). These results suggest that changes in the Na content of sensor cells located on or near the walls of the 3V could be responsible for the movement of water between the cells and their medium, in agreement with the osmoreceptor hypothesis for thirst.