Anteroventral third ventricle (AV3V) has been implicated in body fluid balance and blood pressure control. This study thus was to evaluate the renal response to saline loading in rats with and without AV3V lesion. Lesioned rats were prepared by electrolytic ablation 4 weeks prior to experiments. Arterial pressure (AP) and renal excretory responses were measured before and after intravenous infusion of 154 mM NaCl (0.388 ml/min) for 1 hour in anesthetized control and lesioned rats. There were no significant differences in AP (125 +/- 3 vs 121 +/- 3 mmHg) and glomerular filtration rate (GFR; 1.5 +/- 0.1 vs 1.6 +/- 0.3 ml/min/g kw) between control rats and lesioned rats. Saline loading did not significantly change AP and GFR in both groups of rats. In control rats there was a striking natriuretic (delta 2660%) and diuretic (delta 1870%) response to saline loading but the lesioned rats only exhibited 50% of the normal excretory response. A similarly attenuated natriuresis and diuresis was also found in conscious, lesioned rats with oral saline loading. These data suggest that AV3V exerts substantial influence on the regulation of sodium and water balance.