Preoptic-hypothalamic periventricular lesions reduce natriuresis to volume expansion.

The present experiment was designed to determine if electrolytic ablation of the periventricular tissue surrounding the anteroventral third ventricle (AV3V) altered the natriuresis typically seen during isotonic volume expansion. Control and AV3V-lesioned rats received intravenous infusions of 0.9% NaCl at 0.5 ml/min until 10% body weight was given. Arterial blood pressure was monitored, and urine was collected throughout the experiment. Following expansion, blood was processed for analysis of natriuretic hormonelike activity by chromatographic separation of plasma extracts followed by measuring antinatriferic activity across the isolated toad bladder. Urinary sodium excretion and urine volume during expansion were significantly less in rats with lesions surrounding the AV3V region than in control rats. Toad bladder bioassay showed a high level of natriuretic hormonelike activity in control animals following volume expansion, but no natriuretic hormonelike activity in plasma from volume-expanded rats with AV3V lesions. These data demonstrate that AV3V periventricular ablation attenuates the natriuresis induced by isotonic-volume expansion. In addition, preliminary results indicate the AV3V region may be a central site critical for natriuretic hormonelike activity and control of extracellular fluid volume.