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Acute hypertensive and natriuretic responses following preoptic hypothalamic lesions.

The tissue surrounding the anteroventral portion of the third ventricle (the AV3V region) is critical for control of sodium balance and cardiovascular regulation. Ablation of this brain area results in an acute natriuresis and an increase in blood pressure. The purposes of these experiments were to determine the mechanism of the natriuretic response and assess whether the natriuresis contributes to the decreased blood volume following AV3V ablation. Rats were instrumented with metal lesioning electrodes in the AV3V region and with catheters in the femoral artery and jugular vein. Following electrolytic lesioning or control procedures, blood pressure, heart rate, urine flow rate and urinary sodium excretion were monitored. In separate groups of animals, plasma and blood volume were measured by calculating dilution of 125I-labelled serum albumin and hematocrit. Results from these studies showed that ablation of the AV3V region resulted in a significant elevation in blood pressure (18 +/- 3 mm Hg), increase in sodium excretion (212 +/- 36 mu Eq/hour), and decrease in plasma volume (10.3 +/- 0.4 mL) compared with control-treated animals (2 +/- 4 mm Hg; 89 +/- 34 mu Eq/h, 12.0 +/- 0.5 mL). This natriuretic response was accompanied by an increased plasma aldosterone concentration. Further, prevention of the hypertensive response abolished the natriuresis. These data suggest that AV3V ablation produces an acute pressure-mediated natriuresis, resulting in decreases in plasma and blood volume.