PREOPTIC RECESS LESIONS REDUCE RIGHT ATRIAL PRESSURE RESPONSES TO VOLUME EXPANSION

Ablation of the periventricular tissue surrounding the anteroventral p ortion of the third cerebral ventricle (AV3V-X) abolishes natriuresis and diuresis during volume expansion. Although deficits in several eff erent mechanisms have been identified, effects of AV3V-X on afferent i nput to the volume reflex have not been investigated. Therefore, these experiments measured right atrial pressure (RAP) in conscious AV3V-X and control-operated (CONT) rats before, during, and following acute ( 60 s) or continuous (60 min) infusion of isotonic saline, or vascular volume expansion with whole blood (15 min). Changes in RAP were signif icantly smaller in AV3V-X rats than CONT animals during acute isotonic saline infusion and during whole-blood expansion. Treatment with hexa methonium abolished the difference in RAP during acute volume infusion . However, then was no significant difference in RAP between groups du ring continuous isotonic saline expansion. These data suggest that AV3 V-X reduces afferent input from cardiopulmonary stretch receptors duri ng acute volume expansion, which may contribute to diminished natriure sis and diuresis observed in these animals.