Preoptic recess lesions reduce right atrial pressure responses to volume expansion

Ablation of the periventricular tissue surrounding the anteroventral portion of the third cerebral ventricle (AV3V-X) abolishes natriuresis and diuresis during volume expansion. Although deficits in several efferent mechanisms have been identified, effects of AV3V-X on afferent input 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 significantly smaller in AV3V-X rats than CONT animals during acute isotonic saline infusion and during whole-blood expansion. Treatment with hexamethonium abolished the difference in RAP during acute volume infusion. However, there was no significant difference in RAP between groups during continuous isotonic saline expansion. These data suggest that AV3V-X reduces afferent input from cardiopulmonary stretch receptors during acute volume expansion, which may contribute to diminished natriuresis and diuresis observed in these animals.