Plasma corticosterone and volume after preoptic recess lesions and volume depletion

The effects of extracellular fluid volume depletion on plasma corticosterone concentration (Pcort) and plasma volume in rats were determined after recovery from either electrolytic ablation of the periventricular tissue surrounding the anteroventral third ventricle (AV3V region) or control surgery. Rats received either furosemide injections and sodium-free chow or isotonic saline injections and continued access to sodium-replete food. One week after these injections some animals were decapitated and trunk blood collected for analysis of Pcort by radioimmunoassay. The remainder of the rats were implanted with femoral arterial catheters to obtain blood samples for measurement of plasma and blood volumes by calculating dilution of 125I-labeled serum albumin. Volume-replete rats with AV3V lesions had significantly higher Pcort concentrations and smaller plasma and blood volumes than volume-replete control-operated animals. Furthermore, volume depletion induced by furosemide caused a significant increase in Pcort concentration only in rats with AV3V ablations, whereas plasma and blood volumes were significantly lowered in both groups. These data demonstrate that AV3V periventricular ablation results in a chronic elevation of Pcort in the volume-replete animals and an exaggerated glucocorticoid response to volume depletion. These data show that decreased PV characteristic of animals with AV3V lesions is not due to glucocorticoid insufficiency.