Volume expansion potentiates cardiac sympathetic afferent reflex in dogs

Our previous study (27) showed that the cardiac sympathetic afferent reflex (CSAR) was enhanced in dogs with congestive heart failure. The aim of this study was to test whether blood volume expansion, which is one characteris tic of congestive heart failure, potentiates the CSAR in normal dogs. Ten d ogs were studied with sino-aortic denervation and bilateral cervical vagoto my. Arterial pressure, left ventricular pressure, left ventricular epicardi al diameter, heart rate, and renal sympathetic nerve activity were measured . Coronary blood flow was also measured and, depending on the experimental procedure, controlled. Blood volume expansion was carried out by infusion o f isosmotic dextran into a femoral vein at 40 ml/kg at a rate of 50 ml/min. CSAR was elicited by application of bradykinin (5 and 50 mug) and capsaici n (10 and 100 mug) to the epicardial surface of the left ventricle. Volume expansion increased arterial pressure, left ventricular pressure, left vent ricular diameter, and coronary blood flow. Volume expansion without control led coronary blood flow only enhanced the RSNA response to the high dose (5 0 mg) of epicardial bradykinin (17.3 +/- 1.9 vs. 10.6 +/- 4.8%, P< 0.05). H owever, volume expansion significantly enhanced the RSNA responses to all d oses of bradykinin and capsaicin when coronary blood flow was held at the p revolume expansion level. The RSNA responses to bradykinin (16.9 +/- 4.1 vs . 5.0 +/- 1.3% for 5 mg, P< 0.05, and 28.9 +/- 3.7 vs. 10.6 +/- 4.8% for 50 mg, P< 0.05) and capsaicin (29.8 +/- 6.0 vs. 9.3 +/- 3.1% for 10 mg, P< 0. 05, and 34.2 +/- 2.7 vs. 15.1 +/- 2.7% for 100 mug, P< 0.05) were significa ntly augmented. These results indicate that acute volume expansion potentia ted the CSAR. These data suggest that enhancement of the CSAR in congestive heart failure may be mediated by the concomitant cardiac dilation, which a ccompanies this disease state.