Hemodynamic responses to acute volume expansion in Dahl salt-sensitive rats

The purpose of this study is to evaluate hemodynamic responses to acute volume expansion in chronically instrumented, conscious Dahl salt-sensitive (Dahl-S) and Dahl salt-resistant (Dahl-R) rats that have been maintained on either 0.45% NaCl, 1% NaCl, or 7% NaCl (5 days) intakes. Total peripheral resistance (TPR), but not arterial pressure, was increased by 5 days of 7% NaCl in Dahl-S (P less than 0.05) but not in Dahl-R. In Dahl-S, but not in Dahl-R, right atrial pressure increased with increasing dietary NaCl (P less than 0.05). On the 0.45% NaCl intake, atrial pressure did not differ in the two strains, whereas on both the 1 and 7% NaCl diets atrial pressure was higher in Dahl-S than in Dahl-R (P less than 0.05). In response to acute extracellular fluid volume expansion, arterial pressure did not change, and cardiac output increased in Dahl-S and in Dahl-R. On the 0.45% NaCl intake, TPR decreased (P less than 0.01) similarly in response to volume expansion in both strains; however, on the 1% NaCl intake TPR decreased in Dahl-R (P less than 0.05) but not in Dahl-S. In contrast, in animals fed 7% NaCl for 5 days, TPR decreased acutely in Dahl-S (P less than 0.01) but not in Dahl-R. These observations suggest that cardiopulmonary baroreflex activity is impaired in Dahl-S on a 1% NaCl intake, possibly as a consequence of elevated right atrial pressure. This alteration of the cardiopulmonary baroreflex may contribute to increased TPR in Dahl-S on a high-NaCl intake.