Hemodynamic effects of high dietary intakes of sodium or chloride in the Dahl salt-sensitive rat.

Abstract

In the Dahl salt-sensitive (Dahl-S) rat, a high sodium without chloride diet (NaAA) and a chloride without sodium diet ("X"Cl) do not increase arterial pressure to the same extent as a high NaCl diet. To explain these differences, hemodynamic responses to acute volume expansion were compared in conscious Dahl-S and Dahl salt-resistant (Dahl-R) rats fed either 7% NaCl, NaAA, or "X"Cl diets for 5 weeks. Before acute volume expansion, on each of the three diets, mean arterial pressures and total peripheral resistances were higher (p less than 0.01) in Dahl-S than in Dahl-R rats, and in Dahl-S, arterial pressure was higher (p less than 0.05 or less) on the 7% NaCl intake than on the other two diets. No group differences were found in cardiac index (thermodilution). Right atrial pressure was also elevated (p less than 0.01) in Dahl-S rats on the 7% NaCl diet. In response to acute volume expansion, arterial pressure did not change, and the decrement of total peripheral resistance was greater in Dahl-S rats than in Dahl-R rats on each of the three diets (p less than 0.05 or less). Assuming that reductions of peripheral resistance in response to acute volume expansion reflect withdrawal of sympathetic tone, these results suggest that sympathetic tone is increased comparably on each of the diets in Dahl-S rats. As suggested by the increased right atrial pressure, higher arterial pressure induced by 7% NaCl may be related to an expanded intravascular volume in conjunction with increased neural activity.