Role of epinephrine in the development of hypertension in Dahl salt-sensitive rats

Abstract

The present experiments were designed to test the hypothesis that adrenal epinephrine contributes to the development of hypertension in the Dahl salt-sensitive (DS) rat. All studies were carried out in conscious male DS and Dabi salt-resistant (DR) rats weighing 200-240 g. An indwelling femoral arterial catheter was placed for blood sampling and measurement of blood pressure. After 5 days of either a high salt (7% NaCl) or a normal salt (1% NaCl) dietary regimen, DS and DR rats were subjected to an acute stress paradigm (graded electrical footshock). There were no differences in basal plasma catecholamine concentrations or in the acute pressor responses to graded footshock between the four substrain/diet groups. However, in both DS and DR rats, plasma epinephrine responses to acute footshock were greater on a 7% than on a 1% NaCl diet. Additional groups of DS rats were treated with an inhibitor of adrenal phenylethanolamine N-methyltransferase, SK&F 29,661 (1-2 g/kg body wt/day) or with vehicle. Three days after placement of an arterial catheter, rats were placed on a 7% NaCl diet, and blood pressure was measured daily for an additional 3 weeks. Although SK&F 29,661 treatment was effective in reducing adrenal epinephrine content and apparent release by approximately 80%, treatment did not alter the time course of salt-induced changes in blood pressure. We conclude that: 1) acute presser responses to mild stress do not differ between DS and DR rats and are not enhanced by high dietary NaCl intake, 2) 5 days of high salt diet induces an apparent increase in adrenomedullary responsiveness to mild stress that is independent of DS or DR substrain, and 3) epinephrine of adrenal origin is not essential for the development of salt-sensitive hypertension in the DS rat.