Low Sodium Diet Augments Plasma and Tissue Catecholamine Levels in Pithed Rats

Plasma and tissue (cardiac, vascular, renal, and adrenal) catecholamine concentrations were measured in pithed male Wistar rats maintained on low (10 mEq/kg diet), basal (115 mEq/kg diet), or high (1200 mEq/kg diet) sodium test diets for five weeks. Significant differences in catecholamine disposition were observed only in response to sodium restriction; responses to basal and high sodium intakes were consistently similar. Baseline plasma catecholamine levels (p less than 0.01) as well as those in response to stimulation of the entire sympathetic outflow at 4 Hz were markedly enhanced in low sodium rats (p less than 0.001). The facilitation of stimulation-induced increments in plasma norepinephrine levels in low sodium rats may be related to the finding that norepinephrine content was also elevated in noradrenergically innervated tissues (atria, ventricles, mesenteric artery, and kidneys) (p less than 0.01). Adrenal catecholamine levels, however, were not affected by dietary sodium restriction. Despite the peripheral catecholamine changes associated with a low sodium intake, pressor and tachycardic responses to sympathetic nerve stimulation were similar across dietary sodium groups. The results indicate that a low sodium intake enhances plasma and tissue catecholamine levels, adaptations that may be important in the maintenance of sympathetic responsiveness.