Reduced sympathetic responsiveness resulting from a high dietary sodium intake in the rat

The effects of a high sodium diet on sympathetic nervous function were evaluated in normotensive male Wistar rats maintained on a standard (141 mEq/kg) or high (1400 mEq/kg) sodium chow for 4 weeks. No differences were observed in the blood pressures of conscious catheterized rats on the two diets; however, heart rates were significantly lower in rats on the high sodium intake. Hypotensive responses produced in these animals by one minute intravenous infusions of sodium nitroprusside were greater in rats on the high sodium diet, whereas, reflex tachycardia was similar. In pithed rats on either diet, basal blood pressures and heart rates were similar. In contrast, blood pressure responses to electrical stimulation of the spinal sympathetic outflow were significantly attenuated in the high sodium rats but the tachycardic responses were unaltered. In addition, norepinephrine induced blood pressure and heart rate increases were not different between the diets. Similarly, the sensitivity of isolated atria to isoproterenol was not affected by dietary sodium, nor were the responses of isolated aortic strips to phenylephrine altered. The results of this investigation indicate that a chronic high sodium intake may result in an attenuation of vascular sympathetic function.