Blood Pressure and Sodium Excretion in the Sinoaortic Denervated Rat During Chronic High and Low Sodium Intake and Acute Sodium Loading

Abstract

The effects of dietary Na on the magnitude of hypertension were studied in sinoaortic denervated (SAD) rats. Groups of SAD rats and sham-operated (SO) controls drank tap water and received chows with different amounts of Na: low (0.08%), regular (0.4%), high (3%) or very high (7%) Na; other groups, some after unilateral nephrectomy, received regular chow and 1% saline to drink. These various Na regimens were started before operations and were continued for at least 12 wk after SAD and SO. Weekly systolic tail-cuff pressures of SAD rats were significantly higher throughout the 12 wk postoperative period than those of SO rats regardless of Na regimen (P < 0.05 to < 0.01). Analysis of variance indicated no significant differences between pressures of SAD rats on regular or low Na chows and those receiving any of the high Na regimens. When SAD rats were switched from regular to high Na diets no significant change was induced in systolic pressures. Renal Na excretion was examined in response to oral Na loading or to i.v. saline infusion in groups of SAD and SO rats. Both types of studies revealed that SAD rats excreted the extra Na significantly faster than SO rats. Hypertension induced by SAD is not dependent on the amount of Na in the diet. The magnitude of hypertension is not increased by chronic high Na intake. The rapid excretion of Na suggests that SAD rats have an enhanced sensitivity to activation and/or to effects of neural and/or humoral factors affecting renal Na excretion.