Longitudinal changes during the development of hypertension in rats fed excess chloride and sodium

The effects of supplemental NaCl, KCl, and Na acetate on the blood pressure of weanling rats fed semipurified diets and diets based on naturally high salt products, like cottage cheese, were examined in two studies. Within 2 weeks of initiation of dietary treatments, rats fed supplemental chloride had elevated blood pressure and lowered plasma renin activity, which persisted throughout the 8-week study. The effect of supplemental sodium on blood pressure was not significant until after 6 weeks of dietary treatment. The initial increase in blood pressure preceded the slowed growth observed in rats fed excess chloride or sodium. Urinary volume and urinary excretion of calcium, magnesium, phosphorus, sodium, and chloride were increased when supplemental chloride or sodium was fed, but tissue electrolyte and plasma atrial natriuretic peptide concentrations remained constant. Two changes preceded the rise in blood pressure: rats fed supplemental chloride had enlarged kidneys, and those fed supplemental sodium had elevated hematocrits, suggesting a transient shift among fluid compartments, after only 6 days of treatment. These data suggest that the hypertension induced by ingestion of supplemental (14.6 mg CI/g of diet) chloride is mediated by changes in renal function. Ingestion of excess sodium depressed bone magnesium concentrations in Study 1 and after 24 days in Study 2; the impact of this "relative" magnesium depletion on blood pressure deserves further study.