Effects of Chronic Excess Salt Ingestion

Abstract

A strain of rats that will predictably develop experimental hypertension by means of different techniques was used to study NaCl-induced hypertension. Observations were continued for 1 year after weaning unless death intervened. Among groups of rats on 0.4, 1, 2, 4, and 8% NaCl chow, respectively, blood pressures generally rose as dietary NaCl increased. Average blood pressures ranged from 146.8 mm Hg in the group on the lowest, to 210.2 mm Hg in the group with the highest NaCl intakes. Morbidity and mortality also increased. Even transient high NaCl diets were capable of inducing permanent hypertension; 4 of 34 rats on 8% NaCl chow for only 2 weeks after weaning had pressures of 180 to 206 mm Hg, although most rats did not become significantly more hypertensive than those on the low (0.4%) NaCl diet. When this same diet was continued for a total of 6 weeks in a group of 29 animals, the blood pressure averaged 198.6 mm Hg. The age at which the high NaCl intake began also influenced the course of the hypertension. Weanling rats rapidly developed fulminating hypertension on the high NaCl diet. After 3 months on this regimen, the average pressure of 40 rats exceeded 200 mm Hg, and 35 animals were dead or terminally ill. In rats that were older when high NaCl diets were started, hypertension developed more slowly and was less fulminant. Among 38 rats in which NaCl was not begun until 3 or 6 months past weaning, blood pressures averaged 175 to 180 mm Hg after 3 months on NaCl; 31 appeared in good health but none survived 8 months.