Further evidence of the toxicity of NaCl. Increased blood pressure and mortality in the spontaneously hypertensive rat.

The spontaneously hypertensive rat (SHR) of Okamoto and Aoki (4) develops significant hypertension without added dietary salt. Many patients with hypertension have little or no alteration in blood pressure from increments or decrements of salt intake. Such observations have led to a widespread belief that dietary NaCl is important in hypertensives only if blood pressure changes are observed after changes in NaCl intake. Such a simplistic view of hypertension fails to take into account the possibility that morbidity and mortality might be lowered by restricting dietary NaCl, without a concomitant lowering of blood pressure. The effect of a high NaCl intake for periods up to 1 yr has been studied in the SHR with the following conclusions: (a) NaCl accelerated the rate at which hypertension developed in both sexes. (b) The ultimate levels of blood pressure reached by males on either high or low salt diets were similar, however. (c) In females, (1) on high NaCl the average blood pressure ultimately became indistinguishable from males whereas (2) on low NaCl pressure remained significantly lower than that of males. (d) The addition of NaCl to the regimen had a devastating effect on mortality of both sexes and was not directly correlated with the level of blood pressure. Earlier reports were reviewed bearing on the possibility that NaCl is inimical to blood vessels without a necessary relationship to its hypertensinogenic effect. It was concluded that restriction of dietary NaCl would reduce morbidity and mortality in hypertension, whether or not blood pressure was reduced by such measures.