Blood pressure reduction by fish oil in adult rats with established hypertension--dependence on sodium intake.

The effects of fish oil combined with dietary sodium restriction on blood pressure and mesenteric vascular resistance were examined in a series of experiments with adult normotensive (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP). Rats were fed normal or low sodium diets containing fish oil, olive oil or safflower oil. Small but significant reductions of blood pressure (measured directly in conscious rats) were seen in SHRSP but not in WKY after 8 weeks on a fish oil/low sodium diet, compared with rats fed olive or safflower oil diets with normal sodium content. This antihypertensive effect was not dependent on neurally mediated vasoconstriction but was associated with a reduction of basal resistance in the blood-perfused mesenteric artery. Subcutaneous injection of fish oil reduced blood pressure in adult SHRSP on a normal sodium diet. However, there was a further fall in blood pressure when sodium intake was reduced. The results indicate the antihypertensive effect of fish oil can be enhanced by restricting sodium intake.