COMBINED EFFECTS OF DIETARY FISH OIL AND SODIUM RESTRICTION ON BLOOD-PRESSURE IN ENALAPRIL-TREATED HYPERTENSIVE RATS

Sodium restriction and fish oil supplementation are effective dietary measures for preventing or treating mild hypertension. However, their usefulness as an adjunct to drug treatment of hypertension requires further evaluation. In the present study, we examined the influence of dietary sodium and fish oil on the antihypertensive effect of the angiotensin converting enzyme (ACE) inhibitor enalapril in stroke-prone spontaneously hypertensive rats (SHRSP). Rats were fed experimental diets containing fish oil or olive oil (5% w/w) and low (0.04% w/w) or normal (0.23% w/w) sodium from 1 to 4 months of age. Tail-cuff blood pressure (BP) rose by 8.4 and 4.3 mm Hg/week, respectively, in untreated and enalapril-treated (2.5 mg/kg/day, orally) rats fed the olive oil/normal sodium diet. Feeding fish oil further reduced the rise in enalapril-treated rats to 2.8 mm Hg/week. When sodium intake was also restricted, the BP rise was almost prevented (1.1 mm Hg/week). In older rats with established hypertension, the low sodium/fish oil diet also potentiated the blood pressure reduction by enalapril (tail-cuff BP fell by 61 mm Hg compared to 25 mm Hg with enalapril alone). These observations were confirmed by direct BP recording in conscious rats following the implantation of aortic catheters. Factorial analysis revealed a highly significant antihypertensive effect of fish oil in both young and adult SHRSP receiving enalapril, and a further interactive effect of dietary sodium restriction with fish oil feeding in young rats. The antihypertensive effects of the dietary interventions were associated with further reductions of cardiac hypertrophy. The possibility that dietary fish oil supplementation may improve the antihypertensive efficacy of ACE inhibitors, especially when sodium intake is restricted, warrants evaluation in humans.