Effect of dietary polyunsaturated fatty acids on contraction and relaxation of rat femoral resistance arteries.

We investigated the effects of dietary polyunsaturated fatty acids (PUFA) derived from fish oil (n-3 PUFA) and plant seed oil (n-6 PUFA), in amounts relevant to human consumption, on the alpha 1-adrenoceptor-mediated contractile responses of isolated rat resistance arteries. Rats were fed semisynthetic diets, deriving 40% of total calories from fat. The control diet, which had sufficient linoleic acid to prevent essential fatty acid deficiency, had a polyunsaturated/saturated fatty acid (P/S) ratio of 0.3. The n-3 PUFA were given as a daily oral supplement of fish oil. For the n-6 PUFA diet, the proportion of linoleic acid in the diet was increased to obtain P/S ratio of 2.0. Diets were administered for 8 weeks. At the end of the feeding period, second-order branches of the femoral artery (< 300-micros diameter) were mounted in pairs in an isometric myograph, and responses to norepinephrine (NE) 3 nM-10 microM with addition of yohimbine 1 microM and timolol 1 microM were examined. Subsequently, the vessels were preconstricted with NE to 60% of their maximal response and relaxation to acetylcholine 1 nM-0.1 mM was observed. Dietary n-3 PUFA supplements led to attenuation of the contractile responses of isolated resistance arteries (p < 0.01, repeated-measures analysis of variance, ANOVA-RM) versus control. The n-6 PUFA diet did not exert this effect although there was a downward trend. Diet did not affect EC50 values for NE. Neither n-3 nor n-6 PUFA diet influenced relaxation responses. The fatty acid composition of myocardial phospholipid fractions was significantly altered by both diets.(ABSTRACT TRUNCATED AT 250 WORDS)