Effect of Dietary Polyunsaturated Fatty Acids on Contraction and Relaxation of Rat Femoral Resistance Arteries

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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 α1-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-μ.m diameter) were mounted in pairs in an isometric myograph, and responses to norepinephrine (NE) 3 n M-10 μM with addition of yohimbine 1 μ.M and timolol 1 μ.M were examined. Subsequently, the vessels were preconstricted with NE to 60% of their max- imal 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, ANOVARM) 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. Supplementation of a diet relevant to that consumed by humans with a small dose of n-3 PUFA attenuated α1-adrenoceptor-mediated contractile responses in rat femoral resistance artery without affecting acetylcholine (ACh)-induced relaxation. The findings may help explain the BP-lowering effects of fish oil

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