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

Summary 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