Selective modulation of vascular smooth muscle function and endothelium-dependent relaxation by dietary omega-3 polyunsaturates

In order to investigate the effect of dietary unsaturates on vascular responsiveness, weanling rats were fed purified diets in which the lipid was replaced with corn oil (CO) or menhaden oil (MO). After 2 months of feeding the ratio of ω-3/ω-6 fatty acids in plasma lipids, aortic smooth muscle and cardiac phospholipids was significantly elevated (p<0.01) in MO vs CO fed rats. The responsiveness of aortic rings to norepinephrine (NE), angiotensin II (All), arginine vasopressin (AVP), 80 mM potassium chloride (KCl), acetylcholine (ACH), the calcium ionophore A23187 and sodium nitroprusside (SNP) was determined. There were no differences in the vasoconstrictor responses of intact rings to NE, All, AVP or KCl for MO vs CO fed rats. However, the All constrictor response tended to be reduced for intact rings from MO fed rats. The vasoconstrictor responses of endothefium-denuded rings to NE, All and KCl were not statistically different, however, the constrictor response to AVP was significantly (p<0.01) reduced in rubbed rings from CO fed rats. ACH mediated relaxation was significantly enhanced in aortic rings from MO fed rats (55 ± 4% vs 30 ± 6%, MO vs CO, respectively, p<0.01). However, the maximum relaxation response to A23187 was not different (56 ± 7% vs 53 ± 7%, MO vs CO, respectively). Similarly, the maximal relaxation response to SNP was not altered by the diets (100% vs 99.7%, MO vs CO). The results indicate that 2 months of feeding diets rich in w-3 fatty acids does not alter NE, AVP or KCl-induced vasoconstriction of intact aortic rings but selectively alters the constrictor response of endothelium-denuded rings to AVP. Dietary w-3 fatty acids selectively enhanced the endothelium dependent relaxation to ACH but not to A23187.