Effect of omega-3 polyunsaturated fatty acids in modulation of vascular tone under physiological and pathological conditions

Omega-3 polyunsaturated fatty acids (n-3 PUFAs), including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are mainly found in marine fish oils and commercially available fish oil supplements. Several studies have documented that n-3 PUFAs can reduce the risk of cardiovascular diseases through anti-inflammatory, anti-thrombotic, and anti-atherosclerotic properties. Notably, regulation of vascular tone is one of the most important bases of cardiovascular health and especially for maintaining blood pressure within optimal physiological ranges. Recent clinical and animal studies indicate an association between n-3 PUFAs and vascular functions. In this regard, many clinical trials and basic experimental studies have been conducted so far to investigate the influence of n-3 PUFAs on vascular tone. In this review, we have summarized the results obtained from both clinical and basic studies that evaluated the effect of n-3 PUFAs under physiological and pathological conditions. Moreover, we also focus on verifying the underlying basic molecular mechanism of n-3 PUFAs on the vascular system.

Effects of docosahexaenoic acid on vascular pathology and reactivity in hypertension

Previous studies have shown that docosahexaenoic acid (DHA) has an antihypertensive effect in spontaneously hypertensive rats (SHR). To investigate possible mechanisms for this effect, vascular pathology and reactivity were determined in SHR treated with dietary DHA. SHR (7 weeks) were fed a purified diet with either a combination of corn/soybean oils or a DHA-enriched oil for 6 weeks. Histological evaluation of heart tissue, aorta, coronary, and renal arteries was performed. Vascular responses were determined in isolated aortic rings. Contractile responses to agonists, including norepinephrine (10(-9) to 10(-4) M), potassium chloride (5-55 mM), and angiotensin II (5 x 10(-7) M) were assessed. Vasorelaxant responses to acetylcholine (10(-9) to 10 (-4) M), sodium nitroprusside (10(-9) to 10(-6) M), papaverine (10(-5) to 10(-4) M), and methoxyverapamil (D600, 1-100 microM) were determined. DHA-fed SHR had significantly reduced blood pressure (P < 0.001) and vascular wall thicknesses in the coronary, thoracic, and abdominal aorta compared with controls (P < 0.05) Contractile responses to agonists mediated by receptor stimulation and potassium depolarization were not altered in DHA-fed SHR. Endothelial-dependent relaxations to acetylcholine were not altered which suggests endothelial-derived nitric oxide production/release is not affected by dietary DHA. Other mechanisms of vascular relaxation, including intracellular cyclic nucleotides, cGMP, and cAMP were not altered by dietary DHA because aortic relaxant responses to sodium nitroprusside and papaverine were similar in control and DHA-fed SHR. No significant differences were seen in relaxant responses to the calcium channel blocker, D600, or contractile responses to norepinephrine in the absence of extracellular calcium. These results suggest that dietary DHA does not affect mechanisms related to extracellular calcium channels or intracellular calcium mobilization. Moreover, the contractile and vasorelaxant responses are not differentially altered with dietary DHA in this in vivo SHR model. The findings demonstrate that dietary DHA reduces systolic blood pressure and vascular wall thickness in SHR. This may contribute to decrease arterial stiffness and pulse pressure, in addition to the antihypertensive properties of DHA. The antihypertensive properties of DHA are not related to alterations in vascular responses.