Blood pressure-lowering effect of fish oil is independent of thromboxane A(2) level in spontaneously hypertensive rats

Whether the alterations in the synthesis of thromboxane A(2) (TXA(2)) is the direct mechanism underlying the blood pressure-lowering effect of fish oil was investigated in this study. Six groups of 11 male spontaneously hypertensive rats were fed semipurified diets containing corn or fish oils and graded levels (50, 5000 or 15 000 ppm) of dietary vitamin E for 8 weeks. Plasma TXA(2), assayed by RIA, was significantly greater in the corn oil group than in the fish oil group (P < 0.05). Compared to 50 ppm dietary vitamin E, 5000 and 15 000 ppm dietary vitamin E, respectively, significantly decreased plasma TXA(2) (P < 0.05). Systolic, mean or diastolic blood pressure, evaluated by the tail cuff method, were significantly higher in the corn oil group than in the fish oil group (P < 0.05). However, vitamin E had no effect on blood pressure. No relationship between TXA(2) and blood pressure was found. Experimental results indicated that the alterations in the synthesis of TXA(2) were not the direct antihypertensive effect of fish oil.