Dietary fish protein lowers blood pressure and alters tissue polyunsaturated fatty acid composition in spontaneously hypertensive rats

Objectives To investigate the effect of two types of dietary protein on blood pressure, liver fatty acid desaturation and composition, and urine 6-keto-prostaglandin-F (PGF1α) level, the metabolite of prostacyclin. Methods 5-wk-old spontaneously hypertensive rats were fed 20% casein or purified fish protein. The fat source was 5% ISIO oil, which contains 47.9% (ω-6) and 1.7% (ω-3) total polyunsaturated fatty acids. After 2 mo on the diet, systolic blood pressure was reduced with fish protein compared with casein (189.8 ± 10.5 versus 220.7 ± 8.7). Results Excretion of 6-keto-PGF1α in urine was negatively correlated with blood pressure. Liver cholesterol and phospholipid concentrations were 1.71- and 1.27-fold lower with fish protein than with casein, respectively. The fish protein diet lowered the 20:4(ω-6) proportion and the ratio of 20:4(ω-6) to 18:2(ω-6) in liver microsomal lipids and phospholipids, which was due to the reduced microsomal Δ6(ω-6) desaturation activity. Dietary protein source did not affect ω-3 fatty acid composition, and this was associated with a similar activation of Δ6(ω-3) desaturation in liver microsomes. Conclusions The present data indicated a significant blood pressure–lowering effect caused by fish protein, rather than by casein, that modified the fatty acid composition of liver phospholipids and liver microsomal total lipids.