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

Objective: 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 (PGF(1alpha)) 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% (omega-6) and 1.7% (omega-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-PGF(1alpha) 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(omega-6) proportion and the ratio of 20:4(omega-6) to 18:2(omega-6) in liver microsomal lipids and phospholipids, which was due to the reduced microsomal Delta6(omega-6) desaturation activity. Dietary protein source did not affect omega-3 fatty acid composition, and this was associated with a similar activation of Delta6(omega-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.