Abstract P236: Alginic Acid May Not Play a Major Role in the Mechanism of Alleviating Hypertension by Dietary Saccharina Japonica in 2-kidney, 1-clip Renovascular Hypertensive Rats

Abstract

Objective: Saccharina japonica (SJ), one of brown algae, is cultivated or grows wild in East Asia. The extract ‘dashi’ is used for soup stock in Japan. The intake of SJ was reported to decrease blood pressure (BP) in 2-kidney, 1-clip renovascular hypertensive (2K1C) rats in our previous study, as well as in spontaneously hypertensive rats (SHR) in other studies. Some investigators suggested that a major mechanism of reducing BP by dietary SJ in SHR includes alginic acid (AA). However, in our preliminary study it was not confirmed in 2K1C model, because we observed that dashi containing AA as much as 5% of what the original SJ contained alleviated the hypertension, too. To detect how AA in SJ contributes to the mechanism, we observed BP in 2K1C rats fed a diet containing SJ or extracts from SJ. Methods: Male Sprague-Dawley rats (6 wks) were treated with sham operation (SHAM) or clipping the left renal artery (2K1C). After surgery, the rats started receiving a control diet (C) or a diet containing 5% (w/w) SJ (S), dashi extracted from the same amount of SJ in a correct method (D), extract from SJ equal in amount by boiling for a long time, in which AA was much eluted (B) or the SJ leftover after dashi was extracted (L) for 6 weeks. The systolic BP (SBP) was measured by a tail-cuff method every week. At the end, mean arterial BP (MAP) was measured in each rat under anesthesia. After euthanasia, the aortas were collected for extracting mRNA and protein. Endothelial nitric oxide synthase (eNOS) mRNA expression (eNOS-M) was evaluated in aortas by reverse transcriptase-polymerase chain reaction. eNOS and phosphorylated eNOS protein expression (eNOS-Ps), was determined in aortas by western blot analysis. Results: Six weeks after the surgery, SBP was significantly higher in 2K1C-C than in SHAM-C (182 ± 6 vs 126 ± 5 mmHg, P < 0.001). In 2K1C-S, -D, -B and -L (145 ± 4, 148 ± 4, 133 ± 3 and 146 ± 4 mmHg), SBP was significantly lower than that in 2K1C-C (P < 0.001, each). At the end of the protocol, MAP showed similar results to SBP. No significant differences were found in eNOS-M between each groups. eNOS-Ps were enhanced in 2K1C compared to SHAM (P < 0.05), but showed no significant differences by diet. Conclusion: The role of AA and eNOS may be limited in the mechanism of alleviating hypertension by dietary SJ in 2K1C.