Objective: Saccharina japonica (SJ) is one of brown algae and is cultivated or grows wild in Japan and neighbor countries. SJ is rich in alginate, the intake of which was reported to decrease blood pressure (BP) in spontaneously hypertensive rats. It is also rich in fucoidan, which was reported to improve the renal blood flow in rats with acute renal failure. We recently observed that intake of SJ decreased BP in 2-kidney, 1-clip renovascular hypertensive (2K1C) rats, probably through nitric oxide, and did not change BP in normotensive rats. In Japan, there are many traditional processed foods made of SJ with vinegar, which is originally used for softening SJ and raising its preserving property. Vinegar is also suggested to suppress angiotensin-converting enzyme activity. In this study, we investigated the interactive effects of SJ and vinegar on BP in 2K1C rats.
Methods: Male Sprague-Dawley rats (6 wks) were treated with sham operation (SHAM) or clipping the left renal artery (2K1C). After surgery, SHAM or 2K1C rats started receiving a control diet (CTL) or a diet containing 5.0% (w/w) freeze-dried SJ powder (SJ) for 6 weeks, and a tap water (Veh) or a water containing 5.0% (v/v) of 4.3% acidity rice vinegar (VG). The systolic BP (SBP) was measured by a tail-cuff method every week. At the end of the protocol, mean arterial BP (MAP) was measured in each rat under anesthesia. Then, thoracic aorta was removed and the section of aorta was stained with hematoxylin and eosin.
Results: Analysis of variance revealed significant effects in time, animal model (SHAM vs 2K1C), diet (CTL vs SJ) and model x diet (P < 0.001, each), but not in water (Veh vs VG) or model x water. At the end of the protocol, in CTL-Veh, 2K1C was higher in SBP than SHAM (179 ± 33 vs 130 ± 20 mmHg, P < 0.001). In 2K1C-Veh, the SJ diet decreased SBP (156 ± 6 mmHg) compared with CTL (P < 0.05). Vinegar did not significantly change SBP (184 ± 19 mmHg) in 2K1C-CTL, but decreased SBP (142 ± 11 mmHg) in 2K1C-SJ (P < 0.05) as low as in SHAM-SJ-VG (139 ± 3 mmHg, P = NS). The observations in MAP were similar to in the SBP. Moreover, compared to SHAM, 2K1C-CTL-Veh showed the aortic media thickening, which was reduced in 2K1C-SJ-Veh/VG.
Conclusion: A certain daily intake of vinegar did not lower BP by itself, but enhanced the BP reduction by a SJ diet, in 2K1C rats.