Evidence that nitric oxide mediates the blood pressure lowering effect of a polyphenol-rich cocoa powder in spontaneously hypertensive rats

Abstract

The involvement of endothelial-relaxing factors on the antihypertensive effect of a polyphenol-rich cocoa powder named CocoanOX (CCX) was studied. Thirty 17-20-week-old male spontaneously hypertensive rats (SHR), weighing 314 ± 3 g were used. They were divided into two groups of 15 animals, that were respectively administered by gastric intubation distilled water or 300 mg/kg CCX dissolved in distilled water, between 9 am and 10 am. 2 h after the oral administration, 5 of the animals in each group were intraperitoneally administered 1 ml saline. The remaining rats in both groups were divided into another two groups of 5 animals that were respectively administered 30 mg/kg Nw-nitro-l-arginine methyl ester (l-NAME) dissolved in 1 ml of saline or 5 mg/kg indomethacin also dissolved in 1 ml of saline by the same procedure. Systolic blood pressure (SBP) was recorded in the rats by the tail cuff method before the initial oral administration and also 4 h after this administration. CCX caused a significant decrease in SBP (-49.5 ± 4.9 mm Hg; p < 0.05). l-NAME caused a clear increase in SBP in the rats (+16.2 ± 4.3 mm Hg; p < 0.05), and the effect of CCX was not observed in the SHR that were treated with l-NAME (+4.1 ± 1.7 mm Hg; p < 0.05). Nevertheless, indomethacin treatment did not modify SBP in the SHR and this compound failed to modify the antihypertensive effect of CCX in these animals. In conclusion, this study proves the participation of NO in the antihypertensive effect of CCX in the SHR strain. When CCX is administered, the synthesis, or the bioavailability, of this endothelial factor could increase, but other mechanisms may also participate in the antihypertensive effect of this cocoa powder. In any case, further investigation should be carried out to characterize the signalling pathways involved in the antihypertensive effect of CCX. © 2011 Elsevier Ltd.