Antihypertensive effect of aqueous polyphenol extracts of Amaranthusviridis and Telfairiaoccidentalis leaves in spontaneously hypertensive rats

Abstract

The antihypertensive effects of aqueous polyphenol-rich extracts of Amaranthusviridis (AV) and Telfairiaoccidentalis (TO) leaves in spontaneously hypertensive rats (SHR) were investigated. The dried vegetable leaves were extracted using 1:20 (leaves:water, w/v) ratio for 4 h at 60 °C. Results showed significantly (P < 0.05) higher polyphenol contents in TO extracts (80–88 mg gallic acid equivalents, GAE/100 mg) when compared with the AV (62–67 mg GAE/100 mg). Caffeic acid, rutin and myricetin were the main polyphenols found in the extracts. The TO extracts had significantly (P < 0.05) higher in vitro inhibition of angiotensin I-converting enzyme (ACE) activity while AV extracts had better renin inhibition. Oral administration (100 mg/kg body weight) to SHR led to significant (P < 0.05) reductions in systolic blood pressure for the AV (−39 mmHg after 8 h)and TO (−24 mmHg after 4 and 8 h).The vegetable extracts also produced significant (P < 0.05) reductions in diastolic blood pressure, mean arterial blood pressure and heart rate when compared to the untreated rats. Thus both the AV and TO leaf extracts have the potential to be used as antihypertensive agents, especially the AV, which produced persistent long-lasting effect over a 24 h period.