Antihypertensive effect of an aqueous extract of the calyx of Hibiscus sabdariffa.

The present study was designed to investigate the efficacy of an aqueous calyx extract of Hibiscus sabdariffa (HS) in two forms of experimental hypertension: salt-induced and L-NAME (N(omega)-L-arginine methyl ester)-induced and in normotensive controls. The blood pressure and heart rate fell dose-dependently in both the hypertensive and normotensive rats after intravenous injection of 1-125 mg/kg of HS, suggesting that HS possesses anti-hypertensive, hypotensive and negative chronotropic effects. The fall in mean arterial pressure was significantly pronounced in the hypertensive rats (salt-induced: 94.4+/-8.6 mm Hg; L-NAME-induced: 136.5+/-10.3 mm Hg) than in the normotensive controls (50.2+/-5.1 mm Hg; P<0.05).