Effect of tea-leaf saponin on blood pressure of spontaneously hypertensive rats

Abstract

The antihypertensive effect of tea-leaf saponin (the saponin mixture isolated from leaves of Camellia sinensis var. sinensis) was examined in spontaneously hypertensive rats (SHR). Tea-leaf saponin reduced a time- dependent increase in blood pressure dose-dependently when it was administered orally to young SHR (7 weeks old) for 5d. Oral administration of tea-leaf saponin to elder SHR (15 weeks old) for 5d decreased the mean blood pressure by 29.2 mmHg at the dose of 100 mg/kg compared to the control group. Single administration of tea-leaf saponin at 50 mg/kg, p.o. showed a long- lasting hypotensive effect and this effect was as potent as that of enalapril maleate at the dose of 3mg/kg, p.o. Tea-leaf saponin inhibited angiotensin I- induced contraction of the isolated guinea pig ileum in a dose dependent manner but little depressed angiotensin II-induced contraction. On the other hand, in in vitro experiment using a synthetic peptide as a substrate, tea- leaf saponin showed almost no inhibitory activity against the angiotensin I converting enzyme (ACE) (IC50 > 10 mg/ml).