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 5 d. Oral administration of tea-leaf saponin to elder SHR (15 weeks old) for 5 d 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 50mg/kg, p.o. showed a long-lasting hypotensive effect and this effect was as potent as that of enalapril maleate at the dose of 3 mg/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).
