Different Hypotentive Effects of Various Active Constituents Isolated from Uncaria rhynchophylla The Negative Chronotropic Effect of Isorhynchophylline and Its Mechanism Determination of rhynchophylline and isorhynchophylline in Uncaria rhynchophylla by HPLC Effects of Isorhynchophylline on Physiological Characteristics of Isolated Guinea Pig Atrium