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Relaxant effects of pyranocoumarin compounds isolated from a Chinese medical plant, Bai-Hua Qian-Hu, on isolated rabbit tracheas and pulmonary arteries.

Qian-Hu is a well-known traditional Chinese medicine used for the treatment of respiratory diseases and pulmonary hypertension. We compared the relaxant effects of pyranocoumarin compounds, including (+)-praeruptorin A (Pra-C), Pd-Ia (=(+/-)-praeruptorin A), pteryxin, peucedanocoumarin II (P-II) and 8-methoxy-psoralen (8-MOP) purified from Bai-Hua Qian-Hu (BQ) in isolated rabbit tracheas and pulmonary arteries. Pra-C, pteryxin and Pd-Ia produced significant relaxant effects in tracheal preparations constricted with 40 mM KCl or 10 microM acetylcholine. The relaxant response to Pra-C, pteryxin or Pd-Ia in preparations constricted with KCl was significantly more potent than that in preparations constricted with acetylcholine. Pra-C, pteryxin or Pd-Ia at a concentration of 30 microM completely relaxed tracheas constricted with 40 mM KCl, whereas P-II at the same concentration showed only partial relaxation. In pulmonary arterial preparations, 8-MOP produced a significant relaxant effect on contractions by 10 microM phenylephrine, without any effect on the contraction by 40 mM KCl. These results suggest that Pd-Ia, pteryxin and Pra-C for their calcium antagonistic action, and 8-MOP for its inhibitory effect on contraction induced by phenylephrine, may be the active principles of BQ for relaxing the smooth muscle of tracheas and pulmonary arteries, and the principle may produce a synergistic effect.