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 relaxa nt effects of pyranocoumarin compounds, including (+)-praeruptorin A (Pra-C ), Pd-Ia (=(+/-)-praeruptorin A), pteryxin, peucedanocoumarin II (P-II) and 8-methoxypsoralen (X-MOP) purified from Bai-Hua Qian-Hu (BQ) in isolated r abbit tracheas and pulmonary arteries. Pra-C, pteryxin and Pd-Ia produced s ignificant relaxant effects in tracheal preparations constricted with 40 mM KCI or 10 mu M acetylcholine, The relaxant response to Pra-C, pteryxin or Pd-Ia in preparations constricted with KCl was significantly more potent th an that in preparations constricted with acetylcholine. Pra-C, pteryxin or Pd-Ia at a concentration of 30 mu M 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 significa nt relaxant effect on contractions by 10 mu M phenylephrine, without any ef fect on the contraction by 40 mM KCl. These results suggest that Pd-Ia, pte ryxin and Pra-C for their calcium antagonistic action, and S-MOP for its in hibitory effect on contraction induced by phenylephrine, may be the active principles of BQ for relaxing the smooth muscle of tracheas and pulmonary a rteries, and the principle may produce a synergistic effect.