Abstract: AIM: To investigate the effects of BWYJ (naftopidil's ramification) on the vascular activities in rabbits and to explore its vasodilative mechanisms. METHODS: The isotonic contractions of the thoracic aorta strips in rabbits were recorded, and the effects of BWYJ on the concentration-response curves of noradrenaline (NA), high potassium and 5-hydroxytryptamine (5-HT) was observed.The procedure of Ca²⁺ free-Ca²⁺ addition was designed to indirectly observe the effects of BWYJ on intracellular free Ca²⁺ ([Ca²⁺]_i).RESULTS: BWYJ shifted the concentration-response curves of NA and 5-HT to right in parallel, the maximum responses were unchanged, and the pA2 values were 7.61 and 6.56, respectively.But it did not affect the concentration-response curve of high potassium.In Ca²⁺-free medium, BWYJ 10^-7, 3×10^-7, 10^-6 and 10^-5mol·L^-1concentration-dependently inhibited the transient contraction induced by NA and the long-lasting contraction induced by addition of Ca²⁺.But BWYJ 10^-5mol·L^-1did not inhibit the contraction induced by caffeine.CONCLUSION: BWYJ may be an α-adrenergic receptor blocker and a 5-HT receptor blocker simultaneously.The vasodilative mechanism of BWYJ may be related to its inhibiting effects on the Ca²⁺-influx and Ca²⁺-release mediated by α-adrenergic and 5-HT receptors.

Key words: naftopidil, thoracic aorta strips of rabbit, noradrenaline, KCl, 5-HT