Methylflavonolamine hydrochloride inhibits contractions induced by noradrenaline, calcium and potassium in rabbit isolated aortic strips

1 The effects of methylflavonolamine hydrochloride (4′‐methyl‐7‐(2‐hydroxy‐3‐isopropylaminopropoxy)‐flavone hydrochloride, MFA) were investigated and compared with verapamil and papaverine on rabbit isolated aortic strips, which were contracted by noradrenaline, calcium and potassium. 2 Pre‐incubation for 25 min with either MFA (0.03 to 0.2 m m ) or papaverine (0.03 to 0.2 m m ) induced non‐parallel and concentration‐dependent rightward displacements of the curves to noradrenaline (0.00001 to 0.1 m m ) with the maximal response depressed. The calculated pD′ 2 values (mean ± s.d.) were 3.89 ± 0.15 for MFA and 3.93 ± 0.05 for papaverine, respectively. Verapamil (0.03 to 0.2 m m ) inhibited the contraction induced by noradrenaline in a competitive manner with a pA 2 value of 5.91 ± 0.83. 3 In depolarized aortic strips of the rabbit, prior exposure to MFA (0.03 to 0.3 m m ) and papaverine (0.03 to 0.2 m m ) shifted the cumulative curves to Ca 2+ (0.003 to 100 m m ) parallel to the right with the maximal responses depressed, pD′ 2 values being 3.88 ± 0.05 and 3.89 ± 0.13, respectively. Verapamil produced comparable inhibition of the contraction at much lower concentrations (30 to 300 n m ). 4 MFA (0.03 and 0.1 m m ) inhibited the contraction elicited by graded depolarization at a constant Ca 2+ concentration with a pD′ 2 value of 4.09 ± 0.07. 5 The present results show that MFA has some actions consistent with a calcium antagonist. It resembles papaverine more closely than verapamil.