Effects of 2-[(5-chloro-2-methoxyphenyl) azo]-1H-imidazole (M6434) on alpha adrenergic receptors.

The effects of a newly synthesized compound, 2-[(5-chloro-2-methoxyphenyl)azo]-1H-imidazole (M6434) on alpha-adrenergic receptors were investigated by using the atria of normal and hypothyroid rats, rat vasa deferentia and canine arteries. M6434 showed a positive inotropic effect on rat left atria, which was suppressed by phentolamine but not by propranolol and reserpine. M6434 also showed a positive chronotropic effect on rat right atria. These positive inotropic and chronotropic effects of M6434 were enhanced in propylthiouracil-induced hypothyroid rats. M6434 caused contraction of rat vas deferens and increased its spontaneous movement. These effects on vas deferens were suppressed by phentolamine. M6434 induced contraction of canine arteries. The pD2 values for vasoconstrictive effects of M6434 on the aorta, pulmonary artery, renal artery and femoral artery were about equal to those of phenylephrine, and the intrinsic activity of M6434 was somewhat lower than that of phenylephrine. These results suggest that M6434 is an adrenergic alpha-agonist which is about as potent as phenylephrine and that M6434 has neither a beta-stimulating activity nor a catecholamine-releasing one.