Activity of ibopamine on some isolated organs

The pharmacological activity of ibopamine (SB-7505), the 3,4-diisobutyryl ester of N-methyldopamine, was compared with that of epinine (N-methyldopamine) and dopamine on some isolated organs. The results of this study show that ibopamine and epinine exerts a positive inotropic effect on cat papillary muscle by stimulating the cardiac beta 1- and alpha-adrenoceptors; a positive chronotropic effect on cat right atrium by stimulating the cardiac beta 1-adrenoceptors; a relaxing effect on guinea-pig trachea by stimulating beta 2-adrenoceptors; a relaxing effect on rabbit splenic artery pretreated with phenoxybenzamine and contracted with PGF2 alpha by stimulating the DA1 receptors; an inhibitory effect on the vasoconstriction of rabbit ear artery induced by electrical stimuli by stimulating the DA2 receptors. Esterase activation, either by organ or plasma enzymes, appeared to be a prerequisite of ibopamine activity. Suppression of this activity by esterase inhibitors confirmed that the pharmacological responses are related to the formation of epinine. The magnitude and rate of response of some isolated organs to ibopamine appeared to be related to the esterase content of the tissue.