Catechol system—isoproterenol

The brief duration of bronchodllation is a result of facile metabolic Inactivation. Upon reaching systemic circulation isoproterenol is rapidly accumulated into extraneuronal cells, perhaps by an uptake-2 process (13), where, except in the gut, it is inactivated in a reaction catalyzed by catechol 0-methyltransferase (COMT) which methylates the meta-OH group (14). Isoproterenol s lack of activity following oral administration is a consequence of its metabolic conversion into readily excreted meta- or para-ethereal sulfates by sulfoklnases in the Intestine (15). 

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