The potentiating effect of an alpha-adrenergic blocking agent (E-643) on the action of bronchodilators.

The effect of 2-[N-(n-butyloyl)homopiperazin-N'-yl]-4-amino-6,7-dimethoxy quinazoline hydrochloride (E-643), a new alpha-adrenergic receptor blocking agent, on the relaxing responses and on the change of cyclic AMP and cyclic GMP contents in guinea pig tracheal (GPT) tissues induced by various bronchodilators was examined. The relaxing responses and the cyclic AMP and cyclic GMP contents in GPT induced by isoprenaline, adrenaline, prostaglandin E2 and chlorprenaline were markedly enhanced with continuous infusion of E-643. These results may suggest that E-643 can be used together with various bronchodilators for the treatment of chronic obstructive pulmonary diseases.