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The actions on the bronchial smooth muscle and cardiovascular system S-1540 (Bitolterol) (Shionogi Pharmaceuticals), a new bronchodilator which is chemically related to isoprenaline, and S-1541 which is the active metabolite of S-1540 were studied in comparison with the action of isoprenaline (isoproterenol) and orciprenaline (metaproterenol). 1) The relaxing effect on isolated guinea-pig tracheal muscle constricted previously with histamine BaCl2 or acetylcholine was highest with S-1541, followed by isoprenaline and orciprenaline, in that order, and lowest with S-1540. The relaxing effect of S-1541 on acetylcholine-induced tracheal constriction was reduced and that of S-1540 was completely abolished by a previous treatment with propranolol. The relaxing actions of those drugs on bronchial spasms induced by histamine in vivo were highest with S-1541, followed by isoprenaline, and lowest with S-1540. 2) All these drugs exhibited the depressor and positive chronotropic actions in guinea-pigs. The potencies of the actions were found to be in the following order; isoprenaline was most potent, followed by S-1541 with a little less intensity, orciprenaline much weaker, and S-1540 still weaker with a positive chronotropic action of about 1/1000 of S-1541 and depressor action about 1/500. In the open chest guinea-pig, positive inotropic and chronotropic actions of S-1541 were about the same or slightly more potent than those of isoprenaline; S-1540 had a very weak action, being only about 1/1000 as active as S-1541. These actions of S-1540 were completely eliminated by propranolol pretreatment. S-1540 induced to remarkable changes in the electrocardiogram wave forms even in high doses. 3) Those drugs elicited the depressor, positive chronotropic and inotropic actions in rabbits and dogs. In rabbits, isoprenaline was most potent; S-1541 was similar to or a little weaker than isoprenaline; and S-1540 was extremely weak. In the dog, isoprenaline showed the highest of the above effect, followed by S-1541, orciprenaline and S-1540 in that order, with S-1540 having an extremely low activity. 4) The actions of S-1541 and isoprenaline appeared very rapidly but were of short duration, the duration of orciprenaline was moderate, and the actions of S-1540 rapidly appeared and were of an extremely long duration. It is suggested that S-1540 itself has pharmacological activities in vivo and the active metabolites such as S-1541 also have the activities. S-1540 can be administered by the oral route, is of long duration, and is thus considered to be a bronchodilator with a relative high specificity.

Effects of S-1540 (Bitolterol) and S-1541, a new bronchodilator on tracheo-bronchial muscle and cardiovascular system