Effects of trapidil on musculature and vasculature of the dog trachea in situ.

In anesthetized dogs the trachea in situ was perfused with blood through the cannulated cranial thyroid arteries. The effects of trapidil on tracheal musculature and vasculature were assessed in comparison with those of isoproterenol and theophylline. All drugs were injected intra-arterially. Isoproterenol (0.03--0.3 microgram), trapidil (10--300 micrograms) and theophylline (30--300 micrograms) all produced an increase in tracheal blood flow (tracheal vasodilatation) and a decrease in the tracheal intraluminal pressure elevated by neostigmine (tracheal dilatation). In high doses the three drugs all produced maximal tracheal dilatation. Dose-response curves for tracheal vasodilatation to the three drugs were all parallel together, and trapidil was about 2700 time less potent than isoproterenol and about 3 times more potent than theophylline on a weight basis in producing tracheal vasodilatation. Dose-response curves for tracheal dilatation to the three drugs were also parallel together, and trapidil was about 880 times less potent than isoproterenol and about 3 times more potent than theophylline on a weight basis. When compared with isoproterenol, trapidil was about 3 times more effective on tracheal musculature than on tracheal vasculature, and theophylline resembled trapidil. The results suggest that trapidil can also be used as a bronchodilator.