Mechanism of flavoxate antispasmodic activity comparative in vitro studies.

In order to clarify the pharmacological activity of flavoxate, its effect on the tone and spontaneous activity of the guinea-pig isolated ureter and of the muscle strip from rat urinary bladder were studied. Flavoxate, as well as papaverine, reduced all three parameters considered on the guinea-pig isolated ureter, namely: peristaltic motility, endoluminal pressure and longitudinal muscle contractility. In the same test, verapamil (a calcium antagonist), emepronium and atropine (both anticholinergic drugs) were used for comparison. Using strips of rat urinary bladder depolarized by KCl, flavoxate, papaverine and verapamil displayed a relaxant activity, while anticholinergic compounds such as atropine, hyoscine and emepronium failed to relax this tissue. In another series of experiments the effects of flavoxate and anticholinergic drugs on the contraction elicited by vagal electrical stimulation of the guinea-pig isolated stomach in toto were assayed. The results obtained suggest that the action of flavoxate is due to direct smooth muscle relaxation and does not involve anticholinergic activity.