Comparative in vitro effects of imipramine, oxybutynin, and flavoxate on rabbit detrusor

The ability of imipramine, oxybutynin, and flavoxate to antagonize carbamylcholine and barium chloride (BaCl2)-induced contractions of rabbit detrusor, and to block impulse conduction in desheathed frog sciatic nerves has been assessed in vitro. Impiramine exerts noncompetitive carbamylcholine and BaCl2 blockade by 10(-5) M and a local anesthetic effect equipotent with that of tetracaine. Oxybutynin exerts a strong competitive antagonism of carbamylcholine by 10(-8) M, a noncompetitive antagonism of BaCl2 equivalent to that of imipramine, and moderate local anesthetic activity. Flavoxate, under these experimental conditions exerts little anticholinergic, antispasmodis, or local anesthetic activity. Imipramine and oxybutynin thus demonstrate a number of smooth muscle effects by which their therapeutic actions may be exerted. The mechanisms of action of flavoxate remain obscure.