Further studies on the pharmacodynamic properties and organ selectivity of octylonium bromide.

At concentrations ranging from 8.5 to 30 microM, octylonium bromide (OB) did not affect sodium channel availability measured as maximal rate of depolarization (Vmax) of cardiac action potential. On the other hand, at equieffective spasmolytic concentrations (1.1 mM), procaine markedly inhibited Vmax as well as other electrophysiological parameters. These experiments indicate that at fully effective spasmolytic concentrations OB is devoid of local anaesthetic properties. In concentrations up to 10 microM OB did not affect phosphodiesterase activity in crude homogenates of rat colon which were inhibited by both papaverine (EC50 = 0.7 mM) and theophylline (EC50 = 3.5 mM). OB was more effective in antagonizing spasmogen-induced contractions on colonic as compared to tracheal preparations. Inhibition of Neurohormone-induced calcium ion mobilization from cellular and extracellular pools remains the mechanism of action which best explains the spasmolytic effects of OB on intestinal smooth muscle.