An analysis of the contractile responses of the rat vas deferens to xylocaine (lidocaine) and procaine

Xylocaine (lidocaine) and procaine but not nupercaine caused contractions of the rat vas deferens. Xylocaine produced a persistant type of contraction whereas procaine produced phasic contractions with marked spontaneous activity. An analysis of their contractions suggests that both agents act directly on the smooth muscle cells. The contractions were found to be modified by various experimental procedures. They were reduced or abolished by lowering the temperature of the bathing media to 25°C. The contractions to both agents were highly dependent of the glucose concentration of the medium. Inhibitors of both glycolysis and oxidative phosphorylation abolished their contractile responses suggesting that glucose is essential for providing metabolic energy for the actions of xylocaine and procaine. Contractions to these two local anesthetics were highly dependent of the pH of the physiological solution. An increase in the pH increased their contractions and vice versa. Though studies of the pH effect indicate that the unionized forms of the local anesthetics are necessary for their action, the molecular species responsible for inducing contractions still remains unsolved.