Evidence for an 2-presynaptic blocking activity of levamisole in the isolated rat vas deferens

ABSTRACT

The effects of levamisole on the sympathetic transmission and the mechanism underlying these effects were investigated in the field- stimulated rat vas deferens. Levamisole [5-80 muM] potentiated the contraction of the vas deferens induced by field stimulation at low and high frequencies [2, 20 Hz] in a concentration-dependent manner. The extent of potentiation at low frequency was greater than that at high frequency. However, noradrenaline-induced contractions were only potentiated at high concentrations of levamisole [40, 80 muM]. The potentiating effect of levamisole on electrically evoked muscle twitches was completely abolished in the presence of yohimbine and only a slight potentiation was obtained with high concentrations of levamisole. Moreover, in the presence of levamisole [20 muM], the concentration-response curve of clonidine was shifted to the right and the ED50 of clonidine was increased by three-fold. Levamisole was capable of recovering the electrically-evoked muscle contraction after being abolished by cocaine. These data provided a strong evidence for an alpha2-presynaptic blocking activity of levamisole in the isolated rat vas deferens and confirmed its reported uptake blocking activity, only at high concentration