Effect of amitraz on intestinal contractility

장평활근의 수축성에 대한 amitraz의 영향

Amitraz frequently causes the side effect of intestinal stasis or bloat in mammals. It is very similar to the side effect of xylazine or clonidine which produce the inhibition of intestinal motility through the stimulation of ${\alpha}_2$ adrenoceptor. Therefore, we examined whether amitraz causes intestinal stasis or bloat through the inhibition of intestinal motility or whether amitraz produces the inhibition of intestinal motility through the stimulation of ${\alpha}_2$ adrenopceptor. Amitraz inhibited the intestinal motility in a dose-dependent manner in isolated rabbit jejunum and isolated pig ileum. These inhibitory effects of amitraz were blocked by yohimbine but not by prazosin. The effect of intestinal contraction of carbachol or high-potassium was not affected by the pretreatment of amitraz. However, the con-traction of histamine was inhibited by the pretreatment of amitraz. It is concluded that amitraz mainly inhibits the intestinal motility through the stimulation of ${\alpha}_2$-adrenoceptor although partially antihistaminic action of amitraz can be involved.