Clonidine Attenuates the Carbachol-induced Contractile and Phosphatidylinositol Responses of Rat Trachea

Abstract

Abstract Although Clonidine is known to affect vascular smooth muscle, its effects on airway smooth muscle are not fully understood. This study was designed to examine the effects of Clonidine on carbachol-induced contractile and phosphatidylinositol responses of rat trachea. Clonidine, at a dose of 100 μM or greater, attenuated carbachol-induced contraction and the accumulation of carbachol-induced inositol monophosphate (IP1). Clonidine also attenuated the accumulation of aluminium fluoride-induced IP1. The concentration-effect relationship of IP1 accumulation was similar to that of carbachol-induced contraction; r = 0.797, P< 0001. These results suggest that Clonidine attenuates contractile responses, at least in part, through the inhibition of phospholipase C (coupled with G-proteins) in phosphatidylinositol responses.