Effects of α2‐agonists upon colonic propulsion

The α2‐adrenoceptor agonists clonidine and lidamidine were found to be effective in decreasing colonic propulsion in conscious mice after oral administration. Propulsive activity was measured using evacuation of a rectally administered glass bead as the endpoint. The ED50's of clonidine and lidamidine in this assay were 55 μg/kg and 1.4 mg/kg, respectively. The effects of these compounds were selectively blocked by the α2‐antagonists SK&F 72223 and RX 781094 (idazoxan) but not by other standard receptor antagonists. Administration of lidamidine to cats over the same dosage range as was markedly active in mice icreased circular, but not longitudinal, colonic contractile activity, an effect that could be reversed by injection of idazoxan.