AN ANALYSIS OF THE DISCREPANCY BETWEEN THE EFFECTS OF CENTRAL AND PERIPHERAL α-ADRENOCEPTOR STIMULATIONS

In pentobarbital anaesthetized rabbits, intravenous injection of 1 mg/kg of yohimbine, an α-adrenoceptor antagonist, or 1 mg/kg of picrotoxin, a GABA antagonist, could significantly antagonize the hypotensive action of 5 μg clonidine given intraventricularly. But yohimbine could not antagonize the central hypotensive action of GABA, while picrotoxin could entirely block it.In rabbits pretreated with semicarbazide, an inhibitor of GABA synthesis, the hypotensive action of clonidine 50 μg/kg injected intravenously was markedly attenuated.The results suggest that the hypotensive effect of central α-adrenoceptor stimulation is mediated by GABA-nergic neuron.