CHLOROETHYLCLONIDINE IS A PARTIAL ALPHA(2)-ADRENOCEPTOR AGONIST IN AORTA AND CAUDAL ARTERIES OF THE WISTAR-KYOTO RAT

The interaction between chloroethylclonidine N-beta-chloroethyl-N-meth ylamino-methyl-clonidine) and alpha(1)-adrenoceptors mediating contrac tion in Wistar Kyoto rat arteries was examined. In caudal (alpha(1A)-a drenoceptors) and aorta (alpha(1D)-adrenoceptors) arteries, chloroethy lclonidine (10(-4) M) elicited contraction with different time frames (maximal effect within 4 min in the caudal artery and at 30-45 min in aorta). Phentolamine (10(-6) M) completely prevented chloroethylclonid ine-induced contraction in aorta, but partially did so in the caudal a rtery. Rauwolscine (10(-7) M) partially prevented the chloroethylcloni dine contractile effect in both arteries. Chloroethylclonidine attenua ted the contractile effect of low concentrations of norepinephrine, ho wever, maximal contraction was observed at catecholamine concentration s above 10(-7) M in the caudal artery and 10(-6) M in the aorta. It is concluded that chloroethylclonidine interacts with caudal alpha(1A)-a drenoceptors as an irreversible partial agonist, inducing vascular con traction probably due to Ca2+ mobilisation, and with aorta alpha(1D)-a drenoceptors as a partial agonist, inducing slow-onset muscular contra ction. (C) 1998 Elsevier Science B.V. All rights reserved.