ALPHA(1)-ADRENOCEPTORS MEDIATING CONTRACTION IN ARTERIES OF NORMOTENSIVE AND SPONTANEOUSLY HYPERTENSIVE RATS ARE OF THE ALPHA(1D) OR ALPHA(1A) SUBTYPES

alpha(1)-Adrenoceptor subtypes mediating contraction in carotid, aorta , mesenteric and caudal arteries from both Wistar Kyoto (WKY) normoten sive and spontaneously hypertensive (SHR) rats were investigated by us ing the alpha(1A)-adrenoceptor agonist methoxamine and antagonized wit h selective, competitive antagonists WB-4101, 5-methyl urapidil or BMY 7378 piperazinyl)ethyl)-8-azaspiro(4,5)decane-7,9-dione dihydrochlori de). Isometric tension changes were recorded after methoxamine additio n to the arterial rings, and the effects of the antagonists determined . All the antagonists shifted to the right the concentration-response curve to methoxamine. pA(2) values indicate that all arteries but caud al express the alpha(1D)-adrenoceptor subtype, since BMY 7378 values w ere high in these arteries. Due to the high pA(2) values for 5-methyl urapidil and WB-4101 and the low values for BMY 7378 we conclude that the tail artery expresses the alpha(1A) and not the alpha(1B) subtype. No differences were found between both strains of rats, suggesting th at hypertension does not modify the alpha(1)-adrenoceptors in conducta nce arteries.