ATYPICAL ADRENOCEPTOR-MEDIATED RELAXATION OF CANINE PULMONARY-ARTERY THROUGH A CAMP-DEPENDENT PATHWAY

We studied the existence of beta(3)-adrenoceptors in canine pulmonary artery smooth muscle under isometric conditions in vitro. A rank order potency of vascular relaxation was isoproterenol > salbutamol > selec tive beta(3)-adrenoceptor agonists, CL 316243 and BRL 37344, A marked desensitization to salbutamol occurred by pretreatment with salbutamol but not with CL 316243, When beta(1)-adrenoceptors were blocked, the relaxant responses to salbutamol were competitively antagonized by the beta(2)-adrenoceptor antagonist ICI 118551, whereas the response to C L 316243 was not. Cyanopindolol, a non-selective beta-adrenoceptor ant agonist, antagonized CL 316243-induced relaxation in a competitive man ner with a pA(2) of 6.10, and this value was lower than that when salb utamol was used as an agonist (6.69), Intracellular cAMP levels were i ncreased by CL 316243, an effect that was not altered by ICI 118551, T herefore, beta(3)-adrenoceptors may be present and functioning in cani ne pulmonary artery. (C) 1998 Academic Press.