Vasodilator pre-treatment of human radial arteries - Comparison of effectsof phenoxybenzamine vs papaverine on norepinephrine-induced contraction invitro

Aims The radial artery, increasingly used for coronary artery bypass grafti ng (CABG), has a potential for spasm which may increase peri-operative risk . Increased alpha-adrenoceptor activation is a key candidate for the spasm. We studied the effects of vasoconstriction in a radial artery, which had u ndergone brief exposure to the alpha-adrenoceptor antagonist phenoxybenzami ne vs the opioid derivative papaverine. Methods and Results Using standard classical organ bath techniques, concent ration, responses were obtained to norepinephrine in segments of radial art ery from 12 CABG patients pre- and post-incubation for 20 min in either phe noxybenzamine 10(-6) M or papaverine 3 x 10(-3) M. Responses were reassesse d 2, 4 and 18 h after washout of phenoxybenzamine and 2, 4, 8 and 18 h afte r washout of papaverine. There was concentration-dependent constriction to norepinephrine (maximum response 0(.)89 +/- 0(.)20 (SEM) g.mm(-1), n=6). Co nstriction to norepinephrine was abolished immediately after incubation in phenoxybenzamine and remained completely inhibited for at least 18 h (P <0( .)0001 ANOVA phenoxybenzamine pre-treated vs controls). Most of the inhibit ion of concentration-dependent constriction to norepinephrine following pre -treatment with papaverine was lost 8 h later. Conclusion Radial artery vasoconstriction induced by a clinically relevant agonist, norepinephrine. may be prevented for at least 18 h by pre-incubati on ill phenoxybenzamine, in contrast to the brief inhibition achieved by pr e-treatment with papaverine. Adding phenoxybenzamine to radial artery graft bathing solution may improve early outcome following CABG. (C) 2001 The Eu ropean Society of Cardiology.