Differential effects of calcium channel antagonists in the amelioration ofradial artery vasospasm

Background. Radial artery (RA) is being used for coronary artery bypass gra fting (CABG) with greater frequency. However, RA is prone to post-CABG vaso spasm, which may be neurohormonally mediated. Use of the calcium channel an tagonist diltiazem has been advocated as a strategy to reduce post-CABG RA vasospasm. However, whether and to what degree different calcium channel an tagonists influence neurohormonally induced RA vasoconstriction remains unk nown. Methods. RA segments were collected from patients undergoing elective CABG (n = 13), and isometric tension was examined in the presence of endothelin (10 nM) or norepinephrine (1 mu M). In matched RA, endothelin- or norepinep hrine-induced contractions were measured in the presence of diltiazem (277 nM), amlodipine (73 nM), or nifedipine (145 nhl). These concentrations of c alcium channel antagonists were based upon clinical plasma profiles. Results. Endothelin and norepinephrine caused a significant increase in RA- developed tension (0.54 +/- 0.1 and 0.68 +/- 0.1 g/mg, respectively; p < 0. 05). Amlodipine or nifedipine significantly reduced RA vasoconstriction in the presence of endothelin (30 +/- 6% and 41 +/- 9%, respectively; p < 0.05 ) or norepinephrine (27 +/- 8% and 53 +/- 9%, respectively; p < 0.05), wher eas diltiazem did not significantly reduce RA vasoconstriction. Conlclusions. These results demonstrate that neurohormonal factors released post-CABG can cause RA vasoconstriction, and that calcium channel antagoni sts are not equally effective in abrogating that response. Both amlodipine and nifedipine, which have a higher degree of vascular selectivity, appear to be the most effective in reducing RA vasoconstriction. (C) 2000 by The S ociety of Thoracic Surgeons.