Coronary vasomotor disorders during hypoxia-reoxygenation: do calcium channel blockers play a protective role?

During heart surgery, myocardial dysfunction may occasionally appear when e xtracorporeal circulation is discontinued, causing serious haemodynamic dis orders. Many mechanisms are involved in this hypoxia-reoxygenation syndrome . The aim of this experimental study was to characterize the vasomotor diso rders that take place in the isolated porcine coronary artery during in vit ro hypoxia-reoxygenation and to analyse the effect of nifedipine on them. R ings of porcine coronary artery were placed in an organ chamber connected t o a system that recorded isometric forces. The vascular rings were divided into two groups: control group (no nifedipine) and study group (nifedipine, 10(-6) mol/l). The vascular rings were precontracted with 30 mmol/l KCl an d then hypoxia-reoxygenation was induced. Control arterial rings showed imp ortant changes in coronary vasomotor tone: severe hypoxic contraction (from 14.48+/-1.16 g of stable contraction to 17.6+/-0.44 g after the imposition of hypoxia), and transient vasodilation during reoxygenation (69.9+/-10.1% of the maximum contraction achieved). The nifedipine group experienced a s low, progressive, vasodilation throughout the whole experiment (73+/-3.5% o f the maximum contraction). Neither hypoxic vasospasm nor fluctuations of t he coronary vascular tone occurred. Thus, at the end of the hypoxia, the co ntrol vessels presented a degree of contraction similar to the initial leve l. However, in the rings treated with nifedipine, the percentage of dilatio n was 73+/-3.5% (P<0.05). In the isolated porcine coronary artery with inta ct endothelium undergoing a situation of hypoxia-reoxygenation, we have det ected transient vasoconstriction during the first period of hypoxia, follow ed by vasodilation during reoxygenation. The intracoronary administration o f nifedipine prior to the imposition of hypoxia prevents hypoxic contractio n, achieving a greater and more stable degree of coronary vasorelaxation du ring the complete process of hypoxia-reoxygenation.