Ao. Fernandez et al., Coronary vasomotor disorders during hypoxia-reoxygenation: do calcium channel blockers play a protective role?, RES EXP MED, 199(6), 2000, pp. 319-331
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.