Normothermic and hypothermic models for studying the deleterious effects of hypoxia-reoxygenation on EDHF-mediated relaxation in isolated porcine coronary arteries

IntroductionThe vasomotor response of the coronary artery is altered by hypoxia–reoxygenation (H–R) induced damage. The aim of our study was to compare and evaluate normothermic and hypothermic models which are suitable for future drug studies of vasoprotective action against H–R injury.MethodsPorcine coronary arterial rings were isolated and placed in Krebs–Henseleit (K–H) solution. Rings were exposed to normoxic conditions (control group) and two different H–R conditions: the first induced by a 95% N2–5% CO2 gas mixture (40- and 60-min hypoxia) in a normothermic protocol, and the second induced by hypothermic (4 °C) hypoxia–reoxygenation in an air-tight beaker filled with K–H solution (24- and 48-hours hypoxia). Reoxygenation was applied by introducing K–H solution aerated with a 95% O2–5% CO2 mixture under normothermic (37 °C) conditions. To test the EDHF-mediated relaxation by substance P, rings were first incubated in L-NNA, nitric oxide synthase inhibitor, and indomethacin, cyclooxygenase inhibitor, and then pre-contracted with thromboxane analogue U-46619. Analysis of the maximum relaxation of the arterial rings was performed by one-way ANOVA, followed by Bonferroni's post-test.ResultsDistal segments of the coronary artery responded faster to contraction induced by U-46619 and were relaxed by substance P to a greater extent than proximal segments. Maximal relaxations of arterial rings induced by a 10 nM solution of substance P were significantly reduced (p < 0.001) from the values for normoxic rings (81.0 ± 1.0%, n = 30) after 40-min H–R (50.5 ± 5.3%, n = 30), 60-min H–R (32.1 ± 3.5%, n = 30), 24-hours hypothermic H–R (56.0 ± 2.3%, n = 30) and after 48-hours hypothermic H–R (38.5 ± 5.1%, n = 30).ConclusionsThe model employing 40-min normothermic H–R is as effective as 24-hours hypothermic H–R, and 60-min normothermic H–R as 48-hours hypothermic H–R for studying the deleterious effects of H–R on EDHF-mediated relaxation.