713-6 Functional and Metabolic Protection of the Ischemic Rabbit Heart by NO Synthase Inhibitor

Abstract

To assess the role of the NO pathway in ischemic injury, the NO synthase inhibitor L-N-Monomethylarginine (L-NMMA) was tested on isolated rabbit hearts retrogradely perfused with Krebs-Henseleit buffer containing 5.5 mM glucose and submitted to 30 min equilibration at 5 ml/min per g, followed by a 60 min low-flow ischemia (10% baseline) and 30 min reperfusion. Metabolic and physiological parameters of hearts treated with 1 μ M LNMMA added 15 min before ischemia (n = 10) were compared with similar parameters in controls (ctrl, n = 15) without the inhibitor. Before ischemia, L-NMMA did not influence left ventricular developed pressure or coronary perfusion pressure but lowered cyclic GMP by 25% (P = 0.01). During ischemia, L-NMMA decreased the severity of ischemic contracture (25 ± 3 vs 54 ± 4 mmHg in ctrl, P < 0.001). Perfusion with D-NMMA did not protect the heart against ischemic contracture. The effect of L-NMMA was suppressed by 1 mM L-arginine or 10 μ M sodium nitroprussiate but not by 10 μ M 8Br- cyclic GMP. a cyclic GMP analogue. At the end of ischemia, exogenous glucose uptake was 0.90 ± 0.08 and 4.0 ± 0.2 μ mol/min per g DW (P < 0.01). lactate production was 4.0 ± 0.7 and 8.0 ± 0.7 μ mol/min per g DW (P < 0.01), glycogen was 15 ± 2 and 29 ± 5) μ mol glucose eqJg DW (P < 0.01) and ATP was 2.5 ± 0.4 and 4.6 ± 0.3 μ mol/g DW (p < 0.01) in ctrl and treated hearts, respectively. With reperfusion, the developed pressure was doubled (65 ± 5 vs 32 ± 3 mmHg, P < 0.001) and the CPK release reduced by 50% (P < 0.01) in hearts treated with L-NMMA vs ctrl. A dose-response curve of protection against ischemic damage by L-NMMA showed that the NO synthase inhibitor decreased ischemic contracture and enhanced glucose uptake between 1 nM and 1 μM, i.e. below concentrations inducing vasoconstriction. It is concluded that L-NMMA protects the ischemic rabbit heart against cellular damage by stimulating exogenous glucose uptake, thereby preserving endogenous energetic resources as glycogen. This protection during ischemia leads to an improvement of post-ischemic functional recovery. This effect during ischemia seems cGMP-independent.