L-arginine during long-term ischemia: Effects on cardiac function, energetic metabolism and endothelial damage

Background: We have evaluated the addition of L-arginine, a precursor of ni tric oxide, to a cardioplegic solution (named CRMBM) designed for long-term heart preservation. Methods: Isolated isovolumic-perfused rat hearts (n = 22) were arrested wit h the CRMBM solution either with (Arg) or without L-arginine (2 mmol/L) (Ar g group, n = 12, vs control group n = 10), submitted to 8 hours of cold sto rage (4 degrees C) in the solution, and then reperfused for 60 minutes at 3 7 degrees C. In 11 hearts, we evaluated the quality of cardiac preservation with P-31 magnetic resonance spectroscopy and the measure of function and cellular integrity. Endothelium-dependent and independent vasodilatations w ere measured in 11 other hearts, using 5-hydroxytryptamine and papaverine t o assess endothelial and smooth muscle function. Results: Adding L-arginine to the cardioplegic solution improved functional recovery during reflow, as shown by the rate pressure product (31% +/- 3% for control vs 47% +/- 3% for Arg, p = 0.003) together with higher coronary flow and diminished contracture. Purine release in coronary effluents duri ng reperfusion was lower in the Arg group. During ischemia and reflow kinet ics of intracellular pH and high-energy phosphates were similar ill both gr oups. Coronary endothelium-dependent vasodilatation was similarly impaired in both groups, but smooth muscle was less altered with L-arginine. Conclusion: As an additive to the CRMBM cardioplegic solution, L-arginine p rovides a protective effect for long-term heart preservation. Our data do n ot show coronary endothelial protection as the prominent mechanism.