PROTECTIVE EFFECTS OF HISTIDINE DURING ISCHEMIA-REPERFUSION IN ISOLATED-PERFUSED RAT HEARTS

We investigated the efficacy of histidine in reducing ischemia-reperfu sion (I/R)-induced myocardial injury in isolated perfused rat hearts. In I/R hearts, the contractile function and coronary flow were 59 +/- 10 and 78 +/- 6% of control. Perfusion with histidine resulted in sign ificant increase in contractility (94 +/- 4%) and coronary flow (92 +/ - 4%). The incidence of arrhythmias during reperfusion was 100% (10 ou t of 10) in the I/R hearts with an average duration of 12.22 +/- 1.55 (SE) min. The duration of arrhythmias was shortened to 8.24 +/- 1.46, 2.15 +/- 0.9, and 2.49 +/- 1.50 min with 10, 25, and 50 mM histidine, respectively. The duration of sinus rhythm increased from 6.26 +/- 1.5 6 min in I/R hearts to 10.66 +/- 1.55, 14.99 +/- 1.61, and 17.18 +/- 0 .95, and 11.73 +/- 0.93 min after perfusion with 10, 25, and 50 mM his tidine, and superoxide dismutase (SOD)-catalase-mannitol, respectively . Electron microscopy revealed significant ultrastructural damage of m yocytes in I/R hearts, which included swelling of the mitochondria and disruption of both the sarcolemma and the myofibrils. Histidine reduc ed the ultrastructural damage in a dose-dependent fashion. In general, the protective effect of histidine was superior than SOD-catalase-man nitol. We conclude that histidine protects myocardium against I/R dama ge most likely by a singlet oxygen scavenging mechanism.