The effect of L-arginine on myocardial recovery after cardioplegic arrest and ischemia under moderate and deep hypothermia.

Background Depletion of L-arginine (L-arg), the substrate for nitric oxide (NO) synthesis, could be one of the mechanisms responsible for the reduced production of NO and decreased coronary flow (CF) during reperfusion. This, in turn, may adversely affect mechanical function. We aimed to study the benefits of exogenous administration of L-arg under conditions that mimick preservation of the heart for transplantation and routine cardiac surgery. Methods and Results Isolated working rat hearts perfused with oxygenated Krebs-Henseleit buffer were subjected to one of the two experimental protocols: (1) cardioplegic arrest with St Thomas' No 1 cardioplegic solution and 240 minutes of deep hypothermic (4°C) ischemia, and (2) cardioplegic arrest with St Thomas' No 1 cardioplegic solution and 60 minutes of moderate hypothermic (20°C) ischemia. In each protocol, hearts were divided into four groups (I to 4 for protocol A and A through D for protocol B; n=6 in each group). In groups 1 and A (controls), hearts were arrested with the St Thomas' No 1 and were reperfused with standard Krebs-Henseleit buffer. In groups 2 and B,L-arg was added to cardioplegic fluid; in groups 3 and C, L-arg was added to reperfusate; and in groups 4 and D. L-arg was added to both cardioplegic fluid and reperfusate. Cardiac output, dP/dt, CF, and NO concentrations in the coronary effluent were evaluated in all groups before and after ischemia. After 4°C ischemia (protocol A), the postischemic recovery of dP/dt for the control hearts in group1 was 51.0±3.4%, which increased significantly to 73.3±2.7% and 70.1±4.4% in groups 3 and 4, respectively. In group 2, recovery of dP/dt was similar to the control group's and was 56.5±4.5%. Increased postischemic cardiac output and CF and increased production of NO correlated with improved functional recovery. After 20°C ischemia (protocol B), the postischemic recovery of dP/dt was 47.2±3.5% in control group A and significantly increased to 79.2±2.6% in group B, to 82.0±3.5 in group C, and to 83.9±3.3 in group D. Increased postischemic CF and increased production of NO were closely related to improvement in mechanical function. Conclusions Exogenous L-arg considerably improves the postischemic recovery of cardiac mechanical function and CF after cardioplegic arrest and ischemia by stimulation of NO production when given in the reperfusate after both 4°C and 20°C ischemia. However, L-arg as an additive to cardioplegia was only beneficial after 21°C, and not after 4°C ischemia.