Aims: Nitric oxide (NO) is vital for the integrity of the cardiovascular system and protection against ischaemic heart disease. Arginase is up-regulated during ischaemia-reperfusion (IR) and this enzyme might compete with NO synthase (NOS) for arginine. The present study investigated whether arginase blockade protects from myocardial IR injury and whether such an effect is coupled to increased NO bioavailability.
Methods and results: Sprague-Dawley rats were subjected to 30 min of coronary artery ligation, followed by 2 h of reperfusion. The animals were given either saline, or the arginase inhibitor N-omega-hydroxy-nor-l-arginine (nor-NOHA) with or without the NO scavenger carboxy-2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (cPTIO) or the NOS inhibitor N(G)-monomethyl-l-arginine (l-NMMA) iv 15 min before ischaemia. The infarct size was 79 +/- 4% of the area at risk in the control group. Nor-NOHA treatment reduced the infarct size to 39 +/- 7% (P < 0.001). Administration of cPTIO or l-NMMA completely abolished the protective effect of nor-NOHA. Expression of arginase I was significantly (P < 0.05) increased in ischaemic myocardium. Nor-NOHA treatment resulted in higher plasma levels of nitrite (P < 0.05) and a 10-fold increase in the citrulline/ornithine ratio (P < 0.001), indicating a shift in arginine utilization towards NOS.
Conclusion: Inhibition of arginase protects from myocardial infarction by a mechanism that is dependent on NOS activity and bioavailability of NO by shifting arginine utilization from arginase towards NOS. These findings suggest that targeting of arginase is a promising future therapeutic strategy for protection against myocardial IR injury.