[Norepinephrine of the rat myocardium during repeated ischemia].

Background: Ischemic preconditioning improves myocardium survival during test ischemia and removes the start of massive norepinephrine (NE) release from sympathetic terminals into the myocardial interstitium. We studied the influence of long and relatively short occlusions on NE release during test occlusion. The possibility has been studied to provoke NE release by local tyramine application on the background of ischemia.

Methods And Results: In rats, anesthetized with urethane, interstitial catecholamine concentrations were measured by implanted microdialysis probe in the perfusion areas of the left anterior descending coronary artery (LAD). After stabilization, the LAD was occluded for 10-60 minutes, reperfused for 20-120 minutes and occluded again for 30-80 minutes. Mean dialysate concentration of NE increased to 50 minute of first LAD occlusion from 0.208±0.038 ng/ml to 6,73±1,42 (maximal increase was by 232). Effect of occlusion was highly significant (p <0,00005). 30 min LAD occlusion suppressed massive NE release during subsequent 30 min test occlusion, but 10 min preocclusion did not. Local tyramine application through microdialysis probe provoked big NE overflow to the myocardial interstitium even on the background of occlusion.

Conclusion: 30 min LAD occlusion damages the mechanism of massive NE release under the influence of ischemia but not of tyramine application.