Regional reduction in ventricular norepinephrine after healing of experimental myocardial infarction in cats

Regional ventricular norepinephrine and myosin heavy chain concentrations were measured in two models of healed left ventricular myocardial infarction in cats. One model was characterized by a well-defined dense transmural scar (discrete myocardial infarction), while the other demonstrated a pattern of nontransmural diffuse patchy fibrosis in the infarct area (diffuse myocardial infarction). Norepinephrine and myosin heavy chain concentrations were measured in the scarred area, the non-infarcted zone surrounding the scar(s), and in sites remote from the scar. Corresponding tissue sites from unoperated animals and sham operated animals served as controls. Myosin heavy chain concentration was used as an index of surviving muscle mass to express norepinephrine concentration. Norepinephrine concentration, as a function of crude tissue mass, was significantly reduced in both the scarred tissues and the non-scarred tissues surrounding the scar in the discrete infarction model but was significantly reduced only in non-scarred tissues adjacent to the dense scar when expressed as a function of myosin heavy chain. The heavily scarred area of the discrete preparation approached normal values when corrected for myosin heavy chain content. The diffuse infarct preparation demonstrated normal norepinephrine concentration at all three sites studied, whether expressed as a function of tissue mass or myosin heavy chain. These data indicate a long-term regional reduction in norepinephrine concentration specific to non-infarcted tissues adjacent to a dense transmural myocardial infarction scar. This regional reduction in norepinephrine concentration corresponds to reported regions of increased sensitivity to sympathetic nerve stimulation in the discrete myocardial infarction model.