REGIONAL DIFFERENCES IN LV COLLAGEN ACCUMULATION AND MATURE CROSS-LINKING AFTER MYOCARDIAL-INFARCTION IN RATS

To determine the extent of and any regional differences in remodeling response of the extracellular matrix (ECM) to myocardial infarction (M I), moderate-to-large transmural infarcts were surgically produced in left ventricular (LV) free wall of rats. Animals were killed 13 wk aft er surgery. In comparison to age-matched controls, infarction was asso ciated with an overall increase in heart weight, which included hypert rophy of both the right ventricle and LV. Although the remaining viabl e myocardium in LV free wall was significantly reduced, the interventr icular septum was hypertrophied some 30% compared with control tissues (247 +/- 9 vs. 189 +/- 8 mg). Collagen concentration more than double d in remaining viable free wall (8.92 +/- 0.59 vs. 3.95 +/- 0.25 mg/10 0 mg, P < 0.0001), and a smaller but still highly significant 27% incr ease occurred (P < 0.01) in the more remote septum. Degree of covalent cross-linking of collagen fibrils as assessed by hydroxylysylpyridino line (KP) concentration also revealed regional differences in response of the ECM to infarction. Although HP concentration was increased 60% in viable free wall (P < 0.05) post-MI, it was unchanged in the septu m. With respect to collagen characteristics of the transmural infarct per se, the scar exhibited still further increases in both collagen an d HP concentrations compared with the already elevated values for thes e two parameters in viable free wall. The results indicate that any ev aluation of the remodeling response of viable myocardium post-MI must include not only the myocyte but also the ECM, the principal component of which is collagen.