Sequential Changes in Laminin and Type IV Collagen in the Infarct Zone

BACKGROUND: The healing process, which affects ventricular remodeling, is an important factor in the prognosis of myocardial infarction. We hypothesized that laminin and type IV collagen contribute to extracellular matrix assembly in healing after myocardial infarction. We examined sequential changes in these two components after experimental myocardial infarction in rats. MATERIALS AND METHODS: Hearts were excised from 1 day to 10 weeks after permanent left coronary ligation in rats. Immunohistochemical staining with a polyclonal antibody to laminin and type IV collagen was performed by the avidin-biotin-peroxidase method. RESULTS: Laminin: On day 3, laminin initially appeared in a wavy fashion in the granulation tissue of the infarct peripheral zone and was not restricted to the cell membrane; the staining distribution in the peripheral zone then gradually increased, reaching a maximum on days 7-11. The distribution progressed from the peripheral zone to the outer lesion of the central zone of the infarct for 1-2 days, and reached the center point after 2 weeks. The extent of the staining distribution gradually decreased after reaching this maximum, but the staining did not completely disappear. Type IV Collagen: Changes in type IV collagen were essentially the same as those in laminin. A wavy staining pattern of type IV collagen appeared in the infarct peripheral zone from day 3, reached its maximum extent on days 7-11, and decreased gradually thereafter. The distribution progressed from the peripheral zone to the outer lesion of the central zone for 1-2 days, reaching the center point after 2 weeks. CONCLUSIONS: Laminin and type IV collagen contribute to extracellular matrix formation in the infarct zone relatively early after myocardial infarction.