DILATED CARDIOMYOPATHY IS ASSOCIATED WITH AN INCREASE IN THE TYPE-I TYPE-III COLLAGEN RATIO - A QUANTITATIVE ASSESSMENT/

Objectives. The aim of this study was to quantify total collagen and t he type I/type III collagen ratio and their localization in hearts wit h dilated cardiomyopathy. Background. Patients with dilated cardiomyop athy have an increase in intramyocardial fibrillar collagen. Types I a nd III are the main constituents and have different physical propertie s that may affect cardiac compliance. Methods. Nineteen hearts with di lated cardiomyopathy were studied (17 cardiac explants, 2 hearts obtai ned at autopsy) and compared with reference hearts. Total collagen was determined by hydroxyproline analysis. Collagen types I and III were analyzed using the cyanogen bromide method and immunohistochemical ana lysis followed by microdensitophotometric quantification. Localization of collagen types I and III was established at the light and electron microscopic levels. Immunoelectron microscopy provided information re garding their localization. Results. Total collagen and the collagen t ype I/type III ratio were increased in hearts with dilated cardiomyopa thy (p < 0.05). Electron microscopy shoved a diffuse increase in colla gen fibrils in the endomysium; the perimysium showed an inhomogeneous increase. Collagen fibrils were thicker, and fibrous long-spacing coll agen occurred in the endomysium. Immunoelectron microscopic findings c onfirmed an increase in type I collagen. Conclusions. Hearts with dila ted cardiomyopathy have a statistically significant increase in the co llagen type I/type III ratio. The changes occur in the endomysium and perimysium, although with differences in distribution. These changes i n intramyocardial collagen may be clinically relevant because they may affect cardiac rigidity and, therefore, eventually may render the hea rt less compliant. Further studies are needed to evaluate at what poin t in the course of the disease these changes appear.