EXTRACELLULAR-MATRIX ARRANGEMENT IN THE PAPILLARY-MUSCLES OF THE ADULT-RAT HEART - ALTERATIONS AFTER DOXORUBICIN ADMINISTRATION AND EXPERIMENTAL-HYPERTENSION

In the present study, we analyzed the components of the extracellular matrix (ECM) and its arrangement at the level of the papillary muscles in the adult rat heart using light and transmission and scanning elec tron microscopy techniques. Our results reveal that after a single dos e (6 mg/kg) of dexorubicin to cause a significant decrease and disorga nization of the endomysium and perimysium in the first week after inje ction, affecting the endomysial struts and perimysial strands. Degener ating myocytes and alterations of the coiled perimysial fibers were ch aracteristic 4 weeks after treatment. After 8 weeks, ultrastructural a lterations at the level of the plasma membrane of the myocytes and adj acent collagen network were present in the tip of the papillary muscle s. These alterations may be responsible for the inefficiency of the va lvular apparatus as an initial factor implicated in doxorubicin-induce d congestive heart failure. Experimental hypertension, produced by con striction of the abdominal aorta, induced hypertrophy of the left vent ricle, with increased perimysium and endomysium of the ECM at the leve l of the papillary muscles 4 weeks after aortic banding. Interstitial and perivascular fibrosis were observed 8 weeks after treatment. These alterations of the ECM network have been correlated with their possib le implication in ventricular biomechanical properties.