Effect of ramipril and losartan on collagen expression in right and left heart after myocardial infarction.

Although increased deposition of collagen proteins has been described after myocardial infarction (MI), little is known of time-dependent transcriptional alteration of specific cardiac collagen sub-types as well as the degradative mechanisms for cardiac collagens in right and left ventricular myocardium remote to large left ventricular infarction. We sought to study collagen mRNA abundance and the deposition of specific collagen subtypes in noninfarcted left and right rat heart muscle at different times after MI. We also assessed the activity of different myocardial matrix metalloproteinases (MMP) using zymography to gain some information about degradative pathways for collagen. Furthermore, we assessed passive compliance properties of the right ventricle in experimental hearts. Finally we investigated the role of the renin angiotensin system in the collagen gene expression by administration of an angiotensin converting enzyme (ACE) inhibitor (ramipril) and an angiotensin II receptor type I antagonist (losartan) in experimental animals. We observed that the mRNA abundance of types I and III collagen were increased 3 days after myocardial infarction in both viable left and uninfarcted right ventricular tissues, that they peaked at 7-14 days, and were maintained at relatively high levels in the 28 and 56 days experimental groups. Stiffness of the right ventricular myocardium was significantly increased in the 56 days experimental group when compared to that of control values. These findings correlated with increased immunohistochemical staining patterns of different collagen species in the surviving right (and left) cardiac interstitium of 14, 28, and 56 day experimental cardiac groups. The elevation of fibrillar collagen mRNA abundance in noninfarcted muscle from ventricular chambers was not significantly altered after treatment of experimental animals with ramipril and losartan for up to 14 days. MMP activity was increased in viable left ventricle at 14, 28 and 56 days and at 14 days in the right ventricle in experimental animals when compared to controls. These results indicated that (1) activation of transcription of collagen types I and III gene occurs in acute and chronic MI, and that fibrillar collagen proteins are deposited in the noninfarcted cardiac interstitium after a lag period relative to increased corresponding mRNA abundance; (2) an increase in MMP activity in chronic experimental hearts indicates that increased collagen deposition may be due to an increment in collagen synthesis rather by reduced degradation of collagen, and that MMP activation may be important in remodeling of the noninfarcted cardiac stroma; (3) an increase of right ventricular stiffness was associated with increased deposition of collagen; (4) as losartan treatment is not associated with any normalization of elevated collagen mRNA abundance, the upregulation of collagen gene expression in this model is not mediated by AT1 receptor; and (5) the reduction of cardiac fibrosis mediated by ACE inhibition and losartan treatment may reside at the post-translational level in cardiac collagen metabolism.