REACTIVE AND REPARATIVE FIBRILLAR COLLAGEN REMODELING IN THE HYPERTROPHIED RAT LEFT-VENTRICLE - 2 EXPERIMENTAL-MODELS OF MYOCARDIAL FIBROSIS

Study objective - The aim was to compare the temporal sequence and structural relationship between perivascular and interstitial fibrosis and microscopic scarring seen in the left ventricle in response to either a transient or sustained stimulus to fibrosis.Design - In 72 male Wistar rats (250 - 350 g) the transient stimulus model was based on the administration of isoprenaline (500 μg·kg-1) while the sustained stimulus model was produced by abdominal aortic banding with right renal artery constriction. Serial sections of myocardium were examined and compared at 4 and 12 weeks in each model and to corresponding controls.Experimental material - The collagen specific stain, Sirius Red F3BA, was used to determine collagen volume fraction and the fibrillar nature of the fibrous tissue response seen by light microscopy.Measurements and main results - Following isoprenaline a stable reparative fibrosis of the endomyocardium and increase in collagen volume fraction was seen without an interstitial or perivascular fibrosis of the non-involved myocardium. In unilateral renal ischaemia, on the other hand, a progressive perivascular fibrosis was evident throughout the myocardium and from which fibrillar collagen extended into the extracellular space between muscle bundles creating an interstitial fibrosis; microscopic scarring of the endomyocardium became evident at 12 weeks.Conclusions - The reactive perivascular fibrosis of intramyocardial coronary arteries seen in renovascular hypertension is a progressive process that leads to an interstitial fibrosis and eventual microscopic scarring. In contrast, the endomyocardial scarring that follows isoprenaline induced myocyte necrosis is stable and intramural vessels in remote regions are not involved.