[Collagen remodeling of a mitral periannular cardiac muscle lesion in experimental mitral regurgitation rabbits induced by vagus stimulation].

A peculiar mitral periannular cardiac muscle lesion was developed in experimental mitral regurgitation rabbits induced by vagus stimulation. In this model, a pansystolic murmur was heard during one week after vagus stimulation, and it disappeared thereafter. We investigated the periannular cardiac muscle lesion one week (MR-1 group, N = 30) and four weeks (MR-4 group, N = 15) after vagus stimulation using pathohistological, immunohistochemical and biochemical techniques, and found that the lesion had regressed in four weeks. Non-treated rabbits (C-1 group and C-4 group) were used as controls. The periannular cardiac muscle lesion in MR-1 group was characterized by swelling and increased stiffness which corresponded to swelling and degeneration of the myocardial cells and interstitial fibrosis on microscopic observation. On the other hand, in MR-4 group, the swelling and degeneration of the myocardial cells restored and an increase of interstitial collagen was regressed. The hydroxyproline content of the periannular cardiac muscle lesion in MR-1 group was significantly abundant compared with that in C-1 group (10.5 +/- 1.6 mg/g. wet wt, vs 7.8 +/- 0.9, mean +/- SD, p less than 0.01). In MR-4 group, the hydroxyproline content was significantly decreased compared with that in MR-1 group (8.8 +/- 1.4 vs 10.5 +/- 1.6, p less than 0.05). Immunohistochemical study clearly indicated that the increased collagen in the periannular cardiac muscle lesion in MR-1 group was type III collagen, and that the increased type III collagen regressed in MR-4 group.(ABSTRACT TRUNCATED AT 250 WORDS)