Elektronenmikroskopische Untersuchungen über die Amyloidose der Atrioventrikularklappen des Hundes

Abstract

Introduction The most frequent valvular disease in dogs is endocardiosis which is characterized by early edema and formation of ground substance and valvular fibrosis in late stages. In a light microscopic study of 100 dogs of various ages 7 cases of valvular amyloidosis were detected and investigated with the electron microscope. Material and methods Several samples of diseased atrioventricular valves were obtained under general anesthesia, fixed in 5% buffered glutaraldehyde and post-fixed in 1% OsO 4. The blocks were embedded in Epon. Ultrathin sections were stained with uranyl acetate and lead citrate and examined with a Siemens Elmiskop I. Amyloid was identified in paraffin sections with a Congo red stain using polarized light and thioflavine S and T using fluorescence microscopy. Results A total of 7 cases of valvular amyloidosis were detected on the basis of the electron microscopic demonstration of characteristic amyloid fibrils. The average diameter of the fibrils was 100 Å; the length of the fibrils varied considerably. In all cases a close relationship of amyloid deposits to active fibroblasts, collagen fibers and macrophages was noted. Small collections of amyloid fibrils were often encountered in cytoplasmic vacuoles of macrophages. Discussion Valvular amyloidosis of aged dogs may be classified as senile cardiac amyloidosis with no other organ being involved. It is often associated with congophilic angiopathy of myocardial arteries. It is postulated that amyloid is most likely synthesized locally by valvular stromal cells such as macrophages and fibroblasts.