An electron microscopic study on digestive tract amyloidosis in ferric nitrilotriacetate (Fe-NTA)-induced "F1 amyloidosis" mice.

The histological distribution and ultrastructural findings were investigated in 52 amyloid-positive cases obtained from 80 F1 mice (32 males and 48 females) receiving 126 to 502 daily intraperitoneal injections of ferric nitrilotriacetic acid (Fe-NTA) resulting from reciprocal crossing of 20 parental mice receiving daily intraperitoneal injections of Fe-NTA for 5 months. Of 52 amyloidotic F1 mice 49 (94%) developed a moderate degree of amyloid deposits in the gastrointestinal tract. Moderate amounts of amyloid deposits were sporadically discernible in the lamina propria of the stomach pars glandularis, the duodenal mucosa, and to a lesser extent in that of the rectal mucosa. Electron microscopic observation revealed that macrophages adjacent to amyloid mass were radiating outward abundant bundles of non-branching amyloid fibrils from the cytoplasmic invaginations. In the cytoplasm of the macrophages there were occasionally acid phosphatase-positive lysosomes including amyloid fibrils measuring approximately 100 A in width. Moreover, it is discussed whether fibroblasts or fibroblast-like interstitial cells are involved in amyloid formation.