Despite the fact that much is known about chronic renal disease, few studies have described renal osteodystrophy (ROD) in rats. The present study describes pathological features of spontaneously occurring ROD in 84 (70 males and 14 females) out of 545 (269 males and 276 females) aged rats used in life-span and carcinogenecity studies.
1. Bone changes: The time course of histological change in the bone is as follows: 1) increased bone resorption with active osteoblasts (-increase in plasma PTH level), 2) proliferation of osteoblasts and fibrous connective tissue (marrow fibrosis) -reparative process, 3) osteoid formation (hyperosteoidosis) -defective rate of mineralization, and increase in matrix synthesis.
2. Chronic renal disease: Histopathological changes in the kidney of ROD were typical of age-related renal disease in the various strains of rats and revealed an end-stage of renal damage. The lesion consisted of glomerular sclerosis, tubular dilatation with flattened epithelium and proteinaceous casts, and cell infiltration and fibrosis in the interstitium.
3. Parathyroid hyperplasia (hyperparathyroidism): Both glands were grossly enlarged to 1-2 mm in diameter. Microscopically the chief cells were significantly increased in their size and number, indicating that the gland enlargement was due to both hyperplasia and hypertrophy of these cells.
4. Metastatic calcification: Metastatic calcification in the soft tissue was found in most cases with ROD. The deposit was present in multiple sites, particularly in the aortic media, medium-sized arteries of various organs, lung, stomach, and kidney.
