Experimental studies on the bone metabolism of male rats chronically exposed to cadmium intoxication using dual-energy X-ray absorptiometry.

Cadmium (Cd) has been identified as the etiologic agent of itai-itai disease. The purpose of this study was to investigate whether chronic Cd exposure affects bone metabolism in a male rat model and to estimate the bone mineral density (BMD) differences in lumbar and femoral bone because of Cd exposure. Six-week-old male Hos Donryu rats were used in this experiment. Cadmium was administered at a dose of 200 ppm to rats in the diet to produce experimental chronic Cd poisoning. Bone mineral density was measured using dual-energy X-ray absorptiometry (DEXA) with a high-resolution scan collimator (0.25 mm diameter) (Hologic QDR-2000). The Cd content in renal tissue reached a critical concentration of 128.42 +/- 14.38 microg/g 10 months after the administration of the element (Table 3). The average blood urea nitrogen (BUN) value was increased throughout the period of the experiment, and the serum creatinine value of the experimental group showed an increase after 2 months of Cd administration (0.46 +/- 0.09 mg/dL). The concentration of urinary calcium changed in the experimental group after exposure to Cd for 12 months (15.4 +/- 0.13 mg/dL). DEXA showed a greater reduction in the bone mineral density of the 5th vertebral body (L5) in rats that had ingested Cd for 4 months (0.359 +/- 0.013 g/cm2) than in control rats (0.372 +/- 0.012 g/cm2, P < 0.01). On the contrary, the difference in bone mineral content between rats ingesting Cd for 6-8 months and control rats was not significant. However, significant reductions in bone mineral content were again noted in rats that had ingested Cd for 12 months (0.339 +/- 0.023 g/cm2) compared with the control group (0.385 +/- 0.012 g/cm2, P < 0.01). The bone mineral density of the right femoral bone in control rats was 0.328 +/- 0.018 g/cm2 and that in experimental rats was 0.306 +/- 0.012 g/cm2, and a meaningful difference was recognized (P < 0.05). Histological examination of the rats exposed to Cd for 12 months showed that the 5th lumbar vertebral body (L5) exhibited osteomalacia. The results of our studies show that Cd stimulated a loss of bone mineral at an early stage to a great extent in male rats. In the examination of male rats, bone injury and renal functional disorder were encountered simultaneously. This study suggested that osteomalacia was induced by a direct action of Cd on the bone through abnormal calcium homeostasis at an early stage in male rats.