Experimental studies on renal injury of subacute cadmium-intoxication by 1H-MR imaging and 31P-MR spectroscopy

Six-weeks-old male Hos Donryu rats were used. After the subcutaneous injection of cadmium chloride (1 mg/kg), examinations by 1H-MR imaging and 31P-MR spectroscopy were performed every 3 weeks up to the 24th week after administration. Renal tissue cadmium content reached 175.5±33 μg/g after 21 weeks, and 160.8±13 μg/g after 24 weeks of cadmium administration. Our results indicated that renal tissue cadmium content had reached critical concentration 21 weeks after the initiation of its administration. Changes in 1H-MR imaging; the cortico medullary junction in the kidneys of control rats was clearly delineated by T1 and T2 weighted images of 1H-MR imaging scans. In contrast, the cortex as well the outer and inner medulla in rats which had injected cadmium for 24 weeks could not be visualized in the T1 weighted images, indicating the disappearance of these structures. The rate of disappearance of the three renal layers was evaluated in the MR images according to weeks of cadmium administration. 1H-MR imaging showed that the borders separating the cortex, outer medulla and inner medulla had disappeared in some rats ingesting cadmium for 18 weeks. After 24 weeks, the T1 weighted images demonstrated an 80% and the T2 weighted images showed a 60% disappearance rate of the cortex and outer medulla. CMR-I was obtained from the ratio of the cortical and inner medullary signal intensities. The T2 weighted images showed that the CMR-I was higher in rats which had been administered cadmium for more than 15 weeks compared with control rats. Change in 31P-MR spectroscopy: Signal intensity ratios with regard to high energy phosphate metabolism were detected by 31P-MR spectroscopy. The Pi/β-ATP and Pi/ATP ratio was reduced in the early groups and Pi/β-ATP and Pi/ATP ratio was increased in the delayed group after the initiation of administration of cadmium. (K.H.)