Risk of renal stone formation induced by long-term bed rest could be decreased by premedication with bisphosphonate and increased by resistive exercise

Objectives: To clarify the influence of long-term bed rest on renal stone formation and to analyze the mechanism of bed-rest-induced stone formation and prevention by bisphosphonate and bed-rest exercise. Methods: Twenty-five men aged 26–48 years and divided into control (CON: n = 9), exercise (EX: n = 9), and pamidronate (PMD: n = 7) groups, rested on a 6° head-down tilt bed for 90 days. The exercise group carried out resistive exercise every 3 days. Pamidronate (60 mg) was intravenously given 2 weeks before the initiation of bed rest. Abdominal X-ray examination and urine biochemistry were carried out during 90 days of bed rest and 90 days of reloading. Results: Renal stone formation was observed in two (22.2%) and four (44.4%) subjects in the control and exercise groups, respectively. No stone was seen in the pamidronate group. In the exercise group, urinary oxalate and phosphate excretion were significantly higher than in the control group. In the pamidronate group, urinary calcium excretion and relative supersaturation of calcium oxalate and brushite were lower than in the control group throughout the bed-rest and recovery period. Conclusion: Long-term bed-rest-induced renal stone formation was found to be induced by increased urinary calcium and subsequent crystal formation of calcium oxalate and calcium phosphate. Exercise during bed rest for the prevention of bone mineral loss and contracture might increase the risk of renal stone formation. Pamidronate is useful for the prevention of renal stone formation during and after bed rest.