Response of renal transplanted patients to oral calcium load

In a previous study we demonstrated that cyclosporin-treated renal transplanted patients have a reduced 1,25(OH)₂D3 synthesis in comparison with azathioprine-treated transplanted patients. To assess the impact of this defect on intestinal calcium transport we compared the plasma calcium variation and the urinary calcium excretion in 14 cyclosporin-treated and in 12 azathioprine-treated patients, in fasting conditions and 4 hours after an oral calcium load (1 g). In ten cyclosporin patients we also correlated cyclosporin plasma values with plasma 1,25(OH)₂D3 values before and after a 25(OH)D3 oral load. After the oral calcium load, plasma and urinary calcium increased significantly in the azathioprine group, while remaining unchanged in the cyclosporin group. A negative correlation between plasma concentrations of cyclosporin and the increment in 1,25(OH)₂D3 after 25(OH)D3 oral load was also observed. Thus, our data suggest that cyclosporin impairs 1-alpha hydroxylase activity and alters the response to an oral calcium load.