Increased kidney glucose utilization induced by cyclosporine: lack of relation to magnesium excretion

Cyclosporine enhances D-[5-3H]glucose utilization in homogenates of rat kidney medulla but not kidney cortex or liver. This is true whether cyclosporine is added to fresh tissue homogenates or is given to rats prior to sacrifice. Through the use of isolated perfused rat kidneys, an attempt was made to relate increased glucose utilization by cyclosporine to a possible consequence of cyclosporine nephrotoxicity, viz., loss of magnesium in urine. Although an enhanced rate of glucose utilization by cyclosporine was evident in isolated kidneys, glucose consumption was not related to urinary magnesium loss. In fact, kidneys from cyclosporine-treated rats actually showed a normal or even diminished urinary magnesium loss. The data suggest that cyclosporine-induced magnesium imbalance may be extrarenal in origin and that the kidney medulla may be a primary site of the nephrotoxic action of cyclosporine since the drug increases glucose utilization at this site.