Increased Renal Tubular Reabsorption of Calcium and Magnesium by the Offspring of Diabetic Rat Pregnancy

Diabetic pregnancy has a marked influence on offspring calcium and magnesium homeostasis. Urinary excretion of calcium and magnesium is reduced, yet offspring of diabetic pregnancy exhibit hypomagnesemia and hypocalcemia. The aim of this study was to measure renal hemodynamic and tubular function in the offspring of diabetic (OD) and control, nondiabetic (OC) rats at 4 and 8 wk of age to determine the glomerular and tubular mechanisms through which renal calcium and magnesium handling are programmed in utero. The fraction of filtered calcium that was excreted was significantly lower in OD at both 4 and 8 wk of age [8 wk: OC (n = 6), 11.8 ± 2.9 versus OD (n = 5), 4.3 ± 0.6%; p < 0.05] and that of magnesium was lower at 8 wk of age [OC (n = 6), 42.4 ± 7.5 versus OD (n = 5), 13.0 ± 1.7%; p < 0.01]. This increased reabsorption occurred despite an elevated GFR in OD. These findings clearly indicate that tubular reabsorptive mechanisms for calcium and magnesium are increased markedly in OD. Serum PTH concentration was reduced in 8-wk-old OD [OC (n = 7), 539.4 ± 142.1 versus OD (n = 9), 174.3 ± 69.4 pg/ml; p < 0.05], consistent with previous reports in human infants. Taken together, these observations suggest that the basis for the altered renal magnesium and calcium handling in OD involves increased tubular transport activity and possibly increased sensitivity of these mechanisms to PTH.