Effect of diets high in sodium and potassium on the magnitude of theophylline-induced hypercalciuria in the rat.

The effects of dietary sodium and potassium, given as salts of chloride or bicarbonate, on theophylline-induced hypercalciuria in the rat were investigated. In experiment 1, rats fed diets containing 0.3 mmol/g diet NaCl, KCl, NaHCO3, or KHCO3 exhibited a calciuria of NaCl > KCl > controls = NaHCO3 = KHCO3. This study indicated that cation effects were dependent on the accompanying anion, however the dose of added salt was inadequate to produce a consistent, significant salt effect. A second experiment was run in which animals were given salts at 0.4 mmol/g diet; the salt-induced pattern of calciuria was similar. After one week of salt pretreatment, rats were given diets containing theophylline (7.72 mumol/g diet), which induced calciuria all groups regardless of salt pretreatment. Urinary volume and urinary phosphate changes were parallel to each other and not to the changes in urinary calcium induced by salt or theophylline. Changes in urinary excretion of prostaglandin E2 were directly proportional to changes in urinary calcium. In the rat, pretreatment with sodium bicarbonate or sodium chloride reduces the extent of theophylline-induced diuresis, but does not reduce theophylline-induced hypercalciuria. Further, potassium chloride increases and potassium bicarbonate does not reduce urinary calcium excretion. Theophylline-induced calciuria is correlated with prostaglandin E2 excretion rates.