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 chlorid e or bicarbonate, on theophylline-induced hypercalciuria in the rat we re 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 sa lt was inadequate to produce a consistent, significant salt effect. A second experiment was run in which animals were given salts at 0.4 mmo l/g diet; the salt-induced pattern of calciuria was similar. After one week of salt pretreatment, rats were given diets containing theophyll ine (7.72 mumol/g diet), which induced calciuria all groups regardless of salt pretreatment. Urinary volume and urinary phosphate changes we re parallel to each other and not to the changes in urinary calcium in duced by salt or theophylline. Changes in urinary excretion of prostag landin E2 were directly proportional to changes in urinary calcium. In the rat, pretreatment with sodium bicarbonate or sodium chloride redu ces the extent of theophylline-induced diuresis, but does not reduce t heophylline-induced hypercalciuria. Further, potassium chloride increa ses and potassium bicarbonate does not reduce urinary calcium excretio n. Theophylline-induced calciuria is correlated with prostaglandin E2 excretion rates.