Lithium administration and urinary electrolyte excretion in the rat.

The effect of lithium administration on urine eletrolyte excretion is controversial with reports of increased, unaltered and reduced excretion rates of sodium, potassium, calcium, magnesium and inorganic phosphate. Therefore rats treated with daily intraperitoneal lithium chloride for 3 weeks were studied and were found to have marked fluctuations in electrolyte excretion when compared to untreated rats. Although lithium-treated rats were always polyuric, urinary sodium, potassium and calcium excretion was significantly elevated immediately following intraperitoneal lithium but their excretion rates then returned towards normal. Magnesium excretion was initially unaltered by lithium administration (6.8 +/- 1.3 compared with 7.3 +/- 1.7 mumol/100 g/8 h) but then decreased (2.5 +/- 0.5 with 7.8 +/- 1.1 mumol of magnesium/100 g/8 h; p less than 0.01) during the final collection period. A persistent phosphaturia also occurred with lithium treatment (122 +/- 5 compared with 92 +/- 6 mumol/100 g body weight/24 h). Despite these significant changes in renal electrolyte transport with lithium administration, similar changes were also noted in rats similarly treated with equimolar doses of sodium chloride although polyuria did not occur. Thus it is postulated that lithium ions exert their effect on renal electrolyte transport in a similar manner to that of sodium.