Plasma aldosterone and magnesium in serum and urine during lithium treatment

Serum magnesium, urinary magnesium excretion and plasma aldosterone were determined in 8 manic-depressive before and at intervals during 3 months of lithium treatment (longitudinal study), and in 27 manic-depressive patients who had been treated with lithium for 3 months to 20 years (transversal study). In the longitudinal study urinary magnesium excretion and urine flow increased slightly after 1-3 months of therapy; serum magnesium and plasma aldosterone were unchanged. In the transversal study urinary magnesium excretion, serum magnesium and plasma aldosterone were within normal limits, and they did not differ significantly from levels in the longitudinal study. No correlation was found between serum magnesium or urinary magnesium excretion and plasma aldosterone in either study. The results indicate that changes in urinary magnesium excretion during lithium therapy are not mediated via changes in plasma aldosterone, but may be secondary to diminished renal water reabsorption induced by lithium.