Effect of an increase in the plasma potassium concentration on renal magnesium handling in healthy volunteers

Background. Lower plasma magnesium concentrations are associated with clinical problems such as arrhythmias and hypertension. Plasma magnesium conc~nt.ration is tightly controlled by the kidney. Modifying renal magnesium threshold may provide a means to increase the plasma magnesium concentra­ tion. Since evidence has been presented that potassium deficiency by itself may increase renal magnesium loss, the hypothesis that elevating plasma potassium would result in an increase in plasma magnesium concentra­ tion was tested in healthy volunteers. Methods. Plasma potassium was raised in nine healthy volunteers by oral administration of 20 mg amiloride daily during 3 weeks. Magnesium metabolism was as~essed before and after this period by plasma levels, ~nnary m~gnesium excretion and fractional magnes­ 1U~ excretion, and magnesium loading test (MLT). ThIS MLT allows calculation of renal retention of a magnesium load. Results. Basal plasma magnesium levels (0.84±0.07 vs 0.84 ±0.05 mmoljl) as well as urinary magnesium excretion (4.37 ± 1.73 vs 3.67 ± 1.37 mmoljday) and erythrocyte magnesium levels (1.72±0.16 vs 1.76±0.14mmol Mg/l red blood cells) were similar before and on amiloride. Plasma potassium rose signi­ ficantly on amiloride (3.64 ± 0.24 vs4.07 ±0.54 mmoljl, P<0.05). No change was observed in magnesium retention with the MLT: 22.7±26.7 vs 29.2+20.6% (P=0.5). Conclusions. Despite an increased plasma potassium concentration, no change was observed in plasma magnesium levels, urinary magnesium excretion or ~enal magnesium retention of an intravenously admin­ istered magnesium load. This indicates that increasing plasma potassium within the normal range does not modify the renal magnesium threshold.