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

Background: Lower plasma magnesium concentrations areassociated with clinical problems such as arrhythmias and hypertension.Plasma magnesium concentration is tightly controlled by the kidney.Modifying renal magnesium threshold may provide a means to increase theplasma magnesium concentration. Since evidence has been presented thatpotassium deficiency by itself may increase renal magnesium loss, thehypothesis that elevating plasma potassium would result in an increase inplasma magnesium concentration was tested in healthy volunteers.Methods: Plasma potassium was raised in nine healthyvolunteers by oral administration of 20 mg amiloride daily during 3 weeks.Magnesium metabolism was assessed before and after this period by plasmalevels, urinary magnesium excretion and fractional magnesium excretion, andmagnesium loading test (MLT). This MLT allows calculation of renalretention of magnesium load. Results: Basal plasmamagnesium levels (0.84±0.07 vs0.84±0.05 mmol/l) as well as urinary magnesium excretion(4.37±1.73 vs 3.67±1.37mmol/day) and erythrocyte magnesium levels (1.72±0.16vs 1.76±0.14 mmol Mg/l red blood cells)were similar before and on amiloride. Plasma potassium rose significantlyon amiloride (3.64±0.24 vs4.07±0.54 mmol/l, P <0.05). No change was observed inmagnesium retention with the MLT: 22.7±26.7vs 29.2±20.6% (P=0.5).Conclusions: Despite an increased plasma potassiumconcentration, no change was observed in plasma magnesium levels, urinarymagnesium excretion or renal magnesium retention of an intravenouslyadministered magnesium load. This indicates that increasing plasmapotassium within the normal range does not modify the renal magnesiumthreshold.