STUDIES OF THE RENAL EXCRETION OF MAGNESIUM IN MAN*†

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Abstract
Factors influencing the renal excretion of Mg were studied by acute clearance techniques and experimental procedures including infusions of sodium lactate, sodium acetate, sodium bicarbonate, acetazolamide, probenecid, p-aminohippurate, Mg salts, Ca salts, and mercurial diuretics. Seventy studies in normal men were performed. The excretory pattern for Mg was distinctly different from that of simultaneously observed excretion rates for Na, K, Cl and PO4. Mg and Ca excretion showed a similarity of behavior with most test procedures, but not with acetazolamide, suggesting that renal mechanisms regulating excretion of Mg are also, at least partly, separate from those of Ca. Changes in glomerular filtration rate, urine flow, renal plasma flow, plasma Mg, and acid-base factors did not correlate well with Mg excretion in most of the conditions tested. Although tubular secretion of Mg cannot be excluded, indirect evidence suggests that tubular reabsorp-tion is the main regulatory process and may operate normally at or near saturation.