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Original Articles

Filterable Plasma Concentration, Glomerular Filtration, Tubular Balance, and Renal Clearance of Heavy Metals and Organic Substances in Metal Workers

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Pages 216-221 | Accepted 21 Nov 1985, Published online: 03 Aug 2010
 

Abstract

To estimate “filterable” plasma concentration (FPx), glomerular filtration, tubular balance, and renal clearance of heavy metals and organic substances, the authors examined the regressions of the 24-hr urinary excretion on glomerular filtration rate [GFR, 24-hr endogenous creatinine (Cn) clearance] in 19 gun-metal foundry workers with blood lead (Pb) concentrations of 25–59 μg/dl. It was estimated that the proportion of FPx to total plasma concentration was on average 15,7,3,0.6,0.06, and 0.008% for Pb, cadmium (Cd), manganese (Mn), zinc (Zn), chromium (Cr), and copper (Cu), respectively. The estimated FPx value was 2.8 × 102, 4,0.08, and 2.8 × 104 μg/dl. for hippuric acid (HA), delta-aminolevulinic acid (ALA), coproporphyrin (CP), and total urinary solutes (TUS), respectively. The estimated glomerular filtration was significantly greater than the zero level for all substances but inorganic mercury (Hg). Similarly, the estimated net tubular secretion was significantly greater than the zero level for Cr, Cu, and TUS; the net tubular reabsorption was significantly greater than the zero level for Pb, ALA, and CP. The renal clearance of “filterable” plasma substance was significantly greater than GFR for Cr, Cu, and TUS and was significantly smaller for Pb, ALA, and CP. Thus the renal excretory mechanisms of substances were classified into four major categories: (1) glomerular filtration for Cd, Mn, Zn, HA, and Cn; (2) glomerular filtration and net tubular secretion for Cr, Cu, and TUS; (3) glomerular filtration and net tubular reabsorption for Pb, ALA, and CP; and (4) no glomerular filtration, i.e., suspected tubular secretion, for Hg.

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