Renal handling of 'filterable' plasma metals and organic substances in man

To estimate the plasma 'filterable' form concentration, glomerular filtration and tubular reabsorption in man for metals and organic substances, the regressions of the 24-h urinary excretion of lead (Pb), inorganic mercury (Hg), delta-aminolevulinic acid (ALA) and coproporphyrinogen (CP-gen) on glomerular filtration rate were examined. The regressions were significant for ALA in two 'healthy' men examined and for Pb and for CP-gen in one of them. From these data, it was estimated that the plasma concentration of 'filterable' Pb was approximately 0.01 microgram dl-1; the ALA concentration was 2.3 and 4.5 micrograms dl-1; and CP-gen was 0.11 microgram dl-1. Similarly, the filtered loads of Pb, ALA and CP-gen were assumed to be nearly twice as large as their urinary excretion. Hg was not considered to undergo glomerular filtration.