Circadian Rhythms in the Urinary Excretion of Metals and Organic Substances in “Healthy” Men

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Abstract
Circadian rhythms in the urinary excretion of metals and organic substances were examined in 10 healthy men under conditions of water loading and restriction. Four characteristic rhythms were observed: decreased excretion during the night for Pb and urinary flow rate, decreased excretion of hippuric acid, .delta.-aminolevulinic acid, coproporphyrin, creatinine and total urinary solutes during the night and morning hours, increased excretion of Hg and Zn during the morning hours and no significant variation for Cu. Excretion of Pb, hippuric acid, .delta.-aminolevulinic acid and total urinary solutes was significantly correlated with urinary flow rate and creatinine excretion, which suggested that their circadian rhythms were the consequence of reduced glomerular filtration and increased reabsorption by the distal tubule and collecting duct during the night and morning hours. The Hg and Zn rhythms resulted partly from increased reabsorption during the night hours; the coproporhyrin rhythm reflected reduced glomerular filtration of coproporphyrinogen during the night and morning hours.