It has been suggested by various workers that porphyrin concerned in body metabolism arises during the process of formation rather than destruction of hemoglobin1 and that the rate of excretion of coproporphyrin in the urine and bile depends chiefly on the rate of production of porphyrin to be excreted (a series I isomer arising as a useless by-product and any series III isomer not immediately utilized in hemopoiesis) and the efficiency of the liver, which is the more important organ involved in excretion of porphyrin.2 The kidneys normally excrete a small fraction of the total porphyrin excreted, but in the event of hepatic damage they excrete increased amounts, a mechanism similar to that for the excretion of bile pigments. It has been claimed that in complete obstruction of the common bile duct the total excretion of coproporphyrin is not altered but that coproporphyrin practically or entirely disappears from
NESBITT S, SNELL AM. EXCRETION OF COPROPORPHYRIN IN HEPATIC DISEASE: II. URINARY AND FECAL EXCRETION IN BILIARY OBSTRUCTION. Arch Intern Med (Chic). 1942;69(4):582–588. doi:10.1001/archinte.1942.00200160033004
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