Piomelli et al1 studied events both in vitro and in vivo. Protoprophyrin diffusion from intact human protoporphyric erythrocytes into plasma was shown in vitro. Rapid in vivo disappearance of intraerythrocytic protoporphyrin as a function of increasing cell age was shown in the blood of several protoporphyric patients, and rates for this were determined. The discussion section of that report contains the following commentary and also notes the contributions of Scholnick et al2 and Schwartz et al3:Diffusion of PP from EPP erythrocytes into the plasma had been suspected by the elevation of plasma PP observed in this condition (1). Recently, Sholnick [sic] et al. suggested that the majority of plasma PP in EPP may be of hepatic origin, on the basis of in vivo studies using radioactive precursors (7). Their interpretation was based in part on the assumption that diffusion of PP from the erythrocytes
Poh-Fitzpatrick MB, Mathews-Roth MM. Effect of Oral Carotenoid Therapy on Erythrocyte Protoporphyrin Levels-Reply. Arch Dermatol. 1980;116(8):864. doi:10.1001/archderm.1980.01640320013008
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