To the Editor:—
In the inherited hepatic porphyria diseases, acute attacks may be precipitated by low doses of certain sedative drugs such as barbiturates. Large doses of these drugs may induce an "experimental" or "chemical" porphyria in normal animals. We have developed an in vitro method for determining which chemicals have the potential to induce porphyria.The in vitro method we have used is described in a preliminary communication in the Journal of Biological Chemistry (238:PC2247 [June] 1963). It utilizes chick embryo liver cells grown on coverslips in primary culture. These cells respond to an inducing chemical by forming large amounts of porphyrins which can be visualized in the cells with a fluorescence microscope. The more immediate action of an inducing chemical appears to be the induction of an increase in the synthesis of δ-aminolevulinic acid synthetase, the limiting enzyme of porphyrin biosynthesis in the chick embryo liver cells.