Time dependence of hematoporphyrin distribution in selected tissues of normal rats and in ascites hepatoma.

The distribution of hematoporphyrin was determined in normal rats and in rats bearing ascites hepatoma as a function of time after i.p. injection of 10-20 mg/kg of dye. In both cases, hematoporphyrin displayed a high affinity for the tumor cells. At 20 mg/kg, the maximum difference between the amount of hematoporphyrin accumulated in the tumor and in the liver was obtained at 12 h after injection (tumor/liver ratio = 28). Our results suggest that hematoporphyrin is almost exclusively metabolized in the liver and excreted via the biliary tract, whereas only minor amounts are metabolized in the tumor cells. Moreover, the binding between the porphyrin and tumor cells is competitive with serum protein binding.