Enhancing effect of co-administration of polychlorinated biphenyls and diethylnitrosamine on enzyme-altered islands induced by diethylnitrosamine in rat liver.

The effect of co-administration of diethylnitrosamine (DEN) and Clophen A 50, a commercial mixture of polychlorinated biphenyls (PCB), on pre-neoplastic enzyme-altered islands in livers of female Sprague-Dawley rats was studied. The islands were identified by the loss of adenosine-5'-triphosphatase (ATPase), emergence of gamma-glutamyltranspeptidase (GGTase) and glycogen storage after fasting. DEN was given p.o. (0.4 or 4 mg/kg body wt respectively) twice a week for 11 consecutive weeks. Clophen A 50 (1 or 5 mg/kg body wt respectively) was given alternatively three times a week for 11 weeks. Four groups of rats each received either DEN or PCBs in the respective doses. Control animals were treated with the vehicle or remained untreated. All animals were killed at week 12. In rats treated with 4 mg DEN/kg body wt approximately 80 ATPase-deficient islands/cm2 were observed. Additional treatment with Clophen A 50 enhanced the island number 3-fold. Treatment with 0.4 mg/kg body wt DEN induced 17 islands/cm2. Additional application of Clophen A 50 enhanced the island number approximately 3-fold. The total island area was enhanced to the same extent in both groups. The island incidence in PCB-treated rats and controls was below 1/cm2 with all markers tested. The results indicate that PCBs may exhibit a co-carcinogenic activity.