Influences of diethylnitrosamine on longevity of surrounding hepatocytes and progression of transplanted persistent nodules during phenobarbital promotion of hepatocarcinogenesis.

The possibility that phenobarbital (PB) selectively promotes liver nodule development by decreasing survival of surrounding hepatocytes previously exposed to diethylnitrosamine (DENA) was evaluated. Livers of F-344 rats were labelled with [3H-methyl]-thymidine (3H-TdR) during developmental or regenerative growth. Neonatal rats given 3H-TdR between days 3 and 12 were subjected at 12 weeks of age to partial hepatectomy (PH) followed 24 hr later by DENA (10 mg/kg) or saline. Subsequent administration of PB (0.1% in drinking water) for 28 weeks reduced total liver label to 46 +/- 10% (saline group) or 40 +/- 4% (DENA group). Adult male rats initiated with DENA (200 mg/kg) and later labelled with 3H-TdR after PH also lost total liver label during 28 weeks' promotion with PB (0.05% in water) at rates similar to those exhibited by noninitiated rats given PB, and by DENA-treated or control rats not given PB. Large persistent (12 weeks) liver nodules generated by DENA in the Solt-Farber model were transplanted as small fragments into the spleens of syngeneic rats previously given 0, 100 or 200 mg/kg of DENA. Subsequent exposure to PB (0.05% in drinking water for 40 weeks) or Aroclor 1254 (6 X 300 mg/kg per month) promoted nodule and cancer development only in livers of DENA-initiated recipients. Surviving transplanted nodules remained as small microscopic clusters even after 40 weeks of promotion. However, PB increased transplant survival (50% vs. 21% in controls) whereas Aroclor reduced it to 8%. These findings indicate that promotion of liver nodules by PB occurs without enhanced mortality of surrounding hepatocytes previously damaged by DENA. They further suggest that promoters such as PB and PCBs do not directly influence the progression of established persistent nodules.