Enhancement of the clonability of adult parenchymal hepatocytes with the liver tumor promoter phenobarbital.
An in vivo clonogenic assay system was utilized to investigate the effect of the tumor promoter, phenobarbital (PB), on adult parenchymal hepatocyte proliferation. Enzymatically dispersed hepatocytes from female Fischer 344 rats were injected into the interscapular and mammary fat pads of isogeneic recipient animals where they proliferate to form hepatocyte colonies within 3 weeks. The number of hepatocytes required to form a colony in 50% of the transplantation sites (LND50) was 23 700 cells and 520 cells when normal adult liver cells were injected into non-hepatectomized and 2/3 hepatectomized normal recipient animals, respectively. Thus, a partial hepatectomy increased the hepatocyte clonogenicity by a factor of 40. A 2-week pre-treatment of both the donor and recipient animals with PB (0.1% in the drinking water) significantly increased the clonogenicity of the liver cells when transplanted into non-hepatectomized (15-fold) and 2/3 hepatectomized (2-fold) animals. However, PB treatment of the recipient animals was not required for the majority of this mitogenic effect since the clonability of PB-treated donor cells was increased (92% of the maximum stimulation observed) even when they were transplanted into untreated control animals. Furthermore, the PB-induced effect on hepatocyte clonability was reversible since the removal of PB from the donor animals 2 weeks prior to their use reduced the clonability of the hepatocytes (LND50 = 20,500 cells) to that observed for cells which were never exposed to PB. These results are consistent with the postulate that rather than PB being directly mitogenic, it primarily increases the clonability of adult parenchymal hepatocytes by inducing a reversible cellular alteration which enhances their responsiveness to endogenous growth stimuli.
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D004247:DNA / Q000096:biosynthesis; D005260:Female; D006498:Hepatectomy; D008099:Liver / Q000187:drug effects* / Q000473:pathology; D008114:Liver Neoplasms, Experimental / Q000139:chemically induced; D016031:Liver Transplantation; D010634:Phenobarbital / Q000633:toxicity*; D051381:Rats; D011916:Rats, Inbred F344
D004247:DNA; D010634:Phenobarbital