Aberrant expression of adaptation to phenobarbital may cause selective growth of foci of altered cells in rat liver

Abstract

According to the multistage concept of carcinogenesis, promoters induce selective or preferential multiplication of initiated cells, thereby accelerating one of the rate-limiting steps in cancer formation. The driving force for this selective growth of initiated cells is not known. In normal liver, various liver tumour promoters induce expression of adaptive programmes. One such programme, induced by phenobarbital, consists of organ growth and an increase in the activity of various enzymes involved in the metabolism of lipophilic substrates. In foci of altered rat liver cells (the putative progeny of initiated cells), expression of the programme is still possible and is coupled to certain regulatory defects (excessive, unbalanced proliferation; independence from position-specific restrictions within the hepatic acinus; autonomous expression of some adaptive changes). Promoters seem to switch on this aberrant expression of the programme of adaptation, thereby leading to preferential growth of foci.