Some effects of acute and chronic dosing with aflatoxin B1 on rat liver nuclei.

A study has been made of changes occurring in rat liver nuclei as a result of the chronic and acute administration of aflatoxin B1. This has involved resolution of the nuclei into populations of differing ploidy by means of centrifugation in a zonal rotor. Chronic feeding of the toxin to weanling rats prevents the development of the predominant tetraploid hepatocyte nuclear population, which normally takes place during maturation. Increased populations of diploid and octaploid hepatocyte nuclei are observed. Chronic feeding of the toxin to adult animals also causes a reduction in the tetraploid population already established and, again, leads to increased numbers of diploid and octaploid nuclei. Once an abnormal nuclear population has been established by feeding the toxin, it persists until the development of hepatocarcinoma (if a 6-week carcinogenic feeding regimen has been used). The hepatomas have diploid nuclei. Labeling hepatic RNA and DNA in vivo has indicated that feeding the toxin causes a reversion to the immature distribution of DNA synthesis among the nuclear population, with little effect on the pattern of distribution of RNA synthesis. Acute administration of aflatoxin to adult rats also causes a reduction in the size of the tetraploid population, with increased proportions of diploid, octaploid, and higherploidy nuclei. These results are discussed in terms of a dual action of the toxin, antimitotic and necrogenic, and the possible relationship of these to the carcinogenic process.