NUCLEAR LESIONS DURING RAT HEPATOCARCINOGENESIS .1. MEASURING THE SISTER-CHROMATID EXCHANGES DURING INITIATION, PROMOTION AND PROGRESSION OF RAT HEPATOCARCINOGENESIS INDUCED WITH DIETHYLNITROSAMINE

Cytogenetic endpoints such as sister-chromatid exchanges (SCEs), chrom osomal aberrations and micronuclei (MNs) have been widely used as indi cators of genetic damage. However, no systematic attempts have been ma de to correlate the levels of these cytogenetic endpoints with the dif ferent steps of carcinogenesis. In the present report, the induction, accumulation and persistence of SCEs and high frequency cells (HFCs) w ere measured in liver cells during the initiation, promotion and progr ession steps of rat hepatocarcinogenesis induced by diethylnitrosamine (DEN). The results indicate that lesions leading to SCEs accumulate d uring initiation only. When DEN administration is longer than the dura tion of this first step, SCE values stabilize. After stopping the carc inogenic treatment, the SCE levels decrease to control values whether or not promotion and progression occur.