Effects of separate and combined treatments with gamma radiation and diethylnitrosamine in neonatal rats on the induction of altered hepatocyte foci and hepatic tumors

To characterize the effects of combined treatments with gammaradiation and diethylnitrosamine (DEN) on the induction of histochemicallydetectable altered hepatocyte foci and hepatic tumors, we assessedthe yields of these lesions in the livers of 150-day-old ratsthat had been treated neonatally with a single dose of gammaradiation (75 red, whole body) and i.p.-injected DEN (0.15 µmol/gbody wt), either separately or in combination. The combinedtreatments involved the administration of the two stimuli inboth possible sequences, with the interval between treatmentsset at 1 h. The focus population was examined for two histochemicalmarkers (elevated gamma-glutamyl transpeptidase [GGT(+)J andiron exclusion [FE(–)], giving rise to three detectablefocus phenotypes, i.e. GGT(+) foci, FE(–) foci, and GGT(+),FE(–) foci. Frequencies of the three phenotypes were quantitatedthrough the use of serial frozen sectioning techniques and computer-assistedimage analysis. GGT(+) focus induction was synergistkally enhancedby the combined treatment irrespective of the order in whichthe two stimuli were administered; the remaining two phenotypesdid not show such enhancement. The magnitude of the GGT(+) focusresponse was significantly greater when the treatment sequencewas gamma DEN as opposed to DEN gamma. Tumor yields in ratsreceiving combined gamma-DEN treatment were similar to thosein rats receiving the DEN alone, irrespective of the gamma-DENtreatment sequence. These results suggest that (i) phenotypicallydistinguishable lesions, including foci with different histochemicalmarker patterns and tumors, originate from specific types ofdamage at different genetic loci and are developmentally independent;and (ii) the expression of the GGT(+) marker per se in alteredhepatocyte foci is not a reliable index of incipient hepaticneoplasia.