PIVOTAL ROLE OF HEPATOCELLULAR REGENERATION IN THE ULTIMATE HEPATOTOXICITY OF CCL4 IN CHLORDECONE-PRETREATED, MIREX-PRETREATED, OR PHENOBARBITAL-PRETREATED RATS

Our earlier histomorphometric and biochemical studies suggested that t he progressive phase of the interactive toxicity of chlordecone (CD) CCl4 involves suppression of hepatocellular regeneration. The objecti ve of the present work was to correlate hepatocellular regeneration wi th CCl4 (100 mul/kg)-induced hepatotoxicity in rats maintained for 15 days on a normal (N) diet, relative to the regenerative response in ra ts maintained on a diet containing either 10 ppm CD, 225 ppm phenobarb ital (PB), or 10 ppm mirex (M). Hepatocellular regeneration was assess ed by measuring DNA and H-3-thymidine (H-3-T) incorporation, followed by autoradiographic analysis of liver sections. Hepatotoxicity was ass essed by measuring plasma transaminases (aspartate and alanine) follow ed by histopathological observations of liver sections for necrotic, s wollen, and lipid-laden cells. Lethality studies were also carried out to assess the consequence of hepatotoxicity on animal survival. Dieta ry 10 ppm CD potentiated the hepatotoxicity of CCl4 to a greater exten t than PB or M, as evidenced by elevations in plasma enzymes. Although the serum enzymes were significantly elevated in PB rats in contrast to the slight elevations in N and M rats, they returned to normal leve ls by 96 hr. However, serum enzyme elevations in CD rats were progress ive with time until death of the animals. Actual liver injury by CCl4 was greater in PB- than in CD-pretreated rats, as evidenced by histopa thological observations. A 100% mortality occurred in CD-pretreated ra ts at 60 hr after CCl4 administration, whereas no mortality occurred i n either N-, M-, or PB-pretreated rats, indicating recovery from liver injury. Hepatocellular nuclear DNA levels were significantly decrease d starting at 6 hr after CCl4 administration to CD-pretreated rats, bu t not in M- or PB-pretreated rats. H-3-T incorporation into nuclear DN A as well as percentage of labeled cells showed a biphasic increase in N rats: 1 at 1-2 hr, and the other at 36-48 hr after CCl4 administrat ion. However, only 1 peak of H-3-T incorporation at 36-48 hr was obser ved in the CD + CCl4 combination, which was also significantly lower w hen compared to that observed after the M or PB + CCl4 combination tre atments. These findings suggest that there is recovery in N-, PB-, or M-pretreated rats from CCl4-induced injury by virtue of the stimulated hepatocellular regeneration and tissue repair. In CD-pretreated rats, CCl4 toxicity is progressive because of mitigated hepatocellular rege neration (at 2-6 hr), supporting the concept that hepatocellular regen eration plays a critical role in determining whether hepatotoxicity be comes permissively progressive or actively regressive, owing to tissue repair mechanisms. In the absence of hepatocellular regeneration and tissue repair, progressive liver injury leads to sustained hepatic fai lure (24 hr), culminating in animal death. These findings underscore t he importance of assessing additional parameters of hepatobiology indi cative of the ultimate outcome of toxicity rather than relying solely on indices of liver injury, particularly during the inflictive phase o f chemically-induced liver injury.