The Biphasic Change of Cytosolic Acetyl‐CoA Hydrolase in Rat Liver during 3′‐ Methyl‐4‐dimethylaminoazobenzene Hepatocarcinogenesis

When Donryu male albino rats were given diet containing 0.06% 3′–methyl‐4‐dimethyl‐ aminoazobenzene (3′–Me‐DAB) for 20 weeks, the activity of cytosolic acetyl‐CoA hydrolase in their livers decreased to about one‐third the initial level in week 2, returned to the control level in week 7, and then decreased again to about one‐tenth of the control in week 20. These changes in enzyme activity were parallel with changes in the amount of enzyme protein determined by ELISA. In 3′–Me‐DAB‐resistant rats, however, the enzyme activity and enzyme protein remained within the normal range during administration of 3′–Me‐DAB‐containing diet for 20 weeks and no tumors were detectable macroscopically. Interestingly, the biphasic change in this enzyme activity was inversely associated with the well known change of γ‐glutamyltranspeptidase activity during azo‐dye‐induced hepatocarcinogenesis.