The mechanism responsible for the changes in serum and liver γ-glutamyl
transpeptidase (γ-GT) activity was studied in a model of experimental hexachlorobenzene
porphyria in rabbits. Porphyria followed the administration of hexachlorobenzene in
doses of 280 μmol • kg^-1 body weight, which were given daily through a gastric tube over
a 20-day period.
Serum γ-GT activity and the activities of the lysosomal enzymes β-N-acetylglucosaminidase
and α-mannosidase were increased, whereas L-aspartate: 2-oxoglutarate aminotransferase
and L-alanine: 2-oxoglutarate aminotransferase remained unaltered. There was
a considerable increase in liver microsomal protein, γ-GT, cytochrome P-450, anilinehydroxylase,
aminopyrine-demethylase and δ-aminolevulinic acid synthase. In the liver
γ-GT was detected in the microsomes as well as in the cytoplasm where enzymatic activity
was higher. The high correlation coefficient between liver γ-GT, cytochrome P-450 and δ-
aminolevulinic acid synthase witnesses a hexachlorobenzene-induced γ-GT formation in
the liver. A statistically significant correlation between serum and liver γ-GT activity was
also found. These data strongly suggest that the increase in serum γ-GT activity may
result from the induction of the enzyme in the liver.
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