Studies on the mechanism of the changes in serum and liver gamma-glutamyl transpeptidase activity. II. Experimental hexachlorobenzene porphyria in rabbits.

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