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The study of the gamma-glutamyl transpeptidase (GTase) in colon of adult rats showed that in the sequence: duodenum, jejunum, ileum, cecum and colon, the colon has the lowest activity. There are, on the other hand, relatively small differences between GTase activities in the ascending, transverse and descending portions of the large intestine. GTase activity in the colon of neonatal rat is several times higher than in the colon of adult rats. Colon adenocarcinoma induced by 1,2-dimethylhydrazine were found to have a much higher GTase activity than the homologous normal tissue. Because these tumors resemble human colonic adenocarcinomas, it is suggested that the assay of GTase levels of human colon mucosa might be of potential value in the diagnosis of neoplastic changes.

Continued administration of several hepatocarcinogens led to an increase in the concentration of glutathione (GSH) in the livers of intact, but not of hypophysectomized or adrenalectomized rats. The concentration of GSH remained high untill the development of hyperplastic nodules. Subsequently, the concentration of GSH dropped to the normal level or below. A single dose of 3'-methyl-4-dimethylaminoazobenzene (3'-Me-DAB) produced an increase of GSH which, within a certain range, depended upon the amount of the carcinogen. In well differentiated, slowly growing hepatomas, the concentration of GSH approached the level in normal adult rat liver. On the other hand, in nondifferentiated and rapidly growing hepatomas, GSH was only 30-40% of that in normal liver. The activity of gamma-glutamyl transpeptidase (GTase) increased within 24-48 hours after a single large dose of 3'-Me-DAB. Continued feeding of 3'-Me-DAB led to an exponential increase of GTase. During hepatocarcinogenesis, the level of GTase activity corresponded to the degree and size of pathologic changes produced in rat liver. Chloramphenicol partially inhibited the increase of GTase induced by 2-acetylaminofluorene. Pretreatment with 3-methylcholanthrene partially inhibited the increase of GTase that had been induced by a single dose of 3'-Me-DAB. Puromycin partially inhibited the increase of GTase induced by several doses of dimethylnitrosamine. These observations indicated a close connection between the activation of GTase and chemical carcinogenesis in rat liver. Measurements of GTase activity in 12 Morris hepatomas supported this conclusion; their GTase levels were greatly elevated compared with that in normal adult rat liver.

The concentration and total amount of DNA in the livers of SD rats fed 3'-methyl-4-dimethylaminoazobenzene (3'-Me-DAB) gradually increased and reached a maximum in developing tumors. In SD rats fed 3'-Me-DAB plus disulfiram (DSF), the concentration of DNA was higher than in controls, but it soon became stabilzed and the total amount of DNA in the liver did not differ substantially from that in rats fed DSF alone. In rats given 3'-Me-DAB, neoplastic nodules and liver carcinomas appeared after 3 months, but in those fed both compounds these formations were absent even after 6 months. The activity of gamma-glutamyltransferase (GT-ase), a marker of chemically induced carcinogenesis in rat liver, gradually increased to extremely high levels in tumors even after 75 days when the diet of the animals was changed to a normal one. In rats fed 3'-Me-DAB plus DSF, GT-ase activity increased for the greater part of 80 days, gradually leveled off around the 100th day, and returned to almost normal levels when the rats were given a normal diet after 100 days. We concluded that DSF 1) did not interfere with 3'-Me-DAB-induced proliferation of preneoplastic cells and the increase in GT-ase associated with this reversible adaptation to the influx of 3'-Me-DAB; and 2) inhibited malignant transformation and, consequently, prevented the formation and proliferation of neoplastic cells and the increase in constitutive GT-ase related to neoplasia.