gamma-Glutamyltranspeptidase in dimethylbenz[a]anthracene-induced mammary adenocarcinomas and in livers of tumor bearing rats.

A single dose of dimethylbenz[a]anthracene (DMBA) at 20 mg/kg resulted in 100% incidence of intraductal mammary adenocarcinomas in Wistar rats, the large tumors averaging 1.87 +/- 0.45 g. gamma-Glutamyltranspeptidase activities were elevated in DMBA-induced mammary adenocarcinomas relative to lactating mammary tissue in all fractions examined: 18.8-fold in homogenates; 22.1-fold in particulate fractions; and 5.7-fold in supernatant fractions. In DMBA-induced mammary adenocarcinomas, gamma-glutamyltranspeptidase was 95% particulate, 5% supernatant, whereas in lactating mammary tissue, gamma-glutamyltranspeptidase was equally distributed between particulate and supernatant fractions. Particulate gamma-glutamyltranspeptidase from DMBA-induced mammary adenocarcinomas as well as lactating mammary tissue displayed classical Michaelis-Menten characteristics: for the adenocarcinoma enzyme Km was 2.5 nM and Vmax 200 nmol mg-1 min-1; for mammary tissue enzyme Km was 2.5 nM and Vmax 11.1 nmol X mg-1 X min-1. Both particulate enzymes were activated at 50 degrees C relative to 37 degrees C to the same extent: 1.37-fold. The activities of gamma-glutamyltranspeptidase were increased 1.8-fold in the livers of rats bearing DMBA-induced mammary adenocarcinomas relative to age-matched controls. Plasma levels of gamma-glutamyltranspeptidase were also increased 1.6-fold in tumor bearing rats. There was no observable sign of liver damage in tumor bearing rats; plasma glutamic pyruvic transaminase levels were normal in these animals. Blood glucose levels were elevated 17% in rats bearing DMBA-induced mammary adenocarcinomas compared to age-matched controls, although plasma insulin levels were the same in both groups: 35.4 +/- 3.5 microIU/ml for the former; 31.9 +/- 3.1 microIU/ml for the latter.