Comparison of the glucuronidation ability of liver microsomes from rats treated with 3-methylcholanthrene or phenolic antioxidants

Abstract

1. UDP-glucuronyltransferase activity was studied in hepatic microsomal preparations isolated from female Sprague-Dawley rats treated with either 3-methylcholanthrene, butylated hydroxyanisole, propyl gallate, ethoxyquin or a combination of 3-methylcholanthrene and butylated hydroxyanisole. 2. The substrates p-nitrophenol, 1-naphthol and phenolphthalein were used. With p-nitrophenol all treatments, except propyl gallate, caused a significant increase in activity over the control value; the combined treatment of 3-methylcholanthrene and butylated hydroxyanisole gave an additive response when compared to each treatment used singly. With 1-naphthol as substrate, 3-methylcholanthrene and 3-methylcholanthrene + butylated hydroxyanisole caused 8-fold increases in activity compared to the 2-3 fold increased caused by the other treatments. When phenolphthalein was used, all treatments increased activity to the same extent. 3. When the assays were repeated with various concentrations of each substrate, the results revealed that, except where phenolphthalein was used, distinguishable differences in the activity of each microsomal preparation were discernible, the most significant being the bimodal response of each preparation to low and high concentrations of p-nitrophenol.

Gene Expression Dose-Response of Liver with a Genotoxic and Nongenotoxic Carcinogen

“…The phase II enzyme activities, UDP-glucuronosyl transferase (UGT) and glutathione- S -transferase (GST) were both assayed using a 96-well format. Microsomal UGT activity, which detects several isoforms, was measured using a modified spectrophotometeric method of Stewart and McCrary (1987) and 1-naphthol as a substrate. Cytosolic GST activity, which also included several isoforms, was measured using a spectrophotometric method described by Habig and Jakoby (1981), with CDNB (1-chloro-2,4-dinitrobenzene) as a substrate.…”

Effect of strain and diet upon constitutive and chemically induced activities of several xenobiotic-metabolizing enzymes in rats

“…The activities of the Phase II enzymes, UDP-glucuronosyl transferase (UGT), sulfotransferase (ST), and glutathione-S-transferase (GST) were also assayed. Microsomal mixed isoforms of UGT activity were measured after a modification of the spectrophotometric method of Stewart and McCrary (1987) which measures the conjugation of a 1-naphthol substrate with UDP-glucuronic acid. Cytosolic alpha-, mu-, and pi-GST were measured as a net activity using the spectrophotometric method outlined by Habig and Jakoby (1981), which measured the conjugation of the substrate CDNB (1-chloro-2,4-dinitrobenzene) with glutathione.…”