Selective changes in cytochrome P-450 and UDP-glucuronosyltransferase subpopulations following partial hepatectomy in rats

Following 65% hepatectomy in adult male rats, the cytochrome P-450 in the residual liver decreased continuously from 1.0 to approximately 0.5 nmol/mg protein over a period of 2 to 3 days, and then recovered slowly to presurgery values by 14 days. In contrast UDP-glucuronosyltransferase activity (per mg protein) declined (25 to 40% depending on the aglycone used to assay the enzyme) for only 1 day, with a rapid recovery to presurgery values by 5 days. Transferase activity toward estrone overshot control values during recovery and was elevated above its presurgery value at 7 days. The changes in drug-metabolizing enzymes were accompanied by a surge in mitosis which peaked at 2 days. The extent of the decline in cytochrome P-450 and the increase in the mitotic index were proportional to the amount of liver removed. The decline in cytochrome P-450 was selective for cytochrome P-450 which elutes in the void volume upon anion-exchange high-pressure liquid chromatography of solubilized microsomes. Accompanying the decline in cytochrome P-450 in this eluate was a decline in protein(s) with a molecular weight of 51,500. The decline in cytochrome P-450 also caused disproportionate decreases in microsomal ethylmorphine N-demethylase activity and metabolic-intermediate complex formation from norbenzphetamine and SKF 525-A, but not in p-nitroanisole O-demethylase activity, metabolic-intermediate complex formation from isosafrole or metyrapone binding to cytochrome P-450.

Separation of four glucuronides in a single sample by high-pressure liquid chromatography and its use in the determination of UDP glucuronosyltransferase activity toward four aglycones

A single-solvent, reverse-phase HPLC system that separates glucuronides has been developed, and its applicability to the separation of glucuronides of four substrates (1-naphthol, morphine, testosterone, and estrone), representative of different UDP-glucuronosyltransferase enzymes, has been demonstrated. The combined supernatants from four separate microsomal incubations from which the protein has been precipitated can be used directly for the quantitation of the glucuronides formed. Variations in the four enzyme activities, upon treatment of rats with microsomal enzyme-inducing agents, after liver trauma and in the Gunn strain of rats have been investigated.

Cytochrome P-450 metabolic-intermediate complex formation from p-aminobenzoic acid esters and other arylamines

Metabolism of a series of p-aminobenzoic acid esters by rat liver microsomal fractions resulted in the formation of cytochrome P-450 metabolic - intermediate complexes. With conditions that allowed complex formation to proceed to completion, about 20% of control rat cytochrome P-450 was sequestered as a complex. Phenobarbital, but not beta-naphthoflavone induced additional cytochrome P-450, which with specific esters could be complexed to about 60%. For other esters, the induced cytochrome maximally complexed to about 20%, as was seen in uninduced rats. The two groups of p-aminobenzoic acid esters could not be readily delineated by lipid/water partition coefficients or steric factors.