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Aging is known to decrease hepatic cytochrome P450 content in rats. However, limited information is available on the effects of aging on mixed-function oxidation and conjugation in intact liver. The purpose of these studies was to determine the effects of aging on oxidation and conjugation of p-nitrophenol (pNP) in perfused livers from male Sprague-Dawley rats. Livers from senescent (22-24 months) or young adult (3-6 months) rats were perfused in a nonrecirculating hemoglobin-free system and supplemented with pNP (60 microM). Glucuronide and sulfate conjugates of the oxidation product, 4-nitrocatechol, in effluent perfusate were cleaved enzymatically and 4-nitrocatechol was determined colorimetrically. Rates of 4-nitrocatechol production were decreased in senescent compared with young adult rats (0.67 +/- 0.14 vs 0.92 +/- 0.15 micromol/g/hr). However, the rates of oxidation of pNP in microsomes from senescent rats were similar to those in young adult rats. Hepatic malate content was decreased approximately 50% in livers from senescent compared with young adult rats in the presence and absence of pNP, suggesting that movement of reducing equivalents from the mitochondria to the cytosol, and thus cytosolic NADPH supply, may have been diminished by senescence. The rates of conjugation of 60 microM pNP in perfused livers from senescent rats were similar to those in young adult rats, but Km and Vmax values of microsomal 4-nitrocatechol glucuronyltransferase were about 2.5- and 1.6-fold higher, respectively, in livers from senescent compared with young adult rats. Hepatic glycogen content was about 50% lower in livers from senescent compared with young adult rats, but the contents of UDP-glucose and UDP glucuronic acid were similar between the two groups. Taken together, the data are consistent with the hypothesis that rates of mixed-function oxidation are decreased in intact livers from senescent compared with young adult rats, due possibly to age-related changes in cofactor supplies. Glucuronidation of low, but not high, concentrations of substrates may be affected by age-related changes in Km and Vmax values of microsomal glucuronyltransferase.
J A Handler, and
W R Brian
January 1983,
Pharmacology, biochemistry, and behavior,
J A Handler, and
W R Brian
January 1983,
Pharmacology,
J A Handler, and
W R Brian
March 1981,
The Journal of pharmacology and experimental therapeutics,
J A Handler, and
W R Brian
February 1987,
Chemico-biological interactions,
J A Handler, and
W R Brian
March 1954,
Archives of biochemistry and biophysics,
J A Handler, and
W R Brian
November 1987,
The Journal of pharmacy and pharmacology,
J A Handler, and
W R Brian
October 1969,
European journal of biochemistry,
J A Handler, and
W R Brian
May 1969,
Comptes rendus des seances de la Societe de biologie et de ses filiales,
J A Handler, and
W R Brian
October 1986,
Biochemical pharmacology,
J A Handler, and
W R Brian
December 1974,
European journal of clinical investigation,
