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TITLE:  Comparison of maturation of drug-metabolizing enzymes in calves with functioning or nonfunctioning rumen
 
AUTHORS:  Kawalek JC;El Said KR;
 
YEAR:  1994
 
JOURNAL ABBREV:  Am J Vet Res
 
MONTH:  Nov
 
TYPE:  JOUR
 
REFMAN INDEX:  289
 
JOURNAL FULL:  American journal of veterinary research
 
VOLUME:  55
 
ISSUE:  11
 
START PAGE:  1579
 
END PAGE:  1586
 
KEYWORDS:  7-Alkoxycoumarin O-Dealkylase;Aging;Aminopyrine N-Demethylase;Analysis of Variance;Aniline Hydroxylase;Animal Feed;Animals;Aryl Hydrocarbon Hydroxylases;Cattle;Cytochrome P-450 Enzyme System;Cytochromes b5;Enzymes;enzymology;Food;Food,Fortified;Glutathione Transferase;Liver;Male;metabolism;Microsomes,Liver;Milk;Mixed Function Oxygenases;NADPH-Ferrihemoprotein Reductase;pharmacology;physiology;Rumen;
 
ABSTRACT:  Drug-metabolizing enzyme activities were measured in livers from calves fed commercial milk replacer (nonfunctioning rumen [veal]), and those fed milk replacer supplemented with whole grain and hay from the first week of age (functioning rumen [ruminating calves]). After birth, cytochrome P450 and its NADPH-dependent reductase activities remained unchanged in veal calves; in ruminating calves they increased almost 50%. Cytochrome P450-mediated reactions, such as aniline hydroxylase activity, tripled in ruminating calves, but remained unchanged in veal calves. In both groups of calves, coumarin hydroxylase and 7-ethoxycoumarin 0-deethylase activities increased after birth, but maturation rates and activity values in ruminating calves were considerably greater than those of veal calves. The aminopyrine N-demethylase activity for veal calves was equal to that of calves with functioning rumen. Uridine diphosphoglucuronic acid glucuronyl transferase and glutathione-S-transferase activities also were higher in calves with functioning rumen than in veal calves. This increased activity in calves with functioning rumen probably represents a response to environmental exposure to xenobiotics. Compared with rumen-functional calves, bob veal (0 to 3 weeks old) and fancy veal (15 to 19 weeks old) calves fed commercial milk replacer have a significantly (P = 0.05) diminished capacity for metabolizing drugs and other xenobiotics. From a regulatory perspective, the variance in drug-metabolizing enzyme activities within these different market classes of calves suggests that specific studies designed to determine drug residue-depletion times in veal calves may be needed
 
AFFILIATIONS:  Pharmacology and Biochemistry Branch, Food and Drug Administration, Beltsville, MD 20705
 
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