Large, rapid decreases in hepatic UDP-glucuronic acid concentrations occur in rats following exposure to myriad chemicals. In fact, 80% reductions in UDP-glucuronic acid occur within minutes after exposure to inhalation anesthetics. The present study was designed to determine whether this decrease in hepatic UDP-glucuronic acid may be due to (a) a decrease in the precursor UDP-glucose; (b) decreased activity of UDP-glucose dehydrogenase, which oxidizes UDP-glucose to UDP-glucuronic acid; (c) increased activity of UDP-glucuronosyltransferases; or (d) increased activity of nucleotide pyrophosphatase, which degrades UDP-glucuronic acid to glucuronic acid-1-phosphate. Exposure to halothane, isoflurane and sevoflurane decreased UDP-glucuronic acid concentrations by 40-52% as compared to that in unanesthetized control mice. No sex-dependent or anesthetic-induced effects of UDP-glucose levels and the activities of UDP-glucose dehydrogenase and UDP-glucuronosyltransferase were observed. Nucleotide pyrophosphatase activity was increased by 47-65% in female mice after inhalation of halothane, isoflurane and sevoflurane. The apparent Vmax for hydrolysis of 4-nitrophenol thymidine 5′-monophosphate ester by nucleotide pyrophosphatase was increased by 56-80% in female mice, whereas the apparent Km was unchanged. These alterations in nucleotide pyrophosphate kinetics may be responsible, in part, for the marked decrease of hepatic UDP-glucuronic acid concentrations by the volatile anesthetics.
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