Aim:To investigate the effect and mechanism of morphine on purine nucleotidecatabolism.Methods:The rat model of morphine dependence and withdrawal andrat C6 glioma cells in culture were used.Concentrations of uric acid in the plasmawere measured by the uricase-rap method,adenosine deaminase(ADA)and xan-thine oxidase(XO)in the plasma and tissues were measured by the ADA and XOtest kit.RT-PCR and RT-PCR-Southern blotting were used to examine the relativeamount of ADA and XO gene transcripts in tissues and C6 cells.Results:(i)theconcentration of plasma uric acid in the morphine-administered group was signifi-cantly higher(P<0.05)than the control group;(ii)during morphine administrationand withdrawal periods,the ADA and XO concentrations in the plasma increasedsignificantly(P<0.05);(iii)the amount of ADA and XO in the parietal lobe,liver,small intestine,and skeletal muscles of the morphine-administered groupsincreased,while the level of ADA and XO in those tissues of the withdrawalgroups decreased;(iv)the transcripts of the ADA and XO genes in the parietallobe,liver,small intestine,and skeletal muscles were higher in the morphine-administered group.The expression of the ADA and XO genes in those tissuesreturned to the control level during morphine withdrawal,with the exception of theskeletal muscles;and(v)the upregulation of the expression of the ADA and XOgenes induced by morphine treatment could be reversed by naloxone.Conclusion:The effects of morphine on purine nucleotide metabolism might be an important,new biochemical pharmacological mechanism of morphine action. Aim: To investigate the effect and mechanism of morphine on purine nucleotidecatabolism. Methods: The rat model of morphine dependence and withdrawal andrat C6 glioma cells in culture were used. Contributions of uric acid in the plasmawere measured by the uricase-rap method, adenosine deaminase (ADA) and xan-thine oxidase (XO) in the plasma and tissues were measured by the ADA and XOtest kit. RT-PCR and RT-PCR-Southern blotting were used to examine the relative variable of ADA and XO gene transcripts in tissues and C6 cells. Results: (i) the concentration of plasma uric acid in the morphine-administered group was signifi- cantly higher (P <0.05) than the control group; (ii) during morphine administration and withdrawal periods, the ADA and XO concentrations in the (iii) the amount of ADA and XO in the parietal lobe, liver, small intestine, and skeletal muscles of the morphine-administered groups created, while the level of ADA and XO in those tissues of the withdrawal groups d (iv) the transcripts of the ADA and XO genes in the parietallobe, liver, small intestine, and skeletal muscles were higher in the morphine-administered group. The expression of the ADA and XO genes in those tissues returned to the control level during morphine withdrawal, with the exception of the skeletal muscles; and (v) the upregulation of the expression of the ADA and XOgenes induced by morphine treatment could be reversed by naloxone.Conclusion: The effects of morphine on purine nucleotide metabolism might be an important, new biochemical pharmacological mechanism of morphine action.