| BACKGROUND: TMPz is the medicine which is applyed to treat blood vessel diseases of heart and brain. at present its pharmacokinetics research have been developed in foreign and nation, which make clinic have profound acquaintance to pharmacokintics' characteristic of TMPz, but it have been reported of no research about TMPz biological metabolism. For CYP 450 induce or inhibiting effect in clinic, there is a misuse when we unite to use several medicines. so, It is necessary to have metabolic transformation research of TMPz, supply theory and experience basis for it's reasonable use in clinic. AIM The metabolic character of TMPz (TMPz) in rat liver microsomes was studied in vitro and in vivo to identify which isoforms of cytochrome P450 were responsible for TMPz metabolism in rats,offer the theoretical foundation for the fact that it is rational to use medicine in clinic. METHODS Set up HPLC-UV method of TMPz , determine concentration of TMPz and its formation in rat plasma and liver microsomes incubation solution which have been incubated with different induer including dexamethasone (DEX)(50mg·kg-1, ig×4d), phenobarbital (PB)(75 mg·kg-1, ip×3d) and β–naphthoflavone(β-NF)(80mg·kg-1, ip×3d) ; know enzyme promote kinetics characteristic of TMPz in regenerative system. Analyze the correlation between TMPz's metabolic eliminate rate and each inducer. ERY N-demethylase activity of each sample in rat liver microsomes was measured using N-demethylation reaction of erythromycin (ERY) as probe. The correlation between the rate of TMPz metabolite formation and the demethylase activity was analysed. ERY, a special substrate of CYP3A and Ketoconazole (Ket), a CYP3A selective inhibitor, have the competitive inhibition experiments with TMPz, study its inhibition effect on the metabolism of TMPz in vitro. After the Wistar rats who had been treated with inducer, inhibitor, or untreated respectively for 5 days, received administration of TMPz (10mg·kg-1, i.v.) in vein, blood samples were taken at different time points and the plasma concentration of TMPz were determined by HPLC. Pharmacokinetic parameters of TMPz were computed and compared. RESULTS The metabolism of TMPz in rat liver microsomes showed the good correlation between TMPz metabolite formation and its substrate at 0-4.8μg·ml-1 concentration of TMPz. while its concentration exceed 4.8μg·ml-1, the metabolism appears saturate phenomenon in system, TMPz metabolite does no longer increase along with TMPz's concentration. The disppearing rate of TMPz in the incubation solutions of the rats liver microsomes, which treated with DEX, were markedly quicker than that of control group (p<0.01), while no obvious difference between β-NF group or PB and control group was observed (P>0.05).The average disappearing rate of TMPz after incubation with differently treated rat liver microsomes were as follows: DEX,79.2±9.5%;PB,18.1±6.7%;β-NF,14.3±1.5%;Control, 14.0±1.6%; The activity of ERY-N-demethylase in DEX-induced group (0.71±0.05μmol·mg-1·min-1) was corespondingly enhanced, was much higer than that in control group(0.29±0.02μmol·mg-1·min-1). The correlation between the rate of TMPz metabolic product formation and the activity of CYP3A was significant(r=0.9994). After using Ket, the CYP3A inhibitor, the metabolism of TMPz changed from 362.72±7.41μmol·g-1·30min-1 to 150.38±26.17 μmol·g-1·30min-1, so Ket could significantly inhibit the metabolism of TMPz in rat liver microsomes, andInhibition rate is 58.54%. ERY and KET can both inhibit the metabolism of TMPz, which is characteristic of competitive inhibition.And the index(ki) is 0.45μg·ml-1 and 0.73μg·ml-1. DEX could speed up the metabolism of TMPz in rats, which CL(s) were larger than that of the control group(DEX:13.282±2.235L·h-1·kg-1 ,Control :6.878±1.070 L·h -1·kg-1,P<0.01), t1/2 were smaller than the control group(DEX:1.082±0.157 h,Control :1.602±0.159h,P<0.01). By contraries, Ket could inhibit the metabolism of TMPz in rats, which CL(s) was smaller than the control group(Ket:4.940±0.047 L·h-1·kg-1,Control :6.878±1.070 L·h-1·kg-1,P<0.05), t1/2 was larger than the control group(Ket:1.925±0.177 h,Control :1.602±0.159 h,P<0.05). CONCLUSION Results suggest that CYP3A plays a major role in TMPz metabolism in rats, The metabolism of TMPz have the characteristic of enzyme kinetics. TMPz lie in the possibility of Interaction among the medicines between TMPz and CYP3A inducers or inhibitors when they are used in clinic.
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