Glutamate receptors in the dorsal hippocampus mediate the acquisition,but not the expression,of conditioned place aversion induced by acute morphine withdrawal in rats

Aim： To evaluate the role of glutamate receptors in the dorsal hippocampus （DH） in the motivational component of morphine withdrawal. Methods： NMDA receptor antagonist D-AP5 （5 pg/0.5 pL per side） or AMPA receptor antagonist NBQX （2 pg/0.5 pL per side） was micro- injected into DH of rats. Conditioned place aversion （CPA） induced by naloxone-precipitated morphine withdrawal were assessed. Results： Preconditioning microinjection of D-AP5 or NBQX into the DH impaired the acquisition of CPA in acute morphine-dependent rats. However, intra-DH microinjection of D-AP5 or NBQX after conditioning but before the testing session had no effect on the expres- sion of CPA. Conclusion： Our results suggest that NMDA and AMPA receptors in the dorsal hippocampus are involved in the acquisition, but not in the expression, of the negative motivational components of acute morphine withdrawal in rats.     

Effects of morphine dependence and withdrawal on levels of neurosteroids in rat brain

AIM: To investigate the effects of morphine dependence and withdrawal on the concentrations of neurosteroids in rat brain. METHODS: A method of simultaneous quantification of neurosteroids by gas chromatography-mass spectrometry (GC-MS) had been established. RESULTS: The chronic morphine administration (ip) resulted in a marked decrease in the brain concentrations of pregnenolone (PREG), progesterone (PROG), and pregenenolone sulfate (PREGS) in rats killed 6 h after the last treatment. In contrast, there were no significant effects of morphine dependence on the brain concentrations of allopregnanolone (AP), dihydroepiandrosterone (DHEA), and dihydroepiandrosterone sulfate (DHEAS). Naloxone-induced withdrawal produced a significant increase in the concentrations of PREG, PROG, AP, DHEA, PREGS, and DHEAS as compared with the control group. CONCLUSION: Morphine dependence and withdrawal affected the concentrations of neurosteroids in rat brain, which suggests that endogenous neurosteroids in brain might be     

Expression pattern of neural synaptic plasticity marker-Arc in different brain regions induced by conditioned drug withdrawal from acute morphine-dependent rats

Aim： The immediate early gene Arc （activity-regulated cytoskeletal-associated protein） mRNA and protein are induced by strong synaptic activation and rapidly transported into dendrites, where they localize at active synaptic sites. Thus, the Arc mRNA and protein are proposed as a marker of neuronal reactivity to map the neural substrates that are recruited by various stimuli. In the present study, we examined the expression of Arc protein induced by conditioned naloxone-precipitated drug withdrawal in different brain regions of acute morphine-dependent rats. The objective of the present study was to address the specific neural circuits involved in conditioned place aversion （CPA） that has not yet been well characterized. Methods： Place aversion was elicited by conditioned naloxone-precipitated drug withdrawal following exposure to a single dose of morphine. An immunohistochemical method was employed to detect the expression of Arc, which was used as a plasticity marker to trace the brain areas that contribute to the formation of the place aversion. Results： Marked increases in Arc protein levels were found in the medial and lateral prefrontal cortex, the sensory cortex, the lateral striatum and the amygdala. This effect was more pronounced in the basolateral amygdala （BLA）, the central nucleus of the amygdala （CeA）, and the bed nucleus of the striatal terminals （BNST） when compared with the control group. Conclusion： Our results suggest that these brain regions may play key roles in mediating the negative motivational component of opiate withdrawal.     

Pharmacologic inducers of the uric acid exporter ABCG2 as potential drugs for treatment of gouty arthritis

Uric acid is the end product of purine catabolism and its plasma levels are maintained below its maximum solubility in water(6–7 mg/dl).The plasma levels are tightly regulated as the balance between the rate of production and the rate of excretion,the latter occurring in urine(kidney),bile(liver)and feces(intestinal tract).Reabsorption in kidney is also an important component of this process.Both excretion and reabsorption are mediated by specific transporters.Disruption of the balance between production and excretion leads to hyperuricemia,which increases the risk of uric acid crystallization as monosodium urate with subsequent deposition of the crystals in joints causing gouty arthritis.Loss-of-function mutations in the transporters that mediate uric acid excretion are associated with gout.The ATP-Binding Cassette exporter ABCG2 is important in uric acid excretion at all three sites:kidney(urine),liver(bile),and intestine(feces).Mutations in this transporter cause gout and these mutations occur at significant prevalence in general population.However,mutations that are most prevalent result only in partial loss of transport function.Therefore,if the expression of these partially defective transporters could be induced,the increased number of the transporter molecules would compensate for the mutation-associated decrease in transport function and hence increase uric acid excretion.As such,pharmacologic agents with ability to induce the expression of ABCG2 represent potentially a novel class of drugs for treatment of gouty arthritis.     

Hypoglycemic effect of Astragalus polysaccharide and its effect on PTP1B

Aim: To examine the effects ofAstragalus polysaccharide (APS), a component of an aqueous extract ofAstragalus membranaceus roots, on protein tyrosine phosphatase 1B (PTP1B), a negative regulator of insulin-receptor (IR) signal transduction, and its potential role in the amelioration of insulin resistance. Methods: Ten-week-old fat-fed streptozotocin (STZ)-treated rats, an animal model of type Ⅱ diabetes mellitus (TIIDM), were treated with APS (400 mg/kg po) for 5 weeks. Insulin sensitivity was identified by the insulin-tolerance test. Further analyses on the possible changes in insulin signaling occurring in skeletal muscle and liver were performed by immunoprecipitation or Western blotting. PTP1B activity was measured by an assay kit. Results: The diabetic rats responded to APS with a significant decrease in body weight, plasma glucose, and improved insulin sensitivity. The activity and expression of PTP1B were elevated in the skeletal muscle and liver of TIIDM rats. Thus the insulin signaling in target tissues was diminished. APS reduced both PTP1B protein level and activity in the muscle, but not in the liver of TIIDM rats. Insulin-induced tyrosine phosphorylation of the IR β-subunit and insulin receptor substrate-1 (IRS-1) were increased in the muscle, but not in the liver of APS-treated TIIDM rats. There was no change in the activity or expression of PTP1B in APS-treated normal rats, and blood insulin levels did not change in TIIDM rats after treatment with APS. Conclusion: APS enables insulin-sensitizing and hypoglycemic activity at least in part by decreasing the elevated expression and activity of PTP1B in the skeletal muscles of TIIDM rats.     

Electrophysiological effects of haloperidol on isolated rabbit Purkinje fibers and guinea pigs papillary muscles under normal and simulated ischemia

Aim： Overdoses of haloperidol are associated with major ventricular arrhythmias, cardiac conduction block, and sudden death. The aim of this experiment was to study the effect of haloperidol on the action potentials in cardiac Purkinje fibers and papillary muscles under normal and simulated ischemia conditions in rabbits and guinea pigs. Methods： Using the standard intracellular microelectrode technique, we examined the effects of haloperidol on the action potential parameters [action potential amplitude （APA）, phase 0 maximum upstroke velocity （Vmax）, action potential amplitude at 90% of repolarization （APD90）, and effective refractory period （ERP）] in rabbit cardiac Purkinje fibers and guinea pig cardiac papillary cells, in which both tissues were under simulated ischemic conditions. Results： Under ischemic conditions, different concentrations of haloperidol depressed APA and prolonged APD90 in a concentration-dependent manner in rabbit Purkinje fibers. Haloperidol （3 μmol/L） significantly depressed APA and prolonged APD90, and from 1 μmol/L, haloperidol showed significant depression on Vmax; ERP was not significantly affected. In guinea pig cardiac papillary muscles, the thresholds of significant reduction in APA, Vmax, EPR, and APD90 were 10, 0.3, 1, and 1 μmol/L, respectively, for haloperidol. Conclusion： Compared with cardiac conductive tissues, papillary muscles were more sensitive to ischemic conditions. Under ischemia, haloperidol prolonged ERP and APD90 in a concentration-dependent manner and precipitated the decrease in Vmax induced by ischemia. The shortening of ERP and APD90 in papillary muscle action potentials may be inhibited by haloperidol.     

Tissue distribution of bitespiramycin and spiramycin in rats

AIM: To investigate the tissue distribution of bitespiramycin (BSPM) and spiramycin (SPM) in rats. METHODS: Liquid chromatographic-mass spectrometric assay was applied for the determination of three major components (isovalerylspiramycins, ISV-SPMs) of BSPM and their major active metabolites (SPMs) in rat tissues and plasma after an oral dose of bitespiramycin, as well as SPMs. RESULTS: High levels of drug concentrations were observed in most tissues, especially in the liver, stomach, intestine, spleen, lung, womb, and pancreas. BSPM persisted long time in many rat tissues such that the drug concentration in spleen was 69.4 nmol/g at 60 h post-dose and it was still above the minimum inhibitory concentration of many susceptible pathogens. At 2.5 h post-dose, the total concentrations of ISV-SPMs and SPMs achieved in tissues were from 6 to 215 times higher than the corresponding concentrations in plasma. At 2.5 h post-dose, the mean Ct/CP of BSPM appeared to be 2- or 3-fold those of SPM in most tissues. The     

Role of TGF-β/Smad signaling pathway in pulmonary fibrosis after rheumatoid arthritis in mice北大核心CSCD

Aim To investigate the role of TGF-β/Smad signaling pathway in rheumatoid arthritis (RA) - associated postinterstitial pulmonary fibrosis in mice. Methods The mouse model of RA was constructed by subcutaneous administration of complete Freund's adjuvant (CFA) and chicken II collagen (Col-II) to the tail root of mice. The blank group was given the same amount of distilled water, and the control group was given the same amount of glacial acetic acid (solvent). The degree of toe swelling (joint swelling degree and arthritis index) was monitored to evaluate the mouse modeling. The pathological changes of mouse lung tissues were observed by HE and Masson staining. The expression of TGF-β in lung tissues were observed by immunohistochemical staining. The level of hydroxyproline in lung tissues was measured by chemiluminescence method. The expressions of Smad2, Smad3 and phosphorylated p-Smad2 and phosphorylated p-Smad3 in lung tissues were detected by Western blot. Results Compared with blank group and solvent group, the joint swelling and arthritis index of model group significantly increased. Twenty-one days after administration, HE staining showed inflammatory changes in lung interstitium of the model group, Masson staining showed collagen fiber deposition and obvious fibrosis in lung interstitium of the model group, and immunohistochemical staining showed that the expression of TGF-β in cytoplasm of lung interstitial cells of the model group increased, which was brown and yellow. Meanwhile, hydroxyproline was significantly raised in lung tissue homogenate of the model group. Further WB analysis showed that compared with blank group and solvent group, the expression of p-Smad2 and pSmad3 in lung tissues of the model group was significantly up-regulated (P < 0. 05, P < 0. 01). Conclusions RA can give rise to pulmonary fibrosis, and the expressions of p-Smad2 and p-Smad3 are up-regulated, which is be pivotal in pulmonary fibrosis and RA-related post-interstitial pulmonary fibrosis. © 2023 Publication Centre of Anhui Medical University. All rights reserved.     

Targeting distribution of monomethylhydrazine in mice

<正> Mice which had been administered monomethylhydrazine (MMH) 20 mg/kg iv were killed at 5, 15, 30, 60,120 and 180 min and blood, heart, liver, spleen, lung, kidney, brain, muscle and intestine samples were collected.These tissues were weighted and homogenized in 4 volumes of 0.1 mol/L HCl. The concentration of MMH in blood and the homogenate of tissues were quantitated by a p-dimethylaminobenzaldehyde colorimetric method. The targeting distribution characteristics of MMH in mice were quantitatively discribed by the parameters of tar-     

Exercise ameliorates the detrimental effect of chloroquine on skeletal muscles in mice via restoring autophagy flux

Aim： To study the roles of autophagy in muscle establishment during long-term exercise in mice.
Methods： Female ICR mice were submitted to exercise training with a wheel running regimen： 6 m/min, 15 min/time, 3 times/d （on 8：00, 14：00, and 20：00）, 5 d/week for 2 months. The mice were treated with the autophagy activator trehalose （1% aqueous solution as a daily drinking water） or the autophagy inhibitor chloroquine （10 mg/kg, ip, 5 times a week） before the training. Western blotting analysis, TUNEL staining, H＆E staining and transmission electron microscope were used to evaluate the activity of autophagy and the structure of the muscle fibers.

Results： The exercise training significantly stimulated the formation of autophagosomes, increased the LC3-II, cathepsin L and Bcl-2 levels, lowered the P62 level and increased the antioxidant capacity in the muscles. Meanwhile, the exercise training significantly improved the morphology of mitochondria, reduced the release of cytochrome c from mitochondria to cytoplasm, and slightly decreased the apoptosis rate in the muscles. Administration of trehalose increased the level of autophagy and protected the muscle fibers from apoptosis. Administration of chloroquine blocked autophagy flux and exerted detrimental effects on the muscles, which were ameliorated by the exercise training.

Conclusion： Long-term regular exercise activates autophagy process associated with muscle establishment, and ameliorates the detrimental effects of chloroquine on skeletal muscles via restoring autophagy flux.     

吗啡对嘌呤核苷酸分解代谢的影响—吗啡依赖的生化与分子生物学机制研究

目的 :研究吗啡依赖及戒断对嘌呤核苷酸分解代谢的影响与作用机制。方法 :建立吗啡依赖、戒断的大鼠模型 ,测定大鼠血浆中尿酸及腺苷脱氨酶 (ADA)含量 ;各组织中的腺苷脱氨酶含量以及大鼠脑顶叶、肝脏、小肠和肌肉组织中腺苷脱氨酶的基因转录产物。结果 :吗啡给药大鼠血浆尿酸水平明显升高 (P <0 0 5 ) ;吗啡给药及戒断期间 ,大鼠血浆ADA水平均显著升高 (P <0 0 5 ) ;吗啡给药组大鼠脑顶叶、肝脏、小肠和肌肉组织匀浆中的ADA含量都有不同程度的升高 (P <0 0 5 ) ,而在自然戒断期间 ,上述各组织ADA含量较给药组有所下降 ;吗啡给药 3d组大鼠脑顶叶、吗啡给药 7d组大鼠肝脏、小肠和肌肉组织中ADA的基因表达均明显升高 (P <0 0 5 ) ,除肌肉组织外 ,在自然戒断期间 ,上述各组织ADA的基因表达水平都有不同程度的恢复。结论 :嘌呤核苷酸分解代谢加强可能是吗啡的基本作用 ,也可能是依赖的重要原因之一。     

嘌呤核苷酸补偿对吗啡依赖大鼠嘌呤核苷酸分解代谢的影响

目的探讨外源性补偿嘌呤核苷酸对吗啡依赖大鼠嘌呤核苷酸分解代谢的影响。方法将60只♂Wistar大鼠随机分为对照组、吗啡组、吗啡+嘌呤核苷酸组、对照戒断组、吗啡戒断组和吗啡+嘌呤核苷酸戒断组,戒断组于d8给药后4h观察纳洛酮急性戒断症状。各组检测血尿酸(UA)、尿素氮(BUN)和肌酐(Cre)含量,以及血浆和大脑皮质腺苷脱氨酶(ADA)活性。结果吗啡+嘌呤核苷酸戒断组的戒断症状综合评分明显少于吗啡戒断组(P<0.01)。吗啡组及吗啡戒断组血UA含量均明显高于相应的对照组和相应的吗啡+嘌呤核苷酸组(P<0.05)。各组间BUN和Cre含量差异无显著性(P>0.05)。吗啡组及吗啡戒断组血浆及大脑皮质ADA活性明显高于相应的对照组和相应的吗啡+嘌呤核苷酸组(P<0.05或P<0.01)。结论补充嘌呤核苷酸可改善吗啡增强大鼠嘌呤核苷酸分解代谢作用。     

吗啡对大鼠嘌呤核苷酸分解代谢的促进作用及其可能的作用机制

目的　研究吗啡对嘌呤核苷酸分解代谢的影响及作用机制。方法　剂量递增腹腔注射吗啡 ,建立吗啡依赖大鼠模型。用试剂盒检测血浆尿酸含量、血浆及小肠组织黄嘌呤氧化酶 (XO)的活性。提取小肠组织总RNA ,采用逆转录聚合酶链反应检测小肠组织XOmRNA的水平 ,以β actinmR NA为内标。结果　动物血浆尿酸水平 ,3d和 7d吗啡用药组显示高于对照组 (P <0 0 5,n =10 ) ;3d、7d吗啡用药组动物血浆XO活性高于对照组 (P <0 0 5,n =10 ) ,在自然戒断 2组动物血浆XO活性也高于对照组 (P <0 0 1,n =10 ) ;3或 7d吗啡用药组动物小肠XO活性高于对照组 (P <0 0 5,n =10 ) ;7d吗啡用药组动物小肠XOmRNA表达水平高于对照组 (P <0 0 1,n =3 )。结论　吗啡促进嘌呤核苷酸分解代谢 ;其作用机制可能与吗啡提高大鼠小肠嘌呤核苷酸分解代谢关键酶XO的活性 ,增强其表达有关     

海洛因对大鼠黄嘌呤氧化酶和血尿酸的影响

目的:检测黄嘌呤氧化酶(xanthineoxidase ,XOD)和血浆尿酸含量,研究海洛因给药对嘌呤核苷酸分解代谢的影响。方法:建立海洛因给药、停药大鼠模型,测定尿酸及XOD含量。结果:给药组尿酸及XOD含量高于对照组。与给药组比较,两个停药组尿酸含量、血浆和肝XOD含量降低;停药8d组脑顶叶XOD含量降低,脑干XOD含量略有下降趋势。但两个停药组脑干XOD含量仍高于对照组。结论:海洛因通过增加XOD的含量,使嘌呤核苷酸分解代谢增强,且脑中这一作用消除较慢。     

吗啡在基因水平对脑嘌呤核苷酸代谢的影响

目的:通过研究吗啡对大鼠脑组织嘌呤核苷酸代谢的影响,寻找吗啡依赖相关的调控与效应基因。方法:利用核酸分子杂交测定吗啡依赖与戒断大鼠丘脑及颞叶脑组织次黄嘌呤鸟嘌呤磷酸核糖转移酶(HGPRT)mRNA的含量变化。结果:核酸分子杂交密度扫描结果显示吗啡依赖、急性及慢性戒断时大鼠丘脑及颞叶脑组织HGPRTmRNA均明显低于对照组(P<0.05,P<0.01,P<0.001)。结论:吗啡能明显抑制丘脑及颞叶脑组织HGPRT的基因表达,提示吗啡可能通过调控脑核苷酸代谢的关键酶,影响脑核苷酸及核酸代谢。     

嘌呤核苷酸对吗啡依赖大鼠痛阈及急性戒断症状的影响

目的:探讨嘌呤核苷酸对吗啡依赖大鼠痛阈及急性戒断症状的影响。方法:将30只♂ Wistar大鼠随机分为对照组、吗啡组和嘌呤核苷酸+吗啡组,于实验d1、3、5、7用电子压痛仪检测大鼠尾压痛阈值,d2、4、6、8进行热甩尾实验检测大鼠抗热痛觉过敏能力,于d8给药后4h观察纳洛酮急性戒断症状。结果:与对照组相比,d1起吗啡组及嘌呤核苷酸+吗啡组大鼠尾压痛阈值增高(P<0.01),d3起嘌呤核苷酸+吗啡组压痛阈值明显高于吗啡组(P<0.01);d2起吗啡组热甩尾潜伏期延长(P<0.05),d6起嘌呤核苷酸+吗啡组热甩尾潜伏期时间长于吗啡组(P<0.05);嘌呤核苷酸+吗啡组戒断症状评分与吗啡组比有显著的统计学差异(P<0.01)。结论:嘌呤核苷酸能够明显增强吗啡的镇痛作用,并减轻吗啡依赖大鼠的戒断症状。     

Nitric oxide, adenosine deaminase, xanthine oxidase and superoxide dismutase in patients with panic disorder: alterations by antidepressant treatment

OBJECTIVE: In the present study, we aimed to investigate whether nitric oxide (NO) levels and activities of xanthine oxidase (XO), superoxide dismutase (SOD), and adenosine deaminase (ADA) are associated with Panic disorder (PD) as well as impact of psychopharmacological treatments on NO, SOD, ADA, and XO levels in PD. METHOD: In this study, 32 patients and 20 healthy controls were included. The serum levels of NO, XO, SOD, and ADA were measured in the patients and controls. The patients were treated with antidepressant. RESULTS: ADA and XO levels of the patients were significantly higher than the controls. SOD levels of the patients were significantly lower than the controls but the difference was not statistically significant. Although NO levels of the patients were higher than the controls, the difference was not statistically significant. There was no correlation between PAS and the parameters studied (SOD, ADA, XO, and NO) of the patients. After 8 weeks of antidepressant treatment, ADA and SOD activities were increased whereas NO and XO levels decreased significantly. CONCLUSION: ADA, XO activity may have a pathophysiological role in PD, and prognosis of PD. Activity of these enzymes may be used to monitor effects of the antidepressant treatment.     

海洛因对大鼠谷氨酸脱氢酶基因表达的影响

目的:研究海洛因对大鼠谷氨酸脱氢酶(GDH)基因表达的影响。方法:40只成年♂Wistar大鼠随机分为4组:对照组腹腔注射(ip)生理盐水9d;给药3d组ip海洛因3d;给药9d组ip海洛因9d;停药组ip海洛因9d后停药8d。采用生化自动分析系统检测血浆及组织中GDH活性,逆转录聚合酶链反应法(RT-PCR)检测组织中GDHmRNA的含量。结果:血浆中GDH活性在海洛因给药期间逐渐增高,停药8d后仍无明显降低;大脑组织GDH活性在海洛因给药3d、海洛因给药9d及停药8d后均显著低于对照组(P<0·01);肝脏GDH活性在海洛因给药过程中降低(P<0·01),停药8d后恢复到对照组水平;小肠GDH活性在海洛因给药9d后显著高于对照组(P<0·05),停药8d后小肠GDH活性继续升高并明显高于对照组(P<0·01)和海洛因给药9d组(P<0·05)。大脑、肝脏和小肠GDHmRNA含量分别与其GDH活性变化趋势一致。结论:海洛因对大鼠不同组织GDH基因表达影响不同。     

褪黑素对吗啡戒断大鼠脑脊液和血浆中cAMP水平抑制的影响

目的·· :探讨褪黑素(melatonin,MT)抑制吗啡戒断反应的作用及其与脑脊液(CSF)和血浆中cAMP含量的关系。方法··:建立吗啡依赖大鼠自然戒断模型 ,脑室插管及放免测定吗啡依赖大鼠CSF和血浆中cAMP含量。结果·· :(1)MT对大鼠吗啡戒断反应有明显的抑制作用;(2)吗啡依赖大鼠CSF中(20.07pmol·ml-1±s4.62pmol·ml-1)和血浆中(76.40pmol·ml-1±s8.71pmol·ml-1)cAMP含量均低于正常大鼠,P<0.01 ;吗啡戒断大鼠CSF中(38.19pmol·ml-1±s6.62pmol·ml-1)和血浆中(96.65pmol·ml-1±s5.32pmol·ml-1)cAMP含量则明显高于吗啡依赖大鼠,P<0.001;(3)MT可使吗啡戒断大鼠CSF中(23.28pmol·ml-1±s4.10pmol·ml-1)和血浆中(61.72pmol·ml-1±s3.49pmol·ml-1)cAMP含量明显降低,P<0.01和P<0.001。结论·· :MT可抑制大鼠吗啡戒断反应 ,并与MT降低CSF和血浆中cAMP的含量有关。     

Mathematical modeling analysis of hepatic uric acid disposition using human sandwich-cultured hepatocytes

Uric acid is biosynthesized from purine by xanthine oxidase (XO) mainly in the liver and is excreted into urine and feces. Although several transporters responsible for renal and intestinal handling of uric acid have been reported, information on hepatic transporters is limited. In the present study, we studied quantitative contribution of transporters for hepatic handling of uric acid by mathematical modeling analysis in human sandwich-cultured hepatocytes (hSCH). Stable isotope-labeled hypoxanthine, hypoxanthine-¹³C2,¹⁵N (HX), was incubated with hSCH and formed ¹³C2,¹⁵N-labeled xanthine (XA) and uric acid (UA) were measured by LC-MS/MS time dependently. Rate constants for metabolism and efflux and uptake transport across sinusoidal and bile canalicular membranes of HX, XA and UA were estimated in the presence of inhibitors of XO and uric acid transporters. An XO inhibitor allopurinol significantly decreased metabolisms of HX and XA. Efflux into bile canalicular lumen was negligible and sinusoidal efflux was considered main efflux pathway of formed UA. Transporter inhibition study highlighted that GLUT9 strongly and MRP4 intermediately contribute to the sinusoidal efflux of UA with minor contribution of NPT1/4. Modeling analysis developed in the present study should be useful for quantitative prediction of uric acid disposition in liver.