A chimeric tyrosine/tryptophan hydroxylase

The neurotransmitter biosynthetic enzymes, tyrosine hydroxylase (TH), and tryptophan hydroxylase (TPH) are each composed of an amino-terminal regulatory domain and a carboxylterminal catalytic domain. A chimeric hydroxylase was generated by coupling the regulatory domain of TH (TH-R) to the catalytic domain of TPH (TPH-C) and expressing the recombinant enzyme in bacteria. The chimeric junction was created at proline 165 in TH and proline 106 in TPH because this residue is within a conserved five amino-acid span (ValProTrpPhePro) that defines the beginning of the highly homologous catalytic domains of TH and TPH. Radioenzymatic activity assays demonstrated that the TH-R/TPH-C chimera hydroxylates tryptophan, but not tyrosine. Therefore, the regulatory domain does not confer substrate specificity. Although the TH-R/TPH-C enzyme did serve as a substrate for protein kinase (PKA), activation was not observed following phosphorylation. Phosphorylation studies in combination with kinetic data provided evidence that TH-R does not exert a dominant influence on TPH-C. Stability assays revealed that, whereas TH exhibited a t_1/2 of 84 min at 37°C, TPH was much less stable (t _1/2=28.3 min). The stability profile of TH-R/TPH-C, however, was superimposable on that of TH. Removal of the regulatory domain (a deletion of 165 amino acids from the N-terminus) of TH rendered the catalytic domain highly unstable, as demonstrated by at _1/2 of 14 min. The authors conclude that the regulatory domain of TH functions as a stabilizer of enzyme activity. As a corollary, the well-characterized instability of TPH may be attributed to the inability of its regulatory domain to stabilize the catalytic domain.     

环丙沙星滴眼剂在家兔眼内组织分布及其药物动力学

环丙沙星（ｃｉｐｒｏｆｌｏｘａｃｉｎ，ＣＰＦＸ）滴眼液点入兔眼后，用ＨＰＬＣ法测定眼内各组织中药物浓度。结果在角膜、房水、虹膜－睫状体、晶体、玻璃体内峰浓度值分别为１９．４３μｇ／ｇ，１．５８μｇ／ｍｌ，１６．６８μｇ／ｇ，１．４２μｇ／ｇ和０．９６μｇ／ｍｌ；其半衰期分别为０．７６，０．６９，０．９２，０．６１和１．４０ｈ。结果表明ＣＰＦＸ能在眼内达到较高的抗菌浓度。     

雌、孕激素对IL-6基因在子宫内膜表达的影响

为了进一步了解白介素－６（ＩＬ－６）在生殖过程中的作用，应用斑点杂交和原位杂交方法，研究ＩＬ－６在小鼠子宫内膜的基因表达和雌、孕激素对这种表达的影响。实验证明，正常动情前期子宫内膜间质细胞有ＩＬ－６ｃＲＮＡ基因表达，切除动物卵巢，即可消除这种表达。如给去卵巢动物２ｍｇ孕激素加１０ｎｇ雌激素或２０ｍｇ孕激素加１００ｎｇ雌激素，它们的光密度（ＩＯＤ）值分别可达到２．３和２．５。结果证明，子宫内膜间质细胞是产生细胞因子ＩＬ－６的主要细胞之一，并受卵巢激素的调控。     

A new and highly sensitive method for measuring 3-methoxytyramine using HPLC with electrochemical detection. Studies with drugs which alter dopamine metabolism in the brain

3-Methoxytyramine (3-MT) is a minor metabolite of dopamine which is suggested to reflect the turnover and utilization of dopamine. A novel, isocratic HPLC method has been developed which can be used to analyse 3-MT in homogenates of rat brain without the need for additional purification procedures. Furthermore, the coulometric electrochemical detection system is sensitive enough to measure 3 pg of 3-MT (equivalent to 0.6 ng/g tissue wet weight). 3-Methoxytyramine was measured in the striatum and n. accumbens after decapitation and rapid freezing, using 3-methoxy-4-hydroxybenzylamine as the internal standard. The effects of dopaminergic and other drugs on this metabolite were examined using this method. -Methyl-p-tyrosine (200 mg/kg i.v.) produced parallel linear decreases in dopamine and 3-MT in naive rats, but not those pretreated with tranylcypromine (5 mg/kg i.p.). Methamphetamine (0.3–10 mg/kg i.p.) and amphetamine (0.3–10 mg/kg i.p.) both dose-dependently increased 3-MT in naive and tranylcypromine-pretreated rats. In naive animals, 3-MT was not altered by intraperitoneal injection of the dopamine reuptake inhibitors, bupropion (10 mg/kg) and nomifensine (10 mg/kg) or by sibutramine HCl (3 mg/kg), amitriptyline (10 mg/kg), desipramine (10 mg/kg) and zimeldine (10 mg/kg). 3-Methoxy-tyramine was decreased by apomorphine (5 mg/kg i.p.) and also by large doses of the selective D₂ antagonist, BRL 34778 (5 mg/kg i.p.) or -DOPA (50 mg/kg i.p.). The selective D₁ antagonist, SCH 23390 (0.1 or 5 mg/kg i.p.) was without effect. In tranylcypromine-pretreated rats, 3-MT was dose-dependently reduced and increased by apomorphine (0.01–5 mg/kg i.p.) and BRL 34778 (0.1–5 mg/kg i.p.), respectively. The drug SCH 23390 (0.1–5 mg/kg i.p.) produced much smaller increases in 3-MT which were probably mediated through the striatonigral pathway. Overall, the data suggest that measurement of 3-MT, after inhibition of monoamine oxidase, is a useful index of the release and utilization of dopamine. However, after substantial and prolonged depletion of dopamine, levels of 3-MT in naive animals are a better index. Also, the formation of 3-MT in naive rats provides a sensitive method for distinguishing between dopamine releasing agents and reuptake inhibitors.     

Evidence for nitric oxide participation in down-regulation of CYP2B1/2 gene expression at the pretranslational level

Septic or inflammatory stimuli suppress drug metabolism by cytochrome P-450 in the liver, presumably at the pretranslational level. We have shown previously that nitric oxide is responsible at least in part for the inhibition by bacterial lipopolysaccharide of phenobarbital-induced CYP2B1/2 activity in vivo. This was attributed to the interaction of nitric oxide with heme in the active-center of cytochrome P450, leading to enzyme inactivation. Here, we report of nitric oxide with heme in the active-center of cytochrome P450, leading to enzyme inactivation. Here, we report that endogeneous nitric oxide also contributes to LPS-induced suppression of CYP2B1/2 in vivo by down-regulating the expression of CYP2B1/2 protein and mRNA.     

大鼠肝细胞Ⅰ，Ⅲ型前胶原基因表达及PDGF的影响

目的观察大鼠肝细胞Ⅰ，Ⅲ型前胶原基因的表达及ＰＤＧＦ对其表达的影响．方法应用原位杂交技术检测分离培养的ＳＤ大鼠肝细胞（ｎ＝３０）内Ⅰ，Ⅲ型前胶原基因的表达．同时观察１０μｇ／Ｌ（ｎ＝３０）和３０μｇ／Ｌ（ｎ＝３０）ＰＤＧＦ促进前胶原基因表达的作用．测定基因表达颗粒总面积占细胞总面积的百分比，并作比较分析．结果无论正常肝细胞或是在两种浓度的ＰＤＧＦ存在时，肝细胞内均可见到Ⅰ，Ⅲ型前胶原基因的表达．正常肝细胞Ⅰ，Ⅲ型前胶原基因表达面积的百分比（％）为７７±１９和７５±２１；加１０μｇ／ＬＰＤＧＦ后为１１５±１９和１１２±１０，而加３０μｇ／Ｌ后为１５２±３４及１８１±２８，且在后者中表达明显增强（Ｐ＜００５及Ｐ＜００１）．结论ＰＤＧＦ在转录水平上促进肝细胞胶原的合成．     

成人高原心脏病临床分型的探讨

本文总结了６８０例成人高原心脏病临床资料，依照其临床表现、Ｘ线、心电图等项检查，提出了临床上较为实用的诊断和分型意见。     

高电压胸部摄影诊断和防护效果研究

作者以体模实验为基础。测定了不同管电压拍摄胸片时的病人剂量，考察了提高管电压对胶片影像质量的影响，结果表明，使用高电压拍摄胸片比使用低电压有利于降低病人剂量，在增加影像信息量，提高肋骨阴影区和纵膈区灶检出率方面更有较大优越性，此外，使用高电压技术不家利于延长Ｘ射线管的使用寿命。