Drug-biomacromolecule interaction V

The binding properties of three ginsenosides, Rb₁, Rc and Re, to bovine and human serum albumins have been examined by fluorescence probe technique. 1-anilinonaphthalene-8-sulfonate (ANS) was used as the fluorescence probe. Protopanaxatriol glycoside, Re, did not quench the fluorescence of ANS to the bovine serum albumin. Competitive bindings between protopanaxadiol glycosides, Rb₁ and Rc, and ANS were observed. The numbers of binding sites of bovine serum albumin for Rb₁ and Rc are both 3.3. The binding constants for Rb₁ and Rc with bovine serum albumin were 1.91×10⁴M^?1 and 1.04×10⁴M^?1, respectively. The ginsenosides, Rb₁, Rc and Re did not quench the fluorescence of ANS bound to human serum albumin.     

人参皂苷水溶液热稳定性研究

目的 研究加热时间对人参皂苷水溶液的影响及受热后人参皂苷含量的变化情况。方法 红参须浓缩液加热不同时间,采用高效液相色谱法测定其人参皂苷Rg1、Re、Rb1、Rc和Rd的含量。结果 5种人参皂苷在加热6 h内,发生不同程度的降解反应,二醇类人参皂苷Rb1、Rc和Rd在加热2-3 h时,含量呈明显下降趋势,人参皂苷Rd降解速率最慢。三醇类人参皂苷Rg1和Re在加热3 h内含量快速下降,3 h后趋于平缓。结论 在常压受热条件下,人参皂苷水溶液主要成分人参皂苷Rg1、Re、Rb1、Rc和Rd的含量,随加热时间延长而不断下降,3 h后下降速率减缓。三醇类人参皂苷较二醇类对热更为敏感。     

Adenosine receptors in rat brain synaptosomes: Receptor characterization and relationships with glutamate release

The role of adenosine receptor(s) activation in modulating glutamate release in synaptosomes isolated from different rat brain areas was investigated. Receptor binding studies with selective A₁ and A₂ adenosine receptor ligands were performed in parallel with functional studies on depolarization-induced increases of intrasynaptosomal calcium concentrations and glutamate release. Specific binding to the selective A₁ ligand [³H]-Cyclohexyladenosine was detected, with highest densities in hippocampal synaptosomes, followed by c. striatum and cortex. In contrast, no specific binding to the selective A_2a ligand [³]CGS 21680 was demonstrable in synaptosomes from any of the studied brain areas, suggesting that no adenosine receptors belonging to this receptor subtype are present on rat brain pre-synaptic terminals. In parallel, the adenosine analogue cyclopentyladenosine (CPA) could partially inhibit the KCl-induced glutamate release from hippocampal synaptosomes. The agonist-induced effect was monophasic, dose-dependent, and already demonstrable at the 10^?8 M concentration, which indeed confirms that only A₁ receptors inhibitory on calcium-dependent release are functionally present in synaptosomal preparations. The effect on glutamate release was likely due to the ability of CPA to partially counteract KCl-induced increases of intrasynaptosomal calcium concentrations. IT is therefore concluded that rat hippocampal synaptosomes represent an adequate in vitro model to study the molecular and functional correlates of pre-synaptic adenosine receptors, and therefore investigate their role in both physiological and ischemia-associated pathological neurotransmission. © 1993 Wiley-Liss, Inc.     

一测多评法同步测定人参和三七药材中多种人参皂苷的含量

通过建立人参皂苷Rb₁与其他8种皂苷间的紫外相对校正因子(RCF)，实现只用一个对照品测定人参和三七药材中多个人参皂苷类成分的含量，以解决人参等药材质量控制中，对照品供应不足问题。结果表明，在一定的线性范围内，人参皂苷Rb₁与Rg₁、 Re、 Rf、 Rh₁、 Rc、 Rb₂、 Rb₃、 Rd间的RCF值分别为1.400， 1.215， 1.517， 1.801， 0.944， 1.012， 1.143， 1.135，且在不同实验条件下重现性良好(RSD=0.30%～3.9%)。本方法只需测定人参和三七药材中Rb₁的含量，其余人参皂苷含量由其RCF值计算得到，实现一测多评；并与常规外标法比较，两种药材中一测多评法与外标法所得结果均无显著性差异；所建立的校正因子可同时用于人参及三七药材及其相关产品的定量分析及质量评价。     

Hispidulin inhibits the release of glutamate in rat cerebrocortical nerve terminals

Hispidulin, a naturally occurring flavone, has been reported to have an antiepileptic profile. An excessive release of glutamate is considered to be related to neuropathology of epilepsy. We investigated whether hispidulin affected endogenous glutamate release in rat cerebral cortex nerve terminals (synaptosomes) and explored the possible mechanism. Hispidulin inhibited the release of glutamate evoked by the K⁺ channel blocker 4-aminopyridine (4-AP). The effects of hispidulin on the evoked glutamate release were prevented by the chelation of extracellular Ca^2 + ions and the vesicular transporter inhibitor bafilomycin A1. However, the glutamate transporter inhibitor dl-threo-beta-benzyl-oxyaspartate did not have any effect on hispidulin action. Hispidulin reduced the depolarization-induced increase in cytosolic free Ca^2 + concentration ([Ca^2 +]_C), but did not alter 4-AP-mediated depolarization. Furthermore, the effect of hispidulin on evoked glutamate release was abolished by blocking the Ca_v2.2 (N-type) and Ca_v2.1 (P/Q-type) channels, but not by blocking ryanodine receptors or mitochondrial Na⁺/Ca^2 + exchange. Mitogen-activated protein kinase kinase (MEK) inhibition also prevented the inhibitory effect of hispidulin on evoked glutamate release. Western blot analyses showed that hispidulin decreased the 4-AP-induced phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) and synaptic vesicle-associated protein synapsin I, a major presynaptic substrate for ERK; this decrease was also blocked by the MEK inhibitor. Moreover, the inhibition of glutamate release by hispidulin was strongly attenuated in mice without synapsin I. These results show that hispidulin inhibits glutamate release from cortical synaptosomes in rats through the suppression of presynaptic voltage-dependent Ca^2 + entry and ERK/synapsin I signaling pathway.     

The time course of NMDA-and kainate-induced cGMP elevation and glutamate release in cultured neuron

The levels of extracellular glutamate, intracellular Ca²⁺ ([Ca2+]_i) and cGMP were determined for 1 h with the excitatory amino acids, N-methyl-D-aspartate (NMDA) or kainate in cultured cerebellar granule cells. Both NMDA and kainate produced a time-dependent release of glutamate, and kainate was more potent than NMDA in glutamate elevation. The elevation of extracellular glutamate was not purely governed by intracellular Ca²⁺ concentration. However, in opposite to the time-dependent elevation of glutamate, the elevation of cGMP by NMDA and kainate were at maximum level in short-time (1 min) incubation then remarkably decreased with longer incubation times. Post-applications (30 min after agonist) of EAA antagonst did not block EAAs-induced glutamate elevation. However, NMDA antagonist, phencyclidine (PCP), blocked NMDA-induced cGMP elevation at pre- or post-application, but kainate antagonist, 6,7-dinitroquinoxaline-2,3-dione (DNQX), paradoxically augmented kainate-induced cGMP elevation for 1 h incubation. These results show that NMDA or kainate induces time-dependent elevations of extracellular glutamate, while the elevations of cGMP by these EAAs are remarkably decreased with longer incubation times. However, NMDA- and kainate-induced glutamate release was blocked by pre-application of each receptor antagonist but not by post-application while EAA-induced [Ca²⁺]_i was blocked by post-application of antagonist. These observations suggest that EAA-induced elevation of [Ca²⁺]_i is not parallel with elevation of glutamate release or cGMP.     

Potent homocysteine-induced ERK phosphorylation in cultured neurons depends on self-sensitization via system Xc

Homocysteine is increased during pathological conditions, endangering vascular and cognitive functions, and elevated homocysteine during pregnancy may be correlated with an increased incidence of schizophrenia in the offspring. This study showed that millimolar homocysteine concentrations in saline medium cause phosphorylation of extracellular-signal regulated kinases 1 and 2 (ERK_1/2) in cerebellar granule neurons, inhibitable by metabotropic but not ionotropic glutamate receptor antagonists. These findings are analogous to observations by Zieminska et al. (2003), that similar concentrations cause neuronal death. However, these concentrations are much higher than those occurring clinically during hyperhomocysteinemia. It is therefore important that a ∼ 10-fold increase in potency occurred in the presence of the glutamate precursor glutamine, when ERK_1/2 phosphorylation became inhibitable by NMDA or non-NMDA antagonists and dependent upon epidermal growth factor (EGF) receptor transactivation. However, glutamate release to the medium was reduced, suggesting that reversal of the cystine/glutamate antiporter, system X_c⁻ could be involved in potentiation of the response by causing a localized release of initially accumulated homocysteine. In agreement with this hypothesis further enhancement of ERK_1/2 phosphorylation occurred in the additional presence of cystine. Pharmacological inhibition of system X_c⁻ prevented the effect of micromolar homocysteine concentrations, and U0126-mediated inhibition of ERK_1/2 phosphorylation enhanced homocysteine-induced death. In conclusion, homocysteine interacts with system X_c⁻ like quisqualate (Venkatraman et al. 1994), by “self-sensitization” with initial accumulation and subsequent release in exchange with cystine and/or glutamate, establishing high local homocysteine concentrations, which activate adjacent ionotropic glutamate receptors and cause neurotoxicity.     

Stimulatory effect of ginsenosides on DNA, protein and lipid synthesis in rat bone marrow and participation of cyclic nucleotides.

Effects of several kinds of ginsenosides, saponins from Panax ginseng on DNA, RNA, protein and lipid synthesis in bone marrow were investigated. Single i.p. injection of 0.5--1 mg/100 g body weight of ginsenosides Rb2, Rc, Re and Rg1 4 h prior to the sacrifice increased DNA synthesis in bone marrow cells. RNA, protein and lipid synthesis were also increased. The direct addition of ginsenosides Rb1, Rb2 and Rc mixture (GNS) enhanced DNA synthesis. Cyclic AMP levels in bone marrow cells were decreased 20 min after i.p. injection of ginsenosides Rb2, Rc and Rg1 and the direct addition of ginsenosides Rb2, Rc and Rg1 also decreased cyclic AMP levels. While cyclic GMP levels were increased by administration of ginsenosides Rb2, Re and Rg1. Relationship between chemical structure and actions of ginsenosides and the role of cyclic nucleotides in the stimulatory action of ginsenosides on DNA synthesis in bone marrow cells were discussed.     

Idebenone inhibition of glutamate release from rat cerebral cortex nerve endings by suppression of voltage-dependent calcium influx and protein kinase A

The present study was aimed at investigating the effect and the possible mechanism of idebenone on endogenous glutamate release in nerve terminals of rat cerebral cortex (synaptosomes). Idebenone inhibited the release of glutamate that was evoked by exposing synaptosomes to the K⁺ channel blocker 4-aminopyridine (4-AP), and this phenomenon was concentration dependent. Inhibition of glutamate release by idebenone was prevented by chelating extracellular Ca²⁺, or by the vesicular transporter inhibitor bafilomycin A1, but was insensitive to DL-threo-beta-benzyl-oxyaspartate, a glutamate transporter inhibitor. Idebenone decreased the depolarization-induced increase in the cytosolic free Ca²⁺ concentration ([Ca²⁺]_C),whereas it did not alter the resting synaptosomal membrane potential or 4-AP-mediated depolarization. The inhibitory effect of idebenone on evoked glutamate release was prevented by blocking the Ca_v2.2 (N-type) and Ca_v2.1 (P/Q-type) channels, but not by blocking intracellular Ca²⁺ release or Na⁺/Ca²⁺ exchange. Furthermore, the idebenone effect on 4-AP-evoked Ca²⁺ influx and glutamate release was completely abolished by the protein kinase A (PKA) inhibitors, H89 and KT5720. On the basis of these results, it was concluded that idebenone inhibits glutamate release from rat cortical synaptosomes and this effect is linked to a decrease in [Ca²⁺]_C contributed by Ca²⁺ entry through presynaptic voltage-dependent Ca²⁺ channels and to the suppression of PKA signaling cascade.     

Comparative analysis of ginsenosides in different root parts and cultured cells from Chinese ginseng

HPLC analysis of extracts of different parts of two six-year-old Panax ginseng (Ginseng & Tobacco Company, South Korea) plantation roots demonstrated the presence of seven detectable ginsenosides (Rb₁, Rb₂, Rc, Rd, Rf, Rg₁, and Re). The total contents were 1.16 and 0.64% for main roots, 4.00 and 4.60% for rhizomes, 6.79, 4.38% for side roots (d = 0.4–0.5 cm), and 13.26 and 11.37 for fine roots (d = 0.1–0.15 cm). Four new ginseng callus lines were originated from side and fine roots. HPLC analysis of the qualitative and quantitative composition of the biomass after the first year of cultivation showed that all lines contained the full spectrum of ginsenosides (Rb₁, Rb₂, Rc, Rd, Rf, Rg₁, and Re), the total content of which varied from 0.2 to 0.4%. HPLC monitoring of these callus lines over five years of cultivation demonstrated gradual disappearance of glycosides Rb₂, Rc, Rd, and Rf from the ginsenoside spectrum. Loose calluses growing in medium containing 0.5 and 0.2 mg-liter 6-benzylaminopurine were used to start suspension cultures L-1 and L-2, respectively. HPLC analysis of the qualitative and quantitative composition of glycosides in suspension cultures showed that both lines contained only ginsenosides Rb₁, Rg₁, and Re, with a predominance of R_e ginsenoside. __________ Translated from Khimiko-Farmatsevticheskii Zhurnal, Vol. 42, No. 1, pp. 33–38, January, 2008.     

Inhibitory effect of glutamate release from rat cerebrocortical nerve terminals by α2 adrenoceptor agonist dexmedetomidine

The present study examined the effect of dexmedetomidine, an α₂ adrenoceptor agonist, on endogenous glutamate release in rat cerebral cortex nerve terminals (synaptosomes). We also explored the possible mechanism that triggers dexmedetomidine to act. Dexmedetomidine dose-dependently inhibited the release of glutamate evoked by the K⁺ channel blocker 4-aminopyridine. Presynaptic α_2A adrenoceptors were involved in this release inhibition, with the α_2A antagonist (but not by the α_2B/C antagonist) blocking the dexmedetomidine-mediated inhibition. The effect of dexmedetomidine on the evoked glutamate release was prevented by the chelating extracellular Ca²⁺ ions, and by the vesicular transporter inhibitor bafilomycin A1. However, the glutamate transporter inhibitor DL-threo-beta-benzyl-oxyaspartate did not have any effect on the action of dexmedetomidine. Dexmedetomidine decreased the degree of depolarization-induced increase in the intrasynaptosomal Ca²⁺ levels, but did not affect the synaptosomal membrane potential. The inhibitory effect of dexmedetomidine on evoked glutamate release was abolished by blocking the Ca_v2.2 (N-type) and Ca_v2.1 (P/Q-type) channels, but was insensitive to the endoplasmic reticulum ryanodine receptors or mitochondrial Na⁺/Ca²⁺ exchange. In addition, the mitogen-activated/extracellular signal-regulated kinase kinase (MEK) inhibitors prevented dexmedetomidine from inhibiting glutamate release. Further, western blotting showed that dexmedetomidine decreased the 4-aminopyridine-induced phosphorylation of mitogen-activated protein kinase/extracellular signal-regulated kinase 1 and 2 and synapsin I, the main presynaptic target of mitogen-activated protein kinase. Thus, we concluded that dexmedetomidine acts at α_2A adrenoceptors present on cerebrocortical nerve terminals inhibit the release of glutamate. We further concluded that this effect is linked to the suppression of voltage-dependent Ca²⁺ channels and mitogen-activated protein kinase activity.     

Histamine H3 receptor activation inhibits glutamate release from rat striatal synaptosomes

The release of glutamate from striatal synaptosomes induced by depolarisation with 4-aminopyridine (4-AP) was studied by a method based on the fluorescent properties of the NAPDH formed by the metabolism of the neurotransmitter by glutamate dehydrogenase.Ca²⁺-dependent, depolarisation-induced glutamate release was inhibited in a concentration-dependent manner by the selective histamine H₃ agonist immepip. Best-fit estimates were: maximum inhibition 60±10% and IC₅₀ 68±10 nM. The effect of 300 nM immepip on depolarisation-evoked glutamate release was reversed by the selective H₃ antagonist thioperamide in a concentration-dependent manner (EC₅₀ 23 nM, K_i 4 nM).In fura-2-loaded synaptosomes, the increase in the intracellular concentration of Ca²⁺ ([Ca²⁺]_i) evoked by 4-AP-induced depolarisation (resting level 167±14 nM; Δ[Ca²⁺]_i 88±15 nM) was modestly, but significantly reduced (29±5% inhibition) by 300 nM immepip. The action of the H₃ agonist on depolarisation-induced changes in [Ca²⁺]_i was reversed by 100 nM thioperamide.Taken together, our results indicate that histamine modulates the release of glutamate from corticostriatal nerve terminals. Inhibition of depolarisation-induced Ca²⁺ entry through voltage-dependent Ca²⁺ channels appears to account for the effect of H₃ receptor activation on neurotransmitter release. Modulation of glutamatergic transmission in rat striatum may have important consequences for the function of basal ganglia and therefore for the control of motor behaviour.     

Altered regulation of glutamate release and decreased functional activity and expression of GLT1 and GLAST glutamate transporters in the hippocampus of adolescent rats perinatally exposed to Δ9-THC

The long-term effects of perinatal Δ⁹-tetrahydrocannabinol (Δ⁹-THC) exposure – from gestational day (GD) 15 to postnatal day (PND) 9 – on hippocampal glutamatergic neurotransmission were studied in slices from the 40-day-old offspring of Δ⁹-THC exposed (Δ⁹-THC-rats) and vehicle-exposed (control) dams. Basal and in K+-evoked endogenous hippocampal glutamate outflow were both significantly decreased in Δ⁹-THC-rats. The effect of short Δ⁹-THC exposure (0.1 μM) on K⁺-evoked glutamate release disclosed a loss of the stimulatory effect of Δ⁹-THC on hippocampal glutamate release in Δ⁹-THC-rats, but not in controls. In addition, l-[³H]-glutamate uptake was significantly lower in hippocampal slices from Δ⁹-THC-rats, where a significant decrease in glutamate transporter 1 (GLT1) and glutamate/aspartate transporter (GLAST) protein was also detected. Collectively, these data demonstrate that perinatal exposure to cannabinoids induces long-term impairment in hippocampal glutamatergic neurotransmission that persist into adolescence.     

Biomass and content of ginsenosides and polyacetylenes in American ginseng roots can be increased without affecting the profile of bioactive compounds

Fifty selected roots from a 7-year-old American ginseng (Panax quinquefolium L.) plant population grown in Denmark, with root weights varying from 191 to 490 g fresh weight (FW), were investigated for bioactive ginsenosides and polyacetylenes (PAs) in order to determine the correlation between the content of ginsenosides and PAs and root FW. PAs (falcarinol, panaxydol) and ginsenosides (Rb₁, Rb₂, Rb₃, Rc, Rd, Re, Rg₁) were extracted from roots by sequential extraction with ethyl acetate and 80% methanol, respectively, and quantified in extracts by reverse-phase high-performance liquid chromatography (HPLC) using photodiode array detection. Total concentrations of PAs and ginsenosides varied between 150 and 780 mg/kg FW and 5,920 and 15,660 mg/kg FW, respectively. No correlation existed between the content of ginsenosides and PAs and root FW or between the total concentration of ginsenosides and PAs. Strong significant correlation was found between total content of ginsenosides and ginsenoside Rb₁ (r = 0.8190, P < 0.0001) and between total content of PAs and falcarinol (r = 0.9904, P < 0.0001). Based on the results of this study, it was concluded that it is possible to select large American ginseng roots for increased biomass production and concentration of bioactive ginsenosides and PAs without affecting the profile of bioactive compounds. Ginsenoside Rb₁ and falcarinol were found to be important selection parameters for identifying superior genotypes with the highest content of bioactive compounds.     

RETRACTED ARTICLE: The retention behavior of ginsenosides in HPLC and its application to quality assessment of Radix Ginseng

This study systematically investigated the retention behavior of seven neutral ginsenosides Rg₁, Re, Rf, Rb₁, Rb₂, Rc, Rd, and an acidic ginsenoside R₀, the major pharmacologically active components of Radix Ginseng with RP-HPLC. The effects of solvent, pH value, ionic strength of the mobile phase, and column temperature were investigated using an octadecylsiloxanebonded silica gel column. Based on the ginsenosides’ retention characteristics, the concentration of acetonitrile and the gradient of the mobile phase needed to maintain the baseline separation of the major neutral ginsenosides in Radix Ginseng were theoretically predicted. Furthermore, the ionic strength of mobile-phase necessary to achieve good resolution of the neutral ginsenosides and acidic ginsenosides was carefully investigated. According to the results of the quantitative analysis of ginsenosides in eight batches of ginseng samples from different sources, the developed HPLC technique may be a valuable tool for the quality assessment of Radix Ginseng. This article was retracted as it was printed by error in this issue of APR.     

Regional differences in the effects of isoflurane on neurotransmitter release

Stimulus evoked neurotransmitter release requires that Na⁺ channel-dependent nerve terminal depolarization be transduced into synaptic vesicle exocytosis. Inhaled anesthetics block presynaptic Na⁺ channels and selectively inhibit glutamate over GABA release from isolated nerve terminals, indicating mechanistic differences between excitatory and inhibitory transmitter release. We compared the effects of isoflurane on depolarization-evoked [³H]glutamate and [¹⁴C]GABA release from isolated nerve terminals prepared from four regions of rat CNS evoked by 4-aminopyridine (4AP), veratridine (VTD), or elevated K⁺. These mechanistically distinct secretegogues distinguished between Na⁺ channel- and/or Ca²⁺ channel-mediated presynaptic effects. Isoflurane completely inhibited total 4AP-evoked glutamate release (IC₅₀ = 0.42 ± 0.03 mM) more potently than GABA release (IC₅₀ = 0.56 ± 0.02 mM) from cerebral cortex (1.3-fold greater potency), hippocampus and striatum, but inhibited glutamate and GABA release from spinal cord terminals equipotently. Na⁺ channel-specific VTD-evoked glutamate release from cortex was also significantly more sensitive to inhibition by isoflurane than was GABA release. Na⁺ channel-independent K⁺-evoked release was insensitive to isoflurane at clinical concentrations in all four regions, consistent with a target upstream of Ca²⁺ entry. Isoflurane inhibited Na⁺ channel-mediated (tetrodotoxin-sensitive) 4AP-evoked glutamate release (IC₅₀ = 0.30 ± 0.03 mM) more potently than GABA release (IC₅₀ = 0.67 ± 0.04 mM) from cortex (2.2-fold greater potency). The magnitude of inhibition of Na⁺ channel-mediated 4AP-evoked release by a single clinical concentration of isoflurane (0.35 mM) varied by region and transmitter: Inhibition of glutamate release from spinal cord was greater than from the three brain regions and greater than GABA release for each CNS region. These findings indicate that isoflurane selectively inhibits glutamate release compared to GABA release via Na⁺ channel-mediated transduction in the four CNS regions tested, and that differences in presynaptic Na⁺ channel involvement determine differences in anesthetic pharmacology.     

The retention behavior of ginsenosides in HPLC and its application to quality assessment of radix ginseng

This study systematically investigated the retention behavior of seven neutral ginsenosides Rg₁, Re, Rf, Rb₁, Rb₂, Rc, Rd, and an acidic ginsenoside R₀, the major pharmacologically active components of Radix Ginseng with RP-HPLC. The effects of solvent, pH value, ionic strength of the mobile phase, and column temperature were investigated using an octadecylsiloxane-bonded silica gel column. Based on the ginsenosides’ retention characteristics, the concentration of acetonitrile and the gradient of the mobile phase needed to maintain the baseline separation of the major neutral ginsenosides in Radix Ginseng were theoretically predicted. Furthermore, the ionic strength of mobile-phase necessary to achieve good resolution of the neutral ginsenosides and acidic ginsenosides was carefully investigated. According to the results of the quantitative analysis of ginsenosides in eight batches of ginseng samples from different sources, the developed HPLC technique may be a valuable tool for the quality assessment of Radix Ginseng.     

AMG-1和腺苷对大鼠脑突触体谷氨酸释放的影响

观察了腺苷类化合物AMG-1对大鼠脑突触体前膜谷氨酸(glu)释放的影响。AMG-1在0.1～0.3 mmol·L^-1能明显抑制突触前膜Ca²⁺-依赖性glu的释放,并呈现剂量—效应关系。其作用强度与腺苷基本相似。提示AMG-1对脑保护作用可能与它激活腺苷A₁受体,从而抑制兴奋性氨基酸释放有关。     

Bromocriptine, an ergot alkaloid, inhibits excitatory amino acid release mediated by glutamate transporter reversal

Bromocriptine, a dopamine D₂ receptor agonist, has widely been used for patients with Parkinson's disease. The aim of the present study was to investigate the effect of bromocriptine on glutamate transporter. Since the astroglial glutamate transporter GLT-1 (EAAT2) is the predominant isoform in the forebrain, we generated EAAT2-expressing human embryonic kidney cells and immortalized mouse astrocytes. In the present studies, we observed a GLT-1-immunoreactive band and significant Na⁺-dependent d-[³H] aspartate uptake. Furthermore, the glutamate transporter inhibitors, dl-threo-β-benzyloxyaspartic acid (TBOA) and dihydrokainate (DHK), displayed a dose-dependent reduction of d-[³H] aspartate uptake in both types of cells. In contrast, cells exposed to either chemical anoxia or high KCl elicited a marked release of d-[³H] aspartate, and the release was inhibited by TBOA and DHK, implying the contribution of glutamate transporter reversal. Interestingly, we found that bromocriptine dose-dependently inhibits d-[³H] aspartate release elicited by chemical anoxia or high KCl, while no changes occurred in the uptake. The inhibitory action of bromocriptine was not affected by sulpiride, a dopamine D₂ receptor antagonist. On the other hand, bromocriptine had no effect on swelling-induced d-[³H] aspartate release, which is mediated by volume-regulated anion channels. In vivo studies revealed that bromocriptine suppresses the excessive elevation of glutamate levels in gerbils subjected to transient forebrain ischemia in a manner similar to DHK. Taken together, these results provide evidence that bromocriptine inhibits excitatory amino acid release via reversed operation of GLT-1 without altering forward transport.     

Ginsenosides that produce differential antinociception in mice.

Ginsenoside Rc, Rd, and Re induced antinociception in writhing and formalin tests among five representative ginsenosides: Rb1, Rc, Rd, Re, and Rg1. However, these ginsenosides had no effect in the tail-flick test. The antinociceptive effects induced by three ginsenosides were dose dependent. ED50 was 20.5 (7.3-57.4 mg/kg) for Rc, 17 (11.0-27.6 mg/kg) for Rd, and 3.5 (1-12 mg/ kg) for Re in the writhing test and 62 (42-90 mg/kg) for Rc, 45 (20.5-99.0 mg/kg) for Rd, and 82 (48-139 mg/kg) for Re in the second phase of the formalin test. The antinociceptive effects were not blocked by the opioid receptor antagonist naloxone in the writhing and formalin tests. These three ginsenosides did not affect motor function. Ginsenoside Rc and Rd induced hypothermia for 30 to 60 min, and ginsenoside Rc induced hyperthemia after 150 min of treatment at doses of 100 mg/kg. These results suggest that ginsenosides such as Rc, Rd, or Re inhibit mainly chemogenic pain rather than thermal pain by the nonopioid system in mice.