RESUMO
PURPOSE: We investigated the influence of diabetes mellitus (DM), glycemic control with insulin, cimetidine (Oct2 inhibitor) and metformin (Oct2 substrate) on the kinetic disposition of GAB in rats. MAIN METHODS: Male Wistar rats were divided in five groups and all animals received an oral dose of 50â¯mg/kg GAB: (vehicleâ¯+â¯GAB), cimetidineâ¯+â¯GAB (single dose of cimetidine [100â¯mg/kg] intraperitoneally 1â¯h before GAB), metforminâ¯+â¯GAB (single dose of metformin 100â¯mg/kg by gavage concomitantly with GAB), DMâ¯+â¯GAB (single dose of 40â¯mg/kg streptozotocin (STZ) intravenously) and DMâ¯+â¯GABâ¯+â¯insulin (single dose 40â¯mg/kg STZ intravenously and 2â¯IU insulin twice daily for 15â¯days). Pharmacokinetic analysis was based on plasma and urine data concentrations. KEY FINDINGS: No differences in pharmacokinetic parameters were observed between vehicleâ¯+â¯GABâ¯×â¯cimetidineâ¯+â¯GAB and vehicleâ¯+â¯GABâ¯×â¯metforminâ¯+â¯GAB groups. Diabetes increased the fraction of GAB excreted unchanged in urine (vehicleâ¯+â¯GAB: 0.48 [0.38-0.58]; DMâ¯+â¯GAB: 0.83 [0.62-1.04]; DMâ¯+â¯GABâ¯+â¯insulin: 0.88 [0.77-0.93]) (mean [95% confidence interval]) without any changes in GAB exposure. Insulin treated diabetic animals showed higher renal clearance compared to control (vehicleâ¯+â¯GAB: 0.25 [0.18-0.30] L/h·kg; DMâ¯+â¯GABâ¯+â¯insulin: 0.55 [0.45-1.43] L/h·kg), which was attributed to the diabetes-induced glomerular hyperfiltration. SIGNIFICANCE: Glomerular filtration is the main mechanism of renal excretion of GAB without significant contribution of Oct2 active transport.
Assuntos
Aminas , Cimetidina , Ácidos Cicloexanocarboxílicos , Diabetes Mellitus Experimental/tratamento farmacológico , Metformina , Transportador 2 de Cátion Orgânico/antagonistas & inibidores , Ácido gama-Aminobutírico , Aminas/farmacocinética , Aminas/farmacologia , Animais , Cimetidina/farmacocinética , Cimetidina/farmacologia , Ácidos Cicloexanocarboxílicos/farmacocinética , Ácidos Cicloexanocarboxílicos/farmacologia , Diabetes Mellitus Experimental/metabolismo , Gabapentina , Masculino , Metformina/farmacocinética , Metformina/farmacologia , Ratos , Ratos Wistar , Ácido gama-Aminobutírico/farmacocinética , Ácido gama-Aminobutírico/farmacologiaAssuntos
Ácido gama-Aminobutírico/administração & dosagem , Ácido gama-Aminobutírico/farmacologia , Ácido gama-Aminobutírico/farmacocinética , Analgésicos/uso terapêutico , Ácido gama-Aminobutírico/efeitos adversos , Dor/tratamento farmacológico , Dor/fisiopatologia , Dor Pós-Operatória/tratamento farmacológico , Dor Pós-Operatória/prevenção & controle , Queimaduras/tratamento farmacológico , Cuidados Pré-Operatórios , Doença Crônica , Interações MedicamentosasRESUMO
Gabapentin (GBP) is a water soluble low molecular weight drug with anticonvulsivant and antinociceptive activity. In animal models, systemic administration regimes resembling chronic exposure to this drug (50mg/kg, twice a day during one week), induce memory impairment. Aiming to gain further insight on the mechanisms involved in this process, a monolithic implant that releases constant plasma levels during one-week was designed. GBP-loaded poly(epsilon-caprolactone) matrices were produced by means of a simple and reproducible melt-molding/compression procedure. In vitro release studies firstly comprised uncoated implants that displayed release profiles according to a pseudo-first order model. In order to further regulate the release, two-sided coated implants where drug-free layers would perform as membranes controlling the delivery rate were prepared. A more moderated burst effect and a relatively linear (zero-order) release between days 1 and 7 were apparent. Implants were investigated in vivo and the plasma levels monitored during 10 days. Findings indicated that after a more pronounced release during day 1 and the achievement of the levels in blood comparable to a twice-a-day intraperitoneal management, relatively constant levels were attained until day 7. Overall results support the usefulness of this manufacturing method for the production of implants to attain more prolonged GBP release profiles in memory animal studies.
Assuntos
Aminas/administração & dosagem , Ácidos Cicloexanocarboxílicos/administração & dosagem , Poliésteres/administração & dosagem , Ácido gama-Aminobutírico/administração & dosagem , Aminas/química , Aminas/farmacocinética , Animais , Ácidos Cicloexanocarboxílicos/química , Ácidos Cicloexanocarboxílicos/farmacocinética , Preparações de Ação Retardada , Gabapentina , Masculino , Camundongos , Poliésteres/química , Solubilidade , Tecnologia Farmacêutica , Ácido gama-Aminobutírico/química , Ácido gama-Aminobutírico/farmacocinéticaRESUMO
Postnatal development changes in mechanisms of synaptosomal amino acid transport have been studied in rat cerebral cortex. Specific uptake of radiolabeled L-serine was examined and compared with that of radiolabeled GABA using synaptosomes-enriched fractions freshly prepared from cerebral cortex at different postnatal days from the birth to young adulthood. The preparations were incubated with 10 nM of [3H]L-serine and 10 nM of [3H]-GABA in either the presence or absence of NaCl, KCl or choline chloride, at 2 and 30 degrees C, for different periods up to 30 min. The uptake of [3H]l-serine was temperature dependent in synaptosomal fractions prepared from cerebral cortex of rats in postnatal days 5, 7, 13 and 21, but stronger dependence was observed in adult brain, irrespective of the presence of Na+, K+ or choline ions. At all postnatal ages studied, [3H]-GABA uptake showed a high activity in the presence of Na+ ions and at 30 degrees C. The values of Km were 90-489 microM in L-serine uptake. However, in the uptake of GABA the values of Km were 80-150 microM. The highest values of Vmax were obtained at 5 and 21 postnatal days for both transport systems. These results indicate that the uptake of l-serine and GABA are regulated differentially during postnatal development.
Assuntos
Córtex Cerebral/crescimento & desenvolvimento , Serina/metabolismo , Sinaptossomos/metabolismo , Ácido gama-Aminobutírico/metabolismo , Animais , Animais Recém-Nascidos , Transporte Biológico , Técnicas In Vitro , Cinética , Masculino , Ratos , Ratos Wistar , Serina/farmacocinética , Temperatura , Fatores de Tempo , Ácido gama-Aminobutírico/farmacocinéticaRESUMO
(1) In this study, we examined the effects of crude venom from the spider Parawixia bistriata on glutamate and GABA uptake into synaptosomes prepared from rat cerebral cortex. Addition of venom to cortical synaptosomes stimulated glutamate uptake and inhibited GABA uptake in a concentration-dependent manner. (2) The venom was fractionated using reverse-phase high-performance liquid chromatography on a preparative column. The fraction that retained glutamate uptake-stimulating activity was further purified on a reverse-phase analytical column followed by ion-exchange chromatography. (3) The active fraction, referred to as PbTx1.2.3, stimulated glutamate uptake in synaptosomes without changing the K(M) value, and did not affect GABA uptake. Additional experiments showed that the enhancement of glutamate uptake by PbTx1.2.3 occurs when ionotropic glutamate receptors or voltage-gated sodium and calcium channels are completely inhibited or when GABA receptors and potassium channels are activated, indicating that the compound may have a direct action on the transporters. (4) In an experimental model for glaucoma in which rat retinas are subjected to ischemia followed by reperfusion, PbTx1.2.3 protected neurons from excitotoxic death in both outer and inner nuclear layers, and ganglion cell layers. (5) This active spider venom component may serve as a basis for designing therapeutic drugs that increase glutamate clearance and limit neurodegeneration.
Assuntos
Ácido Glutâmico/farmacocinética , Fármacos Neuroprotetores/isolamento & purificação , Fármacos Neuroprotetores/farmacologia , Venenos de Aranha/isolamento & purificação , Extratos de Tecidos/farmacologia , Animais , Brasil , Isótopos de Carbono , Córtex Cerebral/citologia , Cromatografia Líquida de Alta Pressão/métodos , Cromatografia por Troca Iônica , Modelos Animais de Doenças , Relação Dose-Resposta a Droga , Glaucoma/tratamento farmacológico , Glaucoma/fisiopatologia , Ácido Glutâmico/efeitos dos fármacos , Ácido Glutâmico/metabolismo , Canais Iônicos/efeitos dos fármacos , Canais Iônicos/metabolismo , Canais Iônicos/fisiopatologia , Masculino , Fármacos Neuroprotetores/química , Ratos , Ratos Wistar , Receptores de Glutamato Metabotrópico/efeitos dos fármacos , Receptores de Glutamato Metabotrópico/fisiologia , Retina/efeitos dos fármacos , Retina/patologia , Retina/ultraestrutura , Venenos de Aranha/química , Venenos de Aranha/farmacologia , Aranhas , Sinaptossomos/efeitos dos fármacos , Sinaptossomos/metabolismo , Trítio , Ácido gama-Aminobutírico/efeitos dos fármacos , Ácido gama-Aminobutírico/metabolismo , Ácido gama-Aminobutírico/farmacocinéticaRESUMO
Delta-aminolevulinic acid (ALA) is the precursor in the biosynthesis of porphyrins. The knowledge of both the regulation of ALA entrance and efflux from the cells and the control of porphyrin biosynthesis is essential to improve ALA-mediated photodynamic therapy. In this work, we studied the regulation of ALA uptake and efflux by endogenously accumulated ALA and/or porphyrins in murine mammary adenocarcinoma cells. Under our set of conditions, the haem synthesis inhibitor succinyl acetone completely prevented porphobilinogen and porphyrin synthesis from ALA, and led to an increase in the intracellular ALA pool. However, neither intracellular ALA nor porphyrin pools regulate ALA uptake or efflux during the first 15 min of the process. Based on temperature dependence data, ALA but not gamma-aminobutyric acid (GABA) efflux is mediated by a diffusion mechanism. Moreover, the addition of extracellular GABA not only did not influence the rate of ALA efflux but on the contrary it affected ALA uptake, showing the contribution of a saturable mechanism for the uptake, but not for the efflux of ALA from the cells.
Assuntos
Adenocarcinoma/patologia , Ácido Aminolevulínico/farmacocinética , Neoplasias Mamárias Animais/patologia , Fármacos Fotossensibilizantes/farmacocinética , Animais , Camundongos , Fotoquimioterapia , Porfirinas/biossíntese , Células Tumorais Cultivadas , Ácido gama-Aminobutírico/farmacocinéticaRESUMO
The effect of the beta-scorpion toxin, TiTX gamma on the release of [3H]GABA from rat brain cortical slices is described. The stimulatory effect of TiTX gamma on the release of [3H]GABA was dependent on incubation time and TiTX gamma concentration with an EC50 of 0.19 microM. The scorpion toxin effect was calcium dependent and was completely inhibited by tetrodotoxin. beta-Alanine also induced the release of [3H]GABA and this effect was not inhibited by tetrodotoxin but was additive in the presence of TiTX gamma. The data suggest a neuronal origin for the release of [3H]GABA by TiTX gamma.
Assuntos
Córtex Cerebral/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Neurotoxinas/farmacologia , Canais de Sódio/efeitos dos fármacos , Membranas Sinápticas/efeitos dos fármacos , Ácido gama-Aminobutírico/metabolismo , Animais , Cálcio/metabolismo , Sinalização do Cálcio/efeitos dos fármacos , Sinalização do Cálcio/fisiologia , Córtex Cerebral/metabolismo , Relação Dose-Resposta a Droga , Interações Medicamentosas/fisiologia , Ácido Egtázico/farmacologia , Neurônios/metabolismo , Técnicas de Cultura de Órgãos , Cloreto de Potássio/farmacologia , Ratos , Venenos de Escorpião , Canais de Sódio/metabolismo , Membranas Sinápticas/metabolismo , Tetrodotoxina/farmacologia , Trítio/farmacocinética , beta-Alanina/farmacologia , Ácido gama-Aminobutírico/farmacocinéticaRESUMO
The exact mechanisms by which 3-nitropropionic acid (3-NP), a naturally occurring plant and fungal neurotoxin, exerts its neurotoxic effects are not fully understood. However, blockage of ATP synthesis by the irreversible inhibition of succinate dehydrogenase activity, increased production of free radicals, and secondary excitotoxicity have been implicated in its actions. In the present study, synaptic vesicle preparations from brain of adult rats were incubated with 3-NP at final concentrations ranging from 0.01 to 10 mM for the determination of glutamate uptake. The effect of 3-NP on gamma-aminobutyric acid (GABA) and glycine uptake was also studied. Glutamate incorporation into vesicles was inhibited by 3-NP in a dose-dependent manner, whereas doses of up to 10 mM neurotoxin did not affect GABA or glycine uptake. Moreover, 3-NP did not inhibit the ATPase activity of synaptic vesicles. These findings indicate that low concentrations of 3-NP are able to selectively prevent vesicular glutamate storage, and this may represent at least one of the mechanisms responsible for the neurotoxic effects of 3-NP.
Assuntos
Química Encefálica , Ácido Glutâmico/farmacocinética , Propionatos/farmacologia , Vesículas Sinápticas/efeitos dos fármacos , Vesículas Sinápticas/metabolismo , Adenosina Trifosfatases/metabolismo , Animais , Relação Dose-Resposta a Droga , Ativação Enzimática/efeitos dos fármacos , Glicina/farmacocinética , Masculino , Neurotoxinas/farmacologia , Nitrocompostos , Ratos , Ratos Wistar , Vesículas Sinápticas/química , Ácido gama-Aminobutírico/farmacocinéticaRESUMO
Daily changes in gamma-aminobutyric acid (GABA) turnover rate were studied in the golden hamster retina. This parameter showed significant variations throughout the light-dark cycle, with minimal values during the day. Retinal glutamic acid decarboxylase (GAD) activity was higher at midnight than at noon. Moreover, [3H]GABA binding significantly varied throughout the 24-h cycle, with maximal values during the day. Saturation studies performed at 12:00 and 24:00 h indicated that the maximal concentration of [3H]GABA binding sites (Bmax) was significantly higher at noon, whereas the dissociation constant (Kd) remained unchanged. High K+-induced GABA release was significantly higher at midnight than at midday. Daily variations in retinal GABA turnover rate, GABA release, and in its specific binding persisted in golden hamsters exposed to constant darkness. In summary, these results support the idea of a circadian clock-controlled GABAergic activity in the hamster retina.
Assuntos
Ritmo Circadiano/fisiologia , Glutamato Descarboxilase/metabolismo , Mesocricetus/metabolismo , Inibição Neural/fisiologia , Neurônios/metabolismo , Retina/metabolismo , Ácido gama-Aminobutírico/metabolismo , Animais , Sítios de Ligação/efeitos dos fármacos , Sítios de Ligação/fisiologia , Radioisótopos de Carbono/farmacocinética , Cricetinae , Ácido Glutâmico/metabolismo , Ácido Glutâmico/farmacocinética , Masculino , Mesocricetus/anatomia & histologia , Neurônios/citologia , Neurônios/efeitos dos fármacos , Estimulação Luminosa , Ensaio Radioligante , Retina/citologia , Retina/efeitos dos fármacos , Ácido gama-Aminobutírico/farmacocinéticaRESUMO
The sharp interruption of the intracortical instillation of exogenous gamma-aminobutyric acid (GABA), generates an epileptic focus in mammals. Seizures elicited by GABA withdrawal last several days or weeks. The present work reports that GABA withdrawal-induced hyperexcitability can be produced in vitro: a sudden withdrawal of GABA (5 mM; 120 min) or benzodiazepine (60 microM flunitrazepam) from the superfusion, induced a gradual increase in the amplitude of the evoked population spike (PS) recorded on neocortical slices. PS enhancement reached 150% above the control value 2.5 h after GABA withdrawal. GABA withdrawal-induced hyperexcitability was facilitated by progesterone. PS enhancement induced by GABA withdrawal was associated with an impairment of GABA transmission occurring before epileptiform discharges were fully established. Paired pulse inhibition and evoked [3H]-GABA release appear decreased; suggesting that cortical hyperexcitability as a result of GABA withdrawal involves pre-synaptic changes. Specific muscimol binding decreased during GABA superfusion but recovered after GABA withdrawal. However, the sensitivity of the post-synaptic response to 3alpha-OH-5alpha-pregnan-20-one or allopregnanolone (alloP) was enhanced after GABA withdrawal, suggesting a functional change in the GABA(A) receptors. The changes described may be the cellular correlates of the withdrawal syndromes appearing after interruption of the administration of GABA(A) receptor agonists.