Free interstitial levels of metformin in the liver of healthy and diabetic Wistar rats

Abstract In the present study, free interstitial levels reached by metformin in the liver were investigated in control and diabetic rats by microdialysis. Firstly, a bioanalytical method using an HPLC-UV system to determine the drug concentration in microdialysis samples was validated. The blood glucose levels and biochemical parameters were investigated in control and diabetic animals. Following that, both groups received a dose of 50 mg/kg of metformin iv bolus and the free interstitial levels reached in the liver were assessed by microdialysis. The method was validated according to FDA guidelines being suitable to quantify free concentrations of metformin in the liver of control and diabetics rats. Free exposure to metformin was similar in control and diabetic animals: AUC0-∞ 118.50 ± 40.18 vs 112.93 ± 50.25 µg.h/mL, respectively. The half-life in tissue was similar to that described in the literature for plasma. Hence diabetes induced by streptozotocin after administration of nicotinamide in our study did not damage the renal and hepatic function of the animals. The levels reached in the liver were 1.6 times higher than the free plasma concentrations, demonstrating higher liver penetration of metformin. This is the first investigation in liver interstitial concentration of metformin in control and diabetic rats

Arginine and glutamate levels in the gingival crevicular fluid from patients with chronic periodontitis

The objectives of this study were to determine arginine and glutamate levels in the gingival crevicular fluid (GCF) of adult chronic periodontitis patients versus periodontally healthy controls, and to compare two kinds of microdialysis probes: normal and U-shaped probes. The analysis of GCF components was developed to improve the diagnosis of periodontal disease (PD). Proteolysis in the periodontal tissues increases the concentration of amino acids (aa) in the GCF and the levels of these aa may reveal PD features and stages. GCF samples were collected by microdialysis in situ from 5 periodontally affected sites (probing depth >5 mm, clinical attachment loss >3 mm) in 14 adult chronic periodontitis patients and from 14 adult periodontally healthy controls. Capillary zone electrophoresis coupled to laser induced fluorescence detection was used to measure concentration of arginine and glutamate in the GCF. Data were analyzed statistically by ANOVA and Tukey's post-hoc tests (?=0.05). Arginine concentration was increased (p<0.001) and glutamate concentration was decreased (p<0.001) in chronic periodontitis patients as compared to controls. There were no significant differences (p=0.069) between the normal and U-shaped probes. In conclusion, the increase of arginine and decrease of glutamate concentration in GCF were associated to the presence of periodontitis, and might be used as markers to recognize periodontally susceptible subjects as well as to evaluate the treatment course.

Os objetivos deste estudo foram determinar os níveis de arginina e glutamato no fluido gengival crevicular (FGC) em pacientes com periodontite crônica contra controles saudáveis e comparar dois tipos de cânulas de microdiálise: normais e em forma de U. A análise dos componentes do FGC desenvolveu-se para melhorar o diagnóstico da doença periodontal (DP). A proteólise dos tecidos periodontais aumenta a concentração de aminoácidos (aa) no FGC e os níveis destes aa podem revelar as características e estágios da DP. Amostras de FGC foram obtidas pela técnica de microdiálise in situ de cinco zonas com o periodonto afetado (profundidade de sondagem >5 mm, perda da inserção clínica >3 mm) em 14 pacientes adultos com periodontite crônica e 14 controles saudáveis. Para medir a concentração de arginina e glutamato no GFC, usou-se a técnica de eletroforese capilar com detecção de fluorescência induzida por laser. Nos pacientes com periodontite crônica, a concentração de arginina aumentou significantemente (p<0.001), enquanto a de glutamato diminuiu significantemente (p<0.001) em comparação aos controles. Não houve diferenças significantes (p=0.069) entre as cânulas normais e as cânulas em forma de U. Conclui-se que o aumento da concentração de arginina e diminuição de glutamato no FGC estavam associados à presença de periodontite, e podem ser usados como marcadores para identificar pacientes suscetíveis à periodontite bem como avaliar a evolução do tratamento.

Detection of amino acids in human nasal mucosa using microdialysis technique: increased glutamate in allergic rhinitis.

Amino acids, the smaller basic biochemical units of neuropeptides, have not been evaluated in the nasal cavity. The purpose of this study was to measure the concentration of neurotransmitting amino acids of the central nervous system, glutamate, aspartate, serine, taurine (2-aminoethane sulfonic acid; a conditionally essential amino acids), and GABA (gamma-amino-butyric acid; an amino acid produced in the brain), in nasal mucosa of allergic rhinitis patients and normal controls using a microdialysis technique. A microdialysis probe appropriate for use on human nasal mucosa was developed using Cuprophan hollow fiber. Glutamate concentration in allergy group was significantly higher (p = 0.004) than in control group, while the concentrations of the other four amino acids showed no significant difference between the two groups. Our findings and review of the literature suggest that glutamate is one of the most potent neurotransmitters associated with the parasympathetic nerve in the nasal cavity, and that the microdialysis technique is useful in studying the pharmacokinetics in situ and local organ chemistry of the nasal cavity.

Activación del sistema de los opiodes endógenos por dosis subconvulsivamantes de metrazol / Activation of the endogenous opioid system with metrazol subconvulsivant dosis

Se investigaron las alteraciones en el sistema de los opioides endógenos en el cerebro de la rata, inducidas por la administración de una dósis subconvulsivante de metrazol (PTZ) (30 mg/kg i.p.). Por medio de experimentos de microdiálisis, encontramos durante los primeros 60 min después del tratamiento, una liberación importante de opiodes endógenos en el hipocampo y la amígdala cerebral. Posteriormente, los valores regresaron a los niveles basales. Por autorradiografía se observó un decremento en los niveles de los receptores mu en varias estructuras cerebrales. Mediante el análisis de la unión a receptores las membranas cerebrales, se confirmó un decremento en el número de estos receptores, sin cambios en su afinidad. En la aplicación de la prueba de Randall-Sellito, se encontró un aumento en el umbral de respuesta a estímulos dolorosos, durante los primeros 30 min. después del PTZ. Finalmente, experimentos de hibridación in situ revelaron un incremento en los niveles de la proencefalina a las 24 hrs después del tratamiento. Nuestros resultados indican que la administración de dosis subconvulsivante de PTZ activan de manera importante al sistema de los opiodes endógenos. Estos cambios resultan relevantes para entender el proceso del epileptogénesis y los mecanismos involucrados en el mismo