RESUMEN
Absorption and scattering processes in biological tissues are studied through reflectance spectroscopy in tissue-like phantoms. For this aim, an experimental setup is designed to independently control both processes in hemoglobin and intralipid solutions. From the analysis of the obtained spectra, a simple empirical power law equation is found that relates absorbance with scattering and absorption coefficients. This relationship includes three wavelength independent parameters, which can be determined geometry from in vitro measurements for each particular optical optode. The dependence of the optical path length on the absorption and scattering coefficients is also analyzed, and estimations of this parameter for physiological conditions are presented. This study is useful to better understand the scattering phenomena in biological tissue, and to obtain absolute concentration of absorber particles when a homogeneous medium can be assumed.
Asunto(s)
Emulsiones Grasas Intravenosas/química , Hemoglobinas/química , Análisis Espectral/métodos , Algoritmos , Fantasmas de Imagen , Dispersión de Radiación , Soluciones/químicaRESUMEN
D-Arginine is extensively used in studies on L-arginine/nitric oxide pathway as an inactive form of L-arginine, even in man. In addition, it has previously been reported that this D-amino acid appears to have pharmacological activity. The present work aimed at evaluating the toxicity and pharmacology of D-arginine administered by the intraperitoneally route in albino male mice. Toxicity of D-arginine, alone as well as in the presence of propranolol and betamethasone was evaluated. D-Arginine in mice showed a light toxicity order (DL50: 2800 mg/kg). Previous injection of the beta-adrenoceptor blocker, propranolol (2 mg/kg, intraperitoneally), or betamethasone (0.5 mg/kg, intraperitoneally) produced a decrease in the toxicity of D-arginine (LD50: 3600 mg/kg, 3300 mg/kg, respectively). Also, a neuropharmacological screening of D-arginine using behavioural, neurological, autonomic, barbiturate-induced sleep time and pentylenetetrazole-induced convulsions tests were performed. D-Arginine 700 mg/kg displayed central stimulant properties, whereas a depressant profile was observed at a dose of 1400 mg/kg. In addition, D-arginine 1400 mg/kg produced a potentiation of pentobarbital sleeping time and a marked anticonvulsivant action against pentylenetetrazole.
Asunto(s)
Arginina/toxicidad , Sistema Nervioso Autónomo/efectos de los fármacos , Conducta Animal/efectos de los fármacos , Sistema Nervioso Central/efectos de los fármacos , Antagonistas Adrenérgicos beta/farmacología , Animales , Arginina/administración & dosificación , Arginina/farmacología , Betametasona/farmacología , Relación Dosis-Respuesta a Droga , Interacciones Farmacológicas , Hipnóticos y Sedantes , Masculino , Ratones , Actividad Motora/efectos de los fármacos , Pentilenotetrazol , Fenobarbital , Propranolol/farmacología , Convulsiones/inducido químicamente , Convulsiones/prevención & control , Sueño/efectos de los fármacosRESUMEN
Nitric oxide (NO) is a versatile molecule involved in a wide range of biological processes. Under physiological conditions, NO reacts with oxyhemoglobin (OxyHb) to form methemoglobin (MetHb) at a very high rate. Previous works have shown that MetHb is proportional to NO and that MetHb absorption contributes to the in vivo absorption spectrum recorded with visible spectroscopy using optical fibers. However, in vivo spectrophotometric monitoring of a single molecule has long been a problem because the overlapping of OxyHb, deoxyhemoglobin (DeoxyHb), MetHb, cytochromes and other chromophores absorption spectra make in vivo quantitative spectroscopy difficult. The aim of this work was to evaluate the possibility of obtaining the contribution of each main endogenous chromophore, especially OxyHb, DeoxyHb and MetHb, to the in vivo visible absorption spectrum recorded from rat cortex, hippocampus and striatum. A least-square approach with a fitting equation containing the in vitro spectrum of the main endogenenous chromophores was used. The validity of this approach was studied by increasing the endogenous MetHb level with NO infusion and by biliverdin perfusion. Data indicate that in vivo visible spectroscopy in combination with the least-square fitting method may be a useful tool for gaining insight into the roles of NO, hemoglobins and the interaction between them even from small cerebral areas.
Asunto(s)
Encéfalo/metabolismo , Hemoglobinas/análisis , Neuroquímica/métodos , Óxido Nítrico/análisis , Oxihemoglobinas/análisis , Análisis Espectral/métodos , Animales , Biliverdina/farmacología , Encéfalo/anatomía & histología , Encéfalo/irrigación sanguínea , Química Encefálica/fisiología , Corteza Cerebral/metabolismo , Circulación Cerebrovascular/fisiología , Hemoglobinas/metabolismo , Hipocampo/metabolismo , Masculino , Metahemoglobina/metabolismo , Neostriado/metabolismo , Neuroquímica/instrumentación , Óxido Nítrico/metabolismo , Consumo de Oxígeno/fisiología , Oxihemoglobinas/metabolismo , Ratas , Ratas Sprague-Dawley , Análisis Espectral/instrumentaciónRESUMEN
Nitric oxide (NO) is a versatile molecule involved in a wide range of biological processes. Under physiological conditions, NO reacts with oxyhemoglobin (OxyHb) to form methemoglobin (MetHb) at a very high rate. Microdialysis studies have used hemoglobin solutions as a trapping method to quantify NO in vivo. The methodology described here uses the microcapillary network with endogenous OxyHb instead of microdialysis probe with exogenous OxyHb for monitoring MetHb as an indirect index of NO levels by in vivo spectroscopy using optical fibers. This new method has been validated in rat cerebral cortex by the infusion of NO or well-known drug-induced changes in NO concentration (NMDA agonists and a NO-synthase inhibitor) and by comparing results with simultaneous voltammetric recordings. Results indicate that this spectroscopy technique is able to record large increases in MetHb levels and to detect reductions of its basal levels. In addition, data show that similar changes and kinetics can be observed with both techniques. Thus, intravascular MetHb can be used as an indirect index of NO levels. It is proposed that in vivo spectroscopy may be a useful tool to gain insight into the roles of NO in hemodynamic parameters and in other physiological processes such as the regulation of the mitochondrial respiratory chain.