RESUMO
Transport of a polyamine (PA), spermidine (SPMD) into rat brain at various early postischemic periods was studied. Rats underwent 20 min of four-vessel occlusion (4VO) followed by 5, 10, 30 and 60 min of recirculation (RC) periods with natural brain temperature. 3H-aminoisobutyricacid (AIB) and 14C-SPMD were utilised to search dual functions of the blood-brain barrier (BBB); barrier and carrier functions, respectively. Unidirectional blood-to-brain transfer constant (Kin) was calculated for AIB and SPMD in four brain regions-parieto-temporal cortex, striatum, hippocampus and cerebellum. Kin for SPMD ranged between 1.2+/-0.3 x 10(3) ml g(-1) min(-1) (for striatum) and 2.2+/-0.4 x 10(3) ml g(-1) min(-1) (for cerebellum) in controls. Kin for AIB showed similar values. At 5 and 10 min RC periods, Kin for both substances increased in a non-specific manner in all brain regions studied. In the cortex, Kin for SPMD at 5 and 10 min RC periods were 3.2+/-0.4 x 10(3) and 2.9+/-0.3 x 10(3) ml g(-1) min(-1), respectively, and found to be maximum with respect to other brain regions studied. 30 and 60 min RC groups showed specific transport for SPMD, whilst there were no changes for Kin for AIB, in all brain regions studied. Hippocampus showed the maximum increase in Kin SPMD at 60 min RC (2.7+/-0.3 x 10(3) ml g(-1) min(-1)), corresponding to a percentage rise of 121%. Intraischemic mild brain hyperthermia (39 degrees C) gave rise to a striking increase in Kin at 60 min postischemia for both substances. These results suggest that there is a specific transport of SPMD into brain at 30 and 60 min RC periods following 20 min of forebrain ischemia. Moreover, dual functions of the BBB were perturbed with intracerebral mild hyperthermia during ischemia.
Assuntos
Barreira Hematoencefálica , Isquemia Encefálica/metabolismo , Hipotermia Induzida , Traumatismo por Reperfusão/metabolismo , Espermidina/farmacocinética , Ácidos Aminoisobutíricos/farmacocinética , Animais , Encéfalo/metabolismo , Masculino , Ratos , Ratos Sprague-Dawley , Distribuição TecidualRESUMO
The aim of this study was to determine whether respiratory acidosis favors the cerebral distribution of cyanide, and conversely, if respiratory alkalosis limits its distribution. The pharmacokinetics of a nontoxic dose of cyanide were first studied in a group of 7 rats in order to determine the distribution phase. The pharmacokinetics were found to best fit a 3-compartment model with very rapid distribution (whole blood T(1/2)alpha = 21.6 +/- 3.3 s). Then the effects of the modulation of arterial pH on the distribution of a nontoxic dose of intravenously administered cyanide into the brains of rats were studied by means of the determination of the permeability-area product (PA). The modulation of arterial blood pH was performed by variation of arterial carbon dioxide tension (PaCO2) in 3 groups of 8 anesthetized mechanically ventilated rats. The mean arterial pH measured 20 min after the start of mechanical ventilation in the acidotic, physiologic, and alkalotic groups were 7.07 +/- 0.03, 7.41 +/- 0.01, and 7.58 +/- 0.01, respectively. The mean PAs in the acidotic, physiologic, and alkalotic groups, determined 30 s after the intravenous administration of cyanide, were 0.015 +/- 0.002, 0.011 +/- 0.001, and 0.008 +/- 0.001 s(-1), respectively (one-way ANOVA; p < 0.0087). At alkalotic pH the mean permeability-area product was 43% of that measured at acidotic pH. This effect of pH on the rapidity of cyanide distribution does not appear to be limited to specific areas of the brain. We conclude that modulation of arterial pH by altering PaCO2 may induce significant effects on the brain uptake of cyanide.
Assuntos
Acidose Respiratória/metabolismo , Alcalose Respiratória/metabolismo , Encéfalo/metabolismo , Cianetos/farmacocinética , Animais , Pressão Sanguínea/efeitos dos fármacos , Encéfalo/efeitos dos fármacos , Dióxido de Carbono/farmacologia , Cianetos/administração & dosagem , Cianetos/sangue , Concentração de Íons de Hidrogênio , Hiperventilação/induzido quimicamente , Hipoventilação/induzido quimicamente , Oxigênio/farmacologia , Ratos , Ratos Sprague-Dawley , Sacarose/sangue , Fatores de TempoRESUMO
Doxorubicin delivery to the brain is often restricted because of the poor transport of this therapeutic molecule through the blood-brain barrier (BBB). To overcome this problem, we have recently developed a technology, Pep:trans, based on short natural-derived peptides that are able to cross efficiently the BBB without compromising its integrity. In this study, we have used the in situ mouse brain perfusion method to evaluate the brain uptake of free and vectorized doxorubicin. Doxorubicin was coupled covalently to small peptide vectors: L-SynB1 (18 amino acids), L-SynB3 (10 amino acids), and its enantio form D-SynB3. We first confirmed the very low brain uptake of free radiolabeled doxorubicin, which is most likely due to the efflux activity of the P-glycoprotein at the level of the BBB. Vectorization with either L-SynB1, L-SynB3, or D-SynB3 significantly increased the brain uptake of doxorubicin (about 30-fold). We also investigated the mechanism of transport of vectorized doxorubicin. We show that vectorized doxorubicin uses a saturable transport mechanism to cross the BBB. The effect of poly(L-lysine) and protamine, endocytosis inhibitors, on the transport across the brain was also investigated. Both inhibitors reduced the brain uptake of vectorized doxorubicin in a dose-dependent manner. These studies indicate that the transport of vectorized doxorubicin appears to occur via an adsorptive-mediated endocytosis.
Assuntos
Encéfalo/metabolismo , Doxorrubicina/análogos & derivados , Peptídeos/farmacocinética , Algoritmos , Sequência de Aminoácidos , Animais , Barreira Hematoencefálica , Encéfalo/irrigação sanguínea , Doxorrubicina/administração & dosagem , Doxorrubicina/metabolismo , Doxorrubicina/farmacocinética , Endocitose/efeitos dos fármacos , Lateralidade Funcional , Técnicas In Vitro , Cinética , Masculino , Camundongos , Microcirculação , Dados de Sequência Molecular , Peptídeos/administração & dosagem , Peptídeos/metabolismo , Perfusão , Polilisina/farmacologia , EstereoisomerismoRESUMO
Many therapeutic drugs are excluded from entering the brain, due to their lack of transport through the blood-brain barrier (BBB). To overcome this problem, we have developed a novel method in which short, naturally derived peptides (16-18 amino acids) cross the cellular membranes of the BBB with high efficiency and without compromising its integrity. The antineoplastic agent doxorubicin (dox) was coupled covalently to two peptides, D-penetratin and SynB1. The ability of dox to cross the BBB was studied using an in situ rat brain perfusion technique and also by i.v. injection in mice. In the brain perfusion studies, we first confirmed the very low brain uptake of free radiolabeled dox because of the efflux activity of P-glycoprotein at the BBB. By contrast, we have demonstrated that when dox is coupled to either the D-penetratin or SynB1 vectors, its uptake was increased by a factor of 6, suggesting that the vectorized dox bypasses P-glycoprotein. Moreover, using a capillary depletion method, we have shown that vectorization of dox led to a 20-fold increase in the amount of dox transported into brain parenchyma. Intravenous administration of vectorized dox at a dose of 2.5 mg/kg in mice led to a significant increase in brain dox concentrations during the first 30 min of postadministration, compared with free dox. Additionally, vectorization led to a significant decrease of dox concentrations in the heart. In summary, our results establish that the two peptide vectors used in this study enhance the delivery of dox across the BBB.
Assuntos
Antineoplásicos/farmacocinética , Barreira Hematoencefálica , Doxorrubicina/análogos & derivados , Doxorrubicina/farmacocinética , Peptídeos/metabolismo , Animais , Transporte Biológico , Doxorrubicina/metabolismo , Portadores de Fármacos , Feminino , Masculino , Camundongos , Camundongos Nus , Ratos , Ratos Sprague-DawleyRESUMO
Studies of drug distribution to brain should be controlled for the experimental method used. Numerous methods have been employed to ascertain brain distribution and many of these approaches use anesthetic agents. The in situ rat brain perfusion method is one of the most sensitive and widely used methods for evaluating brain distribution profiles. There has been no evaluation of the effects of anesthetic agents on parameters associated with this method (i.e. cerebral perfusion fluid flow, brain vascular volume and blood-brain barrier permeability). We evaluated the effects of the anesthetic agents pentobarbital and ketamine combinations on these baseline parameters. The results suggest that the anesthetic agent has no effect on these parameters and anesthetic selection is open to the choice of the investigator when using the perfusion method.
Assuntos
Anestésicos/farmacologia , Encéfalo/efeitos dos fármacos , Perfusão/métodos , Animais , Barreira Hematoencefálica/efeitos dos fármacos , Encéfalo/irrigação sanguínea , Circulação Cerebrovascular/efeitos dos fármacos , Masculino , Ratos , Ratos Sprague-DawleyRESUMO
We report the application of multiple time regression analysis with the in situ brain perfusion technique to measure the rates of passage between blood and brain for [14C] L-proline, [14C] L-alanine, and [14C] alpha-aminoisobutyric acid (AIB) and their rapidly reversible volumes following perfusion of these amino acids from 10 to 60 seconds. We also report on their mechanism of transport. Proline diffused through the blood-brain barrier with a transfer coefficient (Kin) of 0.55 +/- 0.15 x 10(-4) ml/s/g and had no reversible compartment. AIB had a low Kin of 0.68 +/- 0.14 x 10(-4) ml/s/g and a significant reversible volume of 4.34 +/- 0.51 x 10(-3) ml/g in parietal cortex. L-alanine had the highest transfer coefficient, 3.11 +/- 0.26 x 10(-4) ml/s/g, and a reversible volume of 10.03 +/- 0.93 x 10(-3) ml/g in the same cerebral region. Postwash procedures which remove any radiotracer in the vasculature and capillary depletion were performed for alanine and AIB, as they had significant reversible compartments, to test the possibility of rapid efflux from the endothelial cells. Results obtained from wash and capillary depletion procedures suggest that a rapid efflux could occur from endothelial cells after entry of alanine and AIB. Mechanisms of transport for L-alanine and AIB were investigated using amino acids (5 mM) as substrates and inhibitors of different amino acid transport systems. AIB transport was reduced by plasma and L-leucine and unchanged by sodium-free buffer, confirming its passage by the L1 system. L-alanine uptake was sodium-independent and not reduced by plasma. L-serine, L-cysteine, L-leucine and L-phenylalanine produced similar inhibition (66%) while L-alanine produced a lower inhibition (41%). L-arginine increased alanine uptake in cortex and thalamus. Adding L-serine to L-phenylalanine reduced the uptake only in cortex and hippocampus. These data suggest that L-alanine is transported by another L transport system different from the L1 system at the luminal membrane.
Assuntos
Alanina/farmacocinética , Ácidos Aminoisobutíricos/farmacocinética , Barreira Hematoencefálica/fisiologia , Endotélio Vascular/metabolismo , Prolina/farmacocinética , Animais , Transporte Biológico/fisiologia , Endotélio Vascular/citologia , Masculino , Membranas/metabolismo , Ratos , Ratos Sprague-Dawley , Análise de RegressãoRESUMO
Classically, drug penetration through the blood-brain barrier depends on the lipid solubility of the substance, except for some highly lipophilic drugs, like colchicine and vinblastine, both substrates of P-glycoprotein, a drug efflux pump present at the luminal surface of the brain capillary endothelial cells. Colchicine and vinblastine uptake into the brain was studied in the rat using the in situ brain perfusion technique and two inhibitors of P-glycoprotein, verapamil and SDZ PSC-833. When rats were pretreated with PSC-833 (10 mg/kg, intravenous bolus), colchicine and vinblastine uptake was enhanced 8.42- and 9.08-fold, respectively, in all the gray areas of the rat brain studied. The mean colchicine distribution volume was increased from 0.67 +/- 0.41 to 5.64 +/- 0.70 microliters/g and vinblastine distribution volume from 2.74 +/- 1.15 to 24.88 +/- 4.03 microliters/g. When rats were pretreated with verapamil (1 mg/kg, intravenous bolus), colchicine distribution volume was increased 3.70-fold. The increase in colchicine and vinblastine did not differ between the eight brain gray areas. PSC-833 and verapamil pretreatment had no influence on the distribution volume of either drug in the choroid plexus. Nevertheless, distribution volumes remained small, considering the highly lipophilic nature of the substances. We suggest that P-glycoprotein is either only partially inhibited (difficulty of fully saturating P-glycoprotein, especially under in vivo conditions) or not the only barrier to these two drugs.
Assuntos
Membro 1 da Subfamília B de Cassetes de Ligação de ATP/sangue , Barreira Hematoencefálica , Encéfalo/irrigação sanguínea , Encéfalo/metabolismo , Colchicina/sangue , Vimblastina/sangue , Membro 1 da Subfamília B de Cassetes de Ligação de ATP/antagonistas & inibidores , Animais , Barreira Hematoencefálica/efeitos dos fármacos , Colchicina/farmacocinética , Ciclosporinas/farmacologia , Masculino , Especificidade de Órgãos , Técnica de Diluição de Radioisótopos , Ratos , Ratos Sprague-Dawley , Sacarose/metabolismo , Distribuição Tecidual , Trítio , Verapamil/farmacologia , Vimblastina/farmacocinéticaRESUMO
Transport of L-glutamate from blood to brain in equithesin-anesthetized rats was examined using in situ brain perfusion combined with multiple-time/graphical analysis. In situ perfusion allowed precise control of the composition of the perfusate, which was necessary for a detailed investigation of glutamate transport, while multiple time/graphical analysis permitted evaluation of the rapidly reversible volume and the period when the influx was unidirectional. Glutamate had no reversible volume and efflux from brain occurred after 30 s of perfusion. The in situ transfer coefficient (Kin) ranged from 0.74 +/- 0.07 mul/s per g in parietal cortex to 0.44 +/- 0.07 mul/s per g in hippocampus. L-Glutamate uptake was unaffected by removal of sodium from the perfusate, reduced by 5 mM L-glutamate, L-homocysteate, L-aspartate, plasma and 0.1 mM L-glutamate, while L-cystine did not reduce its uptake. These results suggest that the transport system for glutamate is saturated mainly by L-glutamate at physiological conditions and that it is not the sodium-independent x-C system since glutamate transport was not reduced by L-cystine except in hippocampus and that it was responsive to L-aspartate.
Assuntos
Barreira Hematoencefálica/fisiologia , Ácido Glutâmico/metabolismo , Sódio/metabolismo , Transportadores de Cassetes de Ligação de ATP/fisiologia , Sistema X-AG de Transporte de Aminoácidos , Animais , Ácido Aspártico/farmacologia , Transporte Biológico/fisiologia , Barreira Hematoencefálica/efeitos dos fármacos , Cistina/metabolismo , Ácido Glutâmico/análogos & derivados , Ácido Glutâmico/farmacologia , Perfusão , Ratos , Ratos Sprague-Dawley , Fatores de TempoRESUMO
Taurine transport into six brain regions of equithesin-anesthetized rats was studied by the in situ brain perfusion technique. This technique gives both accurate measurements of cerebrovascular amino acid transport and allows complete control of the perfusate amino acid composition. Final wash procedure showed that taurine efflux occurred rapidly from endothelial cells. The taurine influx into endothelial cells was sodium and chloride dependent suggesting that the sodium and chloride gradients are the principal source of energy for taurine transport into endothelial cells. Taurine transport could be fitted by a model with saturable components. The kinetic constants in the parietal cortex were 1.4 x 10(-4) mumol/s/g for the apparent Vmax and 0.078 mM for the apparent Km. Competition experiments in the presence of sodium ions showed that [14C]taurine uptake was strongly inhibited by the structural analogs of taurine, hypotaurine and beta-alanine.
Assuntos
Barreira Hematoencefálica/fisiologia , Taurina/farmacocinética , Animais , Cloretos/fisiologia , Endotélio Vascular/citologia , Endotélio Vascular/metabolismo , Metabolismo Energético/fisiologia , Masculino , Perfusão , Ratos , Ratos Sprague-Dawley , Sódio/fisiologia , beta-Alanina/metabolismoRESUMO
Early restriction of nutrients during the perinatal period of life can modify the development of the mammalian fetus and have marked repercussions on the ontogeny of the CNS. The brain is vulnerable to undernutrition, with delayed morphologic and biochemical maturation leading to impaired functions. The aim of the present investigation was to assess whether modified brain neurotransmitter and amino acid concentrations found in an animal model of intrauterine growth retardation were related to modified blood-brain amino acid transport properties. Four amino acids were tested: alanine and taurine, plus two neurotransmitter precursors, tryptophan and tyrosine. Intrauterine growth retardation was induced by restriction of maternal-fetal blood flow from the 17th d of gestation. Blood-brain transport of these amino acids was measured by i.v. injection of radiolabeled amino acids in 7-d-old, 21-d-old, and 60-d-old intrauterine growth-retarded or control rats. No major statistical differences were revealed either for brain regional transport or between intrauterine growth-retarded animals and controls at any age studied. Transfer coefficients and influxes remained statistically similar for almost all brain regions in both groups. A significant decrease and different time course for amino acid transport with age related to the blood-brain barrier maturation are confirmed in this model. Our results are related to a major role of the blood-brain barrier as a part of mechanisms leading to "brain growth sparing."
Assuntos
Aminoácidos/metabolismo , Encéfalo/metabolismo , Retardo do Crescimento Fetal/metabolismo , Fatores Etários , Aminoácidos/sangue , Animais , Transporte Biológico Ativo , Barreira Hematoencefálica , Modelos Animais de Doenças , Feminino , Retardo do Crescimento Fetal/sangue , Retardo do Crescimento Fetal/etiologia , Cinética , Masculino , Gravidez , Ratos , Ratos Sprague-DawleyRESUMO
Regional unidirectional transport of alpha-aminoisobutyric acid (AIB) (mol. wt.: 104) and sucrose (mol wt.: 342) which have a low permeability across the intact endothelium was investigated in brain of rats either treated with synacthène: an analog of ACTH, tetracosactide retard (beta-1-24 corticotrophin) or in brain of placebo-treated controls. Three days treatment with synacthène, reduced the rate of influx of AIB and sucrose in most of the brain regions studied especially in thalamus, hypothalamus, cortex, and caudate nucleus without affecting the vascular compartment. The brainstem, cerebellum and white matter were less affected. These experimental findings may suggest that ACTH exhibits significant influence on hormonal regulation of blood-brain barrier permeability. Thereby such a regulation may involve the entry of polar compounds into the CNS and may influence the central effects of diffusion-limited drugs.
Assuntos
Barreira Hematoencefálica/efeitos dos fármacos , Cosintropina/farmacologia , Ácidos Aminoisobutíricos , Animais , Permeabilidade Capilar/efeitos dos fármacos , Cinética , Sistema Hipófise-Suprarrenal/fisiologia , Ratos , SacaroseRESUMO
Possible alterations in blood-to-brain unidirectional transport of sucrose (mol. wt., 342), alpha-aminoisobutyric acid (mol. wt., 104), and L-phenylalanine (mol. wt., 165) induced by a diet deficient in n-3 polyunsaturated fatty acids were studied with respect to blood-brain barrier function. Two groups of rats were for to two generations with a semisynthetic diet. One group of rats was fed a peanut oil+rapeseed oil diet which contained both essential fatty acids: linoleic acid (18:2 n-6) and alpha-linolenic acid, (18:3 n-3). Another group was fed a diet of peanut oil, this diet (containing 18:2 n-6) was deficient in alpha-linolenic acid. The experiments were performed at 6 months of age. Unidirectional transfer rate constants (Ki) of sucrose, alpha-aminoisobutyric acid and L-phenylalanine were measured. The diet based on peanut oil (deficient in n-3) caused a greater blood-to-brain transport of sucrose but not of alpha-aminoisobutyric acid or L-phenylalanine. These observations indicate that regardless of the mechanisms involved, alterations in essential fatty acids induced by diet can modulate to some extent the blood-brain transport of hydrophilic molecules without a carrier.
Assuntos
Ácidos Aminoisobutíricos/farmacocinética , Barreira Hematoencefálica , Química Encefálica , Gorduras na Dieta/administração & dosagem , Ácidos Graxos Essenciais/deficiência , Ácidos Graxos Ômega-3/fisiologia , Fenilalanina/farmacocinética , Sacarose/farmacocinética , Animais , Transporte Biológico , Endotélio Vascular/metabolismo , Ácidos Graxos Essenciais/fisiologia , Ácidos Graxos Monoinsaturados , Ácidos Graxos Ômega-3/administração & dosagem , Ácido Linoleico , Ácidos Linoleicos/administração & dosagem , Ácidos Linoleicos/fisiologia , Lipídeos de Membrana/metabolismo , Óleo de Amendoim , Óleos de Plantas/administração & dosagem , Óleo de Brassica napus , Ratos , Ratos EndogâmicosRESUMO
Age-related changes in blood-brain barrier permeability were investigated during pentylenetetrazol-induced seizures in rats aged from 15 days to 120 days. Tracers such as [14C]sucrose and [3H]inulin which diffuse very slowly across the intact endothelium were simultaneously injected i.v. in rats treated with pentylenetetrazol (PTZ) or in control animals. Permeability-surface area products (PA) were determined in 9 brain regions. Pentylenetetrazol-induced seizures caused a significant increase in PA for both sucrose and inulin in all brain regions studied. Blood-brain barrier dysfunction was present only in animals in which the mean arterial blood pressure rose at seizure onset. Although increased blood-brain barrier permeability was found partly in similar areas in both young and adult rat brains, in adults the increase was the highest in the preoptic area, septum, colliculus inferior, hypothalamus and in the cerebellum while the increase was comparatively much smaller in the same areas of young brains. The increase in blood-brain barrier permeability was extremely high in the hippocampus, hypothalamus and cerebellum of 15-day-old rat brain and, was least affected in the corpus striatum and cerebral cortex in contrast to older rats. From the results obtained it may be concluded that the increased cerebrovascular permeability induced by pentylenetetrazol differs markedly in localization in young and adult rats. The age-dependent increased blood-brain barrier integrity is not over all dependent on variations in the blood pressure, but rather on progressive maturation of capillaries and changes in their internal structure, and local phenomena in neuronal activity during the seizures.
Assuntos
Envelhecimento/fisiologia , Barreira Hematoencefálica/fisiologia , Epilepsia/fisiopatologia , Animais , Permeabilidade Capilar/fisiologia , Circulação Cerebrovascular/fisiologia , Epilepsia/induzido quimicamente , Masculino , Pentilenotetrazol , Ratos , Ratos EndogâmicosRESUMO
Pathways taken by peripherally administered small molecules when entering the brain were investigated in 6-day-old rats by radioautography and fluorescence microscopy after intravenous administration and rapid freezing. L-[U-14C]Phenylalanine, [U-14C]sucrose and sodium fluorescein reached the brain within less than 5 seconds. These blood-borne molecules were found in the subarachnoid cisterns and the superficial parenchyma. These results suggest a special permeability of the arachnoid layer and/or the pial vessels. Phenylalanine alone reached the deep parenchyma because of the existence of a specific endothelial carrier.
Assuntos
Vasos Sanguíneos/metabolismo , Meninges/metabolismo , Animais , Autorradiografia , Barreira Hematoencefálica/efeitos dos fármacos , Encéfalo/anatomia & histologia , Difusão , Fluoresceína , Fluoresceínas/metabolismo , Meninges/anatomia & histologia , Microscopia de Fluorescência , Fenilalanina/metabolismo , Ratos , Ratos Endogâmicos , Sacarose/metabolismoRESUMO
In this study we measured the effect of acute and chronic estrogen treatment on cerebrovascular permeability to sucrose and inulin. Animals were subcutaneously injected once with 0.1 micrograms/rat of ethinyl estradiol or injected daily with the same drug dose for 3 weeks. Control rats received the same amount of arachis oil vehicle. Three weeks treatment but not the single injection of ethinyl estradiol produced significant increases in the cerebrovascular permeability-surface area product for sucrose and inulin in almost all brain regions.
Assuntos
Barreira Hematoencefálica/efeitos dos fármacos , Etinilestradiol/farmacologia , Animais , Radioisótopos de Carbono , Esquema de Medicação , Feminino , Ratos , Ratos Endogâmicos , TrítioRESUMO
The influence of neonatal hypo- and hyperthyroidism on different aspects of tyrosine metabolism in the hypothalamus, striatum, brainstem, adrenal glands, heart and brown adipose tissue (BAT) were studied in 14-day old rats. The synthesis rate of catecholamines (CA) was also determined in vivo after the injection of labelled tyrosine. Hypothyroidism increases tyrosinaemia and endogenous tyrosine concentration in the hypothalamus and BAT. Hyperthyroidism decreases tyrosinaemia and endogenous tyrosine levels in the striatum, adrenals and heart. The accumulation rate of tyrosine determined 30 min after an intravenous injection of the labelled amino acid has been determined in the organs, together with the influx of the amino acid, determined within 20s. Hypothyroidism increases tyrosine accumulation rate in all the organs studied, and tyrosine clearance is decreased in the striatum and brainstem; together with an increased tyrosinaemia, this leads to a normal influx. The influx of tyrosine is increased in the hypothalamus. Hyperthyroidism decreases tyrosine accumulation rate in all the organs except the adrenals. These results indicate that the thyroid status of the young rat can influence tyrosine uptake mechanisms, without modifying an organ's tyrosine content. The fact that hypothyroidism increases tyrosine influx in the hypothalamus without modifying it in the brainstem and striatum reflects an heterogeneous reactivity to the lack of thyroid hormones in different brain structures. Neonatal hypothyroidism decreases the CA synthesis rate in the striatum, the heart and the interscapular brown adipose tissue, while synthesis was enhanced in the brainstem and the adrenals. It is likely that these variations in CA synthesis are due to thyroid hormone modulation of tyrosine hydroxylase activity, the enzyme which catalyses the rate limiting step in CA biosynthesis.
Assuntos
Animais Recém-Nascidos/metabolismo , Encéfalo/metabolismo , Catecolaminas/biossíntese , Hipertireoidismo/metabolismo , Hipotireoidismo/metabolismo , Tirosina/metabolismo , Tecido Adiposo Marrom/metabolismo , Tecido Adiposo Marrom/patologia , Glândulas Suprarrenais/metabolismo , Glândulas Suprarrenais/patologia , Animais , Tronco Encefálico/metabolismo , Tronco Encefálico/patologia , Corpo Estriado/metabolismo , Corpo Estriado/patologia , Hipertireoidismo/patologia , Hipotálamo/metabolismo , Hipotálamo/patologia , Hipotireoidismo/patologia , Cinética , Miocárdio/metabolismo , Miocárdio/patologia , Tamanho do Órgão , Ratos , Distribuição TecidualRESUMO
Transport of taurine has been demonstrated in capillary preparations from adult rat brains using [3H]taurine. Taurine transport is mediated by a saturable high-affinity system which is entirely dependent on sodium ions. The apparent maximal influx (Vmax) and half-saturation concentration (Km) corresponded to 1.06.10(-4) mumol/min per mg protein and 27.5 microM, respectively. Competition experiments in the presence of sodium ion showed that [3H]taurine uptake was strongly inhibited by 0.1 mM unlabeled structural analogues of taurine such as beta-alanine and hypotaurine as well as unlabeled taurine. gamma-Aminobutyric acid (GABA) (0.1 mM) inhibited the uptake of labeled taurine by 30%, whereas isethionic acid, L-methionine, L-2,4-diaminobutyric acid, glycine, L-cysteinesulfonic acid and cystamine did not exhibit any inhibitory effect. The results suggest that the Na+ gradient is the principal source of energy for taurine transport into isolated brain capillaries. This transport system may play an active role in the regulation of taurine concentration in the brain extracellular space.
Assuntos
Capilares/metabolismo , Circulação Cerebrovascular , Sódio/farmacologia , Taurina/metabolismo , Aminoácidos/farmacologia , Animais , Transporte Biológico/efeitos dos fármacos , Feminino , Técnicas In Vitro , Cinética , Masculino , Músculo Liso Vascular/metabolismo , Ouabaína/farmacologia , Ratos , Ratos EndogâmicosRESUMO
Lipid synthesis and its regulation by serum lipoproteins at the microvascular blood-brain barrier were studied using primary cultures of microvascular endothelial cells from rat brain. These cells are capable of synthesizing all their lipids (neutral lipids, phospholipids, glycolipids) from the water-soluble compounds, glucose, acetate, acetoacetate and beta-hydroxybutyrate. The ketone bodies, especially acetoacetate, are the preferred substrates for lipid synthesis. The incorporation patterns of acetate, acetoacetate and beta-hydroxybutyrate are very similar, indicating that these precursors contribute to lipid synthesis via the same metabolic route. However, the metabolic pathway is different for glucose, which is preferentially incorporated into phospholipids. The existence of an inverse relationship between lipid synthesis and the serum lipoprotein concentration suggests that cultured cerebral endothelial cells are capable of taking up lipids, principally cholesterol, contained in the serum lipoproteins. Cellular lipids would thus be supplied both by intracellular lipid synthesis and by serum lipoproteins. The difference between cholesterol synthesis rates in cultured cerebral endothelial cells and in isolated brain microvessel cells could be partly explained by the fact that the lipoprotein concentration is much lower in the culture medium than in rat serum.
Assuntos
Encéfalo/metabolismo , Capilares/metabolismo , Lipídeos/biossíntese , Acetatos/metabolismo , Animais , Encéfalo/irrigação sanguínea , Encéfalo/citologia , Radioisótopos de Carbono , Técnicas de Cultura , Endotélio/metabolismo , Masculino , Ratos , Ratos EndogâmicosRESUMO
The effect of dexamethasone administration and withdrawal was studied with respect to blood-brain barrier function. The tracers alpha-[3H]aminoisobutyric acid (AIB) (MW 104) and [14C]sucrose (MW 342), which have a low permeability across the intact endothelium, were simultaneously injected intravenously in rats treated with dexamethasone and placebo-treated control animals or in rats in which dexamethasone treatment was discontinued 3 days before the experiment. Unidirectional transfer constants (Ki) were determined in discrete brain regions. Steroid administration reduced the rate of influx of AIB and sucrose, whereas discontinuation of drug resulted in an increased permeability. These findings suggest that when exposure to glucocorticoids is prolonged, the efficiency of medical treatment of CNS diseases may decrease due to reduction of drug delivery to CNS. Thus, these experimental findings may have particular importance in the clinical setting of drug administration when considering the combination of steroids with other drugs, and may aid in understanding better the pathogenesis of some types of brain edema seen in patients from whom corticosteroid therapy has been withdrawn.
Assuntos
Ácidos Aminoisobutíricos/metabolismo , Barreira Hematoencefálica/efeitos dos fármacos , Encéfalo/metabolismo , Dexametasona/farmacologia , Sacarose/metabolismo , Animais , Transporte Biológico/efeitos dos fármacos , Permeabilidade Capilar/efeitos dos fármacos , Dexametasona/administração & dosagem , Masculino , Ratos , Ratos EndogâmicosRESUMO
Exposure of immature rats to lead acetate results in hemorrhagic encephalopathy of variable evolution. As the maintenance of adequate protection against peroxides may be critical in this condition, the activities of selenium-glutathione peroxidase and catalase in cerebrum and cerebellum of suckling rats poisoned with lead acetate were studied from day six to day sixteen post-exposure. Age-related decreases of glutathione peroxidase and catalase activities in both controls and lead poisoned animals were observed. An increase in catalase activity was observed in cerebrum and cerebellum of lead-treated rats compared to controls. Glutathione peroxidase activity did not change significantly in cerebrum over the period studied. By contrast, glutathione peroxidase activity in cerebellum of lead-treated rats remained at about twice the control level over most of the study period. This apparent increase in glutathione peroxidase activity may be due either to a slower ontogenic decrease of its specific activity or to enzyme induction in response to oxidant stress in cerebellum.