Stress and the blood brain barrier.
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Blood-Brain Barrier↗
Biomedical subjects
I Azevedo
Publications and source records attributed to I Azevedo.
Reversion of phenotype of endothelial cells in brain tissue around glioblastomas.
With the aim of studying the putative involvement of peritumoral microvessels in the formation of brain edema, small pieces of peritumoral brain tissue were removed from six patients with glioblastoma multiforme submitted to surgery. All patients had cerebral edema, as shown by preoperative C.T. and N.M.R. Control specimens were obtained from four patients undergoing ventriculo-peritoneal shunt. The tissue fragments were fixed in glutaraldehyde-osmium and embedded in Epon. In semi-thin sections observed under light microscopy peritumoral endothelial cells exhibited voluminous cytoplasm and nucleus. Under the electron microscope, capillary cells from glioblastoma patients differed from controls mainly by showing nuclei rich in euchromatin, cytoplasm rich in pinocytotic vesicles and with occasional fenestrations. All these morphological characteristics are compatible with a process of reversion of phenotype of capillaries around glioblastomas to that of periphery as well as an increase in permeability. Both events may be due to diffusion of a tumoral vascular permeability/endothelial growth factor. This peripheral vessel phenotype of peritumoral microvessels supports their participation in the formation of brain edema and may provide a new clue for therapeutic intervention: for example it fits quite well to the known increase in permeability by leukotrienes and decrease in permeability by corticosteroids in tumoral edema.
Aged↗
Inward transport of [3H]-1-methyl-4-phenylpyridinium in rat isolated hepatocytes: putative involvement of a P-glycoprotein transporter.
1. The liver has an important role in the detoxification of organic cations from the circulation. [3H]-1-methyl-4-phenylpyridinium ([3H]-MPP+), a low molecular weight organic cation, is efficiently taken up and accumulated by rat hepatocytes through mechanisms partially unknown. 2. The aim of the present work was to characterize further the uptake of MPP+ by rat isolated hepatocytes. The putative interactions of a wide range of drugs, including inhibitors/substrates of P-glycoprotein, were studied. 3. The uptake of MPP+ was investigated in rat freshly isolated hepatocytes (incubated in Krebs-Henseleit medium with 200 nM [3H]-MPP+ for 5 min) and in the rat liver in situ (perfused with Krebs-Henseleit/BSA medium with 200 nM [3H]-MPP+ for 30 min). [3H]-MPP+ accumulation in the cells and in tissue was determined by liquid scintillation counting. 4. Verapamil (100 microM), quinidine (100 microM), amiloride (1 mM), (+)-tubocurarine (100 microM), vecuronium (45 microM), bilirubin (200 microM), progesterone (200 microM), daunomycin (100 microM), vinblastine (100 microM), cyclosporin A (100 microM) and cimetidine (100 microM) had a significant inhibitory effect on the accumulation of [3H]-MPP+ in isolated hepatocytes. Tetraethylammonium (100 microM) had no effect. 5. In the rat perfused liver, both cyclosporin A (100 microM) and verapamil (100 microM) had much less marked inhibitory effects as compared to their effects on isolated hepatocytes (0% against 35% and 45% against 96% of inhibition, respectively). 6. Inhibition of alkaline phosphatase activity by increasing or decreasing the pH of the incubation medium or by the presence of vanadate (1 mM) or homoarginine (500 microM) led to a significant increase in the accumulation of [3H]-MPP+ in isolated hepatocytes. 7. It was concluded that, in addition to the type I organic cation hepatic transporter, [3H]-MPP+ is taken up by rat hepatocytes through P-glycoprotein, a canalicular transport system that usually excretes endobiotics and xenobiotics. We proposed that the reversal of transport through P-glycoprotein may be related to the loss of efficacy of alkaline in isolated hepatocytes.
1-Methyl-4-phenylpyridinium↗
The fate of [3H]-(-)-noradrenaline in the perfused rat liver.
1. Hepatic removal and metabolism as well as biliary excretion of noradrenaline were studied. Rat livers were perfused in situ for 60 min with Krebs-Henseleit buffer at 37 degrees C containing 2 nM [3H]-(-)-noradrenaline. [3H]-noradrenaline and its [3H]-metabolites were determined in liver, venous effluent and bile. 2. Removal of [3H]-noradrenaline by the liver, calculated as the sum of total radioactivity in the liver at the end of perfusion plus total radioactivity in the bile formed during perfusion plus [3H]-metabolites in the venous effluent formed during perfusion, was 40.2 +/- 6.9 pmol g-1 h-1. This removal corresponded to about 25% of the amount of [3H]-noradrenaline offered to the liver. 3. A proportion of the [3H]-noradrenaline (86.8%) taken up by the liver was metabolized, 13.2% remained unmetabolized in the liver and 0.019% was excreted unmetabolized into the bile. The most abundant metabolites were those present in the [3H]-OMDA fraction (72.5%), followed by [3H]-NMN (15.8%), [3H]-DOPEG (6.1%) and [3H]-DOMA (5.6%). Some of these metabolites (66.6%) were recovered from the venous effluent, 32.7% from the liver and only 1.3% from the bile. The amount of [3H]-noradrenaline present in the liver at the end of the perfusion produced a tissue:perfusion medium ratio of 2.6. 4. Simultaneous inhibition of monoamine oxidase and catechol-O-methyl transferase with pargyline (75 mg kg-1, i.p., 3 h before) and tolcapone (1 microM), respectively, markedly reduced the formation of [3H]-NMN, [3H]-DOPEG and [3H]-DOMA, but did not affect the hepatic removal of [3H]-noradrenaline, the content of [3H]-noradrenaline in the liver, the formation of [3H]-OMDA or the excretion of [3H]-noradrenaline and its [3H]-metabolites into the bile. 5. Treatment with an uptake2 blocker, corticosterone (40 microM), did not change the hepatic removal and metabolism of [3H]-noradrenaline or the biliary excretion of [3H]-noradrenaline and its [3H]-metabolites. 6. These findings indicate that the perfused rat liver efficiently removed and metabolized [3H]-noradrenaline, both monoamine oxidase and catechol-O-methyl transferase being involved in the metabolism of this amine. The apparent lack of effect of monoamine oxidase and catechol-O-methyl transferase inhibition on the formation of [3H]-OMDA may be due to the presence, especially in the liver, of conjugated metabolites of [3H]-noradrenaline in the [3H]-OMDA fraction. These results also show that uptake2 does not seem to be involved in the hepatic uptake of [3H]-noradrenaline, confirming previous findings. Finally, the results indicate that the rat liver perfused with Krebs-Henseleit buffer is not a suitable experimental model for studies on the biliary excretion of catecholamines.
Adrenergic Uptake Inhibitors↗
Enhanced arachidonic acid metabolism in alveolar macrophages from wheezy infants. Modulation by dexamethasone.
To test the hypothesis that alveolar macrophages (AM) from wheezy infants release increased amounts of eicosanoids, as do AM from adults with asthma, we compared eicosanoid release by unstimulated- and ionophore-A23187-stimulated AM from 13 wheezy and six nonwheezy infants and analyzed its regulation by dexamethasone in vitro. Alveolar macrophages from wheezy infants released greater amounts of thromboxane A2 (TxA2) and leukotriene B4 (LTB4) under resting conditions and of TxA2 upon stimulation than did those from control subjects. Dexamethasone induced a dose-dependent inhibition of the spontaneous and A23187-stimulated release of TxA2, but not of the A23187-stimulated release of lipoxygenase products. The inhibition of TxA2 formation was maintained when free arachidonic acid was added during A23187 stimulation, demonstrating that dexamethasone acted mainly at a postphospholipase A2 site. AM exposed to acetylsalicylate and then incubated overnight exhibited de novo cyclooxygenase synthesis, suggesting the presence of the inducible cyclooxygenase as a target for inhibition by dexamethasone. In conclusion, our findings suggest that AM from wheezy infants are activated in vivo to release eicosanoids, as are AM from asthmatic adults, and they support the therapeutic indications of glucocorticoids in severe recurrent wheezing of infancy.
Adult↗
Changes in brain microvessel endothelial cell monolayer permeability induced by adrenergic drugs.
Brain microvessel endothelial cell monolayers have been shown to be a suitable blood-brain barrier in vitro system to study adrenergic regulation of permeability. We tested adrenergic drugs on bovine brain microvessel endothelial cell monolayer permeability to a biomembrane impermeant molecule, sodium fluorescein. Endogenous catecholamines noradrenaline and adrenaline were tested as well as the alpha-adrenoceptor agonist phenylephrine, the beta-adrenoceptor agonist clenbuterol and the alpha-adrenoceptor antagonist prazosin. Results showed an alpha-adrenoceptor mediated increase and a beta-adrenoceptor mediated decrease in monolayer permeability. Both alpha- and beta-adrenoceptor mediated changes in permeability were abolished by inhibiting fluid-phase pinocytosis, either by vincristine or by avoiding bovine brain microvessel endothelial cell's energy utilization. The reverse transport (i.e., from brain to blood side) was also influenced by adrenergic drugs; alpha- or beta-adrenoceptor stimulation induced a permeability-reducing effect. We conclude that alpha-adrenoceptor stimulation increases bovine brain microvessel endothelial cell monolayer permeability and that beta-adrenoceptor stimulation has the opposite effect. Reverse transport results obtained with beta-adrenoceptor stimulation seem controversial and deserve further study. These results also support in vivo findings that demonstrated adrenergic influences on blood brain barrier permeability.
Adrenergic Agents↗
Uptake of 3H-catecholamines by rat liver cells occurs mainly through a system which is distinct from uptake1 or uptake2.
Isolated rat hepatocytes were incubated with 200 nmol/l 3H-(-)-noradrenaline or 50 nmol/l 3H-(-)-adrenaline for 15 min, in Krebs-Henseleit solution at 37 degrees C, gassed with 95% O2 5% CO2. Monoamine oxidase and catechol-O-methyl transferase were inhibited with pargyline (500 mumol/l) and Ro 01-2812 (3,5-dinitropyrocatechol; 2 mumol/l), respectively. Total radioactivity present in the cells, which corresponded mostly to intact 3H-amine, was measured. The content of 3H-noradrenaline increased with time of incubation, a plateau having been reached after 15 min of incubation. After 15 min of incubation, the cell: medium ratio for 3H-noradrenaline and 3H-adrenaline was 0.6-0.7. Desipramine (an inhibitor of the neuronal uptake of catecholamines-uptake1; 1 mumol/l) did not affect the uptake of either 3H-noradrenaline or 3H-adrenaline into hepatocytes. Corticosterone (an inhibitor of the extraneuronal uptake of catecholamines-uptake2; 40 mumol/l) slightly inhibited (by 28%) the uptake of 3H-adrenaline, and did not significantly reduce 3H-noradrenaline uptake. Probenecid (an inhibitor of the renal transport of organic anions; 100 mumol/l) did not influence the amount of either 3H-noradrenaline or 3H-adrenaline in hepatocytes. Cyanine 863 (an inhibitor of the renal transport of organic cations; 10 mumol/l) decreased by 62% the uptake of 3H-adrenaline into cells but did not significantly affect 3H-noradrenaline uptake. Bilirubin (a substrate of a hepatic transport for organic anions; 200 mumol/l) produced a significant increase (50%) in the amount of 3H-noradrenaline and 3H-adrenaline present in the cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Nonspecific refractoriness to adenylyl cyclase stimulation in alveolar macrophages from infants with recurrent bronchiolitis.
Epidemiologic studies suggest an association between recurrent bronchiolitis in children younger than 3 years of age and diagnosis of asthma later in life. Bronchoalveolar lavages from 20 infants with recurrent wheezing and 18 nonwheezy control subjects were analyzed to determine whether alveolar macrophages of wheezy infants present abnormalities similar to those described in adults with asthma. Alveolar macrophages from both groups responded in vitro, in a concentration-dependent manner, to prostaglandin E2, salbutamol, and forskolin, drugs that increase cyclic adenosine monophosphate levels. However, alveolar macrophages from infants with recurrent wheezing accumulated less cyclic adenosine monophosphate than those from control subjects in response to all three stimulations. These results are in agreement with the reduced cyclic adenosine monophosphate response to different agonists demonstrated in leukocytes from patients with asthma, and suggest that this refractoriness could be one of the precipitating events in the development of asthma observed in a large proportion of infants who have had bronchiolitis.
Adenylyl Cyclases↗
Extraneuronal uptake and O-methylation of 3H-adrenaline in the rabbit aorta.
The influence of uptake2 inhibitors on the O-methylation and accumulation of 3H-adrenaline by the isolated rabbit aorta was studied. Strips were incubated with 0.05 mumol/l 3H-(-)-adrenaline during 15 min. Monoamine oxidase and uptake1 were inhibited and the 3H-adrenaline present in the tissue was measured as well as the metabolites found in the tissue and in the incubation fluid. In another series of experiments, monoamine oxidase, uptake1 and catechol-O-methyl transferase (COMT) were inhibited, and tritium accumulation was measured in the tissue. When COMT was inhibited, inhibitors of uptake2 produced a maximal reduction of 3H-adrenaline accumulation that did not exceed 50%. When COMT was intact, inhibitors of uptake2 diminished total 3H-removal and, more markedly, O-methylation and concomitantly increased the tissue content of 3H-adrenaline. Mineralocorticoids (corticosterone and deoxycorticosterone acetate) inhibited 3H-adrenaline uptake (when COMT was inhibited) and 3H-metanephrine formation (when COMT was functional) as effectively as did sexual steroids (17-beta-oestradiol, progesterone and testosterone); hydrocortisone (hemisuccinate or phosphate) had no effect (for concentrations up to 120 mumol/l). At the end of the incubation some strips were washed out with amine-free solution. Compartmental analysis of the efflux showed that the amine had distributed into three extraneuronal compartments (compartment I, II and III, with half times of 0.4, 4 and 15 min, respectively). Corticosterone (120 mumol/l) decreased the amount of 3H-adrenaline in compartment III and simultaneously increased the amount of the amine in compartment I (extracellular space).(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Release and disposition of 3H-noradrenaline in the saphenous vein of neonate and adult dogs.
Release of 3H-noradrenaline and formation of 3H-metabolites were studied in the saphenous vein of newborn (mean age, 18 h) and adult dogs. Vein strips were incubated with 0.23 mumol/l of 3H-noradrenaline during 1 h and washed out for 110 min; thereafter, the perifusion fluid was collected in 5-min samples. Electrical stimulation was applied at 120 min (1 Hz, 2 ms, 100 V, for 5 min). In some experiments the tissues were preincubated with 1 mmol/l pargyline (to inhibit monoamine oxidase). In these experiments, 12 mumol/l cocaine (to inhibit uptake1), 41 mumol/l hydrocortisone (to reduce uptake2) and 50 mumol/l U-0521 (to inhibit COMT) were present during the perifusion. 3H-noradrenaline, 3H-DOPEG, 3H-NMN, 3H-DOMA and 3H-OMDA were separated by column chromatography. The noradrenaline content of the tissue was estimated by HPLC followed by electrochemical detection. A morphological study was also carried out by light and electron microscopy. The endogenous noradrenaline content of the saphenous vein was 4.3 times higher in adults than in neonates. The number of varicosities was similar in adults and newborns but the number of vesicles per varicosity profile was 5 times higher in adults. Hence, the endogenous noradrenaline content per vesicle was about the same in adults and newborns. The accumulation of 3H-noradrenaline per vesicle was about 5 times higher in newborns than in adults. On the other hand, the vein wall media of neonates was about 3 times thinner than that of adults. The evoked fractional release of tritium was about 10 times higher in neonates than in adults, whether the inactivation pathways were blocked or not.(ABSTRACT TRUNCATED AT 250 WORDS)
Aging↗
Uptake and metabolism of 3H-adrenaline and 3H-noradrenaline by isolated hepatocytes and liver slices of the rat.
Isolated rat hepatocytes were incubated with 0.05 mumol/l or 0.2 mumol/l 3H-(-)-noradrenaline or 0.05 mumol/l 3H-(-)-adrenaline for 15 min and the content of amines as well as the formation of metabolites was measured. The removal of both amines from the incubation medium was quantitatively similar, and mainly due to metabolism (which represented 96% of the removal of 3H-adrenaline and 98% of the removal of 3H-noradenaline). O-methylation predominated for 3H-adrenaline: O-methylated and deaminated metabolites (3H-OMDA) and 3H-metanephrine (3H-MN) were the most abundant metabolites, accounting for 63% and 34% of total metabolite formation, respectively. Deamination predominated for 3H-noradrenaline: 3H-OMDA and 3H-dihydroxymandelic acid (3H-DOMA) were the most abundant metabolites, representing respectively 56% and 36% of total metabolite formation. The following activities of monoamine oxidase and catechol-O-methyl transferase were determined for 3H-noradrenaline: kCOMT 0.70 +/- 0.15 min-1 and kMAO 2.27 +/- 0.14 min-1. In experiments with 3H-noradrenaline, inhibition of monoamine oxidase reduced the formation of 3H-OMDA and deaminated metabolites [3H-dihydroxphenylglycol (3H-DOPEG) and 3H-DOMA] and increased the formation of 3H-normetanephrine (3H-NMN). Inhibition of catechol-O-methyl transferase, on the other hand, decreased 3H-NMN and increased 3H-DOPEG formation. When both enzymes were inhibited, the formation of all metabolites was strongly reduced but surprisingly there was no accumulation of 3H-amines in the cells, as the cell: medium ratio for 3H-noradrenaline or 3H-adrenaline was about unity.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
A comparative study of the distribution of tritiated and endogenous noradrenaline in the rat vas deferens and in the dog spleen capsule.
The aim of the present work was to study the influence of tissue morphological characteristics on the neuronal release (and by inference the distribution) of tritiated and endogenous noradrenaline. Rat vas deferens and dog spleen capsule were loaded with 0.2 mumol/l 3H-noradrenaline, after inhibition of the noradrenaline metabolizing enzymes. Some preparations were washed out under control conditions (spontaneous efflux) and others were washed out in the presence of the releasing agents: 40 mumol/l of Ro 4-1284 (a reserpine-like compound), 100 mmol/l potassium or 100 mumol/l tyramine. The fractional rate of loss (efflux/tissue content) of each amine was determined and the ratio "endogenous amine/3H-noradrenaline" in the efflux and in the tissue were also calculated. The results showed no preferential release of one of the amines in the spleen capsule, whereas a preferential release of tritiated noradrenaline was observed in the vas deferens. The smooth muscle layer in the vas deferens was much thicker and more compact than that of the spleen capsule. The 3H-sorbitol space was smaller in the former than in the latter. We conclude that the morphological characteristics of the tissues contribute to the differences in 3H-noradrenaline distribution in the adrenergic varicosities of these preparations.
2H-Benzo(a)quinolizin-2-ol, 2-Ethyl-1,3,4,6,7,11b-↗
Neurotoxicity and induction of fibroblast proliferation by acetaldehyde in the rabbit liver.
1. Acetaldehyde may, directly or through the formation of condensation products with biogenic amines, be involved in the pathogeny of alcoholic disease. 2. Rabbits were treated acutely (200 mg kg-1, i.p., 1 h before sacrifice) or subacutely (200 mg kg-1 per day, during 5 days; sacrificed 2 days after end of treatment) with acetaldehyde. Another group was administered 6-OHDA (2 x 50 mg kg-1 on day 0 and on day 1, killed on day 5). 3. Acetaldehyde induced a depletion of hepatic noradrenaline. Both in the acute experiments and 2 days after the subacute treatment with acetaldehyde the levels of hepatic noradrenaline were 25% of control. These effects were similar to, but less intense than those induced by 6-OHDA. 4. Both subacute acetaldehyde and 6-OHDA led to a significant increase in the density of fibroblasts in the portal tract spaces of the rabbit liver. 5. The neurotoxic effects of acetaldehyde and the subsequent increase in liver fibroblast density may play a role in the pathogenesis of alcoholic disease.
Acetaldehyde↗
The influence of the density of adrenergic innervation on the extracellular steady-state concentration gradient for 3H-noradrenaline.
After inhibition of extraneuronal uptake by corticosterone, isolated right atria and lengthwise halved vasa deferentia of the rat were incubated with 0.2 mumol/l 3H-noradrenaline for 60 min, washed out for 100 min and then prepared for autoradiography. The autoradiographic images were digitized, and silver grain density was determined as a function of the distance from the surface. Silver grain density declined towards the centre of the tissue; the decline was monophasic exponential and significantly steeper in the vas deferens (0.016 microns-1) than in the less densely innervated right atrium (0.011 microns-1). Silver grain density at the surface of the tissue was higher in vas deferens than in right atrium. The results show that the extracellular steady-state concentration gradient for 3H-noradrenaline (generated by uptake1 during the incubation with this amine) largely depends on the density of the adrenergic innervation.
Animals↗
Does adenosine malfunction play a role in hypertension?
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Adenosine↗
Brief transient ischemia induces long-term depletion of norepinephrine without affecting the aromatic amino acid decarboxylase and monoamine oxidase activities in the rat kidney.
Renal artery occlusion (RAO) for 30, 60 or 90 sec was found to reduce norepinephrine tissue levels in both the cortex and medulla of the rat, respectively, by 2 to 5%, 56 to 65% and 92 to 97%, but no significant change in dopamine tissue levels was found to occur. Similar effects were obtained with occlusion of the aorta proximally to the renal arteries for 90 sec. Administration of superoxide dismutase (40 mg/kg) immediately before RAO resulted in a marked protection of the norepinephrine depletion effect as caused by transient ischemia. The sodium-dependent formation of dopamine and 3,4-dihydroxyphenylacetic acid, the deaminated metabolite of dopamine, in renal slices loaded with L-3,4-dihydroxyphenylalanine (50 microM) was found to be similar in denervated and control kidneys. Type A and B monoamine oxidase activities were measured with the deamination of two specific substrates, respectively, [3H]-5-hydroxytryptamine and [14C]-beta-phenylethylamine, in homogenates of the renal cortex and renal medulla; neither type of monoamine oxidase, A or B, was found to be affected by denervation. The renal tissues collected for morphological observation were those in which RAO was performed for 90 sec. The general structure of the renal cortex was not affected by RAO, being similar in the control and the denervated kidney. In conclusion, the results presented suggest that the tissue damaging effect produced by RAO appears to be selective for the renal sympathetic innervation and seems to involve the generation of some reactive oxygen species, namely superoxide.
3,4-Dihydroxyphenylacetic Acid↗
Long-term administration of 1,3-dipropyl-8-sulfophenylxanthine causes arterial hypertension.
Adenosine has been shown recently to be the main factor responsible for the trophic effects of sympathetic innervation. As sympathetic denervation causes hypertrophic and hyperplastic changes reminiscent of those occurring in blood vessels of spontaneously hypertensive rats, we decided to study the effect of a continuous blockade of adenosine receptors on both blood vessel structure and blood pressure. A continuous infusion of 1,3-dipropyl-8-sulfophenylxanthine (DPSPX; 30 micrograms/kg per h for 7 days) to Wistar rats caused hyperplastic changes in peritoneal fibroblasts and mesenteric arterioles, hypertrophic changes in the smooth muscle of the tail artery and significant increase in the size of left ventricle myocardial cell nuclei. Both diastolic and systolic blood pressure increased significantly above control values. The results confirmed the trophic effects of adenosine and showed that chronic blockade of adenosine receptors causes arterial hypertension.
Adenosine↗