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1.
Nat Commun ; 14(1): 7037, 2023 Nov 03.
Artigo em Inglês | MEDLINE | ID: mdl-37923745

RESUMO

A promising route to discover exotic electronic states in correlated electron systems is to vary the hole or electron doping away from a Mott insulating state. Important examples include quantum criticality and high-temperature superconductivity in cuprates. Here, we report the surprising discovery of a quantum insulating state upon electron doping the Mott insulator CeMnAsO, which emerges below a distinct critical transition temperature, TII. The insulator-insulator transition is accompanied by a significant reduction in electron mobility as well as a colossal Seebeck effect and slow dynamics due to decoupling of the electrons from the lattice phonons. The origin of the transition is tentatively interpreted in terms of many-body localization, which has not been observed previously in a solid-state material.

2.
Nature ; 436(7052): 829-32, 2005 Aug 11.
Artigo em Inglês | MEDLINE | ID: mdl-16094364

RESUMO

The mechanism of high-transition-temperature (high-T(c)) superconductivity in doped copper oxides is an enduring problem. Antiferromagnetism is established as the competing order, but the relationship between the two states in the intervening 'pseudogap' regime has become a central puzzle. The role of the crystal lattice, which is important in conventional superconductors, also remains unclear. Here we report an anomalous increase of the distance between copper oxide planes on cooling, which results in negative thermal volume expansion, for layered ruthenium copper oxides that have been doped to the boundary of antiferromagnetism and superconductivity. We propose that a crossover between these states is driven by spin ordering in the ruthenium oxide layers, revealing a novel mechanism for negative lattice expansion in solids. The differences in volume and lattice strain between the distinct superconducting and antiferromagnetic states can account for the phase segregation phenomena found extensively in low-doped copper oxides, and show that Cooper pair formation is coupled to the lattice. Unusually large variations of resistivity with magnetic field are found in these ruthenium copper oxides at low temperatures through coupling between the ordered Ru and Cu spins.

3.
Phys Rev Lett ; 104(17): 177202, 2010 Apr 30.
Artigo em Inglês | MEDLINE | ID: mdl-20482134

RESUMO

We report on the unconventional magnetism in the cubic B-site ordered double perovskite Ba2YMoO6, using ac and dc magnetic susceptibility, heat capacity and muon spin rotation. No magnetic order is observed down to 2 K while the Weiss temperature is approximately -160 K. This is ascribed to the geometric frustration in the lattice of edge-sharing tetrahedra with orbitally degenerate Mo5+ s=1/2 spins. Our experimental results point to a gradual freezing of the spins into a disordered pattern of spin singlets, quenching the orbital degeneracy while leaving the global cubic symmetry unaffected, and providing a rare example of a valence bond glass.

4.
Dalton Trans ; 47(41): 14726-14733, 2018 Oct 23.
Artigo em Inglês | MEDLINE | ID: mdl-30280742

RESUMO

The colossal magnetoresistance (CMR) observed in the oxypnictide NdMnAsO1-xFx has been further investigated. The magnetotransport is dominated by magnetopolarons. Magnetoresistance measurements of the series Nd(Mn1-xCox)AsO0.95F0.05 show that doping with cobalt on the manganese site pins the magnetopolarons and suppresses the CMR, which is completely destroyed by x = 0.047. The chemical doping results in non-stoichiometric samples, with both As and O vacancies. The relationship between the non-stoichiometry, magnetic order, electron doping and CMR is explored. The Nd antiferromagnetic transition and simultaneous reorientation of the Mn spins into the basal plane at 23 K (TSR) is not effected by Co doping. However, there is a significant decrease in TN(Mn) as the antiferromagnetic transition is suppressed from 360 K to 300 K as x increases from 0-0.047. The manganese moment at 10 K is also reduced from 3.86(2)µB to 3.21(2)µB over the same doping range. This reduction in the in-plane Mn moment decreases the electron-electron correlations below TSR and acts to further diminish the magnetoresistance.

5.
J Clin Invest ; 96(1): 126-31, 1995 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-7615782

RESUMO

Patients on long-term zidovudine (AZT) therapy experience muscle fatigue and weakness attributed to AZT-induced mitochondrial toxicity in skeletal muscle. To determine if the clinico-pathological abnormalities in these patients correspond to abnormal muscle energy metabolism, we used 31P in vivo magnetic resonance spectroscopy to follow phosphorylated metabolites during exercise. We studied 19 normal volunteers, 6 HIV-positive patients never treated with AZT, and 9 HIV-positive patients who had been treated with AZT for a mean period of 33 mo (range 12-48 mo) and had muscle biopsy-proven AZT-myopathy with abnormal mitochondria. Changes in phosphocreatine, ATP, and intracellular pH in the gastrocnemius muscle were followed during a graded steady state exercise protocol, and the recovery of phosphocreatine was followed on cessation of exercise. We found that graded steady state exercise produced a greater depletion of muscle phosphocreatine levels in the AZT-treated patients, compared to either HIV-positive patients who were not treated with AZT or normal controls. No differences in the effects of steady state exercise on muscle phosphocreatine levels were observed between the control group and the HIV-positive patients who had not been treated with AZT. The results suggest that the effect of AZT on muscle energy metabolism is significant, and similar to the effect observed in patients with known mitochondrial myopathies. Using a well-known model for control of mitochondrial metabolism, the observed differences in steady state phosphocreatine levels during exercise suggest that AZT treatment decreases the maximal work output and the maximal rate of muscle ATP synthesis.


Assuntos
Músculo Esquelético/efeitos dos fármacos , Zidovudina/efeitos adversos , Trifosfato de Adenosina/análise , Infecções por HIV/tratamento farmacológico , Infecções por HIV/metabolismo , Humanos , Concentração de Íons de Hidrogênio , Espectroscopia de Ressonância Magnética , Masculino , Músculo Esquelético/metabolismo , Fosfocreatina/análise
6.
Chem Commun (Camb) ; (22): 2273-4, 2007 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-17534514

RESUMO

An unexpected enhancement of the large negative magnetoresistance (MR) observed in RuSr(2)Nd(0.95)Y(0.15)Ce(0.9)Cu(2)O(10-delta) up to -47% at 4 K and 9 T is evidenced upon dilution of the Ru magnetic order by substitution of Ta for Ru; this enhancement of -MR scales with the cell volume.

8.
Sci Rep ; 6: 20705, 2016 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-26875693

RESUMO

The recent discovery of high temperature superconductivity in Fe arsenides has invigorated research into transition metal pnictides. Colossal magnetoresistance (CMR) has recently been reported for NdMnAsO1-xFx for x = 0.05-0.08, with a maximum magnetoresistance achieved at low temperature (MR9T(3 K)) = -95%). This appears to be a novel mechanism of CMR, which is as a result of a second order phase transition in field from an insulating antiferromagnet to a semiconducting paramagnet. Here we report a variable temperature synchrotron X-ray powder diffraction study of the CMR oxypnictide NdMnAsO0.95F0.05 between 4 K-290 K. An excellent fit to the tetragonal unit cell with space group P4/nmm is obtained over the entire temperature range, with no change in crystal structure detected down to 4 K. A coupling of the lattice and magnetic order is observed, where subtle discontinuities in the temperature variation of a and the c/a ratio are apparent as the Nd spins order antiferromagnetically and the Mn moments reorient into the basal plane at TSR. The results suggest that very small changes in lattice parameters effect the coupling between lattice, electronic and magnetic degrees of freedom.

9.
Biochim Biophys Acta ; 646(2): 320-8, 1981 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-6895319

RESUMO

We have studied the kinetics of ionophore X-537A-mediated transport of manganese ions into small unilamellar vesicles formed from dipalmitoylphosphatidylcholine. To follow the transport we used the paramagnetic effect of manganese on the 1H-NMR signal from choline trimethylammonium groups on the inner phospholipid monolayer. The transport of only one manganese ion produces an intravesicular concentration which is high enough (approx. 1 mM) to substantially broaden this signal. The observed signal thus arises predominantly from those vesicles which contain no manganese. Therefore, as manganese is transported into the vesicles the observed signal decreases in intensity, but does not broaden. The initial time-dependence of the intensity of the signal, S(t), can be approximated by the simple first-order rate law: S(t) = S(0) exp(-k't), where k' is the probability per unit time for the transport of a manganese ion from the external medium to the intravesicular space. From the dependence of k' on the ionophore X-537A concentration we conclude that manganese is transported into the vesicles via both 1 : 1 and 2 : 1 complexes with ionophore X-537A. At low ratios of ionophore X-537A to vesicles transport via the 1 : 1 complex predominates; at high ratios transport via the 2 : 1 complex predominates. From the dependence of k' on manganese concentration we determined that under our conditions the equilibration of ionophore X-537A between vesicles is much faster than the transport of manganese through the vesicles. Lastly, from the dependence of k' on temperature, we conclude that the ionophore X-537A-mediated transport of manganese into the dipalmitoylphosphatidylcholine vesicles is very sensitive to the gel-liquid crystalline phase transition.


Assuntos
Lasalocida , Manganês , Surfactantes Pulmonares , Cinética , Espectroscopia de Ressonância Magnética , Matemática , Conformação Molecular , Espectrometria de Fluorescência , Termodinâmica
10.
Biochim Biophys Acta ; 643(1): 1-16, 1981 Apr 22.
Artigo em Inglês | MEDLINE | ID: mdl-7236680

RESUMO

31P-NMR spectra were obtained from oriented multilayer preparations of normal sarcoplasmic reticulum and reconstituted sarcoplasmic reticulum with lipid to protein ratios varying between 41 : 1 and 110 : 1. The dependence of the 31P-NMr spectra on the alignment of the membranes with respect to the magnetic field was used to draw two conclusions about the motion of the phospholipid molecules that contribute to the observed spectra. First, the phosphate group and the two adjacent methylene groups are able to rapidly rotate (i.e., tau R much less than 10-5 S) around the normal to the plane of the membrane. Second, the restricted internal motion of the phosphate group and the glycerol CH2OP group is very similar to that found in liposomes formed from sarcoplasmic reticulum phospholipids. Calibration experiments showed that all (100 +/- 7%) of the phospholipid molecules in the membrane can be accounted for in the observed spectra. Thus, essentially all the phospholipid molecules in the sarcoplasmic reticulum and the reconstituted sarcoplasmic reticulum membranes have the same motion in the polar headgroup region as found in model bilayer membranes. Since a large fraction of the phospholipid molecules (between one-quarter and one-half, depending on ;the lipid to protein ratio) are immediately surrounding the calcium-pump protein, we conclude that the calcium-pump protein does not perturb the motion of these 'boundary-layer' lipids.


Assuntos
Lipossomos , Lipídeos de Membrana/análise , Fosfolipídeos/análise , Retículo Sarcoplasmático/ultraestrutura , Animais , Espectroscopia de Ressonância Magnética , Microscopia Eletrônica , Conformação Molecular , Músculos/análise , Coelhos
11.
J Phys Condens Matter ; 27(11): 116001, 2015 Mar 25.
Artigo em Inglês | MEDLINE | ID: mdl-25721358

RESUMO

A high pressure neutron diffraction study of the oxypnictide NdMnAsO0.95F0.05 has been performed at temperatures of 290-383 K and pressures up to 8.59 GPa. The results demonstrate that the antiferromagnetic order of the Mn spins is robust to pressures of up to 8.59 GPa. TN is enhanced from 360 to 383 K upon applying an external pressure of 4.97 GPa, a rate of 4.63 K GPa(-1). NdMnAsO0.95F0.05 is shown to violate Bloch's rule which would suggest that NdMnAsO0.95F0.05 is on the verge of a localized to itinerant transition. There is no evidence of a structural transition but applied pressure tends to result in more regular As-Mn-As and Nd-O-Nd tetrahedra. The unit cell is significantly more compressible along the c-axis than the a-axis, as the interlayer coupling is weaker than the intrinsic bonds contained within NdO and MnAs slabs.

12.
Cell Calcium ; 14(6): 465-72, 1993 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-8358770

RESUMO

Fluorescent calcium indicators have been widely used to assess cytoplasmic calcium concentration in cells. To examine the role of calcium ions on different physiological functions (e.g. in case of liver; bile secretion, glucose metabolism, etc.) there is a need for whole organ studies. We have developed a technique to estimate intracellular free calcium changes in perfused rat liver. Krebs-Henseleit perfused livers were loaded with 7 microM or 35 microM Indo-1/AM. An area 3 mm in diameter and approximately 300 microns in depth was illuminated at 340 nm. Fluorescence was monitored with photomultiplier tubes at 3 wavelengths (400 nm for Ca-bound dye, 504 nm for free dye and 464 nm for NADH). The viability of liver preparations was assessed by measurement of the concentrations of lactate dehydrogenase and alanine aminotransferase in the effluent. Loading of the livers with 7 microM Indo-1/AM via the portal vein resulted in a 5-fold increase of fluorescence at 400 nm. However the dye 'leaked' out of the liver with a half-time of 18 min. Probenecid (a specific anion carrier blocker) inhibited loss of dye in a dose dependent fashion (2.5-10 mM). Transient calcium elevations were observed in response to vasopressin (5-50 nM) at physiological levels, ethanol (0.3-0.8 M) and the calcium ionophore, ionomycin. Certain limitations were apparent with this approach: (1) it was necessary to use an anion carrier blocker to maintain a relatively steady dye concentration; (2) endogenous NADH fluorescence interfered with the calcium signal; and (3) absolute values of calcium concentration could not be determined.


Assuntos
Cálcio/metabolismo , Corantes Fluorescentes/metabolismo , Indóis/metabolismo , Líquido Intracelular/metabolismo , Fígado/metabolismo , Animais , Proteínas de Transporte de Ânions , Artefatos , Proteínas de Transporte/antagonistas & inibidores , Permeabilidade da Membrana Celular/efeitos dos fármacos , Etanol/farmacologia , Fluorometria , Ionomicina/farmacologia , Masculino , NAD/metabolismo , Perfusão , Probenecid/farmacologia , Ratos , Ratos Wistar/metabolismo , Sensibilidade e Especificidade , Vasopressinas/farmacologia
13.
Cell Calcium ; 21(2): 115-24, 1997 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-9132294

RESUMO

Indo-1 fluorescence was used to monitor intracellular calcium levels in the cat brain in vivo, using the approach proposed by Uematsu et al. [Uematsu D., Greenberg J. H., Reivich M., Karp A. In vivo measurement of cytosolic free calcium during cerebral ischemia and reperfusion. Ann Neurol 1988; 24: 420-428]. In addition, extracellular calcium and potassium levels, NADH redox state, electrocorticogram (ECoG), DC potential and relative cerebral blood flow were monitored simultaneously. Changes in the Indo-1 fluorescence ratio F400/F506 were monitored during anoxia, reversible ischemia and irreversible ischemia. Although these perturbations resulted in the expected changes in extracellular calcium and potassium levels, NADH redox state, ECoG and other physiological parameters, they did not result in significant increases in the F400/F506 ratio. The apparent insensitivity of the in vivo Indo-1 approach is due to the difficulty in obtaining accurate fluorescence signals from Indo-1 in the brain. Two reasons for this difficulty appear to be problems in loading Indo-1 into the brain, and problems in correcting Indo-1 fluorescence signals for changes in NADH fluorescence and changes in absorption of intrinsic chromophores. Under the conditions of our in vivo cat experiments, Indo-1 fluorescence is not a viable approach for measuring changes in cerebral intracellular calcium levels.


Assuntos
Isquemia Encefálica/metabolismo , Cálcio/metabolismo , Corantes Fluorescentes , Hipóxia Encefálica/metabolismo , Indóis , Animais , Encéfalo/irrigação sanguínea , Encéfalo/metabolismo , Gatos , Circulação Cerebrovascular , Fluorometria/instrumentação , Fluorometria/métodos , Potenciais da Membrana , NAD/química , Oxirredução , Potássio/análise
14.
J Cereb Blood Flow Metab ; 14(3): 503-9, 1994 May.
Artigo em Inglês | MEDLINE | ID: mdl-8163593

RESUMO

The effect of the nitric oxide (NO) synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) on the response of cerebrocortical oxygen consumption (CMRO2) and blood flow (CBF) to two levels of hypercapnia (PaCO2 approximately 60 mm Hg and PaCO2 approximately 90 mm Hg) was investigated in ketamine-anesthetized rats. CBF was calculated using the Kety-Schmidt approach and CMRO2 was calculated from the product of CBF and the arteriovenous (superior sagittal sinus) difference for oxygen. L-NAME treatment did not have a significant effect on either CMRO2 or CBF under normocapnic conditions but inhibited the hypercapnic increase of CMRO2 and the hypercapnic increase in CBF. These results suggest that NO plays a role in the response of CMRO2 and CBF during hypercapnia and are consistent with the suggestion that at least part of the increase in CBF observed during hypercapnia is coupled to an increase in CMRO2.


Assuntos
Córtex Cerebral/metabolismo , Circulação Cerebrovascular , Hipercapnia/fisiopatologia , Óxido Nítrico/fisiologia , Consumo de Oxigênio , Animais , Arginina/análogos & derivados , Arginina/farmacologia , Pressão Sanguínea/efeitos dos fármacos , Córtex Cerebral/irrigação sanguínea , Circulação Cerebrovascular/efeitos dos fármacos , Masculino , NG-Nitroarginina Metil Éster , Óxido Nítrico/antagonistas & inibidores , Ratos
15.
J Cereb Blood Flow Metab ; 15(2): 312-20, 1995 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-7860664

RESUMO

17O and 19F magnetic resonance (MR) imaging were used to determine simultaneously the concentrations of H2 17O and CHF3 in 0.8-cc voxels in the cat brain during inhalation of a gas mixture containing both 17O2 and CHF3. The arterial time course of CHF3 was determined by "on-line" mass spectrometer detection of expired CHF3, and the arterial time course of H2 17O was determined by 17O MR analysis of arterial samples withdrawn during the inhalation period. The brain data and the arterial data for the two tracers were combined to calculate the cerebral oxygen consumption (CMRO2) and the CBF. The protocol was repeated on seven cats, using pentobarbital anesthesia. The average values of CMRO2 and CBF for a 0.8-cc voxel in the parietal cortex were 1.5 +/- 0.5 mmol kg-1 min-1 and 38 +/- 15 ml 100 g-1 min-1, respectively. In individual animals the average uncertainty in CMRO2 and CBF, calculated from Monte Carlo approaches, was +/- 9%.


Assuntos
Encéfalo/metabolismo , Circulação Cerebrovascular , Flúor , Imageamento por Ressonância Magnética , Consumo de Oxigênio , Radioisótopos de Oxigênio , Animais , Gatos , Modelos Cardiovasculares
16.
J Cereb Blood Flow Metab ; 14(4): 656-63, 1994 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-8014213

RESUMO

19F magnetic resonance imaging techniques were used to determine "wash-in" and "wash-out" curves of the inert, diffusible gas CHF3 from 0.4-cc voxels in the cat brain, and mass spectrometer gas detection was used to determine the CHF3 concentration in expired air. These two sets of data were used to calculate cerebral blood flow values in the 0.4-cc voxels, and the blood flow images were registered with high-resolution 1H magnetic resonance images. Data were collected both during the wash-in and wash-out phases of the experiment, but the two sets of data were analyzed separately to obtain independent estimates of the blood flow during the two phases, i.e., Qin and Qout. Repeated determinations of cerebral blood flow images were performed in individual animals, and the entire protocol was repeated on five different animals. The average values of Qin and Qout for a typical 0.4-cc voxel in the parietal cortex were 83 ml 100 g-1 min-1 and 72 ml 100 g-1 min-1, respectively. Monte Carlo calculations utilizing the noise in the 19F NMR signal from this voxel predict an average standard deviation for Qin and Qout of +/- 10%. The average standard deviation for repeated measurements (in the same animal) of Qin and Qout in this voxel was +/- 14%. We conclude that 19F magnetic resonance imaging approaches have the potential to image cerebral blood flow in humans.


Assuntos
Circulação Cerebrovascular , Flúor , Imageamento por Ressonância Magnética , Animais , Encéfalo/anatomia & histologia , Gatos , Clorofluorcarbonetos de Metano , Feminino , Espectrometria de Massas
17.
J Cereb Blood Flow Metab ; 9(6): 886-91, 1989 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-2511213

RESUMO

19F NMR was used to determine washout curves of an inert, diffusible gas (CHF3) from the cat brain. The cerebral blood flow was estimated from a bi- or tri-phasic fit to the deconvoluted wash-out curve, using the Kety-Schmidt approach. Cerebral blood flow values determined by 19F NMR show the expected responsiveness to alterations in Paco2, but are approximately 28% lower than cerebral blood flow values determined simultaneously by radioactive microsphere techniques. High concentrations of CHF3 have little effect on intracranial pressure, mean arterial blood pressure or Paco2, but cause small changes in the blood flow to certain regions of the brain. We conclude that 19F NMR techniques utilizing low concentrations of CHF3 have potential for the noninvasive measurement of cerebral blood flow.


Assuntos
Encéfalo/metabolismo , Circulação Cerebrovascular , Animais , Barreira Hematoencefálica , Dióxido de Carbono/sangue , Gatos , Flúor , Espectroscopia de Ressonância Magnética/métodos , Microesferas , Especificidade de Órgãos , Pressão Parcial
18.
J Cereb Blood Flow Metab ; 7(5): 543-51, 1987 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-3654794

RESUMO

The objective of this study was to evaluate simultaneous 31P/1H nuclear magnetic resonance (NMR) spectroscopy as a technique for monitoring and correlating changes in brain energy metabolism during hypoxia and ischemia. Five cats were studied with a protocol that involved 20 min of hypoxia (PaO2 20 mm), 60 min of recovery, 10 min of hypoxia with relative ischemia (bilateral carotid occlusion, PaO2 20 mm), and 60 min of recovery. Bifrontal and biparietal electrocorticograms (ECoG) were monitored continuously during the entire protocol. The results demonstrate that the degree of metabolic response is different in individual cats, but a number of quantitative relationships between metabolic parameters are consistently observed for all cats. First, there is agreement between increases in lactate and changes in intracellular pH; the observed relationship corresponds to an in vivo cerebral buffer capacity of 29 mumol/g/pH unit. Second, the delayed recovery of PCr is due to the effect of metabolic acidosis on the creatine kinase equilibrium and not to a delayed recovery of the ATP/ADP ratio. Third, the observed rate of lactate clearance from the cell is zero-order (k = 0.36 mumol/g/min) for lactate levels greater than 5 microns/g and may be composed of both lactate efflux from the cell and lactate oxidation.


Assuntos
Isquemia Encefálica/metabolismo , Encéfalo/metabolismo , Hipóxia/metabolismo , Espectroscopia de Ressonância Magnética , Trifosfato de Adenosina/metabolismo , Animais , Encéfalo/fisiopatologia , Isquemia Encefálica/fisiopatologia , Gatos , Eletroencefalografia/métodos , Hidrogênio , Hipóxia/fisiopatologia , Lactatos/metabolismo , Ácido Láctico , Masculino , Fosfocreatina/metabolismo , Fósforo
19.
Brain Res ; 573(2): 293-8, 1992 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-1504767

RESUMO

The role of adrenal medulla-derived enkephalins in the control of hypercapnic cerebrocortical blood flow (CBF) and oxygen consumption (CMRO2) was investigated in the ketamine anesthetized rat. Three experimental interventions were utilized: inhibition of opioid receptors with naloxone, decrease of adrenal enkephalin production with chronic adrenal medullectomy, and treatment of adrenal demedullated animals with the synthetic enkephalin analog, D-Ala2, N-Me-Phe4, Gly5-ol-enkephalin (DAGO). In intact, untreated animals hypercapnia increased CBF and CMRO2 by approximately 300 and 35%, respectively. Naloxone reduced the hypercapnic increase of CBF, and transformed the hypercapnic increase of CMRO2 into a decrease. The mid-points of the dose-response curves for (1)-naloxone and (d)-naloxone were 10 micrograms/kg and 100 micrograms/kg, respectively. Adrenal demedullation and treatment with (1)-naloxone (0.2 mg/kg) decreased the hypercapnic CBF and CMRO2 by approximately 50%. DAGO treatment of adrenal demedullated animals restored the hypercapnic CBF and CMRO2 to values similar to those found in intact animals. These observations suggest that opioid peptides (most likely adrenal medulla-derived enkephalins) play a significant role in the regulation of CMRO2 and CBF during moderate hypercapnia.


Assuntos
Medula Suprarrenal/fisiologia , Dióxido de Carbono/farmacologia , Córtex Cerebral/fisiologia , Encefalinas/farmacologia , Naloxona/farmacologia , Consumo de Oxigênio/efeitos dos fármacos , Fluxo Sanguíneo Regional/efeitos dos fármacos , Adrenalectomia , Animais , Córtex Cerebral/irrigação sanguínea , Córtex Cerebral/efeitos dos fármacos , Circulação Cerebrovascular/efeitos dos fármacos , Ala(2)-MePhe(4)-Gly(5)-Encefalina , Masculino , Ratos , Ratos Endogâmicos F344 , Valores de Referência , Estereoisomerismo
20.
J Neurosurg ; 73(6): 927-32, 1990 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-2230975

RESUMO

In order to test the hypothesis that the cerebral arteriovenous oxygen difference (AVDO2) and venous oxygen content (VO2) could be used to monitor brain energy metabolism in the setting of increased intracranial pressure (ICP). 12 cats were studied with 31P-magnetic resonance spectroscopy. six cats were subjected to intracranial hypertension by cisternal infusion of saline. Energy failure occurred at an average AVDO2 of 8.4 +/- 3.2 vol% (+/- standard deviation) (range 4.7 to 14.7 vol%). The VO2 at the point of metabolic failure averaged 1.45 +/- 0.6 vol% and extended over a narrower range (1.0 to 2.9 vol%). In an additional six cats, ICP was raised to the threshold of metabolic failure and hyperventilation was then instituted (pCO2 10 to 18 torr). Five of the six cats experienced a drop in VO2 with hyperventilation. In two of these animals, hyperventilation resulted in a VO2 of 1.1 vol% or less and in metabolic failure as evidenced by a fall in phosphocreatine. It is concluded that a VO2 of less than 2 vol% is correlated with brain ischemia and that the safety of hyperventilation in the setting of increased ICP can be monitored by the use of VO2.


Assuntos
Encéfalo/irrigação sanguínea , Encéfalo/metabolismo , Metabolismo Energético , Hiperventilação/metabolismo , Oxigênio/sangue , Pseudotumor Cerebral/metabolismo , Animais , Gatos , Circulação Cerebrovascular
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