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31.
THE EFFECT OF HYPOCHOLESTEREMIC AGENTS ON MYELINOGENESIS 总被引:4,自引:1,他引:3
Abstract— Three drugs known to inhibit biosynthesis of cholesterol, Clofibrate, 20, 25-diazacholesterol and AY-9944 were administered by stomach intubation to suckling rats. At weaning the rats were killed and subcellular fractions, including myelin, were prepared from the brains and spinal cords and analysed for sterol content. Central nervous tissue fractions from Clofibrate-treated rats showed some decrease in total sterols, but the sterol species were qualitatively normal. AY-9944 given to rats caused high amounts of 7-dehydro-cholesterol to accumulate in all brain and spinal cord fractions with the highest amounts (32–38 percent of total sterols) in myelin. In diazasterol-treated rats desmosterol reached 48 per cent of the sterols of myelin. A group of rats was allowed to survive after the final drug intake (21 days) and their brain and spinal cord sterol content followed up to 60 days. At 30 days the proportion of dehydrocholesterol or desmosterol comprised over half the total myelin sterol. By 60 days of age the 7-dehydrocholesterol had almost completely disappeared from all fractions while substantial amounts of desmosterol were retained in myelin. Myelination was retarded by treatment with AY-9944 and 20, 25-diazasterol, possibly by the limited amount of sterols available. The metabolism of the abnormal myelin constituents in drug-treated animals is discussed in relation to the molecular structure of the myelin membrane. 相似文献
32.
—The lipid composition of the central nervous system of some marine vertebrates and two mammalian species (rat and man) was analysed by one- and two-dimensional quantitative thin-layer chromatography, and the cerebroside fatty acids were analysed by gas chromatography. The concentrations of sphingomyelin and cerebrosides are higher in mammals than in fishes, while no significant differences are observed for other lipid classes. Furthermore, in mammals the ratio between hydroxy and normal fatty acids in the cerebrosides is much higher than in fishes. The cerebrosides of mammals contain more very long chain fatty acids than those of marine vertebrates. 相似文献
33.
Stand microclimate and physiological activity of tree leaves in an oak-hornbeam forest 总被引:1,自引:0,他引:1
Michal Marek Elena Masarovičovà Irena Kratochvílová P. Eliáš D. Janouš 《Trees - Structure and Function》1989,3(4):234-240
Summary In an uneven-aged, multi-species oak-hornbeam forest at Báb, SW Slovakia (former IBP Forest Research Site), a series of micrometeorological and ecophysiological measurements started in 1985. The aims of the work are to improve understanding of physiological processes (photosynthesis, respiration, and transpiration) of adult trees and stand microclimate, to collect data for simulation of the canopy (stand) photosynthesis and for ecological synthesis of the functioning of the forest ecosystem. In this paper, photosynthetically active radiation (PAR), air temperature (AT) and relative humidity (RH), wind speed (WS), and CO2 concentration ([CO2]) in and above the forest are characterized for the fully leaved season, using diurnal courses, vertical profiles and isodiagrams (isopleths). Approximately 50% of incident PAR was absorbed by the upper 4–5 m layer of leaves and only approximately 5% or less penetrated to the forest floor. Vertical gradients of AT and RH were generally low, but large differences in diurnal ranges of AT and RH were observed between vertical levels. The upper leaf canopy greatly reduced WS, and at a height of about 14 m above the ground it was close to zero. The highest diurnal [CO2] maximum and variations occurred at 1 m above the ground, and the lowest above the forest. In good light conditions in the forest, the entire leaf canopy (overstorey and understorey canopy) is a large sink of CO2. At night the forest stand is a source of CO2, the largest internal source being the soil and forest floor. 相似文献
34.
Pier Giorgio Borasio Carla Biondi Maria Enrica Ferretti Elena Fabbri Maria Cristina Pareschi 《Neurochemical research》1989,14(12):1181-1186
Agonists modulation of Mg2+-dependent adenylate cyclase activity has been studied in guinea-pig superior cervical ganglion crude membrane preparations. In the absence of receptors ligands, Mg2+ stimulates the enzyme in a concentration-dependent manner. The dose-activation curve shows heterogeneity and two components with higher and lower apparent affinity states, are extrapolated. In the presence ofD-Ala2-met-enkephalinamide only one component is present and the apparent affinity of the ganglionic adenylate cyclase system for the divalent cation as well as Vmax are inhibited. On the contrary, prostaglandin E2 increases affinity and Vmax values of the lower and, to a lesser extent, of the higher Km component. When the two drugs are tested in combination, not only the inhibitory effect of the opiate is overcome, but a large increase of the apparent affinities and Vmax values for both components is obtained, suggesting the involvement of the Mg2+-regulated subunits of the adenylate cyclase system in the supra-additive stimulation mechanism of the enzyme. 相似文献
35.
Marina Cinco Elena Banfi Carmelo Stornello F. Campo H. Korver 《FEMS microbiology letters》1989,47(8-9):499-504
Abstract A strain of Leptospira interrogans was isolated from a patient suffering from leptospirosis and was typed by the Gross Agglutination Absorption test using monoclonal antibodies prepared against different serovars of the Australis serogroup. This newly isolated strain belonged to serovar bratislava . It is the first reported isolation from man, in Italy, of Leptospira bratislava , thus supporting the emerging role of this serovar in human leptospirosis. 相似文献
36.
37.
Fabrizio Villani Milena Galimberti Elena Monti Francesco Piccinini Enrica Lanza Annalinda Rozza Luigia Favalli Paola Poggi Franco Zunino 《Free radical research》1990,11(1):145-151
The effects of two sulfhydryl compounds, glutathione (GSH) and N-acetylcysteine (NAC), on the cardiotoxicity of doxorubicin (DXR) were tested on in vitro and in vivo models. DXR was administered to rats as 4 weekly i.v. doses of 3mg/kg. GSH (1.5 mmoles/kg), given i.v. 10 min before and 1 hr after DXR, was found to prevent the development of the delayed cardiotoxic effects of DXR, as assessed by electrocardiographic and mechanical parameters, as well as by histological examination of left ventricular preparations. In contrast, equimolar oral doses of NAC (1 hr before and 2hrs after DXR) were found to be ineffective. Both GSH and NAC prevented the negative inotropic effect produced by DXR on isolated rat atria. A good correlation exists between the cardioprotective effects of the two agents and their ability to enhance the non-protein sulfhydryl group content of the myocardium. Differences observed in vivo between GSH and NAC might be accounted for by pharmacokinetic factors. 相似文献
38.
I. S. Novella J. J. Holland S. F. Elena A. Moya E. Domingo 《Molecular & general genetics : MGG》1996,252(6):733-738
The population dynamics of RNA viruses have an important influence on fitness variation and, in consequence, on the adaptative potential and virulence of this ubiquitous group of pathogens. Earlier work with vesicular stomatitis virus showed that large population transfers were reproducibly associated with fitness increases, whereas repeated transfers from plaque to plaque (genetic bottlenecks) lead to losses in fitness. We demonstrate here that repeated five-plaque to five-plaque passage series yield long-term fitness stability, except for occasional stochastic fitness jumps. Repeated five-plaque passages regularly alternating with two consecutive large population transmissions did not cause fitness losses, but did limit the size of fitness gains that would otherwise have occurred. These results underscore the profound effects of bottleneck transmissions in virus evolution. 相似文献
39.
40.
Cristina Elena Canteros Laura Rodero Maria Cristina Rivas Graciela Davel 《Mycopathologia》1996,136(1):21-23
A rapid method to evidence urease activity is described. Urea hydrolysis and consequent production ammonia are detected by a chemical reaction producing a blue phenol compound (indophenol blue). Three hundred and three yeast were tested. Out of 107 urease-positive organisms detected by Christensen's Urea Agar Test (CUAT) 102 were positive by our method. No false negatives were observed by this method when testing 87 Cryptococcus strains. Ths practical screening test for presumptive identification of Cryptococcus neoformans is simple, unaffected by pH changes and requires 15 minutes to be performed. 相似文献