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991.
Maryna van de Venter Derek Litthauer Willem Oelofsen 《Journal of cellular biochemistry》1994,54(1):1-10
Adipocyte precursors from the stromal vascular fraction of human adipose tissue were allowed to differentiate in serum-free defined medium, whereafter their catecholamine stimulated lipolytic response was compared to that of mature isolated human adipocytes. Seventy-five to ninety percent of the fibroblast-like cells accumulated lipid droplets and glycerol-3-phosphate dehydrogenase activities of 1,000–2,800 mU/mg protein were measured in cell homogenates of differentiated cells. Lipolysis could be stimulated by both isoproterenol and norepinephrine in both differentiated preadipocytes as well as mature adipocytes. The results obtained with β-adrenergic agents suggested the presence of a higher affinity receptor in differentiated preadipocytes as compared to mature adipocytes. Mature adipocytes responded well to β-adrenergic agents, but no antilipolytic α2-adrenergic response was observed in the differentiated preadipocytes. The presence of Gi proteins in the differentiated preadipocytes was suggested by the antilipolytic effect of adenosine as well as the lipolytic activity generated by pertussis toxin. In conclusion, our medium supported the differentiation of a very high percentage of human preadipocytes which developed a sensitive β-adrenergic lipolytic response but which lacked an α2-adrenergic antilipolytic response. 相似文献
992.
A. R. Carlini M. E. I. Márquez G. Soave D. F. Vergani P. A. Ronayne de Ferrer 《Polar Biology》1994,14(1):37-42
An analysis of milk constituents during various stages of lactation in the southern elephant seal Mirounga leonina was carried out. Forty-six milk samples were taken from 30 females throughout lactation during 1985, 1987, 1990 and 1991 on Stranger Point, King George Island, South Shetland Islands. Total nitrogen (TN), non-protein nitrogen (NPN), sugar, fat, ash and water were measured, and from some of these data true protein and energy content were calculated. The results showed a high degree of variation in water and fat concentrations among samples at different stages of lactation. During the first 20 days the fat content of milk increased from about 12 to approximately 52%, while water content fell from 70 to 33%. The composition of milk changes rapidly during the first days post-partum. Protein, minerals and sugar appear to remain stable after the fourth day of lactation. Milk samples contain significant levels of sugars; thin layer chromatography indicates the presence of lactose and glucose together with other unidentified components. There is evidence of a striking change in composition of the milk in the later part of lactation; the progressive increase in the fat:water ratio is abruptly reversed just prior to weaning. 相似文献
993.
M. Joëls W. Hesen H. Karst E.R. de Kloet 《The Journal of steroid biochemistry and molecular biology》1994,49(4-6):391-398
Corticosteroid hormones can enter the brain and bind to two receptor subtypes: the high affinity mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR) with approximately 10-fold lower affinity. Under physiological conditions the degree of receptor occupation will range from a predominant MR occupation (at the beginning of the inactive period, under rest) to concurrent activation of MRs and GRs (at the circadian peak and after stress). With in vitro electrophysiological recording techniques we observed that neuronal excitability in the CA1 hippocampal field is under a long-term control of MR- and GR-mediated events. The predominant occupation of MRs is associated with a stable amino acid-carried synaptic transmission; calcium- and potassium-currents are small, as are the responses to biogenic amines. Occupation of GRs in addition to MRs results in a gradual failure of CA1 neurons to respond to repeated stimulation of amino acid-mediated input; ionic conductances and responses to biogenic amines are large. In general, electrical properties recorded when both MRs and GRs are unoccupied (i.e. after adrenalectomy) resemble the responses observed when both receptor types are activated. The corticosterone dependency of electrical properties is thus U-shaped. We conclude that MR occupation may be responsible for the maintenance of information processing in the CA1 field and the stability of the circuit. Additional activation of GRs will initially suppress synaptic activity, but may eventually result in an increased instability and even vulnerability of the neuronal networks. 相似文献
994.
The radiosensitivity of spermatogonial stem cells of C3H/HeH × 101/H F1 hybrid mice was determined by counting undifferentiated spermatogonia at 10 days after X-irradiation. During the spermatogenic cycle, differences in radiosensitivity were found, which were correlated with the proliferative activity of the spermatogonial stem cells. In stage VIIIirr, during quiescence, the spermatogonial stem cells were most radiosensitive with a D0 of 1.4 Gy. In stages XIirr−Virr, when the cells were proliferatively active, the D0 was about 2.6 Gy. Based on the D0 values for sensitive and resistant spermatogonia and on the D0 for the total population, a ratio of 45:55% of sensitive to resistant spermatogonial stem cells was estimated for cell killing.
When the present data were compared with data on translocation induction obtained in mice of the same genotype, a close fit was obtained when the translocation yield (Y; in % abnormal cells) after a radiation dose D was described by Y = eτD, with τ = 1 for the sensitive and τ = 0.1 for the resistant spermatogonial stem cells, with a maximal eτD of 100. 相似文献
995.
E. Zebe G. Gäde 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1993,163(2):107-112
Metabolite concentrations in flight muscles and in abdomen of beetles (Pachnoda sinuata) were measured after various periods of tethered flight and subsequent rest. Three distinct phases of energy metabolism are found in active flight muscles: (1) during the first minutes of flight proline is used as main substrate and concomitantly alanine accumulated as an end product; (2) the second phase is characterized by a large-scale degradation of glycogen; (3) after about 8 min of flight the metabolite levels stabilize, while flight performance appears unchanged. After the termination of flight the preflight proline concentration (70 mol·g-1 fw) is re-established in less than 60 min, whereas restoration of resting levels of other metabolites requires longer. The pattern of maximal enzyme activities and the respiratory rates of mitochondria with different substrates confirm the significance of proline and carbohydrates as the main fuels of working flight muscles.Abbreviations CS
citrate synthetase
- Cytox
cytochrome c oxidase
- EDTA
ethylenediaminetetra-acetate
- fw
fresh weight
- GluDH
glutamate dehydrogenase
- GPT
alanine aminotransferase
- HOAD
hydroxyacyl-coenzyme A dehydrogenase
- HPLC
high pressure liquid chromatography
- ME
malic enzyme
- PCA
perchloric acid
- RQ
repiratory quotient
- TRA
triethanolamine 相似文献
996.
Adult Hyalomma ticks were examined for the presence of Theileria annulata infection using the Polymerase Chain Reaction (PCR). A 372 bp DNA fragment derived from the small ribosomal RNA gene of T. annulata was amplified from 45 out of 50 (90%) H. dromedarii ticks and from 36 out of 50 (72%) H. marginatum marginatum ticks. No product was amplified from non-infected control ticks. Restriction enzyme digestion with Sac II confirmed that the product was derived from the targeted T. annulata gene. As a further confirmation it was shown that both species of Hyalomma ticks were able to transmit T. annulata to experimental calves. PCR detection of Theileria parasites in ticks was compared with conventional staining of dissected salivary glands using methyl green pyronin and its comparative advantages are discussed. 相似文献
997.
Patrice Daniel Erwin de Waele Jean-Noël Hallet 《Applied microbiology and biotechnology》1993,38(5):638-641
Genomic DNA of several strains oof oenological lactic bacteria belonging to the species Lactobacillus plantarum, Leuconostoc oenos and Pediococcus pentosaceus was digested by the rare-cutting endonucleases ApaI and SmaI. The restriction products were separated by transverse alternating field electrophoresis (TAFE). The size of the genome of L. oenos estimated by adding the molecular size of the ApaI fragments was on average 1320 kb. A strong polymorphism was observed between the strains, which could be easily differentiated except for two industrial strains of L. oenos. A simple modification of the TAFE apparatus is proposed to improve the separation of the DNA fragments.
Correspondence to: J.-N. Hallet 相似文献
998.
Jesús Manuel de la Fuente Amalia Vázquez M. Mar González Miguel Sánchez María Molina César Nombela 《Applied microbiology and biotechnology》1993,38(6):763-769
Thermosensitive mutant strains of Saccharomyces cerevisiae that fail to generate an osmotically stable cell wall when grown at a non-permissive temperature release their cell contents upon expression of the mutation. Therefore, they may represent an alternative for the production of homologous or heterologous protein preparations. In order to analyse the expression of two of these mutations, lyt2 and slt2, we grew the corresponding strains under precisely defined conditions in batch and continuous fermentors. A switch in the temperature of batch cultures from 24° C to 37° C determined lysis of the cells with a significant release of intracellular enzymes. These include alkaline phosphatase and periplasmic proteins such as glucan-degrading enzymes, the pattern of cell lysis and protein release being maintained for about 6 h. One-stage continuous cultures of a lyt2 mutant were maintained for long periods at 37° C; a fraction of the population lysed and released the indicated proteins, but eventually a revertant of the lytic phenotype was selected. To avoid this, a two-stage continuous culture system was developed by connecting two fermentors in series, the effluent from the first one at 24°C being fed to the second one adjusted to 37° C. A steady state of cell lysis and protein liberation was reached in the second-stage fermentor without any evidence of selection of revertants. This system can be very useful for developing conditions for the use of yeast strains to produce protein preparations.
Correspondence to: C. Nombela 相似文献
999.
S. Fauré J. L. Noyer J. P. Horry F. Bakry C. Lanaud D. Gońzalez de León 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1993,87(4):517-526
A partial molecular linkage map of the Musa acuminata diploid genome is presented. This map is based on 58 RFLP, four isozyme and 28 RAPD markers segregating in an F2 population of 92 individuals. A total of 90 loci was detected, 77 of which were placed on 15 linkage groups while 13 segregated independently. Segregation distortions were shown by 36% of all loci, mostly favoring the male parent. Chromosome structural rearrangements were believed to be one of the main causes of these distortions. The use of genetic linkage data to further the genetic and evolutionary knowledge of the genus Musa, as well as to help improve the design of breeding strategies, is discussed. 相似文献
1000.
Margarita Ostrowski de Núñez 《Systematic parasitology》1993,24(3):191-199
The life-cycle of Ascocotyle (Phagicola) diminuta (Stunkard & Haviland, 1924) was reproduced experimentally, starting from cercariae from naturally infected Littoridina castellanosae and L. parchappei (Hydrobiidae) collected from artificial ponds in the Zoological Garden in Buenos Aires and from Los Ranchos stream, Buenos
Aires Province, respectively. Metacercariae were found encysted in the gills of experimentally exposed Cnesterodon decemmaculatus (Poecilidae) and of other naturally infected freshwater fishes. Adults were obtained experimentally in chicks and mice and
from a naturally infected egret, Egretta thula. A. (P.) angrense Travassos, 1916 was found parasitising the egret Ixobrychus involucris; it is considered a valid species and the morphological differences between it and A. (P.) diminuta were established. The “Phagicola-form” of the cercaria in the present life-cycle is also known in the genus Pygidiopsis. 相似文献