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  • Adrenergic Alpha-Receptors  (1)
  • Key words Effects of deforestation  (1)
  • 1
    ISSN: 1432-1912
    Schlagwort(e): Vascular Smooth Muscle ; Adrenergic Alpha-Receptors ; Vasopressin ; Potassium Depolarization ; Noradrenaline
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary 1. Determinations of the maximum tension development of the helical strip of rat aorta showed that the maximal response to vasopressin amounted to 75% and that to potassium-induced depolarization to 93% of the contraction caused by noradrenaline (=100%). 2. When phentolamine (1.2-6.2×10−6 g/ml) was added to the bath 15 min before the determination of dose-response curves for noradrenaline, there was a concentration-dependent shift of the curve to the right; the slope of the curve, the ED50 and the concentration of noradrenaline required for maximum activation of the muscle increased. However, when phentolamine (1.2 to 6.2×10−6 g/ml) was administered after the development of a maximum response to noradrenaline, the muscle relaxed nearly completely. In the presence of phenoxybenzamine (3×10−6 g/ml) noradrenaline failed to cause contractions. 3. The dose-response curve for vasopressin was sigmoid. The presence of phentolamine did not affect the ED50 (at 1.6×10−3 IU/ml) or the peak of the curve (at 1.2×10−2 IU/ml). The administration of vasopressin to depolarized muscles always caused a contractile response. When the muscle was activated repeatedly by vasopressin, tachyphylaxis occurred. 4. Block of the adrenergic alpha-receptors influenced the contractile response to depolarization far less than that to noradrenaline. 5. In accordance with earlier studies, the present results lead to the conclusion that the contraction of the vascular smooth muscle in response to noradrenaline, vasopressin, or depolarization, respectively, involves different mechanisms.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Biology and fertility of soils 31 (2000), S. 134-142 
    ISSN: 1432-0789
    Schlagwort(e): Key words Effects of deforestation ; Mountain soil ; Particle-size fractionation ; Phosphorus fractionation ; Phosphorus pools
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract  The amount, quality and turnover of soil P is heavily influenced by changes in soil management. The objective of this study was to investigate the effects of deforestation and pasture establishment on the concentrations, forms and turnover rate of soil P in mountain soils of the Alay Range, Khyrgyzia. A sequential extraction was applied to distinguish soil P pools. We used particle-size fractionation to follow the dynamics of different P pools in soils under forest and pasture and 31P-NMR spectroscopy to investigate the structure of alkali-soluble P forms. In the A horizons of the forest soils, total soil P concentration was 1093 mg kg–1, organic P (Po) representing 46% of the total P. Deforestation followed by pasture establishment not only increased significantly (P〈0.01) the total P concentration (1560 mg kg–1) but also the contribution of Po to total P was increased by 17%. Pasture soils had significantly higher P pools than forest soils except highly labile inorganic P (Pi NaHCO3) and primary Pi (Pi HCldil). Both in forest and pasture soils stable P increased with decreasing particle size (coarse sand 50%, clay 80% of total P) and primary P decreased with decreasing particle size. Phosphate monoesters and diesters represented 80% of P identified by 31P NMR. Low monoester to diester ratios in the alkali extracts of forest and pasture soils indicate low microbial activity. This is consistent with high C/Po ratios and high stable Po concentrations in the fine earth of forest and pasture.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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