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  • 1
    ISSN: 1432-0428
    Keywords: Propranolol ; blood-clucose ; Free-fatty acids ; Plasma-Insulin ; glucose-tolerance ; exercise
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Résumé Trois types d'expérience ont été effectués chez des sujets normaux afin de déterminer l'effet de doses thérapeutiques orales de propranolol sur 1. la glycémie, l'insuline et les acides gras libres (FFA) du plasma au cours du jeûne prolongé et de l'exercice, 2. la tolérance au glucose intraveineux et l'augmentation du taux d'insuline après glucose intraveineux, et 3. la tolérance au glucose intraveineux pendant l'exercice. Le propranolol ne provoquait qu'un léger abaissement de la glycémie chez les sujets normaux, même après 24 h de jeûne. Ceci était plus décelable au cours de l'exercice. Le propranolol n'exerçait aucun effet significatif sur les taux d'insuline à jeun, la tolérance au glucose au repos ou en cours d'exercice, ou sur la réponse des taux d'insuline plasmatique au glucose intraveineux. On a observé un abaissement des taux de FFA plaematiques chez tous les sujets après absorption de propranolol, particulièrement au cours ou après un exercice. Les mécanismes possibles d'hypoglycémie dans les cas décrits dans la littérature sont discutés. Les auteurs concluent que l'hypoglycémie n'est pas un problème majeur dans la thérapeutique par le propranolol.
    Abstract: Zusammenfassung Bei Normalpersonen wurden die Effekte von oral verabreichten Dosen von Propanolol in 3 verschiedenen Versuchsanordnungen überprüft: 1. auf Blutzucker, Plasmainsulin und freie Fettsäuren (FFS) während längerer Fastenperioden und unter körperlicher Belastung, 2. auf die Glucosetoleranz und den Anstieg der Seruminsulinspiegel nach i.v. Glucosezufuhr, 3. auf die i.v. Glucosetoleranz bei Muskelarbeit. Propranolol senkte den Blutzucker bei Normalpersonen auch nach 24-stündigem Fasten nur geringfügig. Dies war besonders auffällig unter körperlicher Belastung. Es ließen sich keine signifikanten Propanolol-Effekte auf die Nüchterninsulinspiegel, auf die Glucosetoleranz in Ruhe und bei Musekelarbeit und auf den Anstieg der Plasmainsulinspiegel nach i.v. Glucosegabe nachweisen. Bei allen Probanden führte Propanolol zu einer Senkung der Plasma FFS-Spiegel, vor allem während und nach Muskelarbeit. Mechanismen, die die in der Literatur beschriebenen Beobachtungen von Hypoglykämien nach Propanolol ausgelöst haben könnten, werden diskutiert. Es wird gefolgert, daß Hypoglykämien bei der Propanolol-Therapie kein größeres Problem darstellen.
    Notes: Summary Three types of experiment were carried out in normal subjects to determine the effect of therapeutic doses of oral Propranolol on 1. the blood sugar, plasma insulin and free fatty acids (FFA) during prolonged fasting and exercise, 2. intravenous glucose tolerance and the rise in insulin level after intravenous glucose, and 3. the intravenous glucose tolerance on exercise. Propranolol caused only slight lowering of the blood sugar in normals, even after 24 h fasting. This was most noticeable during exercise. There was no significant effect of Propranolol on fasting insulin levels, on glucose tolerance at rest or exercise, or on the response of plasma insulin levels to intravenous glucose. Lowering of plasma FFA levels was found in all subjects when taking Propranolol particularly during and after exercise. Possible mechanisms of hypoglycaemia in those cases reported in the literature are discussed. It is concluded that hypoglycaemia is not a major problem in Propranolol therapy.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5168
    Keywords: rainbow trout ; Oncorhynchus mykiss ; white muscle ; enzyme ; purification ; gluconeogenesis ; pH ; fructose-1,6-bisphosphatase ; phosphofructokinase ; exercise
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Studies of the enzyme fructose-1,6-bisphosphatase (FBPase) of rainbow trout (Oncorhynchus mykiss) have been undertaken in order to illuminate aspects of skeletal muscle gluconeogenesis in these animals. Maximal activities in crude homogenates of several organs suggest that the liver possesses the greatest FBPase activity on a unit g−1 tissue basis but that the white muscle, owing to its bulk, contributes substantially to whole body FBPase activity. Studies of fructose-6-phosphate-1-kinase (PFK) and FBPase in crude homogenates of several organs suggests an important role for intracellular pH in regulating the relative carbon flux through the FBPase/PFK locus in vivo. Furthermore, a three-step purification scheme is described for trout white muscle FBPase by which a stable and homogeneous (by SDS PAGE) enzyme preparation (isoelectric point = 7.2; molecular weight = 37.6 kd) was obtained. Kinetic studies of the purified enzyme were undertaken at 20°C under conditions reflective of "rest" and "exercise/recovery" intramuscular pH in vivo. Affinity for substrate (F-1,6-P2) was increased (Km = 6.88 versus 2.44 μmol 1-−1 as was enzyme activity when pH was lowered from 7.0 to 6.5. Various inhibitor metabolites are identified including F-2,6-P2 (mixed-type inhibitor, Ki = 0.201 μmol 1−1, pH 7.0) and AMP (non-competitive inhibitor, Ki = 0.438 μmol 1−1, pH 7.0). Inhibition by F-2,6-P2 was strongly alleviated by a reduction in pH from 7.0 to 6.5 (I50 increased from 0.14 to 0.32 μmol 1−1). AMP on the other hand was a more potent inhibitor at pH 6.5 but this inhibition was totally reversed under conditions of citrate, NH4 + and AMP typical of muscle during recovery from exercise in vivo. In purified white muscle enzyme preparations, FBPase demonstrated maximal activity at pH 6.5 whereas the optimal pH of PFK was 7.0 or greater. Indeed, it appears from these in vitro data that regulation by metabolite levels as well as pH are required for net FBPase flux in vivo. It is concluded, therefore that trout white muscle FBPase demonstrates the potential to play an important enzymatic role in the control of intramuscular gluconeogenesis in these animals. The results are discussed in relation to present knowledge regarding the metabolic responses of trout white muscle to, and its subsequent recovery from, exhaustive exercise.
    Type of Medium: Electronic Resource
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