Search

The synthesis and pharmacological properties of a novel type of vasorelaxant hybrid compounds are described. The investigated compounds originate from fluorinated 4-aryl-1,4-dihydropyridines, which are known calcium channel blockers, and/or from fluorinated analogues of pinacidil, which is an opener of ATP-sensitive potassium channels. In particular, we studied the most potent hybrid, 2,6-dimethyl-3,5-dicarbomethoxy-4-(2-difluoromethoxy-5-N-(N‘ ‘-cyano-N‘-1,2,2-trimethyl-propylguanidyl)-phenyl)-1,4-dihydropyridine (4a), together with its parent compounds, the dihydropyridine 1b and the pinacidil analogue 3. In isolated rat mesenteric arteries, micromolar concentrations of 4a relaxed contractions exerted by K⁺-depolarization or by norepinephrine. The latter effect was sensitive to the potassium channel blocker glibenclamide. Micromolar 4a also inhibited [³H](+)-isradipine and [³H]P1075 binding to rat cardiac membranes, and it blocked L-type calcium channels expressed in a mammalian cell line. The respective parent compounds 1b and 3 were always more potent and more selective regarding calcium channel or potassium channel interaction, respectively. In contrast, 4a combined both effects within the same concentration range, indicating that it may represent a lead structure for a novel class of pharmacological hybrid compounds.

Anhand der Auswertung von zahlreichen Versuchen wird die Möglichkeit aufgezeigt, das Mitwirken des Betons in der Zugzone durch Ansetzen einer Spannungs‐Dehnungs‐Linie zu berücksichtigen, die in der Zugzone affin zum Verlauf in der Druckzone angenommen wird. Dies hätte beispielsweise erhebliche Vorteile bei der Verformungsberechnung von Türmen und Schornsteinen durch Reduzierung der Einspannmomente nach Theorie II. Ordnung am Turmfuss.

P1075 [N-cyano-N'-(1,1-dimethylpropyl)-N"-3-pyridylguanidine], an analogue of the K+ channel opener pinacidil, was shown to be a K+ channel opener in rat aorta, based on (i) its ability to stimulate 86Rb+ efflux, (ii) its ability to relax contractions in response to noradrenaline under normal conditions (5 mM KCl) but not under depolarized conditions (55 mM KCl), and (iii) the sensitivity of these effects to inhibition by the sulfonylurea glibenclamide. In these assays, P1075 was approximately 20 times more potent than cromakalim. Using a tritiated derivative, [3H] P1075, specific binding could not be detected in microsomal preparations from various tissues. However, in rat aortic strips specific binding of [3H]P1075 has been observed and was reduced by lowering the temperature or by decreasing intracellular ATP levels via metabolic inhibition. Specific [3H]P1075 binding was influenced neither by depolarization (55 mM KCl) nor by lowering the pH from 7.4 to 6.0. Binding was inhibited by representatives from all major families of K+ channel openers, with potencies that correlated well with the potencies obtained in 86Rb+ efflux and relaxation studies. However, stimulation of 86Rb+ efflux occurred at 40 times higher concentrations than did binding (and vasorelaxation). Of the various inhibitors of the K+ channel openers tested, only the sulfonylureas inhibited [3H] P1075 binding with the same rank order of potencies as that required for inhibition of P1075-induced 86Rb+ efflux, although at higher concentrations. The results show that binding of [3H] P1075 is independent of membrane potential but decreases concomitantly with the intracellular ATP level. The excellent correlation between the potencies of the openers and sulfonylurea blockers in binding assays and functional studies suggests that the 'drug receptor' labeled by [3H]P1075 in rat isolated aorta is of functional relevance. However, the fact that binding of the openers occurred at concentrations considerably lower than those required for K+ channel opening and that binding of the sulfonylureas was only reflected at concentrations higher than those needed to block the channel requires complex models to link binding and effect, possibly involving two agonist binding sites coupled by negative cooperativity.

The temperature dependence of the interaction of three benzodiazepines with their receptors in rat brain membranes containing about 2 microM (endogenous) gamma-aminobutyric acid was investigated. van't Hoff plots of the equilibrium dissociation constants were linear for [3H]diazepam and its N-desmethyl derivative (N-desmethyldiazepam, NDz), whereas for [3H]flunitrazepam a break between two linear portions occurred at about 10 degrees. Binding of diazepam, NDz, and flunitrazepam (for the latter, at temperature greater than 10 degrees) is enthalpy-driven (delta H approximately -40 to -50 kJ/mole with a negligible contribution from delta S. The latter result indicates that the interaction is not a simple hydrophobic association, but that it may be more complex in nature, possibly involving a conformational transition of the receptor-ligand complex. The activation energy for dissociation of the [3H]flunitrazepam- and [3H]diazepam-receptor complexes is about 100 kJ/mole. Consequently, the complexes dissociate about 100 times faster on changing temperature from 0 degrees to 37 degrees.

Es werden die Vorteile einer Gleichgewichtsbetrachtung am verformten System (Theorie II. Ordnung) einer Bemessung von Stahlbetonstützen nach dem Ersatzstabverfahren erläutert. Dies gilt besonders bei verschiebliche Rahmen.

Es werden die Einzelregelungen angesprochen und mit denen in DIN 1045 verglichen. Die Rechengrundlagen stimmen in ihrer Art weitgehend überein, weil sie auf die CEB/FIP‐Mustervorschrift aus dem Jahre 1978 zurückgehen. Jedoch ergeben sich überwiegend höhere zulässige Lasten wegen des Konzepts geteilter Sicherheitsbeiwerte, höherer Rechenfestigkeiten für Beton höherer Festigkeitsklassen und steiferer Spannungs‐Dehnungs‐Linien für die Berechnung der Verformung. Weil eine Mindestausmitte von 20 mm sowohl für die ungewollte Lastausmitte beim Knicksicherheitsnachweis als auch für den Tragfähigkeitsnachweis des Querschnitts zu beachten ist, können sich aber auch niedrigere zulässige Lasten ergeben. Das Modellstützenverfahren, das dem Ersatzstabverfahren entspricht, bedarf Verbesserungen oder Ergänzungen, um es unmittelbar anwenden zu können. Ein eigener Vorschlag wird in einem Beispiel verdeutlicht. Noch nicht enthalten sind im Eurocode 2 die Fälle, bei denen die maßgebende Verformungsrichtung von der Hauptachsen‐ richtung des Querschnitts oder von der Lastebene abweicht.

Als freistehende Bauteile werden in diesem Beitrag Türme, Schornsteine, Pfeiler und Maste angesprochen. Die Ausführungen treffen auch für nur unten eingespannte Stützen in nicht ausreichend ausgesteiften Bauwerken zu. Es wird das Verhalten im Grenzzustand der Tragfähigkeit beschrieben und ein Vergleich bei der Bemessung nach DIN 1045, DIN 1075, DIN 4228 und DIN 4234 gezogen.

Die Bemessung von Stahlbeton‐Stabtragwerken nach der Theorie II. Ordnung kann vorteilhaft nach dem Reduktionsverfahren durchgeführt werden, wenn der Bewehrungsgehalt als freier Wert in die Anfangsbedingungen eingeführt wird.

Diazoxide caused an increase in 86Rb+ efflux from the rat aorta and portal vein and inhibited spontaneous activity of the latter at concentrations 100 times higher than the K+ channel opener cromakalim. In the rabbit aorta both drugs inhibited vasoconstrictor responses to angiotensin II, noradrenaline and low concentrations (less than or equal to 30 mM) of KCl in a similar manner, the antivasoconstrictor activities being abolished in vessels depolarized with greater than or equal to 35 mM K+. In vivo cromakalim was about 100 times more potent than diazoxide at lowering blood pressure in rats. Diazoxide (30 mg/kg) caused a more than 2-fold increase in plasma glucose in rats and prevented any return toward base line within 1.5 hr after a glucose load. Cromakalim had minimal effects upon glucose homeostasis at equihypotensive doses. Glibenclamide, a potent blocker of ATP-dependent K+ channels, inhibited the stimulation by cromakalim and diazoxide of 86Rb+ efflux from the portal vein and aorta (IC50 approximately 0.1 microM), antagonized their vasorelaxant effects in vitro and in vivo (20-30 mg/kg i.v.) and reversed the diazoxide-induced changes in plasma glucose and insulin levels. These results provide evidence that diazoxide, like cromakalim, is able to open 86Rb+-permeable K+ channels in vascular smooth muscle. This action is likely to be responsible for the in vitro and in vivo vasodilator activity of these two drugs. However, there would seem to be pharmacological differences between the K+ channels affected by these drugs in vascular smooth muscle and the (ATP-sensitive) K+ channels of pancreatic beta-cells, which are thought to be responsible for the effects of diazoxide on plasma glucose.

Planar bilayer membranes containing functional acetylcholine receptor were formed from vesicles of Torpedo marmorata electric organ without extracting the acetylcholine receptor from its native environment. Native vesicles were transformed into monolayers which subsequently were apposed into planar bilayers. In the absence of agonists the membrane conductance was similar to that of lipid bilayers. Addition of carbamoylcholine or succinylcholine caused increased membrane conductance and this could be competitively inhibited by d-tubocurarine and suppressed by alpha-bungarotoxin. The amplitude of the conductance response was proportional to the number of alpha-bungarotoxin binding sites in the bilayers. Asymmetric membranes could be formed with the ligand binding sites on only one membrane surface. Desensitization of acetylcholine receptor was evident from equilibrium and kinetic data of the carbamoylcholine-activated conductance. Carbamoylcholine-induced membrane permeability was about 7 times higher for K+ and Na+ ions than for Cl-. At low levels of conductance, single-channel fluctuations of 20-25 pS in conductance and 1.3-msec lifetime were resolved in physiological saline containing carbamoylcholine. The ratio of observed channels to alpha-bungarotoxin sites present showed that a significant fraction of acetylcholine receptor in the membrane was functional. The quantitative aspects of the cation channel, the desensitization, and the ligand binding properties were in close agreement with established values. This transformation of natural acetylcholine receptor vesicles to planar bilayers conserves the essential properties of the in vivo receptor.

Proton magnetic resonance has been used to monitor binding of choline, a known partial agonist, to acetylcholine receptor-enriched membrane preparations from Torpedo californica electroplax. The interaction between choline and receptor led to a broadening of the resonance of the choline methyl groups and this effect was reversed by alpha-bungarotoxin, a quasi-irreversible antagonist of the acetylcholine receptor. From the concentration dependence of line broadening the equilibrium dissociation constant for choline was obtained (Kd = 190 +/- 65 microM). The temperature dependence of the parameters observed in the choline titrations gave an enthalpy of binding delta H less than 1.5 kcal/mol and allowed estimates for the dissociation rate constant of the receptor-choline complex (kdiss greater than 1.6 x 10(3) S(1) and the respective activation energy, Ea (Kdiss) approximately 5.5 kcal/mol. The association of other ligands with the membrane-bound receptor could also be studied by observing effects of varying concentrations of such ligands on the choline methyl group linewidth at a constant choline concentration.

Abstract: The interaction between the cytoskeleton and the ATP-sensitive K+ channel (KATP channel) was studied in rat aortic rings by examining the binding of the sulphonylurea blocker, 3H-glibenclamide, and of the opener, 3H-P1075. The actin cytoskeleton disrupting agents, cytochalasin D (1μM) and latrunculin B (1μM), abolished the high affinity component of 3H-glibenclamide binding. Preincubation with the actin cytoskeleton stabilizing agent, phalloidin (10μM) prevented the effect of cytochalasin D. In contrast, binding of the opener, 3H-P1075, and inhibition of this binding by glibenclamide, were unaffected by cytochalasin D (3μM). Colchicine (100μM), which disassembles microtubules, had no effect on the binding of 3H-glibenclamide and 3H-P1075. The data show that high affinity binding of glibenclamide, which mediates the effects of the sulphonylurea in this preparation, requires the presence of an intact actin cytoskeleton. Binding of the opener is unaffected by the state of the cytoskeleton and preserves a conformational state in which high affinity binding of glibenclamide to the sulphonylurea receptor can occur.