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  • 1
    Electronic Resource
    Electronic Resource
    Positive inotropic action of angiotensin II in the pithed rat (1993)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 347 (1993), S. 658-663 
    Details
    ISSN: 1432-1912
    Keywords: Angiotensin II ; Myocardial contraction ; Pithed rat ; AT1 receptor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The cardiovascular effects of angiotensin II were examined in aortic blood pressure-controlled and-uncontrolled pithed rats. Angiotensin II induced a dose-dependent increase in diastolic blood pressure, left ventricular pressure (LVP), dP/dt (the first derivative of LVP) and heart rate in pithed rats. The maximal responses for these parameters were similar to those to noradrenaline, except for the rise in diastolic blood pressure, where noradrenaline caused a greater increase than angiotensin II. After treatment with propranolol, the positive chronotropic effect of angiotensin II was abolished. Angiotensin II produced a dose-dependent increase in diastolic blood pressure, which was similar to that of vasopressin, and an increase in dP/dtmax, which proved much greater than that of vasopressin. When aortic blood pressure was controlled and the β-receptors were blocked by propranolol, angiotensin II caused a dose-dependent increase in dP/dtmax without affecting the left ventricular enddiastolic pressure. The same results were obtained after both β- and α-adrenoceptors were blocked by propranolol and phentolamine. Losartan but not PD 123177 caused parallel rightward shifts of the dose-response curve of angiotensin II for dP/dtmax in the aortic blood pressure controlled pithed rat without altering the maximal response. It is concluded that in the pithed rat angiotensin II produced an increase in myocardial contractile force which is not mediated by β- or α-adrenoceptors. The inotropic effect appears to be mediated by angiotensin receptors, of the AT1-subtype.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00166950
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  • 2
    Electronic Resource
    Electronic Resource
    Inhibitory effect of dithiothreitol on angiotensin II-induced contractions mediated by AT1-receptors in rat portal vein and rabbit aorta (1994)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 349 (1994), S. 538-542 
    Details
    ISSN: 1432-1912
    Keywords: AT1-receptors ; Angiotensin II ; Dithiothreitol ; Losartan ; Rat portal vein ; Rabbit aorta
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The disulfide-reducing agent dithiothreitol (DTT) has been shown to reduce angiotensin II (Ang II) subtype 1 receptor (AT,) binding sites in various tissues. Its effect on Ang II-induced contractions was studied in the rat portal vein and rabbit aorta. In the isolated rat portal vein, DTT shifted the concentration-response curve for Ang II to the right (DTT 0.5–3 mmol/l) and depressed the maximal response (DTT 1–3 mmol/l). DTT 5 mmol/l almost abolished the effect of Ang II. In the isolated rabbit aorta, the inhibitory effect of DTT was more pronounced and its pattern of effect was different,since DTT 0.3 and 0.5 mmol/l caused a progressive flattening of the concentration-response curve of Ang II. DTT (1 mmol/l) fully suppressed the effect of Ang II. A biphasic curve consisting of a high sensitivity component and a component of low sensitivity for Ang II was observed after pretreatment with DTT 1 mmol/l in the rat portal vein but not in the rabbit aorta. In the presence of DTT 1 mmol/l, the AT1-receptor antagonist losartan antagonized the high sensitivity response to Ang II in a competitive manner with a pA2 value very similar to that obtained in the absence of DTT, suggesting that this response to Ang II is mediated by those AT1-receptors which were not inactivated by DTT The biphasic curve may be explained by the occurrence of a single AT1-receptor subtype existing in two different states. Another possibility might be the involvement of two AT1-receptor subpopulations. It is concluded that disulfide bonds are critical for the functional role of AT1-receptors in Ang II-induced contractions in the rat portal vein and rabbit aorta.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00169144
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  • 3
    Electronic Resource
    Electronic Resource
    Scaled Optimal Path Trust-Region Algorithm (1999)
    Springer
    Journal of optimization theory and applications 102 (1999), S. 127-146 
    Details
    ISSN: 1573-2878
    Keywords: Trust-region methods ; unconstrained optimization ; Bunch–Parlett factorization ; optimal paths ; global convergence ; local convergence rates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Trust-region algorithms solve a trust-region subproblem at each iteration. Among the methods solving the subproblem, the optimal path algorithm obtains the solution to the subproblem in full-dimensional space by using the eigenvalues and eigenvectors of the system. Although the idea is attractive, the existing optimal path method seems impractical because, in addition to factorization, it requires either the calculation of the full eigensystem of a matrix or repeated factorizations of matrices at each iteration. In this paper, we propose a scaled optimal path trust-region algorithm. The algorithm finds a solution of the subproblem in full-dimensional space by just one Bunch–Parlett factorization for symmetric matrices at each iteration and by using the resulting unit lower triangular factor to scale the variables in the problem. A scaled optimal path can then be formed easily. The algorithm has good convergence properties under commonly used conditions. Computational results for small-scale and large-scale optimization problems are presented which show that the algorithm is robust and effective.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1021846613163
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  • 4
    Electronic Resource
    Electronic Resource
    Projected quasi-Newton algorithm with trust region for constrained optimization (1990)
    Springer
    Journal of optimization theory and applications 67 (1990), S. 369-393 
    Details
    ISSN: 1573-2878
    Keywords: Two-sided projected Hessians ; trust regions ; differentiable penalty functions ; global convergence ; two-step Q-superlinear rate ; constrained optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In Ref. 1, Nocedal and Overton proposed a two-sided projected Hessian updating technique for equality constrained optimization problems. Although local two-step Q-superlinear rate was proved, its global convergence is not assured. In this paper, we suggest a trust-region-type, two-sided, projected quasi-Newton method, which preserves the local two-step superlinear convergence of the original algorithm and also ensures global convergence. The subproblem that we propose is as simple as the one often used when solving unconstrained optimization problems by trust-region strategies and therefore is easy to implement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00940481
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  • 5
    Electronic Resource
    Electronic Resource
    Globally Convergent Inexact Generalized Newton Method for First-Order Differentiable Optimization Problems (2000)
    Springer
    Journal of optimization theory and applications 106 (2000), S. 551-568 
    Details
    ISSN: 1573-2878
    Keywords: nonsmooth optimization ; inexact Newton methods ; generalized Newton methods ; global convergence ; superlinear rate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Motivated by the method of Martinez and Qi (Ref. 1), we propose in this paper a globally convergent inexact generalized Newton method to solve unconstrained optimization problems in which the objective functions have Lipschitz continuous gradient functions, but are not twice differentiable. This method is implementable, globally convergent, and produces monotonically decreasing function values. We prove that the method has locally superlinear convergence or even quadratic convergence rate under some mild conditions, which do not assume the convexity of the functions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004605428858
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    Paper (German National Licenses)
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