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  • 1
    ISSN: 1432-1912
    Keywords: α-and β-Adrenoceptors ; Methoxamine ; Isoprenaline ; cAMP ; Papaverine ; Rabbit Papillary Muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In the isolated papillary muscle of the rabbit the time course of the effects of selective β-and α-adrenoceptor stimulation by isoprenaline and methoxamine, respectively, on the contractile force and on the level of 3′,5′-cyclic AMP (cAMP) was determined. 1. Isoprenaline (3×10−7 M) increased significantly the content of cAMP at 15 sec and elevated it to the maximal level-about twice the control value-at 30 sec after its administration, while the developed tension of the papillary muscle was also increased significantly at 15 sec and reached gradually its maximum at 90 sec. 2. Compared with isoprenaline methoxamine (10−4 M) increased the developed tension very slowly: the maximal response was reached after 20 min. The level of cAMP, on the other hand, was changed neither before nor during the induction of the positive inotropic effect of methoxamine. 3. The phosphodiesterase inhibitor papaverine (10−5 M) inhibited the PDE activity of the papillary muscle by about 40% after an incubation of 1 hr, and increased the level of cAMP significantly. The effects of isoprenaline on the contractile force and on the level of cAMP were considerably enhanced by papaverine: the content of cAMP was increased by isoprenaline (3×10−7 M) to about 3 times the control value and also its positive inotropic effect was significantly greater than in controls without papaverine. On the other hand, the positive inotropic effect of methoxamine (10−4 M) was not affected by papaverine (10−5 M). Further-more, in the papillary muscle treated with papaverine the level of cAMP was significantly reduced by methoxamine: the papaverine-induced increase of cAMP was abolished by methoxamine. 4. The present results are compatible with the hypothesis that cAMP is involved as a mediator in the positive inotropic effect induced by β-adrenoceptor stimulation, and indicate further that the stimulation of α-adrenoceptors evokes its positive inotropic effect through a mechanism other than that elicited by β-adrenoceptor stimulation, i.e., independent of cAMP.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1912
    Keywords: Key words L-type Ca2+ channels ; Na+/H+ exchange ; Phenylephrine ; Endothelin-3 ; Angiotensin II ; Isoprenaline ; Positive inotropic effect ; Rabbit papillary muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The present study was designed to delineate pharmacologically the role of sarcolemmal L-type Ca2+ channels and Na+/H+ exchange in the positive inotropic effect (PIE) of phenylephrine mediated by alpha-1 adrenoceptors, endothelin (ET) and angiotensin II (Ang II) that stimulate phosphoinositide (PI) hydrolysis in the rabbit ventricular muscle. The PIE of these receptor agonists was compared with the PIE of isoprenaline that accumulates cyclic AMP. For this purpose, we investigated the influence of a Ca2+ antagonist, verapamil, and of an inhibitor of Na+/H+ exchange, 5-(N-ethyl-N-isopropyl) amiloride (EIPA), alone or in combination, on the cumulative concentration-response curve (CRC) for phenylephrine (with 0.3 μM bupranolol), ET-3 and Ang II in isolated right ventricular papillary muscles of the rabbit, which were electrically stimulated at 1 Hz in Krebs-Henseleit solution at 37°C. Verapamil at 0.3 and 1 μM decreased the basal force of contraction to 37.0 ± 4.0% and 13.2 ± 1.1% of the control, respectively, while EIPA even at 10 μM affected the basal force to much less extent and decreased it to 87.0 ± 1.4%. Verapamil (0.3 and 1 μM) and EIPA (1 and 10 μM), when used alone, each significantly attenuated but did not abolish the PIEs induced by phenylephrine, ET-3 and Ang II, while the simultaneous administration of verapamil (1 μM) and EIPA (10 μM) consistently and almost completely inhibited the PIE induced by these receptor agonists. By contrast, the PIE of isoprenaline was retained even in the presence of verapamil and EIPA. These results indicate that both the influx of Ca2+ ions through L-type Ca2+ channels and activation of Na+/H+ exchange contribute synergistically to the PIE that is mediated by alpha-1 adrenergic, ET and Ang II receptor agonists, while these mechanisms are not essential for the beta-adrenoceptor-mediated PIE.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 306 (1979), S. 241-248 
    ISSN: 1432-1912
    Keywords: Papaverine ; Isoprenaline ; Carbachol ; Cyclic AMP ; Cyclic GMP ; Ventricular contraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In the isolated ventricular myocardium of the dog the effects of papaverine on the contractile force and on the cyclic nucleotide levels were studied. Furthermore the interaction between papaverine and the adrenergic β-or cholinergic stimulation was investigated. 1. Papaverine (3×10−5 M) induced a positive inotropic action and increased the cyclic AMP level in the majority of preparations. Ventricular muscles isolated from certain dogs showed only a negative inotropic response to papaverine. As a whole, a significant correlation was found between the tension developed and the cyclic AMP level after the administration of papaverine. The cyclic GMP level was not changed or decreased by papaverine. 2. The positive inotropic action of papaverine and elevation of the cyclic AMP level in response to papaverine were not inhibited by a β-adrenoceptor blocking drug, pindolol (3×10−8 M), indicating that these effects are not caused by catecholamine release. 3. In muscles, in which papaverine failed to cause the positive inotropic action, contractile as well as cyclic AMP responses to isoprenaline were significantly enhanced by papaverine. 4. Carbachol (3×10−6M) diminished the positive inotropic actions of isoprenaline and papaverine, abolished the accumulation of cyclic AMP produced by these agents, and increased significantly the cyclic GMP level. The elevation of cyclic GMP level by carbachol in the presence of papaverine was especially marked and amounted to 4-fold the corresponding control value. These results indicate that papaverine inhibits the break down of the intracellular cyclic AMP and GMP in the intact myocardial cells and may thereby interact functionally with the autonomic nervous system.
    Type of Medium: Electronic Resource
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