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  • 1
    Electronic Resource
    Electronic Resource
    The Effects of Theophylline on Aequorin Light Transients and Force in the Isolated Dog Right Ventricular Myocardium
    Amsterdam : Elsevier
    Journal of Molecular and Cellular Cardiology 26 (1994), S. 87-98 
    Details
    ISSN: 0022-2828
    Keywords: Aequorin ; Ca^2^+ transients ; Cyclic AMP ; Dog ventricular myocardium ; Isoproterenol ; Positive inotropic effect ; Theophylline
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/jmcc.1994.1010
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  • 2
    Electronic Resource
    Electronic Resource
    Comparison of the mechanisms underlying the positive inotropic actions of dopamine, adrenaline and isoprenaline on the isolated rabbit papillary muscle (1977)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 297 (1977), S. 257-267 
    Details
    ISSN: 1432-1912
    Keywords: Dopamine ; Contractility ; Papillary muscle ; α- and β-adrenoceptors ; Cyclic AMP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In the isolated rabbit papillary muscle the effects of dopamine on the contractile force and on the level of 3′,5′-cyclic adenosine monophosphate (cAMP) at different frequencies of stimulation were studied and compared with those of isoprenaline and adrenaline. 1. When the frequency of stimulation was increased from 0.5–2.5 Hz the dose-response curves for the positive inotropic effect of dopamine as well as of isoprenaline were shifted to the left, whereas the maximum of the developed tension reached for both drugs remained unchanged. 2. At a frequency of stimulation of 0.5 Hz pindolol (3×10−8 M) and phentolamine (10−6 M), respectively, did not affect the dose-response curve for dopamine; only the simultaneous administration of pindolol plus phentolamine shifted the dose-response curve to the right. In the presence of cocaine (3×10−5 M) as well as in that of cocaine plus corticosterone (4×10−5 M) the dose-response curve for dopamine was shifted to the right. On the other hand, the upper part of the dose-response curve for adrenaline was shifted to the right by pindolol (3×10−8 M), the lower part by phentolamine (10−6 M) and the whole curve by the application of both antagonists. 3. At a frequency of stimulation of 2.5 Hz neither pindolol (3×10−8 M) nor phetolamine (10−6 M) influenced the dose-response curve for dopamine, whereas the simultaneous administration of both drugs shifted the whole curve to the right. 4. Dopamine (10−4 M) increased significantly the content of the cAMP after 60 s by about 40% (at 0.5 Hz) and 50% (at 1.0 Hz), respectively, but this increase was by far less compared with that obtained by isoprenaline (3×10−7 M). 5. Pindolol (3×10−8 M) completely abolished the increase of the cAMP-content evoked by dopamine (10−4 M), while phentolamine (10−6 M) enhanced the elevation of the cAMP-level to nearly the same extent as isoprenaline (3×10−7 M) did. 6. The increase of the cAMP level induced by adrenaline (10−5 M) was comparable with that caused by isoprenaline (3×10−7 M). While phentolamine (10−6 M) did not influence the adrenaline induced increase of the cAMP content, pindolol completely abolished it. 7. The present results are compatible with the view, that the positive inotropic effect via stimulation of β-adrenoceptors is mediated by cAMP, while that of α-adrenoceptors is not. Furthermore it is concluded, that dopamine produces its positive inotropic effect by a cAMP-dependent direct and/or indirect β-adrenoceptor stimulation as well as by a cAMP-independent direct α-adrenoceptor stimulation to about the same degree.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00509270
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  • 3
    Electronic Resource
    Electronic Resource
    Role of alpha1A adrenoceptor subtype in production of the positive inotropic effect mediated via myocardial alpha, adrenoceptors in the rabbit papillary muscle: influence of selective alpha1A subtype antagonists WB 4101 and 5-methylurapidil (1992)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 345 (1992), S. 578-585 
    Details
    ISSN: 1432-1912
    Keywords: WB 4101 ; 5-Methylurapidil ; Alpha1 adrenoceptors ; Positive inotropic effect ; [3H]CGP-12177 ; Rabbit papillary muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In order to elucidate the contribution of alpha1A subtype to the positive inotropic effect mediated by myocardial alpha, adrenoceptors, the influence of the alpha1A selective antagonists WB 4101 and 5-methylurapidil on the alpha,-mediated positive inotropic effect (induced by phenylephrine in the presence of a beta adrenoceptor blocking agent bupranolol) was assessed in the isolated rabbit papillary muscle. WB 4101 (10−9-10−7mol/l) shifted the concentration-response curve of the alpha,-mediated positive inotropic effect to the right in parallel, but the slope of Schild plot did not meet the competitive antagonism: WB 4101 shifted the curve by log one unit at 10−9 mol/1, whereas it did not cause further shift at higher concentrations of 10−8 and 10−7 mol/l. WB 4101 did not affect the beta adrenoceptor-mediated positive inotropic effect. 5-Methylurapidil (10−9 to 10−7 mol/l) shifted the curve of alpha1-mediated positive inotropic effect to the right and downwards in a concentration-dependent manner; the slope of Schild plot calculated at the level of 20% of the maximum response to phenylephrine was close to unity. 5-Methylurapidil at 3 × 10−7 mol/1 abolished the alpha1-mediated positive inotropic effect. In addition, 5-methylurapidil inhibited the beta adrenoceptor-mediated positive inotropic effect in the same concentration range as it antagonized the alpha1-mediated positive inotropic effect, indicating that 5-methylurapidil is not selective for myocardial alpha, adrenoceptors. In the membrane fraction derived from the rabbit ventricular muscle, 5-methylurapidil displaced the specific binding of [3H]CGP-12177 with high affinity, whereas WB 4101 did not affect the [3H]CGP-12177 binding in the concentration range that it antagonized the alpha,-mediated positive inotropic effect. The present results indicate that alpha1A adrenoceptor subtype plays a role in production of the positive inotropic effect mediated by myocardial alpha, adrenoceptors, but the extent is less than that mediated by alpha1B subtype in the rabbit ventricular myocardium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00168952
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  • 4
    Electronic Resource
    Electronic Resource
    The preferential inhibition of α1- over β-adrenoceptor-mediated positive inotropic effect by organic calcium antagonists in the rabbit papillary muscle (1990)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 341 (1990), S. 206-214 
    Details
    ISSN: 1432-1912
    Keywords: Calcium antagonists ; α-Adrenoceptors ; β-Adrenoceptors ; Positive inotropic effect ; Rabbit ventricular myocardium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Experiments were carried out to elucidate the mechanism that the positive inotropic effect mediated by α1-adrenoceptors is more susceptible to organic calcium antagonists than the β-adrenoceptor-mediated effect. Verapamil and diltiazem displaced the specific binding of [3H]prazosin to the membrane fraction derived from the rabbit ventricular myocardium, verapamil being about 70 times more potent than diltiazem. Nifedipine did not displace the binding. While these compounds suppressed the positive inotropic effect mediated via αl-adrenoceptors in α1- concentration-dependent manner, there was no correlation between the potency of the compounds to displace the [3H]prazosin binding and to inhibit the α-mediated positive inotropic effect. The relative potency of three calcium antagonists to decrease the basal force of contraction and the al-mediated effect (of the same extent as compared to basal force of contraction) was consistent to each other. The positive inotropic effect mediated by β-adrenoceptors was inhibited much less, and was enhanced by low concentrations of organic calcium antagonists. The differential action of calcium antagonists on the α- and β-mediated positive inotropic effect was mimicked by lowering the extracellular calcium concentration to 1/2, 1/4 and 1/8 of that in normal Krebs-Henseleit solution (2.5 mmol/l). These results indicate that the α1-adrenoceptor blocking activity does not play an essential role for the preferential inhibition of α-mediated positive inotropic effect by organic calcium antagonists. Difference in the subcellular mechanism involved in mobilization of intracellular Ca2+ subsequent to α1-and β-adrenoceptor activation may be responsible for the differential inhibitory action of calcium antagonists in the rabbit heart.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00169732
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  • 5
    Electronic Resource
    Electronic Resource
    Pharmacological differentiation of synergistic contribution of L-type Ca2+ channels and Na+/H+ exchange to the positive inotropic effect of phenylephrine, endothelin-3 and angiotensin II in rabbit ventricular myocardium (1996)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 355 (1996), S. 87-96 
    Details
    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
    URL: http://dx.doi.org/10.1007/PL00004923
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of papaverine and its interaction with isoprenaline and carbachol on the contractile force and cyclic nucleotide levels of the canine ventricular myocardium (1979)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 306 (1979), S. 241-248 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00507109
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  • 7
    Electronic Resource
    Electronic Resource
    Potent inhibitory action of chlorethylclonidine on the positive inotropic effect and phosphoinositide hydrolysis mediated via myocardial alpha1-adrenoceptors in the rabbit ventricular myocardium (1991)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 343 (1991), S. 669-673 
    Details
    ISSN: 1432-1912
    Keywords: Chlorethylclonidine ; Alpha1-adrenoceptors ; Positive inotropic effect ; [3H]prazosin binding ; Phosphoinositide hydrolysis ; Rabbit papillary muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The influence of the alphalb-adrenoceptor-selective antagonist chlorethylclonidine on the alpha1-adrenergic positive inotropic effect and the phosphoinositide hydrolysis induced by phenylephrine was investigated in the rabbit ventricular myocardium. Pretreatment of membrane fractions derived from the rabbit ventricular muscle with 10−5 mol/l chlorethylclonidine decreased the specific binding of [3H]prazosin (at a saturating concentration of 10−9 mol/l) from the control value of 11.27±0.48 to 4.18±1.87 fmol/mg protein. The inhibition by adrenaline of the binding of [3H]prazosin (slope factor and affinity) was not affected by chlorethylclonidine. The positive inotropic effect of phenylephrine (in the presence of 3 × 10−7 mol/l bupranolol) was inhibited by chlorethylclonidine in a concentration-dependent manner (10−7−10−5 mol/l) and abolished by 10−5 mol/l chlorethylclonidine. The concentration of chlorethylclonidine to inhibit the phenylephrine-induced maximum response to 50% was 2.4 × 10−6 mol/l. The accumulation of [3H]inositol monophosphate and [3H]inositol trisphosphate induced by 10−5 mol/l phenylephrine was inhibited by chlorethylclonidine in the same concentration range. These findings indicate that the myocardial alpha1-adrenoceptors mediating a positive inotropic effect in the rabbit ventricular myocardium may belong to the chlorethylclonidine-sensitive alpha1b-subtype, and that the subcellular mechanism of action involve phosphoinositide hydrolysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00184301
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  • 8
    Electronic Resource
    Electronic Resource
    Pharmacological characteristics of adenosine-induced inhibition of dog ventricular contractility: dependence on the pre-existing level of β-adrenoceptor activation (1991)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 344 (1991), S. 70-78 
    Details
    ISSN: 1432-1912
    Keywords: Adenosine ; Phenylisopropyladenosine ; Negative inotropic effect ; Cyclic AMP ; Ventricular myocardium of the dog
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Experiments were carried out to characterize the adenosine-induced negative inotropic effect in relation to the extent of β-adrenoceptor activation in the isolated dog left ventricular myocardium. Adenosine and R-N6-phenylisopropyladenosine inhibited the positive inotropic effect of isoprenaline (10−7 mol/1 and lower) about 20% of its maximal response, which was antagonized by an A1 adenosine receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine in a concentration-dependent manner. The negative inotropic effect of adenosine disappeared and that of R-N6-phenylisopro-pyl-adenosine decreased when the isoprenaline concentration was elevated to the level higher than 10−7 mol/1. Adenosine deaminase (1.5 U/ml) that abolished the negative inotropic effect of adenosine enhanced the effect of R-N6-phenylisopropyladenosine, indicating that endogenous adenosine released by high isoprenaline concentration (10−6 mol/1) modulates the interaction. The maximal response to adenosine and R-N6-phenylisopro-pyladenosine determined in the presence of 10−7 mol/1 isoprenaline was 50% of that of carbachol which elicited the maximal inhibition even in the presence of 10−6 mol/1 isoprenaline. The negative inotropic effects of R-N6-phenylisopropyladenosine and carbachol were additive to the maximal response equivalent to that of carbachol. The difference in the efficiency between the adenosine and muscarinic receptor agonists may be partly ascribed to the difference in densities of the respective receptors in the dog ventricular myocardium. The negative inotropic effect of R-N6-phenylisopropyladenosine in the presence of isoprenaline was associated with decrease in cyclic AMP levels elevated previously by isoprenaline. The elevation of cyclic AMP levels caused by isoprenaline (3 × 10−7 mol/1) was abolished by R-N6-phenylisopro-pyladenosine (10−4 mol/1), while the contractile response was reduced only by 30% with R-N6-phenylisopro-pyladenosine. In the absence of β-adrenoceptor stimulation R-N6-phenylisopropyladenosine elicited a negative inotropic effect without changes in cyclic AMP levels, but this effect was less than 10% of the basal force of contraction. It is concluded that in the dog ventricular myocardium adenosine receptors play a role for the inhibitory regulation of contractility, which is influenced markedly by the pre-existing level of β-adrenoceptor activation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00167384
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