Comparison of In-Vitro Desensitization at Cardiac β1 - and Vascular β2 - Adrenoceptors

Martin, S.W.; Broadley, Kenneth J.

doi:10.1111/j.2042-7158.1990.tb14560.x

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“…That the concentrations of isoprenaline and dopexamine used here did not produce significant desensitization in the tissues examined may therefore be due to genuine resistance of the P2-receptors therein to undergo that process. This is confirmed by the results of our previous in vitro studies in which incubation of lung parenchymal strips or rat pulmonary artery or aorta with isoprenaline failed to induce desensitization of the 132-receptor-mediated relaxation responses (Martin & Broadley, 1990;Herepath & Broadley, 1992).…”

Section: P2-adrenoceptor-mediated Vascular Responsessupporting

confidence: 86%

Effects of chronic intravenous infusions of dopexamine and isoprenaline to rats on D₁‐, β₁‐ and β₂‐receptor‐mediated responses

Martin

Broadley

1994

British J Pharmacology

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1 Rats received intravenous infusions of dopexamine, an agonist with selectivity for D1-dopamine receptors and P2-adrenoceptors (240 ,g kg-' h-1), isoprenaline, a P,-and P2-adrenoceptor agonist (40 fig kg- and paced left atrium (increase in tension) showed significant reductions in sensitivity to isoprenaline following isoprenaline infusion. The EC5 values were significantly increased from 5.6 to 17.7 nM in right atria and from 7.4 to 27.1 nM in left atria. The maximum rate increase of right atria was also significantly less after isoprenaline infusion compared with controls (164.0 and 251.9 beats min-', respectively) but the maximum tension responses of left atria were not significantly different. After infusion with dopexamine, however, there was no change in sensitivity of the left or right atria to PI-adrenoceptor stimulation by isoprenaline.3 P2-Adrenoceptor-mediated relaxation responses to isoprenaline of the pulmonary artery, constricted with noradrenaline (6 x 108 M), showed no significant difference in maximum response or ECm in tissue from isoprenaline-or dopexamine-infused rats compared with vehicle-infused controls. P2-Adrenoceptormediated vasodilator responses were also examined in the kidney perfused with the thromboxane A2 analogue, U46619 (7.1 x 10-8 M) to raise perfusion pressure. As with the pulmonary artery, there was no significant difference in ED50 or maximum response to isoprenaline in kidneys from isoprenalineinfused animals compared with vehicle controls.4 The DI-receptor-mediated vasodilator responses to dopamine of the kidney perfused with U46619 were reduced after infusion of rats with dopexamine. The maximum fall in perfusion pressure (16.0 mmHg) and ED50 value (5.2 rig) were significantly different from those after vehicle infusion (31.5 mmHg; 1.5 pg). 5 These results show that functional responses mediated via P1-adrenoceptors and DI-receptors are reduced by intravenous infusions of isoprenaline and dopexamine, respectively. In contrast, the P2-adrenoceptor-mediated vasodilator responses of the pulmonary artery and kidney are not reduced by these agonists. Thus, under identical conditions, there appears to be selective down-regulation of peripheral P,-and D,-receptors, but not of P2-adrenoceptors.

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Section: P2-adrenoceptor-mediated Vascular Responsessupporting

confidence: 86%

Effects of chronic intravenous infusions of dopexamine and isoprenaline to rats on D₁‐, β₁‐ and β₂‐receptor‐mediated responses

Martin

Broadley

1994

British J Pharmacology

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show abstract

Comparison of In-Vitro Desensitization at Cardiac β1 - and Vascular β2 - Adrenoceptors

Cited by 1 publication

References 2 publications

Effects of chronic intravenous infusions of dopexamine and isoprenaline to rats on D₁‐, β₁‐ and β₂‐receptor‐mediated responses

Effects of chronic intravenous infusions of dopexamine and isoprenaline to rats on D₁‐, β₁‐ and β₂‐receptor‐mediated responses

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Comparison of In-Vitro Desensitization at Cardiac β1 - and Vascular β2 - Adrenoceptors

Cited by 1 publication

References 2 publications

Effects of chronic intravenous infusions of dopexamine and isoprenaline to rats on D1‐, β1‐ and β2‐receptor‐mediated responses

Effects of chronic intravenous infusions of dopexamine and isoprenaline to rats on D1‐, β1‐ and β2‐receptor‐mediated responses

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Effects of chronic intravenous infusions of dopexamine and isoprenaline to rats on D₁‐, β₁‐ and β₂‐receptor‐mediated responses

Effects of chronic intravenous infusions of dopexamine and isoprenaline to rats on D₁‐, β₁‐ and β₂‐receptor‐mediated responses