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Laboratory and Animal Investigations |

β-Agonistic Bronchodilators*: Comparison of Dose/Response in Working Rat Hearts

Guido Zimmer, MD, PhD; Andreas Dahinten; Andreas Fitzner; Stefan Halbig; Tobias Noll, MD; Fabian Treusch, MD; Herman Libertus, MD
Author and Funding Information

*From the Center of Internal Medicine, Medical Clinic II, Membrane Structure Group, University Clinics (Dr. Zimmer, Messrs. Dahinten, Fitzner, and Halbig, and Drs. Noll and Treusch), and Asta Medica AWD GmbH (Dr. Libertus), Frankfurt, Germany.

Correspondence to: Guido Zimmer, MD, PhD, Center of Internal Medicine, Medical Clinic II, Bldg. 11, Membrane Structure Group, Frankfurt University Clinics, Theodor-Stern-Kai 7, D-60590 Frankfurt, Germany; e-mail: zimmer@zbc.klinik. uni-frankfurt.de



Chest. 2000;117(2):519-529. doi:10.1378/chest.117.2.519
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Study objectives: Different β-agonists are compared with regard to their cardiodepressive side effects.

Design: The metaphenolic bronchodilators reproterol, salbutamol, fenoterol, and terbutaline were introduced at a dosage of 0.0005 μmol to a maximum of 10 μmol per gram of heart tissue into the isolated working rat heart under hypoxic conditions, and the response was observed during subsequent reoxygenation. As an index of external heart work, aortic flow was measured. Heart rate, coronary flow, and developed pressure were recorded. At the end of heart perfusion, mitochondria were isolated and analyzed for adenosine triphosphatase activity, adenosine triphosphate (ATP) synthesis, and membrane fluidity. Moreover, intact mitochondria and lipid peroxidation were investigated using a model system.

Measurements and results: Compared to controls, reproterol gave the most favorable results, with an increase of 25 to 30% of aortic flow during reoxygenation at a concentration of 10 μmol/g heart tissue. In contrast, both fenoterol and salbutamol at a concentration of 1μ mol/g heart tissue decreased aortic flow during reoxygenation, whereas terbutaline had a negative influence on aortic flow at 0.01 to 0.1 μmol/g heart tissue. Mitochondria of these hearts were isolated at the end of the experiment. Mitochondrial ATP synthesis was increased above controls at nearly all concentrations of reproterol. ATP synthesis was decreased at 1 μmol and 10 μmol fenoterol. As little as 0.0005 μmol terbutaline decreased ATP synthesis by 50%. In intact mitochondria, adenosine diphosphate (ADP) to oxygen ratios were found to be increased with terbutaline and fenoterol, indicating ADP consumption by myokinase activation. Lipid peroxidation was increased in a model system between concentrations of 0.002 μmol/mg and 0.04μ mol/mg phosphatidylcholine by fenoterol and terbutaline, whereas a decrease was noted with reproterol. Membrane fluidity was found increased after addition of reproterol, which supports the evidence of efficient ATP synthesis by this compound.

Conclusions: Cardiodepressive side effects and greater toxicity of fenoterol and terbutaline were found under the conditions of our experiment. Salbutamol and, in particular, reproterol appear much better tolerated. In addition to partial β-adrenergic agonism, reproterol may exert an inhibitory influence on adenosine receptor sites and phosphodiesterase, which could result in membrane stabilization by saving cyclic adenosine monophosphate or ATP.

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