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Selectivity of beta-adrenergic stimulating and blocking agents
Abstract:
Studies have been performed to answer two questions: whether there are subgroups of beta 2-receptors separating effects in bronchial and skeletal muscle and whether beta 1-receptors in asthmatic airways mediate bronchoconstriction. Asthmatic patients have been studied in randomised cross-over trials. Effects on FEV1, heart rate and skeletal muscle tremor have been monitored. In some experimental studies, two new compounds, D2343 and QH-25, have shown a selectivity for beta 2-receptors in bronchial muscle compared to skeletal muscle. Studies in asthmatics did not confirm this. Thus, the beta 2-receptors in the two organs appear to be identical. The clinical effect of beta 1-receptors in the the airways was studied by giving selective beta 1-receptor blocking agents. It was shown that pafenolol , a beta-blocker more beta 1-selective than metoprolol, had less effect on FEV1 than metoprolol given in equipotent beta 1-blocking doses. Beta 1-receptor stimulation with a new selective beta 1-stimulating agent, prenalterol, did not give bronchodilation in doses which gave a significant increase of heart rate. Thus, beta 1-receptors do not contribute to bronchodilation in asthmatic patients.
Insights
Beta 2-receptors in bronchial and skeletal muscles appear identical in asthmatics. Beta 1-receptors do not mediate bronchodilation in asthmatic airways, suggesting new therapeutic targets for asthma treatment.
Area of Science:
- Pharmacology
- Respiratory Medicine
- Cellular Biology
Background:
- Asthma treatment often targets beta-adrenergic receptors.
- Understanding receptor subtypes is crucial for developing effective asthma therapies.
- Previous research suggested potential differences in beta-receptor subtypes between tissues.
Purpose of the Study:
- To investigate if beta 2-receptors differ between bronchial and skeletal muscle.
- To determine if beta 1-receptors in asthmatic airways contribute to bronchoconstriction or bronchodilation.
Main Methods:
- Randomized cross-over trials in asthmatic patients.
- Administration of selective beta-receptor agonists and antagonists (D2343, QH-25, pafenolol, metoprolol, prenalterol).
- Monitoring of forced expiratory volume in 1 second (FEV1), heart rate, and skeletal muscle tremor.
Main Results:
- Compounds D2343 and QH-25 did not show selectivity for bronchial over skeletal muscle beta 2-receptors in asthmatics.
- Selective beta 1-receptor blockade with pafenolol had less impact on FEV1 than metoprolol.
- Beta 1-receptor stimulation with prenalterol did not induce bronchodilation.
Conclusions:
- Beta 2-receptors in bronchial and skeletal muscle are functionally identical in asthmatic patients.
- Beta 1-receptors do not play a significant role in mediating bronchodilation in asthmatic airways.
- Findings suggest that targeting beta 1-receptors is unlikely to be beneficial for bronchodilation in asthma.