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Functional characterization of beta-adrenoceptor subtypes in rabbit right atria
T E Tenner1, J A Young, K J Earley
1Department of Pharmacology, Texas Tech University Health Sciences Center.
Life Sciences
|January 1, 1989
Summary
Beta-1 adrenoceptors are primarily responsible for catecholamine-induced heart rate increases in rabbit atria, despite the presence of beta-2 adrenoceptors. The beta-1 subtype plays a dominant physiological role.
Area of Science:
- Pharmacology
- Cardiovascular Physiology
Background:
- Radioligand binding studies identify receptor subtypes but don't confirm physiological roles.
- Beta-1 and beta-2 adrenoceptors coexist in rabbit right atria, necessitating functional investigation.
Purpose of the Study:
- To determine the physiological role of beta-adrenoceptor subtypes in catecholamine-induced chronotropic responses in rabbit right atria.
- To compare functional and radioligand binding data for a comprehensive understanding.
Main Methods:
- Determined rank order of potency for isoproterenol, epinephrine, and norepinephrine on chronotropic and inotropic responses.
- Utilized beta-1 selective antagonist atenolol to assess chronotropic effects of agonists.
- Performed competition binding studies using [125I]iodocyanopindolol and selective antagonists (ICI 89406, ICI 118551).
Main Results:
- Beta-1 adrenoceptors were primarily responsible for catecholamine-induced responses.
- Atenolol equally inhibited responses to nonselective and beta-2 selective agonists, indicating beta-1 mediation.
- Competition studies revealed a 6:1 ratio of beta-1 to beta-2 adrenoceptors.
- Terbutaline's chronotropic effects were mediated via beta-1, not beta-2, adrenoceptors.
Conclusions:
- Beta-1 adrenoceptors are the predominant subtype in rabbit right atria regarding both density and physiological significance.
- Beta-2 adrenoceptors play a minimal role in catecholamine-induced chronotropic responses in this tissue.