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Beta-adrenoceptors in cardiac disease
1Abtlg. Nieren- & Hochdruckkrankheiten, Universitätsklinikum Essen, Germany.
Insights
In chronic heart failure, reduced beta-adrenoceptors impair heart function. Heart transplantation normalizes beta-adrenoceptor function, offering a potential therapy for severe heart failure.
Area of Science:
- Cardiology
- Pharmacology
- Molecular Biology
Background:
- The human heart expresses beta 1 and beta 2-adrenoceptors, crucial for cardiac function.
- Chronic heart failure is associated with reduced beta-adrenoceptor density, likely due to elevated sympathetic activity and noradrenaline.
- A decrease in spare beta-adrenoceptors in heart failure further compromises contractile responses to agonists.
Purpose of the Study:
- To investigate the role of beta-adrenoceptors in chronic heart failure.
- To understand the impact of reduced beta-adrenoceptor number on cardiac contractility.
- To evaluate the effects of heart transplantation on cardiac beta-adrenoceptor function.
Main Methods:
- Analysis of beta-adrenoceptor expression and function in human heart tissue.
- Assessment of cardiac contractility in response to beta-adrenoceptor agonists.
- Comparison of receptor function in failing hearts versus transplanted hearts.
Main Results:
- Chronic heart failure leads to a significant reduction in cardiac beta-adrenoceptor number and impaired contractile responses.
- Increased myocardial G(i)-protein in heart failure may further inhibit beta-adrenoceptor-mediated effects.
- Heart transplantation appears to restore normal beta-adrenoceptor number and function.
Conclusions:
- Reduced beta-adrenoceptor availability and function are key features of chronic heart failure.
- Heart transplantation effectively normalizes cardiac beta-adrenoceptor status.
- The transplanted human heart does not exhibit abnormal sensitivity of postsynaptic beta-adrenoceptors.
Abstract:
The human heart contains both beta 1 and beta 2-adrenoceptors; both mediate positive inotropic and chronotropic effects. In chronic heart failure, beta-adrenoceptor number is reduced, presumably, by down-regulation by endogenous noradrenaline which is elevated due to increased sympathetic activity. Since the human heart contains only a few spare receptors for beta-adrenoceptor-mediated positive inotropic effects and the amount of spare receptors declines in chronic heart failure, it is not surprising that the reduced beta-adrenoceptor number is accompanied by decreased contractile responses to beta-adrenoceptor agonists (including endogenous catecholamines), and the extent of decrease in maximal inotropic response is more pronounced as the disease becomes more advanced. Moreover, in chronic heart failure myocardial G(i)-protein, which inhibits cAMP formation, is increased, which might further contribute to the reduction in beta-adrenoceptor-mediated effects. It appears that, at present, the best therapy for severe heart failure is a successful heart transplant, since in the transplanted heart beta-adrenoceptor number and function seems to be normalized. Moreover, the data currently available do not suggest any development of super- or subsensitivity of postsynaptic cardiac beta-adrenoceptors in the transplanted human heart.