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Beta 1- and beta 2-receptors are differentially desensitized in an experimental model of heart failure
1Department of Cardiology, School of Medicine, University of Brescia, Italy.
Abstract:
Recent reports suggested that a complex alteration in beta-receptor function occurs in failing human myocardium. We evaluated beta-receptor-subtype activity in an experimental model of monocrotaline (MCT)-induced cardiomyopathy in the rat. Through pulmonary hypertension, MCT causes right ventricular hypertrophy (RVH), either associated with heart failure or not, beta-Receptor function was evaluated in both failing-hypertrophic and hypertrophic hearts in binding studies with [125I]iodocyanopindolol (ICYP) and by measuring adenylate cyclase (AC) activity. In the right failing ventricle, beta 1- but not beta 2-receptor density was decreased. Lesion-associated modifications in the adenylate cyclase system were also observed: isoproterenol- and guanosine 5' [beta, gamma-imido]triphosphate [Gpp(NH)p]-stimulated cyclic AMP formation was reduced in the right failing ventricle, while the cyclic AMP responses to NaF and forskolin were unchanged. On the other hand, no changes in either beta-receptor density or function were found in hypertrophic ventricles. MCT-induced heart failure in the rat is thus associated with a selective decrease of beta 1-receptor density and function. These results suggest that MCT-induced cardiac failure may be an appropriate model in which to investigate heart insufficiency further.
Insights
Monocrotaline-induced heart failure in rats selectively decreases beta-1 receptor density and function in the failing right ventricle. This experimental model offers insights into heart insufficiency mechanisms.
Area of Science:
- Cardiology
- Pharmacology
- Molecular Biology
Background:
- Alterations in beta-receptor function are reported in human heart failure.
- Monocrotaline (MCT) induces experimental cardiomyopathy, leading to right ventricular hypertrophy (RVH) and potential heart failure.
- Understanding beta-receptor subtype activity is crucial for investigating cardiac dysfunction.
Purpose of the Study:
- To evaluate beta-receptor subtype activity in a rat model of MCT-induced cardiomyopathy.
- To compare beta-receptor function in failing-hypertrophic versus non-failing hypertrophic ventricles.
- To investigate the role of beta-adrenergic signaling in MCT-induced heart failure.
Main Methods:
- Induction of cardiomyopathy using monocrotaline in rats.
- Assessment of beta-receptor density via radioligand binding studies using [125I]iodocyanopindolol (ICYP).
- Measurement of adenylate cyclase (AC) activity, including cyclic AMP (cAMP) formation stimulated by various agents (isoproterenol, Gpp(NH)p, NaF, forskolin).
Main Results:
- A selective decrease in beta-1 receptor density was observed in the failing right ventricle.
- Reduced isoproterenol- and Gpp(NH)p-stimulated cAMP formation in the failing right ventricle, indicating impaired beta-adrenergic signaling.
- No significant changes in beta-receptor density or function were found in non-failing hypertrophic ventricles.
Conclusions:
- MCT-induced heart failure in rats is characterized by a selective reduction in beta-1 receptor density and function.
- The study identifies a suitable experimental model for further investigation of heart insufficiency.
- Findings highlight the specific involvement of beta-1 adrenergic pathways in the pathophysiology of this cardiac failure model.