Sjaastad I, Schiander I, Sjetnan A, Qvigstad E, Bøkenes J, Sandnes D, Osnes JB, Sejersted OM, Skomedal T. Increased contribution of alpha 1- vs. beta-adrenoceptor-mediated inotropic response in rats with congestive heart failure.
ACTA PHYSIOLOGICA SCANDINAVICA 2003;
177:449-58. [PMID:
12648162 DOI:
10.1046/j.1365-201x.2003.01063.x]
[Citation(s) in RCA: 47] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
AIM
In failing myocardium the mechanical response to beta-adrenoceptor stimulation is attenuated. Alternative signalling systems might provide inotropic support when the beta-adrenoceptor system is dysfunctioning. Accordingly, the inotropic responses to alpha 1- and beta-adrenoceptor stimulation by the endogenous adrenoceptor agonist noradrenaline in non-failing and failing rat hearts were compared.
METHODS
Chronic heart failure was induced in male Wistar rats by coronary artery ligation. Corresponding sham groups were prepared. After 6 weeks, papillary muscles from non-failing and failing hearts were isolated. Receptor binding studies were performed in the corresponding myocardium. The alpha 1-adrenoceptor-mediated inotropic response was not changed while the beta-adrenoceptor-mediated response was substantially reduced in failing compared with non-failing myocardium.
RESULTS
No change in potency for the agonists was observed at the alpha 1-adrenoceptors, while an increased potency for the agonists at the beta-adrenoceptors was found during heart failure. The lusitropic response to beta-adrenoceptor stimulation was intact during heart failure. No over all change in affinity or number of either adrenoceptor type was observed in receptor binding studies. The alpha 1-adrenoceptor-mediated inotropic response became dominating compared with the beta-adrenoceptor-mediated one in failing rat myocardium in contrast to the dominating role of the latter in non-failing myocardium. The attenuation of the beta-adrenoceptor-mediated inotropic response in rat failing myocardium was not because of a reduced number of receptors.
CONCLUSION
Increasing contractility through stimulation of alpha 1-adrenoceptors in situ by the endogenous agonist may be an alternative way of inotropic support during heart failure and even more so during beta-adrenoceptor blockade.
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