Abstract
Stimulation of cardiac beta1-adrenergic receptors is the main mechanism
that increases heart rate and contractility. Consequently, several
pharmacological and gene transfer strategies for the prevention of
heart failure aim at improving the function of the cardiac beta-adrenergic
receptor system, whereas current clinical treatment favors a reduction
of cardiac stimulation. To address this controversy, we have generated
mice with heart-specific overexpression of beta1-adrenergic receptors.
Their cardiac function was investigated in organ bath experiments
as well as in vivo by cardiac catheterization and by time-resolved
NMR imaging. The transgenic mice had increased cardiac contractility
at a young age but also developed marked myocyte hypertrophy (3.5-fold
increase in myocyte area). This increase was followed by progressive
heart failure with functional and histological deficits typical for
humans with heart failure. Contractility was reduced by approximately
50% in 35-week-old mice, and ejection fraction was reduced down to
a minimum of approximately 20%. We conclude that overexpression of
beta1-adrenergic receptors in the heart may lead to a short-lived
improvement of cardiac function, but that increased beta1-adrenergic
receptor signalling is ultimately detrimental.
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