Pressure overload causes cardiac hypertrophy in beta1-adrenergic and beta2-adrenergic receptor double knockout mice.
OBJECTIVE
Cardiac hypertrophy arises as an adaptive response to increased afterload. Studies in knockout mice have shown that catecholamines, but not alpha1-adrenergic receptors, are necessary for such an adaptation to occur. However, whether beta-adrenergic receptors are critical for the development of cardiac hypertrophy in response to pressure overload is not known at this time.


RESULTS
Pressure overload was induced by transverse aortic banding in beta1-adrenergic and beta2-adrenergic receptor double knockout (DbetaKO) mice, in which the predominant cardiac beta-adrenergic receptor subtypes are lacking. Chronic pressure overload for 4 weeks induced cardiac hypertrophy in both DbetaKO and wild-type mice. There were no significant differences between banded mice in left ventricular weight to body weight ratio, in the left ventricular wall thickness, in the cardiomyocyte size or in the expression levels of the load-sensitive cardiac genes such as ANF and beta-MHC. Additionally, the left ventricular systolic pressure, an index of afterload, and cardiac contractility, evaluated as dp/dtmax, the maximal slope of systolic pressure increment, and Ees, end-systolic elastance, were increased at a similar level in both wild-type and DbetaKO banded mice, and were significantly greater than in sham controls.


CONCLUSIONS
Despite chronic activation of the cardiac beta-adrenergic system being sufficient to induce a pathological hypertrophy, we show that beta1-adrenergic and beta2-adrenergic receptors are not an obligatory component of the signaling pathway that links the increased afterload to the development of cardiac hypertrophy.
Department of Drug Research and Evaluation, Istituto Superiore di Sanità, Consiglio Nazionale delle Ricerche, Rome, Italy.
Sergio
S
Palazzesi
Marco
M
Musumeci
Liviana
L
Catalano
Mario
M
Patrizio
Tonino
T
Stati
Simona
S
Michienzi
Maria Grazia
MG
Di Certo
Elisabetta
E
Mattei
Luigi
L
Vitelli
Giuseppe
G
Marano
D000818:Animals; D017209:Apoptosis; D001794:Blood Pressure; D005786:Gene Expression Regulation; D006321:Heart / Q000502:physiology; D006352:Heart Ventricles / Q000473:pathology; D017379:Hypertrophy, Left Ventricular / Q000209:etiology / Q000473:pathology / Q000503:physiopathology*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D032383:Myocytes, Cardiac / Q000473:pathology; D018342:Receptors, Adrenergic, beta-1 / Q000502:physiology*; D018343:Receptors, Adrenergic, beta-2 / Q000502:physiology*; D012084:Renin-Angiotensin System
D018342:Receptors, Adrenergic, beta-1; D018343:Receptors, Adrenergic, beta-2