n(6)-cyclopentyladenosine and Cardiomegaly

Adenosine has been proposed to exert anti-hypertrophic effects. However, the precise regulation and the role of the different adenosine receptor subtypes in the heart and their effects on hypertrophic signalling are largely unknown. We aimed to characterize expression and function of adenosine A1 receptors following hypertrophic stimulation in vitro and in vivo.. Pro-hypertrophic stimuli and adenosine A1 receptor stimulation of neonatal rat cardiomyocytes and male C57/Bl6 mice, sc. drug administration, real-time PCR, (3) [H]-leucine-incorporation assay, immunostaining, tissue staining, Western blots, gravimetric analyses and echocardiography were applied in this study.. In neonatal rat cardiomyocyte cultures, phenylephrine, but not angiotensin II or insulin-like growth factor 1 (IGF1), up-regulated adenosine A1 receptors concentration-dependently. The hypertrophic phenotype (cardiomyocyte size, sarcomeric organization, total protein synthesis, c-fos expression) mediated by phenylephrine (10 μM), but not that by angiotensinII (1 μM) or IGF1 (20 ng·mL(-1) ), was counteracted by the selective A1 receptor agonist, N6-cyclopentyladenosine. In C57/BL6 mice, continuous N6-cyclopentyladenosine infusion (2 mg·kg(-1) ·day(-1) ; 21 days) blunted phenylephrine (120 mg·kg(-1) ·day(-1) ; 21 days) induced hypertrophy (heart weight, cardiomyocyte size and fetal genes), fibrosis, MMP 2 up-regulation and generation of oxidative stress - all hallmarks of maladaptive remodelling. Concurrently, phenylephrine administration increased expression of adenosine A1 receptors.. We have presented evidence for a negative feedback mechanism attenuating pathological myocardial hypertrophy following α1 -adrenoceptor stimulation. Our results suggest adenosine A1 receptors as potential targets for therapeutic strategies to prevent transition from compensated myocardial hypertrophy to decompensated heart failure due to chronic cardiac pressure overload.

Topics: Adenosine; Adenosine A1 Receptor Agonists; Adrenergic alpha-1 Receptor Agonists; Angiotensin II; Animals; Animals, Newborn; Cardiomegaly; Cell Culture Techniques; Dose-Response Relationship, Drug; Fibrosis; Insulin-Like Growth Factor I; Male; Matrix Metalloproteinase 2; Mice; Myocytes, Cardiac; Oxidative Stress; Phenylephrine; Rats; Receptor, Adenosine A1; Up-Regulation

Both beta 1- and beta 2-adrenoceptors (beta 1-AR and beta 2-AR) are functionally present in human and rat ventricular myocytes. The two receptor subtypes are differently regulated during the development of myocardial hypertrophy and failure. I(f) is expressed in human and rat ventricular myocytes. In hypertrophied myocytes isolated from old spontaneously hypertensive rats (SHR) the density is much larger than in age-matched normotensive Wistar Kyoto (WKY). Due to the possible relevance of I(f) as an arrhythmogenic mechanism in the rat and human ventricle, we studied and compared the effects of beta 1-AR and beta 2-AR stimulation on I(f) in both hypertrophied and normal left ventricular myocytes of 18-month old SHR and WKY.. The whole-cell configuration of the patch-clamp technique was employed. Noradrenaline (NA, 1 microM) was used to stimulate beta 1-AR and isoprenaline (ISO, 1 microM) in the presence of the beta 1-AR antagonist CGP 20712A (0.1 microM) to stimulate beta 2-AR.. In SHR, NA increased I(f) by causing a 10.8 +/- 0.9 mV (n = 10) positive shift in the voltage of maximal activation (V1/2); this effect was completely reversed by CGP 20712A. beta 2-AR stimulation was effective in seven out of 13 cells tested, where it caused a small positive shift in V1/2 (4.0 +/- 1.7 mV). Cyclopentyladenosine (CPA), a selective A1-receptor agonist, reversed the effect of NA; the antiadrenergic action of CPA was abolished in cells pre-incubated with pertussis toxin (PTX) to block inhibitory G proteins (Gi). In PTX-treated cells the shift in V1/2 caused by both beta 2-AR (9.6 +/- 1.7 mV, n = 6, p < 0.05) and beta 1-AR (17.6 +/- 1.9 mV, n =7, p < 0.05) was significantly greater than in control cells. Both beta-AR subtypes modulated I(f) activation also in WKY: beta 1-AR shifted V1/2 by 16.0 +/- 1.4 mV (n = 15) and beta 2-AR by 4.2 +/- 1.1 mV (n = 7). However, in PTX-treated WKY cells only the beta 2-AR effect was potentiated (shift in V1/2: 11.4 +/- 1.4 mV, n = 9, p < 0.01), while the beta 1-AR response was unchanged (18.9 +/- 4.2 mV, n = 5, n.s.).. I(f) expressed in SHR hypertrophied ventricular myocytes is modulated by catecholamines mainly through the stimulation of the beta 1-AR subtype. The beta 1-AR response is, however, significantly lower than that observed in myocytes from normotensive rats, probably as a consequence of the presence of an increased inhibitory activity of Gi proteins. This post-receptorial control may be seen as a mechanism to limit the arrhythmogenicity of beta-AR stimulation in myocardial hypertrophy and failure.

Topics: Action Potentials; Adenosine; Adrenergic alpha-1 Receptor Agonists; Adrenergic beta-1 Receptor Antagonists; Adrenergic beta-Agonists; Animals; Cardiomegaly; Catecholamines; GTP-Binding Protein alpha Subunits, Gi-Go; Hypertension; Imidazoles; Isoproterenol; Male; Myocardium; Norepinephrine; Patch-Clamp Techniques; Pertussis Toxin; Propanolamines; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Receptors, Adrenergic, beta; Receptors, Adrenergic, beta-1; Receptors, Adrenergic, beta-2; Stimulation, Chemical; Virulence Factors, Bordetella