Adenosine as an Endogenous Adaptive Cardiac Antihypertrophic and Antiremodelling Factor

Abstract

Adenosine, a product of adenine nucleotide catabolism, has been demonstrated to exert numerous effects on the cardiovascular system which are mediated by activation of various receptor subtypes. The primary adenosine receptor in the myocardium is the A1 subtype which is linked to Gi-mediated inhibition of adenylate cyclase, although both A2a/b and A3 receptors have also been identified. There is increasing evidence that endogenously produced adenosine represents an important negative regulator of the hypertrophic and remodeling processes which contribute to heart failure. An important initial observation linking adenosine to the heart failure process was the report that plasma levels of the nucleoside are elevated in patients with heart failure irrespective of causative factor. Moreover, the degree of elevation was dependent on the severity of heart failure according to New York Heart Association (NYHA) classification with the greatest increases (more than fivefold) observed in NYHA class IV patients. Experimental observations have shown a direct antihypertrophic effect of adenosine receptor agonists on cardiomyocytes, which appears to be mediated by multiple adenosine receptor subtypes through yet to be determined processes. Further evidence obtained from in vivo studies also demonstrates a salutary effect of adenosine in reversing ventricular remodeling following aortic coarctation in rats. In addition to direct effects of adenosine receptor activation, deficiency in ecto-5′-nucleotidase which catalyzes the conversion of extracellular 5′-AMP to adenosine, thus increasing extracellular adenosine production, increases the degree of cardiac hypertrophy following aortic banding. Thus, when experimental evidence is taken together, it can be postulated that endogenous adenosine functions to limit the hypertrophic and remodeling processes which contribute to the development of heart failure.