Are coronary vasodilator effects of inosine and adenosine independent of each other?

Potential influence of the pericardial space on myocardial function: Cardiac interactions of adenosine and endothelin-1

Adenosine (ADO) and endothelin-1 (ET-1) play an important role in the regulation of myocardial functions. The pericardial fluid accumulates these regulatory agents and reflects well their levels in the myocardial interstitium. The aim was to investigate the interaction and cardiovascular effects of ADO and ET-1 evoked from the pericardial space, determine the pericardial elimination of intrapericardially applied adenosine and its first metabolite, inosine (INO) and observe their effects on the cardiovascular function compared to their intravenous administration. The present studies were performed on in situ dog heart using the closed pericardium model. Significant increase of the pericardial concentrations of adenine nucleosides (adenosine and inosine) after intrapericardial administration of ET-1 has been found. Regarding the adenine nucleosides-ET-1 interaction, we have demonstrated ET-1 liberation after intrapericardial administration of adenine nucleosides. The present study confirmed significantly slower elimination of adenine nucleosides in the pericardial space than in the systemic circulation. In conclusion, characteristic cardiovascular effect and bidirectional interaction of adenine nucleosides and ET-1 could be provoked by and detected in the pericardial space, reflecting parallel changes in the myocardial interstitium. The low pericardial turnover rate of adenine nucleosides may offer the opportunity of utilizing their multiple beneficial effects for local pharmaco-therapeutic interventions.

Enhanced accumulation of pericardial fluid adenosine and inosine in patients with coronary artery disease

Adenosine and inosine are believed to have cardioprotective effects. However, little is known about their possible role in the metabolic autoregulation of human coronaries and in pathologic conditions with supply/demand imbalance of the heart such as coronary artery disease. Since these low molecular weight nucleosides freely diffuse through the monolayer of the visceral pericardium, adenosine and inosine concentrations in pericardial fluid may well reflect the conditions in cardiac interstitium. The pericardial fluid and systemic venous blood adenosine and inosine concentrations were measured in 98 human subjects undergoing heart surgery for coronary artery disease or valvular heart disease. Adenosine and inosine concentrations were measured by HPLC with UV detection. In subjects with coronary artery disease pericardial fluid nucleoside concentrations were significantly higher than in patients with valvular heart disease (adenosine: 1545 (996-3146) nmol/L [median (25th-75th quartiles)] vs. 738 (390-2527) nmol/L, P<0.01; inosine: 658 (321-1331) nmol/L vs. 347 (159-1037) nmol/L, P<0.05), while in both patient groups pericardial fluid nucleoside concentrations were higher by an order of magnitude than in venous plasma. Our results show the enhanced release of adenosine and inosine by the ischemic myocardium as a marker of supply/demand imbalance and support the hypothesis that these cardiac nucleosides may have an important role in the adaptation of coronary blood flow in human coronary artery disease.

Localization of adenosine deaminase and adenosine deaminase complexing protein in rabbit heart. Implications for adenosine metabolism

The distribution of adenosine deaminase and adenosine deaminase complexing protein in rabbit heart has been compared using immunohistochemical staining procedures. Sections (4-5 microns) of tissue fixed in Clarke's solution or paraformaldehyde and embedded in paraffin were stained by the peroxidase anti-peroxidase method for adenosine deaminase or complexing protein, using affinity purified antibodies. Staining for adenosine deaminase and complexing protein was observed in the central myocardium of all heart chambers. Adenosine deaminase was detected in endothelial cells of blood vessels and adjacent pericytes. The nuclei of arteries stained heavily for adenosine deaminase, whereas those of venules and small veins, although positive, stained much more lightly. The cytoplasm of blood vessel endothelial cells and smooth muscle cells of the tunica media were also weakly positive for adenosine deaminase. Endothelial cells of the endocardium and epicardium did not stain. Randomly distributed mononuclear inflammatory cells and interstitial connective tissue fibroblasts were also negative for adenosine deaminase. These results raise the possibility that endothelial cells containing adenosine deaminase could serve as a metabolic barrier preventing the free exchange of plasma and interstitial adenosine. Positive staining for complexing protein was restricted to blood vessel endothelial cells, especially cytoplasmic processes. Colocalization experiments carried out with biotinylated primary antibodies indicate that some vessels are positive for both adenosine deaminase and complexing protein. This is the first experimental evidence of possible in situ association of adenosine deaminase and complexing protein.