The long term objective of this proposal is to demonstrate that activation of intravascular coronary adenosine receptors results in the release of endothelial factors that modulate cardiac function. Evidence indicates that the coronary endothelium is relatively """"""""impermeable"""""""" to adenosine, consequently, the hypothesis that intravascular adenosine may exert some of/or its whole action via the endothelium, will be tested by covalently coupling A1- and A2-adenosine agonists and antagonists to carboxylated latex microspheres (0.07 mum diameter); thus insuring their intravascular confinement when infused intracoronarily. We first demonstrated that the bond between the ligands and microspheres is stable during its passage through the coronary vasculature and will show that the ligand is not """"""""internalized"""""""" by the endothelium i.e. no free ligand is formed. Our preliminary results with A1-adenosine agonist demonstrated that sustained coronary infusion of these particles into isolated saline perfused guinea pig hearts caused: a decrease in coronary vascular resistance, ventricular contraction, spontaneous ventricular rhythm, cardiac glycolytic flux, depressed auricular ventricular transmission and adrenergic inotropic and dromotropic effects. We further show that the inotropic, dromotropic and vascular effects of adenosine (and Ach) were mediated partially by the release of nitric oxide. All these effects were reversible and were blocked by the adenosine antagonist sulphophenyltheophylline. Our preliminary results with the sphere-antagonist complex when intracoronarily infused blocked the negative dromotropic effects of hypoxia (due to adenosine release). We have not yet preliminary results with A2-adenosine agonist. The studies here proposed will consolidate our preliminary results which support the project's feasibility. Our studies will demonstrate that selective activation of intravascular coronary purine receptors regulate the function of vascular and the different cardiac cells. These effects may be the result of adenosine-induced release of endothelial bioactive substances such as nitric oxide. Furthermore, the role of nitric oxide in the regulation of cardiac functions will be established.
