Cardiac Effects of Adenosine and Adenosine Analogs in Guinea- Pig Atrial and Ventricular Preparations: Evidence against a Role of Cyclic AMP and Cyclic GMP1

The effects of adenosine, the R site adenosine receptor agonist (-)-N6-phenylisopropyladenosine (PIA), the R5 site agonist 5’-N-ethylcarboxamideadenosine(NECA) and the P site agonist 2 ’,5’-dideoxyadenosine (DIDA) on force of contraction, cydic AMP (cAMP) and cyclic GMP (cGMP) content and on transmembrane action potential were studied in isolated electrically dnven left auricles and papillary muscles from guinea pigs. Furthermore, the effects on adenylate cyclase activity in a particulate mem-brane preparation were investigated. In the auncles, adenosine, PIA and NECA had negative inotropic effects which were accom-panied by a shortening of the action potential. Theophylline antagonized these effects which are likely mediated by A site adenosine receptors. DIDA was ineffective. Except for a small positive inotropic effect of adenosine the analogs were ineffectiv