979-36 Role of Endogenous Adenosine in Coronary Pressure-Flow Relationship In Dogs

There have been conflicting evidence for the role of adenosine in coronary pressure flow relationship; although adenosine release increases when coronary perfusion pressure (CPP) is reduced, adenosine deaminase does not affect changes in coronary blood flow (CBF). To examine the role of endogenous adenosine in coronary pressure flow relationship, responses of CBF were observed during a stepwise reduction of CPP by 10 mmHg with and without 8-phenyltheophylline (8PT). In 32 dogs, the left anterior descending coronary artery was perfused from the carotid artery, where CBF was measured. According to the reduction of CPP, adenosine concentration detected in coronary venous blood was increased (CPP  = 100 mmHg:7 ± 2, 8O mmHg:25 ± 3, 70 mmHg:53 ± 5, 40 mmHg:165 ± 11 pmollml), Administration of 8PT reduced CBF by 8 ± 3% at CPP  = 100 – 70 mmHg, and by 34 ± 7% at CPP = 60-40 mmHg. When CPP was altered between 100 and 70 mmHg, 8PT markedly reduced (p l 0,001) fractional shortening (FS) and lactate extraction ratio (LER) (FS:9,8 ± 1.2 vs. 23.6 ± 1.2%, LER:-6,5 ± 1.9 vs. 26.7 ± 1.9% at CPP = 70 mmHg). Interestingly, 8PT markedly reduced End/Epi flow ratio by 35 ± 4% at CPP = 70 mmHg. Thus we conclude that when CPP is reduced, endogenous adenosine favors endocardial myocardial flow and preserves myocardial contractile and metabolic function.