Myocardial: Blood Purine Nucleoside Concentration Ratios in Canine Myocardium

Abstract

Adenosine is a potent coronary vasodilator which may play an important role in the regulation of coronary blood flow (2). According to this hypothesis, adenosine is produced when adenosine triphosphate is breaking down in response to an increased demand for energy. The resulting increment of adenosine is thought to diffuse out of the myocardial cells and pass through the extracellular fluid to the coronary myocytes where it produces relaxation resulting in vasodilatation and increased flow to establish a new steady state. Increased adenosine content¹ is felt to be dissipated by washout into coronary venous blood (7). The concentration of adenosine in coronary venous plasma and in pericardial fluid has been used for indirect estimates of the adenosine content of the myocardium (11, 12); such estimates imply that adenosine is readily diffusible across biological membranes. Because estimates of the myocardial concentration of adenosine from its concentration in coronary sinus plasma (12) are some 30-fold lower than estimates derived from analysis of heart muscle extracts (9), studies of myocardial: blood and myocardial: pericardial fluid concentration ratios were undertaken. The experiments reported below indicate that there may be significant barriers to the diffusion of adenosine out of canine myocardium and that washout of adenosine by coronary blood flow may not be an important mechanism in the regulation of tissue levels of this nucleoside.