AMERICAN JOURNAL OF PHYSIOLOGY Vol. 2 16, No. 1, January 1969. Printed in U.S.A. Release of adenosine in reactive hyperemia of the dog heart RAFAEL RUBIO, ROBERT M. BERNE, AND MAKOTO KATORI De$mtment of Physiology, University of Virginia School of Medicine, Charlottesville, Virginia 22904 RUBQRAFAEL, ROBERT M. BERNE, AND MAKOTO KATORI. cardial hypoxia were imposed in these studies in order to liberate quantities of adenosine which could be detected by the techniques then available. However, improve- ments in techniques have made possible the detection of extrelnely small amounts of adenosine in coronary venous blood. The present study was undertaken to determine whether adenosine is released from the myocardium in response to moderate degrees of myocardial hypoxia and whether the quantities released can account for the degree of coronary vasodilation observed. Release of adenosine in reactive hypercmia of the dog heart. Am. J. Physiol. 216(l): 56-62. 1969.~Brief (30-60 set) oc- clusions of the left coronary artery were performed in the anesthetized open-chest dog. Samples of arterial and coronary sinus blood were obtained simultaneously prior to occlusion and immediately after release of occlusion. Cellular elements were rapidly removed by centrifugation and the plasma samples were analyzed for purine derivatives. Adenosine (13 mpmoles/lOO ml of blood) was found in coronary sinus blood collected during the reactive hyperemic period but was absent in arterial and venous control samples. Studies on disap- pearance of adenosine in blood indicate that at least 24 mpmoles of adenosine must have been present in the capillary blood for 13 mpmoles to appear in the coronary sinus blood. If all the adenosine is in the extracellular space (a reasonable assumption based on knowledge of the activity of adenosine deaminase in the myocardial cell) a minimum concentration of 75 m~moles/lOO ml of extracellular water is reached. Adenosine infusion at concentrations of 56 m~moles/lOO ml of arterial blood elicits maximal coronary dilation. Hence, the dilation of the coronary resistance vessels in response to short periods of myocardial ischemia can be accounted for by the adenosine released from the myocardium. coronary blood flow regulation; coronary resistance; cardiac vasoactive metabolites; myocardial ischemia; myocardial nucleotides; purine derivatives in heart; coronary occlusion; autoregulation of blood flow; adenine nucleotide degradation in heart; vascular smooth muscle relaxant C ORONARY BLOOD FLOW is intrinsically adjusted, by virtue of changes in vascular resistance, to meet the oxygen demands of the heart at different levels of myo- cardial metabolic activity. Previous studies (4, 14) sug- gested that adenosine is the mediator of coronary vaso- dilation and plays a key role in the regulation of coronary blood flow. This concept is based on the recovery of degradation products of adenosine from the effluents of hypoxic hearts (4) and on the recovery of adenosine itself from hypoxic hearts in the presence of an adenosine dcaminase inhibitor ( 14, 16). Severe degrees of myo- METHODS In viva studies. Experiments were performed on mongrel dogs weighing between 15 and 20 kg. The animals were anesthetized with intravenously administered sodium pentobarbital (30 mg/kg) and placed on artificial respi- ration. A thoracotomy was performed in the fourth left intercostal space. After administration of heparin, the left coronary artery was cannulated with an Eckstein cannula and was perfused with blood from a carotid artery via tubing in series with an electromagnetic probe (3 mm diameter) connected to a Biotronex Aowmeter. The coronary sinus was cannulated with a modified Morawitz cannula (Fig. 1) and the blood directed to a jugular vein. The coronary sinus cannula contained an external tube that entered the lumen of the cannula 1 cm from the tip and was bent so that fluid injected through it moved in the same direction as the blood flow through the cannula. During collection of a coronary sinus blood sample, an ice-cold isotonic solution of NaCl (volume of l-2 times that of the blood collected) was injected through this tube, cooling and diluting the blood at the level of the coronary sinus. Arterial blood samples taken from the aorta were treated in the same way as the venous samples. All blood samples were collected in centrifuge tubes immersed in ice. A flow diagram of the procedures used in processing the blood samples is presented in Fig. 2. Each sample was rapidly transferred to a refrigerated centrifuge, and separation of the cellular elements from the diluted plasma was usually achieved within 15-l 8 56 Downloaded from journals.physiology.org/journal/ajplegacy at (162.224.096.121) on June 1, 2022.