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Adenosine deaminase inhibition and adenosine metabolism in (ischemic) heart
58 ADENOSINE FORMATION; EVIDENCE FOR A DIRECT BIOCHEMICAL LINK WITH ENERGY METABOLISM. A.C. Newby, C.A. Holmquist. Department of Cardiology, Welsh National School of Medicine, Cardiff, Wales. Y. Worku. Department of Clinical Biochemistry, University of Cambridge, Cambridge, England. Adenosine is well-known as a regulator of coronary blood-flow. It also antagonises the inotropic effect of catecholamines and modulates nerve conduction in the heart. However, the precise biochemical mechanism by whrch adenosine concentration is regulated in response to variation in energy supply and demand is unknown. Adenosine formation by a cytoplasmic route has recently been demonstrated in intact polymorphonuclear leucocytes (Newby, A.C .,Holmquist, C.A., (1981) Biochem. J. 200-399)and in the perfused heart (Schutz, W., Schrader, J.,& Gerlach, E, (1981) Amer. J. Physiol, 240 H963-H970) but the identity of the enzyme responsible has remained obscure. We present evidence that a cytoplasmic 5’-nucleotidase whose activity is regulated in response to changes in adenine nucleotide concentrations is responsible for adenosine formation. Thus an increase in adenosine formation is a direct biochemical consequence of an excess of ATP breakdown over ATP formation. The significance of this regulatory mechanism for cardiac function will be discussed. Supported by the Medical Research Council and the World Health Organisation.
~~ADENOSINE DEAMINASE INHIBITION AND ADENOSINE METABOLISM IN (ISCHEMIC) HEART. P.W. Achterberg, J.W. de Jong. Cardiochemical Laboratory, Thoraxcenter, Erasmus University Rotterdam. Rotterdam, The Netherlands. It is generally assumed that myocardial adenine nucleotides are broken down (e.g. during ischemia) via AMP + adenosine + inosine, but contribution of the pathway AMP + IMP + inosine cannot be excluded. We infused isolated, retrogradely perfused rat hearts with adenosine (5 uM) together with the adenosine deaminase inhibitor EHNA krythro-9(2-OH-3-nonyl)adenine] at concentrations of 0, 5 and 50 uM. Rapid deamination of exogenously administered adenosine to inosine took place: 50% of adenosine was converted during a single passage. This deamination and further breakxanthine and uric acid were inhibited for 62 and 92% down of inosine to hypoxanthine, When hearts were made ischemic (80% flow reduction), by 5 and 50 PM EHNA, respectively. addition of EHNA (50 PM) raised the release of adenosine from 1.4 to 9.8 nmoles/min/g wwt, but surprisingly the release of inosine and oxypurines did not change significantly (8.2 -f 8.4 nmoles/min/g wwt). This suggests that, contrary to the established opinion, considerable breakdown of myocardial adenine nucleotides can occur via the AMP-IMP-IN0 (inosine) pathway instead of mainly via AMP-ADO-INO.
601s
THE PURINE NUCLEOTIDE CYCLE IMPORTANT IN HEART MUSCLE? Taegtmeyer, University of Texas Health Science Center at Houston, H. Division of Cardiology, Houston, Texas, 77025, U.S.A. The purine nucleotide cycle (PNC) catalyzes the net reaction: aspartate + GTP + H20 + fumarate + NH and leads to regeneration of AMP. In skeletal must ? e +.GDp Its rate+ pi of operation increases several fold with increased work and results in an increase in citric acid cycle intermediates and release of ammonia. Recause the same mav be expected in heart muscle, isolated rat hearts were perfused for 45 m;n at low or high work load (0.16 vs.O.42 kg.m/min/g dry). Release of ammonia into the perfusate as well as the content of citric acid cycle intermediates (citrate, isocitrate, Z-oxoglutarate, malate and oxaloacetate), related amino acids (aspartate and glu~?mate) and adenine nucleotides in freeze clamped tissue were mecpured. There was no change in the sum of citric acid cycle intermediates (1.295 vs. 1.313 pmol/g in aspartate (13.21 vs.14.32 pmol/g dry), dry), in glutamate (15.58 vs. 15.67 dmol/g dry), ATP (19.6 vs.19.17 limol/g dry), ADP (5.00 vs.4.11 umol/g dry) and AMP (1.45 vs. 1.01 umol/g dry) between low and hiph work load. Ammonia release was insignificant, The data suggest that the PNC is probably not an important metabolic pathway in rat heart.
~~ADENOSINE DEAMINASE INHIBITION AND ADENOSINE METABOLISM IN (ISCHEMIC) HEART. P.W. Achterberg, J.W. de Jong. Cardiochemical Laboratory, Thoraxcenter, Erasmus University Rotterdam. Rotterdam, The Netherlands. It is generally assumed that myocardial adenine nucleotides are broken down (e.g. during ischemia) via AMP + adenosine + inosine, but contribution of the pathway AMP + IMP + inosine cannot be excluded. We infused isolated, retrogradely perfused rat hearts with adenosine (5 uM) together with the adenosine deaminase inhibitor EHNA krythro-9(2-OH-3-nonyl)adenine] at concentrations of 0, 5 and 50 uM. Rapid deamination of exogenously administered adenosine to inosine took place: 50% of adenosine was converted during a single passage. This deamination and further breakxanthine and uric acid were inhibited for 62 and 92% down of inosine to hypoxanthine, When hearts were made ischemic (80% flow reduction), by 5 and 50 PM EHNA, respectively. addition of EHNA (50 PM) raised the release of adenosine from 1.4 to 9.8 nmoles/min/g wwt, but surprisingly the release of inosine and oxypurines did not change significantly (8.2 -f 8.4 nmoles/min/g wwt). This suggests that, contrary to the established opinion, considerable breakdown of myocardial adenine nucleotides can occur via the AMP-IMP-IN0 (inosine) pathway instead of mainly via AMP-ADO-INO.
601s
THE PURINE NUCLEOTIDE CYCLE IMPORTANT IN HEART MUSCLE? Taegtmeyer, University of Texas Health Science Center at Houston, H. Division of Cardiology, Houston, Texas, 77025, U.S.A. The purine nucleotide cycle (PNC) catalyzes the net reaction: aspartate + GTP + H20 + fumarate + NH and leads to regeneration of AMP. In skeletal must ? e +.GDp Its rate+ pi of operation increases several fold with increased work and results in an increase in citric acid cycle intermediates and release of ammonia. Recause the same mav be expected in heart muscle, isolated rat hearts were perfused for 45 m;n at low or high work load (0.16 vs.O.42 kg.m/min/g dry). Release of ammonia into the perfusate as well as the content of citric acid cycle intermediates (citrate, isocitrate, Z-oxoglutarate, malate and oxaloacetate), related amino acids (aspartate and glu~?mate) and adenine nucleotides in freeze clamped tissue were mecpured. There was no change in the sum of citric acid cycle intermediates (1.295 vs. 1.313 pmol/g in aspartate (13.21 vs.14.32 pmol/g dry), dry), in glutamate (15.58 vs. 15.67 dmol/g dry), ATP (19.6 vs.19.17 limol/g dry), ADP (5.00 vs.4.11 umol/g dry) and AMP (1.45 vs. 1.01 umol/g dry) between low and hiph work load. Ammonia release was insignificant, The data suggest that the PNC is probably not an important metabolic pathway in rat heart.