Effect of Glucose in Isoproterenol-Induced Necrotic Heart Under Anoxic Perfusion1

Abstract

Under an anoxic state, the anaerobic glycolytic pathway of the heart becomes the major source of metabolic energy (1). It was reported by Scheuer et al. (2) that the ele vation in cardiac glycogen improved mechanical performance during anoxia and Hearse et al. (3) demonstrated that the presence of glucose in the perfusion fluid during anoxia was essential for complete post-anoxic recovery. Weissler et al. (4) also reported that glucose contributed to the preservation of the functional capacity and structure of the anoxic heart tissue. On the other hand, it was observed in our previous investigation (5) that metabolic shifts were present in the necrotic heart following a s.c. injection of iso proterenol. It was reported by Bester et al. (6) that coronary artery occlusion of perfused rat heart caused a depression in myocardial ATP and creatine phosphate contents.The present study deals with the effect of glucose on metabolisms and mechanical functions in the necrotic heart perfused under an anoxic condition. MATERIALS AND METHODS AnimalsMale Wister strain rats, 200-250 g, maintained on a standard diet, were used. Each experimental group consisted of 5 animals. A,faterialsSubstrates and enzymes used for assay of metabolites in myocardium and perfusion fluids were purchased from Sigma Chemical Company, St. Louis, Mo., USA. D-Glu cose and reagents used for perfusion medium were purchased from Wako Pure Chemicals Ltd., Osaka, Japan. Isoproterenol hydrochloride was procured from Boehringer In gelheim GmbH, Germany. Preparation of necrotic heartThe necrotic heart was produced by a s.c. injection of isoproterenol hydrochloride (5 mg/kg) 24 hr before the perfusion. Perfusion Immediately after the rat was stunned by a blow of head, the heart was rapidly ex cised, mounted on an aortic cannula and transferred to a Langendorff apparatus (7). Gravity-flow reservoirs of the perfusion apparatus were fixed 40 cm above the heart level. Two parallel perfusion systems were employed in which the perfusion lines were switched alternately by a stopcock just above the aortic perfusion cannula. The apparatus was maintained thermostatically at 37°C. The perfusion medium, Krebs-Ringer's bicarbo nate buffer (pH 7.6) modified to contain chloride instead of phosphate was used. Glu cose, 5.5 or 21.0 mM, was included in the medium. All hearts were perfused aerobically (bubbled with 95 °% 02-5 % C02) for 25 min and then subjected to anaerobic perfusion (bubbled with 95 % N2-5 ° ~, C02) for an additional 10 min. The effluent was not recir culated and was allowed to flow into graduated cylinders for lactate determination. Mechanical parameters monitoredContractile force was monitored with a force-displacement transducer (Nihon Koden Kogyo Co., Ltd., SB-IT) and recorded on a polygraph (Nihon Koden Kogyo Co., Ltd., RM-5). Heart rate was recorded using a pulse rate tachometer (Nihon Koden Kogyo Co., Ltd., RT-5). Coronary flow rate was monitored periodically with a drop counter (Natsume Seisakusho Co., Ltd., KN-85). Extraction ~ronr heart /mrsclrTh...