P296	Effect of experimental myocardial infarction on the expression of dimethylarginine dimethylaminohydrolase isoforms (DDAH I and II) and ADMA concentrations in the heart.
1G.Gray, 1M.Patrizio, 2M.Malaki, 1L.Sherry, 1A.Miller, 1A.Wallace, 2J.Leiper, 2P.Vallance
1Centre for Cardiovascular Science, University of Edinburgh, Edinburgh, GB; 2Centre for Clinical Pharmacology and Therapeutics, BHF Laboratories, University College London, London, GB.

Background: ADMA is a naturally occurring endogenous inhibitor of all three isoforms of nitric oxide synthase. ADMA is metabolised by the enzyme DDAH. Increased ADMA levels have been reported in acute myocardial infarction in humans and hindlimb ischaemic in animal models. The aim of this study was to investigate the effects of an experimental model of myocardial infarction on the distribution of immunoreative DDAH I and II and NOS in the heart, as well ADMA concentrations. Methods: Myocardial infarction was induced in male Wistar rats by ligation of the left anterior descending coronary artery. Sham operated rats underwent a thoracotomy but no ligation. At either 7 days or six weeks, infarct size was measured histologically and expressed as a percentage of the whole left ventricle. DDAH I, II, eNOS and iNOS immunoreactivity were determined using specific antibodies. Plasma ADMA concentrations was assayed by HPLC. In separate experiments, myoblasts were grown in normoxic or hypoxic conditions and changes in DDAH expression assessed by western blotting. Results: Significant infarction was measured in hearts removed at either 7 days (41 ±1%, p<0.05) or 6 weeks following coronary artery ligation (60%±3%, p<0.05) compared to sham operated animals (no infarcts). Animals with MI had a significantly higher LVEDP compared to control (15±2 mmHg vs 6±1 mmHg, p<0.05). In control hearts DDAH II was localised to the endocardium in a similar distribution to eNOS, but there was no detectable DDAH I in these hearts. In contrast, animals with MI expressed DDAH I,II and iNOS in the cardiomyocytes within the peri-infarct region and inflammatory cells in the granulation tissue . Plasma ADMA was significantly increased at 7 days (1.85±0.1μM v 1.43±0.2μM, p<0.05), but not 6 weeks post MI compared to controls (1.31±0.06μM v 1.43±0.2μM, p=ns). There were no differences in the expression of either isoforms of DDAH between myoblasts exposed to normoxia or hypoxia. Summary: In healthy myocardium, DDAH II has a similar distribution to eNOS. Its appearance in cardiomyocytes and inflammatory cells following MI, and the accompanying increase in ADMA, suggests a role for the regulation of iNOS. DDAH I may also have this role in cardiomyocytes. These changes are not accounted for by hypoxia alone. Although the role for DDAH induction post MI is not known, it may act to enhance angiogenesis

Copyright © 2005 S. Karger AG, Basel. Any further use of this abstract requires written permission from the publisher.