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Physiological catecholamine supplementation unmasks ischaemia-induced ventricular fibrillation in the wild-type mouse isolated perfused heart Functional genomics using mice has had a significant impact on the investigation of cardiovascular regulation. However, genetically manipulated mice have had only a limited application to the identification of novel modulators of ischaemia-induced lethal arrhythmias, due to the infrequency of ventricular fibrillation (VF) in the wild-type murine heart (Lai et al., 2004; Lerner et al., 2000; Mancuso et al., 2003). The aim of this study was to generate a wild-type murine Langendorff-perfused heart model in which VF occurs spontaneously during regional ischaemia. The strategy was to re-introduce catecholamines and angiotensin II (A-II), putative arrhythmogens in vivo (Curtis et al., 1993) that are part of the normal physiological milieu but are ordinarily absent in perfused heart preparations. Hearts were excised from adult male T/O mice (24-32 g) under i.v. pentobarbitone anaesthesia and perfused in the Langendorff mode with control solution (Krebs modified to contain 3 mM K+ and 2.4 mM Ca2+). After an initial period of stabilisation, hearts were perfused with one of four test solutions (groups randomised and blinded, n = 10 per group) for 15 min before a 30 min period of regional ischaemia, induced by ligation of the left main coronary artery, followed by 10 min of reperfusion. The solutions tested contained catecholamines (adrenaline, 75 nM; noradrenaline, 313 nM) and/or 100 pM A-II, with a control group perfused with Krebs-based solution alone. The ECG was recorded throughout. Standard statistical methods (ANOVA, Dunnett’s test or Mainland’s contingency tables) were used (Clements-Jewery et al., 2002). Controls had no VF during ischaemia (0/10) or during reperfusion (0/10). In contrast, 5/10 catecholamine-perfused hearts had VF during ischaemia (P<0.05) and 5/10 had VF during reperfusion (P<0.05). Individual VF episodes lasted up to 238 s. Catecholamine perfusion had typical haemodynamic effects (P<0.05 versus controls), increasing heart rate from 380 ± 15 to 457 ± 25 beats/min and coronary flow from 18 ± 2 to 30 ± 3 ml/min/g (values 14 min before ischaemia). Risk zone sizes were large (50 ± 2 % ventricular wt in controls), and were not altered by catecholamines (50 ± 2 %). Angiotensin-II had no effect on VF susceptibility, or the VF priming effect of catecholamines. In conclusion, perfusion with catecholamines (at concentrations found in human plasma during exercise) converts the VF-resistant mouse Langendorff heart into a viable bioassay for exploring determinants of VF susceptibility by functional genomics, without the need for unphysiological intervention such as programmed electrical stimulation.
Clements-Jewery, H et al. (2002) Br J Pharmacol 135: 807-15. |
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