The clinical hallmarks of hibernating myocardium include hypocontractility while retaining an inotropic reserve (using dobutamine echocardiography), having normal or increased [18F]fluoro-2-deoxyglucose-6-phosphate (18FDG6P) accumulation associated with decreased coronary flow [flow-metabolism mismatch by positron emission tomography (PET)], and recovering completely postrevascularization. In this study, we investigated an isolated rat heart model of hibernation using experimental equivalents of these clinical techniques. Rat hearts ( n = 5 hearts/group) were perfused with Krebs-Henseleit buffer for 40 min at 100% flow and 3 h at 10% flow and reperfused at 100% flow for 30 min (paced at 300 beats/min throughout). Left ventricular developed pressure fell to 30 ± 8% during 10% flow and recovered to 90 ± 7% after reperfusion. In an additional group, this recovery of function was found to be preserved over 2 h of reperfusion. Electron microscopic examination of hearts fixed at the end of the hibernation period demonstrated a lack of ischemic injury and an accumulation of glycogen granules, a phenomenon observed clinically. In a further group, hearts were challenged with dobutamine during the low-flow period. Hearts demonstrated an inotropic reserve at the expense of increased lactate leakage, with no appreciable creatine kinase release. PET studies used the same basic protocol in both dual- and globally perfused hearts (with 250MBq18FDG in Krebs buffer ± 0.4 mmol/l oleate). PET data showed flow-metabolism “mismatch;” whether regional or global,18FDG6P accumulation in ischemic tissue was the same as (glucose only) or significantly higher than (glucose + oleate) control tissue (0.023 ± 0.002 vs. 0.011 ± 0.002 normalized counts · s-1· g-1· min-1, P < 0.05) despite receiving 10% of the flow. This isolated rat heart model of acute hibernation exhibits many of the same characteristics demonstrated clinically in hibernating myocardium.
Modification by islet-activating protein of receptor-mediated regulation of cyclic AMP accumulation in isolated rat heart cells.
