Naloxone improves functional recovery of myocardial stunning in conscious dogs through its action on the central nervous system

This study tests the hypothesis that naloxone, but not its quarternary salt , naloxone methiodide (which does not enter the central nervous system), im proves recovery from myocardial stunning in conscious dogs. Twenty dogs wer e chronically instrumented for measurement of heart rate, left atrial, aort ic and left ventricular pressure (LVP), LV dP.dt(max)(-1) and myocardial wa ll thickening fraction (WTF). Regional myocardial blood flow was determined with coloured microspheres. Occluder around the left anterior descending a rtery (LAD) allowed induction of reversible LAD ischaemia. Each of the 20 d ogs underwent two LAD ischaemic challenges. Experiments (performed on separ ate days, in crossover fashion) were: (i) 10 min of LAD occlusion after app lication of naloxone 63 mug kg(-1) or naloxone methiodide 63 mug kg(-1) and (ii) occlusion without naloxone or naloxone methiodide. WTF was measured a t baseline and until complete recovery occurred. LAD ischaemia significantl y reduced LAD WTF with (mean (SD) 54 (15)% lower than baseline) and without naloxone (55 (16)% lower than baseline), without significant haemodynamic differences. Between I to 30 min of reperfusion, WTF was significantly high er with naloxone (P<0.05). There was no difference in WTF with or without n aloxone methiodide. We conclude that naloxone improved recovery from myocar dial stunning in conscious dogs, and that this was centrally mediated.