ENERGY GENERATION IN HYPERTROPHIED POSTISCHEMIC MYOCARDIUM FEASIBILITY OF PROLONGED INOTROPIC STIMULATION WITH DOPAMINE IN HYPERTROPHIED REPERFUSED LEFT-VENTRICLES

Background Non-hypertrophied reversibly injured postischemic myocardiu m can be stimulated for a prolonged period without detrimental effects . Since no data on hypertrophied myocardium are available, our aim was to examine the effects of a prolonged postischemic positive inotropic stimulation on moderately hypertrophied left ventricles. Methods Usin g a Langendorff-type isovolumically contracting isolated heart model, moderately hypertrophied (+50 % of ventricular mass) hearts from spont aneously hypertensive rats (SHR) were investigated and compared to dat a from non-hypertrophied hearts of normotensive rats. A 30 minutes no- flow ischemia was performed, and in the postischemic period dopamine w as continuously administered for 20 minutes in order to stimulate the postischemic hearts to the control level of function. Data were compar ed to postischemic hearts without stimulation and to non-ischemic cont rols. After 50 minutes of reperfusion and cessation of the catecholami ne steady state function, maximum contractile response, and high energ y phosphates were determined. Results 30 minutes ischemia followed by 50 minutes reperfusion caused a significant reduction in developed LVP to 77.8 +/- 4.2 % in SHR. Dp/dtmax was reduced to 67.0 +/- 2.3 %. Aft er cessation of dopamine stimulation developed LVP was 64.3 +/- 3.5 % and dp/ dtmax 69.3 +/- 3.7 % in SHR. The double product was identicall y reduced in all postischemic groups. The con tractile reserve was com parable in stimulated and non-stimulated postischemic SHR hearts. In h ypertrophied myocardium, ATP was reduced to 1.1 +/- 0.1 mu mol/gww (no n-ischemic controls 2.5 +/- 0.3 mu mol/gww) in unstimulated and to 1.0 +/- 0.1 mu mol/gww in stimulated postischemic hearts. Comparably the ischemia-induced reduction in ATP in non-hypertrophied myocardium was 1.3 mu mol/gww. Similar results were obtained for ADP and AMP. Creatin e phosphate levels were normal in stimulated and non-stimulated postis chemic myocardium of hypertrophied and nonhypertrophied hearts. Conclu sion These results indicate that prolonged stimulation of stunned hype rtrophied myocardium is feasible without detrimental effects on postst imulation contractile function. The energy generating apparatus is cap able to deliver sufficient energy during stimulation of stunned hypert rophied hearts.