Über die Abhängigkeit der Strophanthinwirkung auf den myokardialen Sauerstoffverbrauch vom Funktionszustand des Herzens

Comparative influence of ouabain, norepinephrine and heart rate on myocardial oxygen consumption and inotropic state in dogs

The purpose of this study was to compare the myocardial oxygen cost of augmented inotropic state produced by ouabain, norepinephrine, or increased heart rate. This problem was examined in dogs using an isovolumically contracting left ventricular preparation. Inotropic state was measured as the maximum observed contractile element velocity at the lowest common level of wall stress (MAX V). Peak left ventricular wall stress was maintained constant in each dog so that it would not influence changes in myocardial oxygen consumption (MVO2). Ouabain (4 X 10(-2) mumoles/Kg.) and norepinephrine (2 X 10(-3) mumoles/Kg./minute) always augmented inotropic state (MAX V) and increased MVO2. The positive slopes of the regression of MVO2 on MAX V for ouabain (45.4 +/- 12.5 microliter/beat/100 Gm./muscle length/sec; mean +/- SEM) and norepinephrine (34.5 +/- 5.6 microliter/beat/100 Gm./muscle length/sec; mean +/- SEM) were not significantly different, indicating that for an equal augmentation of inotropic state, ouabain increases myocardial oxygen demands to the same extent as does norepinephrine. When the results with ouabain or norepinephrine were compared to results obtained by altering heart rate, it was found that increasing inotropic state by these pharmacologic agents is more costly in terms of myocardial energy demands than when inotropic state is enhanced by increasing heart rate.

Heat production and oxygen consumption of the isolated rabbit heart: their relation to mechanical function

A method is described for simultaneous determination of the heat production and the oxygen consumption of the isolated, isovolumetrically beating rabbit heart. The perfusion of the heart was performed via the aorta at a constant flow rate with carbogen saturated Tyrode's solution at a temperature of 37.0 degrees C. Heart function was varied by stepwise augmentation of the left intraventricular volume (LVV) by means of a balloon catheter. The following mechanical parameter of heart function were determined: enddiastolic pressure (EDP), peak pressure (PP), developed pressure (DP), max. contraction and relaxation velocity (dP/dt-A and dP/dt-B), enddiastolic tension (Tens-EDP), peak tension (Tens-PP), developed tension (Tens-DP), and circumferential tension (Tens-Cir). DP, dP/dt-A and dP/dt-R showed a maximum response to changes of the LVV at 2.0 ml LVV and 19.3 mm Hg EDP. Heat production (H) and oxygen consumption (Q) were correlated closely to mechanical function and to each other (r = 0.89, n = 8). The ratio H/Q was 4.9 cal/ml O2 and remained constant during the experiment. The myocardial energy consumption was significantly correlated toall contraction parameters with the best fit to DP and Tens-Cir (r = 0.934 and 0.933 resp.). On the basis of the calculated mean regression lines, the function-independent and the function-dependent energy consumption were calculated.

Interactions of isoprenaline and prostaglandin E2 with respect to myocardial contractile force, coronary vascular resistance and myocardial oxygen consumption in guinea-pig isolated hearts

Left ventricular pressure (LVP), left ventricular pressure derivative (LV dp/dtmax), coronary vascular resistance (CVR) and myocardial oxygen consumption (Qo2) were measured simultaneously in isolated, electrically driven hearts of guinea-pigs at constant perfusion rate. 2 LVP, LV dp/dtmax, CVR and Qo2 were greatly decreased by either the addition of prostaglandin E2 (50 ng/ml) to the perfusion fluid or pretreatment of the animals with reserpine. 3 Isoprenaline (0.5 nM to 100 nM) induced increases in LVP, LV dp/dtmax and Qo2. In the presence of prostaglandin E2, there was a parallel shift of the isoprenaline concentration-response curve for LVP and LV dp/dtmax. This effect was not seen, after the animals had been treated with reserpine. 4 Qo2 was also decreased by prostaglandin E2 only in non-reserpine treated animals. 5 CVR was diminished by isoprenaline in the untreated group. However, there was increase in CVR, when isoprenaline was added to either prostaglandin E2 or reserpine-pretreated hearts which was enhanced in the reserpine plus prostaglandin E2-treated group (P less than 0.01). 6 The results give evidence for different actions of prostaglandin E2 on isoprenaline concentration-response curves for LVP, LV dp/dtmax and CVR.

Actions of prostaglandin E2 on myocardial mechanics, coronary vascular resistance and oxygen consumption in the guinea-pig isolated heat preparation

1 In isolated, electrically driven (3 Hz) hearts of guinea-pigs the action of prostaglandin E2 on left ventricular pressure (LVP), oxygen consumption (Qo2) and coronary vascular resistance (CVR) was studied by establishing cumulative concentration-response curves. The hearts were perfused at a constant flow (10 ml/min) with Tyrode solution (Ca++ 1.8 mM) at 32 degrees C. 2 Under control conditions prostaglandin E2 (2.86 X10(-11) -1.43 X 10(-7) M) decreased LVP, QO2 and CVR in a concentration-dependent manner by maximally 27, 18 and 38%, respectively (P less than 0.05). 3 After reserpine pretreatment there were lower initial values for all parameters measured. The effect of prostaglandin E2 on LVP and QO2 was abolished, but CVR was further diminished, depending on the concentration. 4 The results seem to support the hypothesis of an interaction of prostaglandin E2 with endogenous catecholamines as far as the effects on LVP and QO2 are concerned. In contrast, prostaglandin E2 seems to have a direct action on CVR, which is independent of the presence of catecholamines.