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Nisoldipine reduces carbohydrate utilization during myocardial ischemia
11 13 GLYEDLYTIC ENERGY PRODUCTIDN AND ENZYME RELEASE.*) H.M. Piper,
R. Spahr, J.F. H~tter,
P.G.
Univ.
Spieckermann.
Zentrum
Physiologie,
Abt.
Herzstoffwechsel,
G~ttingen,
FRG
It has been hypothesized that glycolytically generated AlP plays a major role in the m a i n t e n a n c e of cell membrane integrity under conditions of energy depletion. Ue exposed cultured adult ventriculocyted from rat (JMCC 14 (1982) 597) to anoxia in an pHconstant Tyrode solution. In the absence of external substrates, lactate production rates correlate positively with AlP contents and negatively with cytosolie enzyme release. When glycolysis is stimulated by external glucose, both ATP decay and enzyme release are greatly delayed. A detailed analysis reveals that early anoxic enzyme release is due to reversible injury of the individual cells. In order to differentiate between the importance of glycolytic energy production and total ATP content, ~e blocked glycolysis with 1 mM iodoacetate (IAA) and analysed enzyme release under aerobic conditions in the presence or absence of pyruvate, which postpones ATP depletion. Although glycolysis is blocked in both cases, enzyme release is delayed in the presence of pyruvate. Thus, the relation between enzyme release and actual ATP level is identical. This indicates that early enzyme release is not a function of g l y c o l y t i c energy production. However, in tissue this may be the case secondarily, since states with high glyeolytic activities show less contracture and thereby probably less cell disruption. *)Supported
by the Deutsche
Forsehungsgemeinschaft~
SFB 89 - Kardiologie
Gbttingen
14 EFFECTS O F NON-GLUCOSE SUBSTRATES ON MYOCARDIAL RELAXATION. T Noakes, L.H. Opie. Medical Research Council Unit, University of Cape Town Medical School, South Africa and Cardiology Division, Stanford University Medical Center, California. The hypothesis tested was that different substrates could influence the mechanical function of the isolated pumping perfused rat heart with particular reference to myocardial relaxation. Paced hearts perfused with non-glucose substrates (palmitate, lactate, pyruvate) had lower stroke volumes than those perfused with glucose I ImM plus insulin (2u/liter). Substrate combinations with higher stroke volumes were associated with higher rates of left ventricular (LV) peak negative dP/dt (index of relaxation) but there were no consistent changes in LV peak positive dP/dt suggesting that diastolic filling limited the stroke volume. An inhibitor of glycolysis, 2-deoxyglucose, decreased peak negative but not peak positive LV dP/dt. There was a significant correlation between LV loeak negative dP/dt and the rate of glycolytic flux. The addition of isoproterenol (6.5 x 10-7'M) increased heart work, stroke volume and peak n e g a t i v e d P / d t , as ~vell as t h e r a t e o[ glycolysis. Myocardial ATP levels r e m a i n e d high a f t e r isoproterenol infusion showing t h a t the supply of oxygen was not limiting. Thus high r a t e s of glycolysis appear to be a s s o c i a t e d with peak m e c h a n i c a l function of t h e isolated working rat h e a r t a p p a r e n t l y acting chiefly on myocardial r e l a x a t i o n .
15 N I S O L D I P I N E R E D U C E S C A R B O H Y D R A T E U T I L I Z A T I O N D U R I N G M Y O C A R D I A L ISCHEMIA. J.W. de Jong, T. Huizer, P.J. Kempe. Cardiochem. Lab., T h o r a x c e n t e r , E r a s m u s Univ. Rotterdam, The Netherlands. C a l c i u m entry b l o c k e r s can p r e v e n t ATP d e p l e t i o n in ischemic heart, but their m e c h a n i s m of action is uncertain. We i n v e s t i g a t e d the e f f e c t of 30 nM n i s o l d i p i n e (NIS) on m y o c a r d i a l c a r b o h y d r a t e metabolism. I s o l a t e d rat h e a r t s were p e r f u s e d at 37~ w i t h a m o d i f i e d T y r o d e solution (pH 7.4) c o n t a i n i n g i0 m M 3H-glucose (0.02 Ci per mol). H e a r t rate was 300 bpm. A f t e r an e q u i l i b r a t i o n p e r i o d of 15 min, f l o w was red u c e d by 85% for 15 min by l o w e r i n g the p e r f u s i o n p r e s s u r e f r o m 72 to 14 mmHg. L a c t a t e and 3H20 p r o d u c t i o n were m e a s u r e d in the effluent, g l y c o g e n in f r e e z e - c l a m p e d h e a r t s . T h e results are p r e s e n t e d in the table as ~ • SD. * p < 0 . 0 0 5 vs. Ischemia; 9 p < 0 . 0 0 5 vs. Normoxia. Variable L a c t a t e p r o d u c t i o n (~mol/min/g wwt) G l y c o l y t i c flux (Dmol/min/g wwt) G l y c o g e n content (mg/g wwt)
N 7-9 6-7 5
Normoxia 0.12 • 0.04* 0.13 • 0.05* 3.14 • 0.50*
Ischemia 1.89 • 0.51 0.51 • 0.09 2.14 • 0.23
Ischemia + NIS 0.43 • 0.ii *e 0.14 • 0.03* 2.64 • 0.15"
D u r i n g ischemia, NIS d e c r e a s e d g l y c o l y t i c flux and lactate p r o d u c t i o n , and increased g l y c o g e n content. We c o n c l u d e that NIS does n o t a u g m e n t A T P p r o d u c t i o n in this prepar a t i o n via the g l y c o l y t i c pathway; the m a i n t e n a n c e of ATP in ischemic h e a r t must t h e r e f o r e be due to an i n h i b i t i o n of ATP c a t a b o l i s m by NIS.
R. Spahr, J.F. H~tter,
P.G.
Univ.
Spieckermann.
Zentrum
Physiologie,
Abt.
Herzstoffwechsel,
G~ttingen,
FRG
It has been hypothesized that glycolytically generated AlP plays a major role in the m a i n t e n a n c e of cell membrane integrity under conditions of energy depletion. Ue exposed cultured adult ventriculocyted from rat (JMCC 14 (1982) 597) to anoxia in an pHconstant Tyrode solution. In the absence of external substrates, lactate production rates correlate positively with AlP contents and negatively with cytosolie enzyme release. When glycolysis is stimulated by external glucose, both ATP decay and enzyme release are greatly delayed. A detailed analysis reveals that early anoxic enzyme release is due to reversible injury of the individual cells. In order to differentiate between the importance of glycolytic energy production and total ATP content, ~e blocked glycolysis with 1 mM iodoacetate (IAA) and analysed enzyme release under aerobic conditions in the presence or absence of pyruvate, which postpones ATP depletion. Although glycolysis is blocked in both cases, enzyme release is delayed in the presence of pyruvate. Thus, the relation between enzyme release and actual ATP level is identical. This indicates that early enzyme release is not a function of g l y c o l y t i c energy production. However, in tissue this may be the case secondarily, since states with high glyeolytic activities show less contracture and thereby probably less cell disruption. *)Supported
by the Deutsche
Forsehungsgemeinschaft~
SFB 89 - Kardiologie
Gbttingen
14 EFFECTS O F NON-GLUCOSE SUBSTRATES ON MYOCARDIAL RELAXATION. T Noakes, L.H. Opie. Medical Research Council Unit, University of Cape Town Medical School, South Africa and Cardiology Division, Stanford University Medical Center, California. The hypothesis tested was that different substrates could influence the mechanical function of the isolated pumping perfused rat heart with particular reference to myocardial relaxation. Paced hearts perfused with non-glucose substrates (palmitate, lactate, pyruvate) had lower stroke volumes than those perfused with glucose I ImM plus insulin (2u/liter). Substrate combinations with higher stroke volumes were associated with higher rates of left ventricular (LV) peak negative dP/dt (index of relaxation) but there were no consistent changes in LV peak positive dP/dt suggesting that diastolic filling limited the stroke volume. An inhibitor of glycolysis, 2-deoxyglucose, decreased peak negative but not peak positive LV dP/dt. There was a significant correlation between LV loeak negative dP/dt and the rate of glycolytic flux. The addition of isoproterenol (6.5 x 10-7'M) increased heart work, stroke volume and peak n e g a t i v e d P / d t , as ~vell as t h e r a t e o[ glycolysis. Myocardial ATP levels r e m a i n e d high a f t e r isoproterenol infusion showing t h a t the supply of oxygen was not limiting. Thus high r a t e s of glycolysis appear to be a s s o c i a t e d with peak m e c h a n i c a l function of t h e isolated working rat h e a r t a p p a r e n t l y acting chiefly on myocardial r e l a x a t i o n .
15 N I S O L D I P I N E R E D U C E S C A R B O H Y D R A T E U T I L I Z A T I O N D U R I N G M Y O C A R D I A L ISCHEMIA. J.W. de Jong, T. Huizer, P.J. Kempe. Cardiochem. Lab., T h o r a x c e n t e r , E r a s m u s Univ. Rotterdam, The Netherlands. C a l c i u m entry b l o c k e r s can p r e v e n t ATP d e p l e t i o n in ischemic heart, but their m e c h a n i s m of action is uncertain. We i n v e s t i g a t e d the e f f e c t of 30 nM n i s o l d i p i n e (NIS) on m y o c a r d i a l c a r b o h y d r a t e metabolism. I s o l a t e d rat h e a r t s were p e r f u s e d at 37~ w i t h a m o d i f i e d T y r o d e solution (pH 7.4) c o n t a i n i n g i0 m M 3H-glucose (0.02 Ci per mol). H e a r t rate was 300 bpm. A f t e r an e q u i l i b r a t i o n p e r i o d of 15 min, f l o w was red u c e d by 85% for 15 min by l o w e r i n g the p e r f u s i o n p r e s s u r e f r o m 72 to 14 mmHg. L a c t a t e and 3H20 p r o d u c t i o n were m e a s u r e d in the effluent, g l y c o g e n in f r e e z e - c l a m p e d h e a r t s . T h e results are p r e s e n t e d in the table as ~ • SD. * p < 0 . 0 0 5 vs. Ischemia; 9 p < 0 . 0 0 5 vs. Normoxia. Variable L a c t a t e p r o d u c t i o n (~mol/min/g wwt) G l y c o l y t i c flux (Dmol/min/g wwt) G l y c o g e n content (mg/g wwt)
N 7-9 6-7 5
Normoxia 0.12 • 0.04* 0.13 • 0.05* 3.14 • 0.50*
Ischemia 1.89 • 0.51 0.51 • 0.09 2.14 • 0.23
Ischemia + NIS 0.43 • 0.ii *e 0.14 • 0.03* 2.64 • 0.15"
D u r i n g ischemia, NIS d e c r e a s e d g l y c o l y t i c flux and lactate p r o d u c t i o n , and increased g l y c o g e n content. We c o n c l u d e that NIS does n o t a u g m e n t A T P p r o d u c t i o n in this prepar a t i o n via the g l y c o l y t i c pathway; the m a i n t e n a n c e of ATP in ischemic h e a r t must t h e r e f o r e be due to an i n h i b i t i o n of ATP c a t a b o l i s m by NIS.