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Glycolytic impairment in the ATP-depleted perfused rat heart
GLYCOLYTIC P.M. Grinwald,
IMPAIRMENT D.J.
IN Hearse,
THE
ATP-DEPLETED H.B. Segal.
The
PERFUSED Rayne
RAT HEART. Institute,
St.
Thomas’
Hospital, London, U.K. Using the isolated perfused rat heart, we have attempted to ident i Fy factors which prevent recovery after periods of energy shortage. Hearts were subjected to substrate-free anoxic perfusion for 25 min. During this time ATP fell greatly (to approx. 2pmol/g dry wt) and glycolytic activit,, was much impaired, as evidenced by the abnormally low rate of lactate production occurring when the tissue was re-supplied with glucose under maintained anoxia. This impairment appeared to be at the hexokinase stec, since tissue analysis revealed an intracellular accumulation of glucose while glucose-6-phosphate was reduced. From published kinetic data forhexokinase, the inhibition of this enzyme could be explained by changes in adenine nucleotides (inhibition by relatively high levels of ADP an:: AMP and mechanism
a
reduced availability of glycolytic
of
ATP). As a further test of this possi:>le adenine nucleotide levels in ATPdepleted hearts were restored towards normal by transient (1 min) reoxygenation. This led to the re-establishment of active glycolysis (i..?. anaerobic lactate production rate returned to control) again suggesting; that the adenine nucleotide changes may be important in blocking glycolysis. Thus, ATP depletion may give rise to glycolytic impairment which ir: turn would tend to reinforce ATP depletion. Vicious cycles of this kind may cause irreversible loss of metabolic function in tissue which would otnerwi se be capable of recovery and thus may contribute to the mechani 5?: of ccl 1 death. impairment,
GLUCOSE AND FLOW INTERRELATIONSHIPS IN THE PROTECTION OF THE ISCHAEMIC MYOCARDIUM. C. Grousset and D.J. Hearse, The Rayne Institute,St. Thomas’ Hospital, London, U.K. The ability of glucose to protect the myocardium has recently been questioned by the finding that high extracellular glucose concentrations zero flow ischaemia in the rat reduces (in a dose dependduring global, We have now investigated the ent manner) recovery during reperfusion. effect of the presence or absence of glucose and the degree of flow impairment upon resistance to ischaemia. After 20 min control aerobic isolated working rat hearts were subjected to 25 min of perfusion, ischaemia. Coronary perfusion (oxygenated bicarbonate buffer) was varied in the range 0 to l.Oml/min/g wet wt and glucose was absent or present (33mmoles/l). Both with and without glucose a complex flow-recovery relationship was observed. As ischaemic flow fell from 1.0 to O.lOml/min there was a dose dependent fall in post-ischaemic recovery of aortic flow from approx. 80% to 20-305 of the pre-ischaemic control value. However, at lower flow rates recovery improved such that when flow was reduced to zero the recovery in the two groups returned to approx. 80%. Thus, under some circumstances zero or severely reduced flow is less damaging than The results also confirmed that glucose can be moderately reduced flow. toxic at very low flow (0.01 - O.lOml/min). In this range the number of hearts which actually recovered was smaller in the glucose group than in the glucose-free group, however those hearts which did recover, recovered to a similar extent in both groups.
IMPAIRMENT D.J.
IN Hearse,
THE
ATP-DEPLETED H.B. Segal.
The
PERFUSED Rayne
RAT HEART. Institute,
St.
Thomas’
Hospital, London, U.K. Using the isolated perfused rat heart, we have attempted to ident i Fy factors which prevent recovery after periods of energy shortage. Hearts were subjected to substrate-free anoxic perfusion for 25 min. During this time ATP fell greatly (to approx. 2pmol/g dry wt) and glycolytic activit,, was much impaired, as evidenced by the abnormally low rate of lactate production occurring when the tissue was re-supplied with glucose under maintained anoxia. This impairment appeared to be at the hexokinase stec, since tissue analysis revealed an intracellular accumulation of glucose while glucose-6-phosphate was reduced. From published kinetic data forhexokinase, the inhibition of this enzyme could be explained by changes in adenine nucleotides (inhibition by relatively high levels of ADP an:: AMP and mechanism
a
reduced availability of glycolytic
of
ATP). As a further test of this possi:>le adenine nucleotide levels in ATPdepleted hearts were restored towards normal by transient (1 min) reoxygenation. This led to the re-establishment of active glycolysis (i..?. anaerobic lactate production rate returned to control) again suggesting; that the adenine nucleotide changes may be important in blocking glycolysis. Thus, ATP depletion may give rise to glycolytic impairment which ir: turn would tend to reinforce ATP depletion. Vicious cycles of this kind may cause irreversible loss of metabolic function in tissue which would otnerwi se be capable of recovery and thus may contribute to the mechani 5?: of ccl 1 death. impairment,
GLUCOSE AND FLOW INTERRELATIONSHIPS IN THE PROTECTION OF THE ISCHAEMIC MYOCARDIUM. C. Grousset and D.J. Hearse, The Rayne Institute,St. Thomas’ Hospital, London, U.K. The ability of glucose to protect the myocardium has recently been questioned by the finding that high extracellular glucose concentrations zero flow ischaemia in the rat reduces (in a dose dependduring global, We have now investigated the ent manner) recovery during reperfusion. effect of the presence or absence of glucose and the degree of flow impairment upon resistance to ischaemia. After 20 min control aerobic isolated working rat hearts were subjected to 25 min of perfusion, ischaemia. Coronary perfusion (oxygenated bicarbonate buffer) was varied in the range 0 to l.Oml/min/g wet wt and glucose was absent or present (33mmoles/l). Both with and without glucose a complex flow-recovery relationship was observed. As ischaemic flow fell from 1.0 to O.lOml/min there was a dose dependent fall in post-ischaemic recovery of aortic flow from approx. 80% to 20-305 of the pre-ischaemic control value. However, at lower flow rates recovery improved such that when flow was reduced to zero the recovery in the two groups returned to approx. 80%. Thus, under some circumstances zero or severely reduced flow is less damaging than The results also confirmed that glucose can be moderately reduced flow. toxic at very low flow (0.01 - O.lOml/min). In this range the number of hearts which actually recovered was smaller in the glucose group than in the glucose-free group, however those hearts which did recover, recovered to a similar extent in both groups.