94 The Chemistry of the Injured Cell 



of the system. DPN has the lowest potential in the carrier system 

 and the rates of oxidation for energy production will not be altered 

 until DPN has been affected (Huckabee, 1958) . When oxidative 

 potential becomes low enough, the metabolic systems are involved. 

 The first DPN complex system to be reversed will be the one with 

 a potential closest to that of DPN: DPNH 2 or the lactic dehydro- 

 genase system. 



(LDH) 

 Pyruvate -f DPNH 2 *=* Lactate -f DPN 



An increase of DPNH 2 would swing the equation to the right with 

 the production of lactate and the oxidation to DPN. Because lactate 

 does not take part in any other equilibrium, this reaction acts as 

 a safety valve in the presence of anoxia thereby permitting other 

 metabolic systems to go on functioning. Eventually anoxia leads to 

 a decrease in myocardial extraction rate of lactate with serious re- 

 sults for the cell. 



In haemorrhagic shock, the contractile power of the heart is 

 reduced because the muscle cells have less oxygen at their disposal. 

 This is brought about in two ways. (1) through reduced coronary 

 blood flow and (2) by failure of the cells to extract more oxygen 

 from the blood. As a result the heart expels less blood at each beat, 

 stagnant anoxia sets in peripherally and the tissue cells so affected 

 rob the blood of more and more oxygen. This in turn leaves less 

 oxygen for the heart and the blood concentrations of glucose, lactate 

 and pyruvate rise. The heart muscle, however, extracts more lactate, 

 but less pyruvate and glucose, even when the lost blood is replaced 

 by transfusion, which suggests that its metabolic impairment is 

 initiated by loss of blood but is not corrected by such a transfusion. 

 The increased extraction of lactate that we have noted in shock 

 suggests that the enzymatic pathways through which lactate is 

 directed are not interfered with, but the cause of this lactate ex- 

 traction is not known. Co-carboxylase is destroyed under anaerobic 

 conditions, possibly because of its dephosphorylation. Hence the 

 myocardial block in haemorrhagic shock may be similar to that 

 encountered in Beri Beri, although the latter is referable to an 

 inadequate supply of thiamine in the food, the former to anoxia. 



