PHYSIOLOGY AND BIOCHEMISTRY OF SHOCK 431 



asphyxia, which is a prominent symptom of shock, there is a de- 

 crease in the energy-rich adenosine-triphosphate. Increased lactic acid 

 formation in the muscle indicates that the supply of oxygen is in- 

 adequate due to the prevalence of anaerobic conditions. Increase in 

 creatine secretion in the urine indicates that the transfer of high energy 

 phosphate from adenosine-tri-or di-phosphate to creatine and from 

 creatine phosphate to adenosine-diphosphate has suffered a set-back. 

 The breakdown of adenosine-triphosphate (ATP) is the immediate 

 source of contraction energy. 



The muscle contains relatively limited amounts of ATP. Due to the 

 fact that adenosine-diphosphate formed in the above reaction can 

 be rephosphorylated at the expense of phosphocreatine, danger of the 

 exhaustion of ATP does not exist. Under prolonged or sustained 

 activity a newer source of ATP is provided by glycolysis. For every 

 hexose unit of glycogen metabolized four molecules of ATP are pro- 

 duced. Of these three are a net gain, which can be drawn upon for 

 increased muscular activity. 



If the normal, unpoisoned muscle is allowed to work anaerohically, 

 the following are the factors involved: ATP remains unchanged; 

 phosphocreatine disappears yielding free creatine and inorganic 

 phosphate; glycogen disappears yielding lactic acid. Anaerobic recovery 

 permits the resynthesis of phosphocreatine from creatine and inorganic 

 phosphate, and here again with the disappearance of glycogen lactic 

 acid is formed (Baldwin, 1947). Under anaerobic conditions the metab- 

 olism of glycogen to pyruvate provides the means for the formation 

 of lactic acid by the reoxidation of the reduced cozymase I. Without 

 the reoxidation of the reduced cozymase by pyruvate, no further 

 phosphoglyceric acid could be formed and therefore the generation 

 of ATP would come to an end. However, from the standpoint of 

 muscular work the anaerobic metabolism is very inefficient; potential 

 energy is locked in lactic acid molecules. 



Under aerobic conditions, the reduced cozymase I is rapidly oxidized 

 through the flavoprotein-cytochrome-cytochrome oxidase system and 

 no, or a very small trace of, lactic is produced. If the rate of muscular 

 exertion and therefore the rate of glycogen breakdown increases, 

 cozymase is reduced proportionately more readily, requiring therefore 

 an equal pace of oxygen supply. When the oxygen supply fails to keep 

 pace with the demand for the reoxidation of the reduced cozymase. 



