Membrane-bound, ATP-dependent energy systems and tissue hypoxia in human gastric mucosa

1. The biochemical measurements of gastric mucosal ATP, ADP, AMP and cAMP offer excellent information on the extent of tissue oxygenation, when the observations are taken simultaneously from the same tissue sample. 2. Adenosine triphosphate is split by membrane-bound enzymes in two directions (to ADP and cAMP), while ADP and cAMP transform to AMP, supplying further energy liberation. 3. The liberated free energy modifies physiologically or pathophysiologically the functions of target organ cells. 4. Different drugs, hormones and mediators, have different effects on the regulation of ATP breakdown (into ADP vs cAMP). 5. The actual tissue level of ATP is a consequence of the equilibrium between the directions of ATP-ADP and ATP-cAMP breakdown, as well as of ATP resynthesis. 6. The biochemical measurement of the reduction in gastric mucosal ATP alone is not enough proof for the existence of tissue hypoxia, because demonstration of the simultaneous elevation of tissue lactate is also necessary.