H+ secretion and Na+-K+-dependent ATPase system in the human gastric mucosa

Carbonate dehydratase (carbonic anhydrase) and the fetal lung

Carbonic anhydrase activity (carbonic dehydratase, EC 4.2.1.1) has been detected in the fetal lungs of stillborn human infants and rhesus monkeys, but a role for this enzyme in the fetal lung has not been elucidated. In utero the mammalian lung develops as a liquid-filled structure, the liquid being secreted by the lung. In the fetal lamb this liquid, when compared with plasma, has a high chloride and a low bicarbonate concentration, suggesting a possible role for carbonate dehydratase. Studies on 10 fetal lambs confirmed the presence of carbonate dehydratase in the lung. Levels at 60-66 days were negligible and rose to 0.30 Meldrum Roughton units/mg protein at about 140 days (term 147 days), with little change after birth. In another six fetal lambs at 135-136 days, inhibition of this enzyme with 100 mg acetazolamide suppressed the mean rate of secretion of lung liquid by 64.5% (P less than 0.005), which correlated with a significant drop in chloride concentration (P less than 0.001). This magnitude of changes in secretion after acetazolamide is of the same order as that occurring in the secretion of cerebrospinal fluid when carbonate dehydratase is inhibited. This observation supports the hypothesis that carbonate dehydratase in fetal lung affects the secretion of lung liquid, although its mechanism is as yet unknown.

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.

A biochemical and pharmacological approach to the genesis of ulcer disease. I. A model study of ethanol-induced injury to gastric mucosa in rats

Present concepts of acute ulceration in the gastric mucosa include the hypothesis that mucosal ischemia is an important initiating event. The evidence for this is based upon observations on tissue metabolism and determinations of gastric mucosal blood flow. Using the model of gastric mucosal injury in the rat with ethanol, we have found that mucosal injury could be detected at a time when tissue oxygenation as determined by biochemical, and pharmacological studies of ATP metabolism were not compatible with ischemia. We also found that drugs acting at different subcellular levels were able to both inhibit gastric acid secretion in 4 hour pylorus-ligated rats and gastric mucosal injury after ethanol. Certain drugs, such as histamine and pentagastrin, stimulated acid secretion but inhibited the injury to the mucosa by ethanol indicating that increased cellular activity could occur during the development of mucosal injury.

Biochemical gradients in the human gastric and duodenal mucosa in relation to basal acid outputs

The separations and measurements of adenine-adenosine, adenosine monophosphate (AMP), adenosine diphosphate (ADP), adenosine triphosphate (ATP), lipid phosphates (lipid-P), ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) were carried out in the mucosa of the corpus, antrum, and duodenum of patients with decreased, normal, and increased basal acid outputs (BAO). The results were calculated in correspondence to 1.0 mg DNA value. The results indicate: 1) the biochemical composition of the corpus and antral mucosa alters with increase of BAO; 2) a significant difference was found between the biochemical compositions of the mucosa of the corpus and antrum in patients with normal and increased BAO; 3) no significant difference was observed in the biochemical components of duodenal mucosa with different BAO.

Examination of stomach wall Mg2+-Na+-K+-dependent ATPase, ATP, and ADP in pylorus-ligated rats

Stomach wall Mg2+-Na+-K+-dependent ATPase, ATP, and ADP were studied in rats, at 4, 7, 17, and 24 hr after pylorus ligation, in order to relate H+ secretion and ulcer development. It was observed, in both parts of forestomach and corpus + antrum, that the stomach wall Mg2+-Na+-K+-dependent ATPase significantly increased at 4 and 7 hr, while it significantly decreased at 24 hr, after pylorus ligation. Contrary to this, stomach-wall ATP decreased at 4 hr, relatively increased at 7 hr, thereafter significantly decreased in forestomach and corpus + antrum. Ouabain inhibited the H+ secretion, ulcer development, and stomach wall Mg2+-Na+-K+-dependent ATPase activity. The possible causal interrelationships between the examined parameters are studied.