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January 1989, Volume 39, Issue 1

Editorial

INTRA GASTRIC pH

Anjum Shahid  ( PMRC Research Centre, Jinnah Postgraduate Medical Centre, Karachi. )

Role of gastric acid hypersecretion in peptic ulcer disease is an established phenomenon.1 Prolonged measurements of gastric acidity are of interest because they (a) measure the physiologic pattern of acidity, (b) may provide new insights into pathologic changes of acidity in the course of peptic ulcer disease, and (c) are suited for the evaluation of gastric antisecretory drugs2. In most long term studies, gastric contents are usually aspirated through a nasogastric tube and the pH of sample is measured in vitro using a suitably calibrated glass electrode. Aspiration tests, however, have some that comings. The procedure of aspiration affects the measurements directly, by the removal of gastric juice, or indi­rectly by stimulation of duodenogastric reflux or provocation of secretory responses. 3 The presence of solid meals in the stomach poses problems for aspiration, repeated sampling procedures are inconvenient and uncomfortable for the subjects and nocturnal sampling, especially during pharma­cologic acid inhibition, is often impossible because of low intragastric volumes4. Gastric pH measurements with a pH electrode placed in the most dependent part of the stomach will show fluctuations not seen in the aspirated sample. The first study of in situ pH in the gastrointestinal tract was performed by McClendon using a hydrogen electrode but the electrode was too thick to be used and further­more introduction of hydrogen in the gastro­intestinal lumen changed the composition of the contents. The glass electrode was first employed by Eyerly and later by Rovelstad. These first pH recordings confirmed that pH changed frequently and rapidly. The main causes for the wide fluctua­tions were intennittent emptying of acid contents3. Many difficulties associated with in situ pH measurements in the gastro-intestinal tract disap­peared with the development of the glass elec­trode. Recently pH has been measured continuou­sly in vivo by intra gastric electrode5. Continuous recording from a pH electrode gives a more detailed profile of gastric acidity than the sampling technique2. pH measurements represents the negative logarithm of hydrogen ion activity and relate closely, but not exactly, to hydrogen ion concentration. Serial measurements of intra gastric pH are suitable for recording the effect of diet or drugs on gastric acidity in ulcer patients6-8. The major advantage of this technique is that data can be collected over a reasonably long period in subjects given a standard meal. The effect of meal, Coca Cola, smoking and Cimetidine on duodenal pH was determined in controls and patients with duodenal ulcer using intra luminal pH recording for five hours. After a meal, mean pH increased significantly in both controls and patients. Coca Cola significantly increased the periods of duodenal acidification and reduced alkalinization in both groups, whereas Cimetidine increased the periods of duodenal alkalinization to more than normal levels9 - Twenty four hours gastric pH monitoring was done in healthy subjects. During this period, gastric pH rarely rose above a value of 2. Transient elevations of pH were observed after each meal intake and in some subjects at night time2. Post prandial fluctuation of pH probably reflects the heterogeneity of gastric juice composition after a meal10 whereas the nocturnal episodes of alkalinization may be due to duodenal gastric reflux. Acidity reached its highest level in the late evening, followed by a gradual decline in the second half of the night, and a rise before breakfast. 2 The reason for the decline of acidity during the second half of the night is unknown, and has been assumed that a decrease of vagal activity with a subsequent decrease of secretion might be responsible. 11 Spices, especially red chili powder is com­monly consumed in many food preparations in this part of the world. Studies demonstrate their effect on human gastric mucosa and suspect they play a role in the etiology of gastritis and peptic ulcer. 12 As role of spices on gastric pH is not well defined, an attempt was made to find the effect of a Pakistani spicy meal on gastric pH and to see whether any differences exist between a typical Western type of diet and Pakistani spicy diet, on intragastric pH. Ulcer patients diagnosed on upper gàstro­intestinal endoscopy and controls with negative endoscopy were studied. Patients were classified into two groups on the basis of food intake. One group was given Pakistani spicy food and the other a standard western type of food. After an overnight fast and intubation with electrode assembly positioned in the most dependent part of the stomach, pH was monitored for one hour in the basal state and then for another three hours after the meal. No significant difference in pH was noted in both groups. pH Was low in the basal state, followed by an increase after the meal. However the rise due to the buffering effect of the meal did not last long and a gradual return to the basal state pH was observed shortly. It was, therefore, concluded that spicy cooked food does not have a significant and prolonged effect on the lowering of the intragas­tric pH.

REFERENCES

1. Baron, J.H. Clinical tests of gastric secretion. History, methodology and interpretation. London, Macmillan, 1978.
2. Fimmel, C.J., Etienne, A., Oilluffo, T. et al, Longterm ambulatory gastric pH monitoring; validation of a new method and effect of H2 antagonists. Gastroenterology, 1985; 88:1842.
3. Eyerly, J.B. Comparative pH values within the stomach, pylorous and duodenum in antacid therapy. Am. J. Dig. Dis,, 1940; 7:431.
4. Levin, E., Kirsner, LB., Palmer, W.L. and Butler, C. The variability and periodicity of the noc­turnal gastric secretion in normal individuals. Gastroenterology, 1948; 10:939.
5. Etienne, A., Fimmcl, C.J., Bron, BA., Loizeau, E.B. and Blum,A.L. Evaluation of pirenzepine on gastric acidity in healthy volunteers using ambulatory 24 hours intragastric pH-monitoring. Gut, 1985; 26: 241.
6. Bingle, J.P. and Lennard-Jones, J.E. Some factors in the assessment of gastric antisecretory drugs by a sampling technique. Gut, 1960; 1:337.
7. Vakil, B.J., Mulekar, A.M. and Misra, N.C. 24—hours gastric analysis. J. Indian Med. Assoc., 1963; 41:342.
8. Babouris, N., Fletcher, J. and Lennard-Jones, J.E, Effect of different foods on the acidity of the gastric contents in patients with duodenal ulcer. part II. Effect of varying the size and fre­ quency of meals. Gut, 1965; 16:118,
9. McCloy, R.F., Greenberg, G.R. and Baron, J.H. Duodenal pH in health and duodenal ulcer disease, effect of a meal, Coca-Cola, smoking and cimetidine. Gut, 1984; 25 :386.
10. Gotthard, K., Berstad, A., Bodemar, G., Norlander, B. and Walan, A, Effect of cimetidine and oxmetidine on 24-h gastric acid and pepsin in patients. Scand. J. Gastroenterol., 1983;18:809.
11. Machida, TA study of intragastric pH in patients with peptic ulcer — with special reference to the clinical significance of basal pH value. Gastroen­ terol. Jpn., 1981; 16:447.
12. Desai, H.G., Venugopalan, K. and Antia, F.P. Effect of red chilli powder on DNA content of gastric aspirates. Gut, 1973; 14:974.

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