Gastric secretory responses to modified sham feeding (MSF) and insulin after vagotomy

Cephalic phase of acid secretion involves activation of medullary TRH receptor subtype 1 in rats

Mechanisms involved in the cephalic phase of gastric acid secretion were studied in awake fasted rats with chronic gastric fistula and exposed to the sight and smell of chow for 30 min. Acid secretion was monitored using constant intragastric perfusion and automatic titration. Sham feeding induced a peak acid response reaching 82 +/- 7 micromol/10 min within 20 min compared with the average 22 +/- 2 micromol/10 min in controls. The sham-feeding response was abolished by intracisternal pretreatment with the TRH(1)-receptor antisense oligodeoxynucleotides or subcutaneous injection of atropine, whereas TRH(1) mismatch oligodeoxynucleotides had no effect. Serum gastrin was not altered by the sham feeding and increased by refeeding. Gastrin antibody did not block the rise in acid during sham feeding, although the net acid response was reduced by 47% compared with the control group. Glycine-gastrin antibody, indomethacin and nitro-l-arginine methyl ester had no effect. Atropine and gastrin antibody decreased basal acid secretion by 98 and 75%, respectively, whereas all other pretreatments did not. These results indicate that the cholinergic-dependent acid response to sham feeding is mediated by brain medullary TRH(1) receptors in rats.

Quantitative relation between gastric acid secretion and changes in urinary acid excretion

This study was designed to investigate the relations between gastric acid secretion and alkalinisation of the urine. Normal subjects underwent standard pentagastrin (6 micrograms/kg) (n = 5) and sham feeding (n = 6) tests, with additional collection of urine samples before and two and three hours after the start of the test for measurement of titratable urine acidity. Nine subjects provided urine before and two hours after a test meal. Sham feeding (n = 5) and meal (n = 6) tests were carried out in patients who had had a successful vagotomy for duodenal ulcer. There was a significant correlation of gastric acid response in the standard tests with simultaneous changes in urine acidity (r = -0.79, p less than 0.001) and also with urine acid output after the test meal, on another day (r = -0.73; p less than 0.02). The correlation was insufficient to predict gastric function from changes in urinary acidity, but there was clear separation of the results in normal subjects and patients with vagotomy. Changes in urine acidity after a standardised meal may prove to be useful as a screening test after vagotomy to select patients who are likely to have a persisting high gastric acid response to vagal stimulants.

Urine acid output as a test of completeness of vagotomy

Peak acid output in response to sham feeding and changes in urine acid output 2 and 3 hours after a test meal have been measured in 20 normal volunteers, 17 asymptomatic patients after vagotomy, six patients with recurrent duodenal ulcer after vagotomy and ten normal subjects given a 48-h course of ranitidine, 150 mg 12-hourly. Gastric peak acid output in normal volunteers ranged from 6.9 to 22.1 mmol/h. All asymptomatic patients after vagotomy had a peak acid output less than 7 mmol/h, consistent with complete vagotomy. Five patients with recurrent ulcer had a peak acid output greater than 8 mmol/h, suggesting an incomplete vagotomy. Urine acid output after a test meal, expressed as the change from the basal rate of acid output, was always in a negative direction in normal subjects (fall in acid output = postprandial alkaline tide). This change was abolished in patients with complete vagotomy, in whom urine acid output increased after a meal. In five patients with incomplete vagotomy (and one other with recurrent ulcer and unknown vagal status) the urine acid output changed in a negative direction after a test meal. The relationship of urine acid output to gastric secretion was confirmed by the abolition of the postprandial alkaline tide in normal subjects given ranitidine. The results in patients with incomplete vagotomy did not overlap with those from patients with complete vagotomy. This suggests that this test could be used for the routine postoperative assessment of completeness of vagotomy.