24-hour intragastric acidity and plasma gastrin after omeprazole treatment and after proximal gastric vagotomy in duodenal ulcer patients The relationship between suppressed gastric acidity and the increase in plasma gastrin levels after pharmacological and surgical treatment of peptic ulcer disease were compared in this study. Eight patients with chronic duodenal ulcer and referred for proximal gastric vagotomy were studied. 24-hour intragastric acidity and plasma gastrin levels were investigated in the same patients on three consecutive occasions: preentry without any treatment; after 4 weeks of administration of 20 mg of omeprazole daily, and 4-6 months after proximal gastric vagotomy. Intragastric acidity was slightly more reduced by omeprazole (94%) than after proximal gastric vagotomy (78%), with no difference found during the day or night with either. Plasma gastrin levels increased slightly more after proximal gastric vagotomy [284% (median, 2120 pmol.h/L; range, 733-2831 pmol.h/L)] than after omeprazole administration [186% (median, 1586 pmol.h/L; range, 495-2573 pmol.h/L)]. There is strong evidence that the increased plasma gastrin concentration following omeprazole treatment is caused by the reduced intragastric acidity. The slight increase in plasma gastrin concentration following proximal gastric vagotomy despite a lesser reduction in intragastric acidity may be the result of additional effects on gastrin release by the vagotomy. Both treatments resulted in a modest increase in plasma levels of gastrin that were far below the gastrin levels observed in achlorhydric patients, e.g., patients with pernicious anemia. 