Intraoperative pH of the gastric mucosa before and after truncal vagotomy in the dog. The Grassi test.

The intraoperative surface pH of the corpus fundus mucosa in anaesthetized dogs was studied with a glass electrode before and after vagotomy during stimulation with 2.0 micrograms kg-1 h-1 of pentagastrin. Before vagotomy an average pH of 1.9 was noted. A significant rise of pH to an average of 5.9 occurred immediately after vagotomy. Twenty-four hours and 14 days after vagotomy pH was at the initial low level. The immediate high pH after vagotomy could be lowered to the same level as before by addition of a threshold dose of bethanechol chloride. The high pH immediately after vagotomy must be ascribed to the sudden fall in the subthreshold release of acetylcholine previously supplied by the intact vagus. The return of low pH 1 day after vagotomy can be explained by development of denervation supersensitivity caused by the diminished background release of acetylcholine. Acid spots were registered in the distal part of the corpus immediately after vagotomy because that area is more sensitive to pentagastrin than the proximal. It is therefore suggested that histamine, which has a reverse action, is a more suitable stimulant when pH measurements are performed to assess the completeness of a selective proximal vagotomy.