Interstitial fluid pressure and alkaline gastric secretion

The interstitial fluid pressure of the submucosa of the gastric fundus was monitored by means of Guyton's capsules in dogs anesthetized with pentobarbital. The intracapsular pressure (ICP) was measured during secretion produced by: a) hypertonic solutions placed inside the stomach; b) arterial hypertension (200 mmHg) applied during intra-arterial infusion of histamine, and c) intra-arterial infusion of acetylcholine. The first procedure did not modify the ICP. On the other hand, whenever interstitial fluid appeared in the gastric lumen during hypertension plus histamine, the mean ICP increased, mostly due to augmented capillary filtration. The hydraulic coefficient measured in these experiments was at least 4 orders of magnitude larger than the respective osmotic coefficient. The action of acetylcholine was complex: large doses enlarged the net capillary filtration, but small doses increased the mean ICP by muscle stimulation only. Contraction of the muscularis mucosae might be the most important mechanism underlying bulk flow of interstitial fluid in physiological conditions. It is concluded that hydraulic gradients across the epithelium might account for the "secretion" of "alkaline" juice.