Osmotic concentration of the gastric juice of dogs.

1. The freezing point of the gastric juice, produced by histamine stimulation in anaesthetized dogs, of the arterial plasma and of the plasma obtained from a gastric vein were measured.2. The osmolality of the blood that passes through the gastric mucosa increases during secretion of acid juice.3. The amount of water that should be removed from the arterial plasma to obtain a solution isosmolal to the gastric venous plasma is equivalent to the amount of water required to dilute the secreted H(+). From this result it is concluded that the increase of osmolality of the venous plasma is a consequence of the clearance of water free of solute by the gastric mucosa.4. The gastric juice was hyposmotic to the venous plasma in twenty out of thirty dogs, being isosmotic to that plasma in seven dogs. Even in the last group of animals, the gastric secretion might be considered as slightly hypotonic to the venous blood that passes through the secretory part of the mucosa.5. Considerations based on available data suggest that the ;primary' acid juice is usually hyposmotic to the extracellular fluid in the vicinity of the oxyntic cells.