Gastric Secretion. Ii. Absorption of Radioactive Sodium from Pouches of the Body and Antrum of the Stomach of the Dog.

The biochemical process by which cells of the stomach produce hydrochloric acid remains a mystery. Although the approximate concentration of the acid has been calculated on indirect evidence, the exact concentration as it is secreted has not been determined in any animal. This is despite the fact that, over a period of many years, increasingly precise observations have been made. The difficulty confronting observers is that the same area of the stomach which secretes the hydrochloric acid also forms pepsin and mucin, and allows the passage of certain inorganic electrolytes and urea between the blood and stomach lumen. Little light has been thrown on this subject by analyses of the gastric contents of the stomach, since swallowed saliva and regurgitated secretions from the duodenum inconstantly contaminate the contents. Gastric pouches were first conceived to discount the inaccuracies of studying gastric contents, and indeed, examination of fluid collected from a pouch of the stomach of an experimental animal yields accurate information. It is frequently assumed, however, that this fluid from pouches represents true secretion. No account is taken of a possible concomitant absorption of water or. electrolytes from the gastric lumen into the lymphatics or blood stream. Unless reabsorption can be excluded, the fluid within a pouch does not represent secretion but the resultant of secretion and absorption. During the course of experiments on the effect of the osmotic pressure of gastric pouch contents on the volume of secretion (1), it became obvious that absorption from the pouch must be controlled. It is known that some substances are absorbed from the stomach in small quantities (2), but it is not known whether all of the observed absorption takes place from the antrum or from the body of the stomach. In contrast to the body of the stomach which secretes the hydrochloric acid, the antrum secretes a neutral mucoid liquid. Since the main part of absorption from the gastrointestinal tract takes place in the intestine, the contents of which are neutral or alkaline, it is considered possible that most or all of the absorption attributed to the stomach might well occur in the antrum. Recently, Eisenman et al. (3) have reported the absorption of various radioactive isotopes from the stomach, but no attempt to differentiate between antrum and body was reported. The experiments reported in this and the subsequent paper (4) were devised, not only to examine the conditions controlling absorption from the stomach, but also to judge the relative absorptive powers of the antrum and body of the stomach.