Gastric osmolar clearance and ionic barter: two mechanisms of electrolyte secretion by the human stomach

¹ Department of Medicine, Division of Gastroenterology, University of Alabama School of Medicine, Birmingham, Alabama

Measurements of gastric juice volume (V) and H ion (H), chloride ion (Cl_G), Na ion (Na_G) concentrations and of osmolality (O_G) as well as plasma sodium (Na_P) and osmolality (O_P) were made in nine men before and after a subcutaneous injection of histamine. The gastric osmolar clearance (GOC) was calculated from the formula (V·O_G)/O_P and this correlated well with both acid and chloride output. The theoretical clearance of sodium (TC_Na) was calculated for each specimen by the formula (V·O_G·Na_P)/O_P, and this equaled the output of acid plus sodium in the gastric juice V(H + Na_G). The mol-mol relationship furthermore suggests that the gastric acid is secreted on a 1:1 basis in exchange for Na ions theoretically cleared within the framework of a gastric osmolar clearance mechanism. It also explains why, even under the most optimal conditions in man, the maximum value for H⁺ concentration does not exceed 150 mEq/l. On the basis of these observations it is suggested that the various theories which propose a primary acid secretion of 167, 169, 208 or 464 mn, respectively, are unlikely.