The slowing of gastric emptying by nine acids.

1. Test meals containing a range of concentrations of nine different acids were given to twenty healthy subjects. The acids used were hydrochloric, acetic, lactic, tartaric, phosphoric, citric, propionic, butyric and hexanoic.2. The greater the concentration of acid in the meal the greater was the volume of the meal recovered after a fixed interval.3. A rectilinear relationship between the mean concentrations of acid (m-equiv/l.) required to give a recovery of 450 ml. and the molecular weights of the acids used was found. The acids with high molecular weights were less effective than those with low molecular weights.4. The results indicate that the molecular weights of the anions play the dominant part in determining the effectiveness of the various acids. Slowing of gastric emptying by acids does not seem to be dependent upon their pK values provided they are less than 5. The oil/water partition coefficients are also apparently irrelevant to effectiveness.5. These findings are considered to be consistent with the view that a barrier to movement of the anions in an aqueous system limits the access of the hydrogen ions to duodenal receptors, which activate the mechanism slowing gastric emptying.