SUMMARY1. Test meals of solutions and suspensions of potassium and sodium salts of a series of saturated fatty acids, from C2 to C1l, were given to healthy subjects.2. From the volume of these meals recovered after a fixed interval the relative effectiveness of the salts of the acids in slowing gastric emptying was assessed.3. On a molar basis the salts of fatty acids from acetic up to decanoic were relatively ineffective in slowing gastric emptying.4. The salts of fatty acids with 12-18 carbon atoms were much more effective than those with up to 10 carbon atoms. Myristate was the most effective of the salts.5. Buffering the test meals with 33 mm sodium citrate increased the effectiveness of the salts in slowing gastric emptying.

It is known that when test meals containing hydrochloric acid are given, the greater the concentration of acid in the meal the slower is gastric emptying (Shay & Gershon-Cohen, 1934;Van Liere & Sleeth, 1940;Pathak, 1959; Hunt & Pathak, 1960). This slowing of gastric emptying is believed to depend upon the stimulation of duodenal receptors by the duodenal contents recently transferred from the stomach. The present studies are concerned with the rates of emptying of test meals containing citric acid and the various sodium salts of this trivalent acid. These were chosen for study because they allow the preparation of solutions with a variety of pH values and with various degrees of buffering power which can be used to decide on the relative importance of these two variables in exciting the receptors concerned. METHODSThe subjects were four volunteer students and HT. Test meals were given down a tube at 37°C to the fasting subjects after their stomachs had been washed out with 250 ml. of tap water, which was recovered as completely as possible before the meal was given. All meals contained about 60 mg phenol red/1. to act as a marker. Phenol red is not absorbed or secreted by the stomach (for references see Hunt, 1947). After an interval, constant for each subject but varying between 9 and 19 min, the meal waswithdrawn through the tube; when this recovery appeared to be complete 250 ml. tap water was given and this portion was aspirated separately. The amount of phenol red in this second aspirate allowed the volume recorded for the first recovery to be corrected for incompleteness. When a recovery began 9 mm after giving the meal, the meal was recorded as of 10 min duration to allow for the time required to recover the gastric contents. Other times were similarly adjusted by 1 mi.The majority of the test meals were made up from appropriate amounts of citric acid and sodium citrate. Test meals containing ammonium citrate or ammonium chloride were made up with the corresponding salts.Estinwtin of phenol red. Ten millilitres of the test-meal solution or of the recovered gastric contents and 50 ml. of a solution of Na%PO4 (27.5 g/l.) were pipetted into a 250 ml. flask which was then filled up to the mark with distilled water. The mixture had a pH of about 11-12. The optical density of the purple solution so produced was estimated in a single cell photo-electric colorimeter with a green filter (Ilford 404). The concentration of phenol red was then determined from a curve relating concentration of phenol red to optical density. The green filter used minimized the effect of bile.

No abstract

SUMMARY1. Test meals of 750 ml. water containing a range of concentrations of hydrochloric, nitric, sulphuric, cyclamic (cyclohexylsulphamic), tartaric, L-ascorbic and citric acids were instilled into the stomachs of sixteen healthy subjects.2. The greater the concentration of an acid in the instilled meal, the ·greater was the volume of meal recovered after a fixed interval.3. For the weak acids, tartaric, ascorbic and citric, the concentrations which gave a recovery of 450 ml., out of the 750 ml. instilled, increased with increase in the molecular weight of the acid.4. For the strong acids, hydrochloric, nitric, sulphuric and cyclamic, the concentrations which gave a recovery of 450 ml., out ofthe 750 ml. instilled, were approximately equal. These concentrations were less than those for weak acids.5. The strong acids with high molecular weights were slightly more effective in slowing gastric emptying than were those with low molecular weights.6. The approximate equality of effectiveness of nitric, sulphuric and cyclamic acids to hydrochloric acid is attributed to the presence of chloride ion in the duodenal contents. Thus all the strong acids instilled produce an environment of hydrochloric acid around the receptor. 7. A model for a duodenal receptor responding to acids is proposed.