[Methodologic studies of N-acetylneuraminic acid determination in human gastric juice]

Mucus protects the gastric mucous membrane from aggressive substances in the gastric juice. It consists of glycoproteins, the composition of which determines its ability of viscosity, adhesiveness, and cohesiveness. There is a special interest in sialic acids, which are found mostly in humans as N-acetylneuraminic acid (NANA). NANA is estimated by the thiobarbituric acid method. A special feature of this method is that only free sialic acids are estimated. A mild acid hydrolysis is necessary in order to measure the total NANA-content. Some conditions of the hydrolysis are investigated with respect to the special properties of the gastric juice. Hydrolysis sulfuric acid 0.01 mol/l results in an about 10% higher yield than hydrolysis with hydrochloric acid 0.01 mol/l. A maximal yield of hydrolysates is found when the gastric juice pH is adjusted to 2.0. After 45 minutes hydrolysis at 80 degrees C in a water bath there is for at least 60 minutes a constant NANA-concentration in the gastric juice samples. Human bile has no influence on the estimation with the thiobarbituric acid method. In regard to these conditions of hydrolysis pentagastrin (6 micrograms/kg KG s. c.) does not change the NANA-secretion over 60 minutes in patients with duodenal ulcer. During an intragastric bile salt infusion the NANA-output remains unchanged over 45 minutes.