Characterization of secretin release in response to food and intraduodenal administration of fat and hydrochloric acid

Secretin is a 27-amino acid peptide released from the small intestine. It stimulates the secretion of digestive enzymes by the stomach, and the secretion of water and bicarbonate by the pancreas and liver, and inhibits the secretion of gastric acid by the stomach. The presence of various nutrients in the stomach or intestine, and alterations in the acidity of the small intestine have been reported to cause secretin release. To further characterize factors that influence the release of secretin into the general circulation, a sensitive radioimmunoassay (RIA) for secretin was developed and validated. Blood was sampled from mongrel dogs at various time points after alteration of the gastrointestinal milieu. Increases in blood secretin levels were observed within 10 minutes of a slight increase in intestinal acidity. Similarly, instilling small amounts of sodium oleate (a fatty acid salt) into the intestine or administering a mixed meal caused rapid increases in blood levels of secretin. The magnitude of the secretin response was dose-related; increasing the amount of intra-intestinal acid or oleate, or the size of the meal, resulted in a larger release of secretin into the circulation. Release of pancreatic fluid and pancreatic bicarbonate was induced by these three stimuli; the volume and concentration of the output was highly correlated with the stimulus dosage. Hence, intestinal infusions of acid, fats, or mixed nutrients (which mimic the effect of normal food ingestion) cause a rapid increase in blood levels of secretin. (Consumer Summary produced by Reliance Medical Information, Inc.)