Clinical Significance:
Secretin is a 27 amino acid basic peptide produced by S-Cells and released by acid delivered into the duodenum.  Secretin is released into the blood when duodenal pH drops below 4.  Secretin shares structural similarity with Glucagon, Gastric Inhibitory Polypeptide, Vasoactive Intestinal Polypeptide, PHIM, and Growth Hormone-Releasing Hormone. Secretin is a potent stimulus for bicarbonate secretion.  Secretin also stimulates secretion of bile, release of Insulin, and release of gastric Pepsin in the stomach.  Secretin inhibits Glucagon release, intestinal motility, and prevents the uptake of water and sodium ions by the intestine.  In normal patients, Secretin has little effect on Gastrin levels, but stimulates Gastrin greatly in Zollinger-Ellison patients.  Secretin may also be elevated in Zollinger-Ellison patients and in patients with duodenal ulcer.  Secretin levels are low in patients with pernicious anemia and achlorhydria.  Secretin secretion can be suppressed by Somatostatin, Cimetidine, and Methionine-Enkephalin.

Reference Range:
12 – 75 pg/ml

Secretin is measured by direct radioimmunoassay.

Patient Preparation:
Patient should be fasting for 10 – 12 hours prior to collection of specimen.  Antacid medications and medications that affect intestinal motility should be discontinued, if possible, for at least 48 hours prior to collection.

Specimen Collection:
Collect 10mL blood in special ISI GI Preservative tube yielding special GI plasma and separate as soon as possible.  Freeze plasma immediately after separation.  Special G.I. Preservative tubes are available from Inter Science.  Minimum specimen size is 1 ml.

Important Precaution:
Secretin specimens must be collected using the G.I. Preservative.  No other specimens are acceptable.

Special Specimens:
For tumor/tissue and various fluids (i.e. CSF, peritoneal, synovial, etc.) contact the Institute for requirements and special handling.

Shipping Instructions:
Ship specimens frozen in dry ice.

1. A Christ, B Werth, and P Hildebrand.  Human Secretin:  Biologic Effects and Plasma Kinetics in Humans.  Gastroenterology 94:  311, 1988.

2. N Yanaihara, M Sakagami, H Sato, K Yamamoto, T Hashimoto, C Yanaihara, Z Ito, K Yamaguchi, and K Abe.  Immunological Aspects of Secretin, Substance P and VIP.  Gastroenterology 72:  803, 1977.