Motilin, normally present in a specific cell type in the upper small intestine, is believed to have a physiologic role in initiating the interdigestive migrating motor complex.
Motilin may play a pathophysiologic role in the
diarrhea in the
irritable bowel syndrome, the
dumping syndrome, chronic
liver disease, and
chronic renal failure. Furthermore, increased frequency of bowel movements is an important symptom in patients with the
carcinoid syndrome. We have studied 73 patients with metastatic
carcinoid tumors with regard to stool frequency and plasma concentration of
motilin and
neuropeptide K (NPK) and diurnal urinary excretion of 5-hydroxyindoleacetic
acid (5-HIAA). Thirty-eight (52%) of the 73 patients had elevated (greater than 126 pmol/l) plasma concentrations of
motilin, whereas 59 (81%) of the patients had
diarrhea. The increased frequency of bowel motions correlated significantly (p less than 0.01) with the plasma concentrations of
motilin, whereas no significant correlation with
5-HIAA and NPK was found. High-performance liquid chromatography of plasma extracts showed a single component eluting in the position of synthetic porcine
motilin. However, extracts from five
carcinoid tumors did not contain any significant levels of
motilin.
Carcinoid tumors are known to contain and secrete several biologically active substances such as
serotonin,
histamine,
prostaglandins, and
tachykinins, which are likely to cause disturbances of intestinal secretion and motility, which in turn might release
motilin from the
motilin-containing cells of the small intestine. The increased
motilin levels might then participate in a vicious
diarrhea circle together with the other agents.