Decreased Basal and Postprandial Plasma Serotonin Levels in Patients With Functional Dyspepsia

BACKGROUND & AIMS: Patients with diarrhea-predominant irritable bowel syndrome (IBS) have been found to have increased postprandial levels of serotonin (5-HT). Functional dyspepsia (FD) and IBS have been proposed to have common methods of pathogenesis, but little is known about the role of 5-HT in FD. METHODS: We measured postprandial levels of 5-HT in 54 patients with FD (based on Rome III criteria) and 28 asymptomatic healthy individuals (controls). Patients with gastroesophageal reflux disease and IBS as their predominant symptom were excluded. After an overnight fast, the subjects drank a liquid meal (Ensure; 1.06 kcal/mL at 30 mL/min) and underwent a 13C-octanoic acid breath test to measure gastric emptying times. Blood samples were collected at 0, 30, 60, 90, and 120 minutes after the liquid meal for the 5-HT assay. RESULTS: Thirty-five patients with FD (65%) had postprandial distress syndrome, and 6 (11%) had a combination of postprandial distress syndrome and epigastric pain syndrome. There were no differences in rates of gastric emptying between patients with FD (103.6 +/- 19.4 minutes) and controls (83.1 +/- 4.0 minutes; P = .30). However, patients with FD had lower caloric intake (823.40 +/- 44.1 kcal) than controls (1021 +/- 68.2 kcal; P = .026). Patients with FD also had lower basal (P = .03) and postprandial plasma levels of serotonin at 30 minutes (P = .04), 60 minutes (P = .01), 90 minutes (P = .02), and 120 minutes (P = .002) than controls, as well as area under the curve values over the 120-minute time period (P = .005). Repeated-measures analysis of variance correlated 5-HT level with FD (P < .001). CONCLUSIONS: In contrast to patients with diarrhea-predominant IBS, those with FD have decreased basal and postprandial plasma levels of 5-HT. These findings indicate that the pathogenic mechanism of FD differs from that of diarrhea-predominant IBS, and that strategies to alter 5-HT levels or activity might be developed to treat patients with FD.