Decreased Basal and Postprandial Plasma 5-Hydroxytryptamine (5-HT) in Patients With Functional Dyspepsia (FD): A Pilot Study

BACKGROUND: Increased postprandial 5-HT levels have been observed in patients with diarrhea-predominant irritable bowel syndrome (IBS). However, it is unclear whether patients with FD have 5-HT dysfunction. AIM: To compare the plasma 5-HT profile in FD patients and healthy controls. METHODS: Consecutive patients with FD (Rome III criteria) were recruited. Patients with GERD and IBS as predominant symptoms were excluded. After an overnight fast, they underwent caloric drinking test (Ensure O,1.06 kcal/ml at 30ml/min) and 13C-octanoic acid breath test for gastric emptying time measurement. Serial blood samples were collected at 0, 30, 60, 90, 120 min postprandially for plasma 5-HT assay. Healthy controls without history of peptic ulcer and dyspepsia were recruited for the same protocol. RESULTS: 29 FD patients (M:F, 8:21; mean age: 45±2) and 20 controls were studied. 18 (62%) patients had postprandial distress syndrome (PDS) and 11 (40%) had both PDS and epigastric pain syndrome. 7 (24%) patients had concomitant IBS. There was no significant difference in total calorie intake (FD: 762±59 kcal; Control: 940±89 kcal, p= 0.11) and gastric emptying rate (T1/2, FD: 76±4min.; Control: 80±5min., p=0.52). However, FD patients had significantly lower basal (FD: 139±17 ng/109platelets, Control: 238.0±11.7 ng/109platelets, p<0.001) and postprandial plasma serotonin contents at 30min (FD: 127±18 ng/109platelets, Control: 206±10 ng/109platelets, p<0.001), 60 min (FD: 119±18 ng/ 109platelets, Control: 193 ±19 ng/109platelets, p=0.006), 90 min (FD: 110±17 ng/109platelets, Control: 171 ± 23 ng/109platelets, p=0.038) and AUC over the period of 120 min (FD: 14410±1968 ng/109platelets.min, control: 23160±1537 ng/109platelets.min, p=0.0062). Repeated measures of ANOVA revealed high correlation between FD and serotonin profile across 120 min (p=0.0021 for FD, time <0.0001) CONCLUSION: In contrast to IBS, FD patients have decreased basal and postprandial plasma 5-HT concentrations. These findings suggest (1) IBS and FD have different pathophysiological mechanism in particular the 5HT dysfunction and (2) Modulation of 5-HT system may have therapeutic value in treatment of FD.