Serotonin transporter activity and serotonin concentration in platelets of patients with irritable bowel syndrome: effect of gender.

BACKGROUND: In the past decade, a strong argument has been built for the role of serotonin (5HT) and the serotonin transporter (SERT) in irritable bowel syndrome (IBS). However, it is still not clear how SERT contributes to this clinically heterogeneous disease. The present study addressed this issue by implementing platelet (plt) markers of SERT activity in the assessment protocol.
METHODS: Fasting blood samples of 149 (51 male/98 female) subjects with Rome II and III defined IBS subtypes, and 163 healthy control subjects (CSs; 75 male/88 female) were analyzed for platelet 5HT concentration and 5HT uptake activity [maximum uptake rate (V (max)) and affinity constant (K (m))].
RESULTS: Gender had a significant impact on platelet markers of SERT activity. Male IBS patients showed significantly lower median V (max) and K (m) values than the male CS (V (max) 1.706 vs. 2.148 nmol/10(9) plts x min, P < 0.001; K (m) 346 vs. 410 nmol, P = 0.008) without any significant reduction in platelet 5HT concentration (362 vs. 394 ng/10(9) plts). On the other hand, V (max) values were not different between female IBS patients and female CS (1.642 vs. 1.741 nmol/10(9) plts x min), but platelet 5HT concentration was significantly lower in females with diarrhea-predominant IBS (363 vs. 435 ng/10(9) plts, P < 0.05).
CONCLUSION: Although an absolute extrapolation from platelets to the gastrointestinal tissue does not appear to be justified, our findings demonstrated that the contribution of disturbed SERT activity to IBS is not uniform and is possibly gender-specific. The results suggest that an assessment of SERT function in platelets may help to elucidate the differences between IBS patients in response to drugs affecting the 5HT system.