Serum level of serotonin during rest and during exercise in paraplegic patients

The purpose of this study was to evaluate the serum level of serotonin (5-HT) during rest and response to exercise in subjects with spinal cord injury (SCI) with different levels of physical activity. Twenty-five male subjects with traumatic paraplegia, the neurological levels being between T1 and T12, volunteered for the study. They were divided into two groups matched for age, weight and time since injury, according to the level of physical activity: 14 inactive and 11 subjects regularly involved in sports activity and considered active. They all performed a maximal spiroergometric test with an arm crank ergometer. Two samples of blood were collected for 5-HT determination, during rest (PRE) and immediately after exercise test (POST). Serum 5-HT concentration was measured by high performance liquid chromatography using electrochemical detection (HPLC-ED). The results showed that peak oxygen uptake (VO2peak) was higher in the active group (27.08 +/- 2.60 vs 18.89 +/- 5.58 mL.kg-1.min-1, P < 0.001). There were no significant differences between the inactive and active groups for the 5-HT PRE (respectively 176.96 and 193.73 ng.mL - 1, P > 0.05) or POST values (275.44 vs 311.05 ng.mL-1, P > 0.05). Both groups showed an increment in 5-HT after maximal exercise, but only in the active group it reached statistical significance (Wilcoxon test, P < 0.02). Our results show that chronic paraplegic individuals have normal resting serum serotonin levels and normal response to exercise. The relationship between training status, mood elevation and 5-HT in SCI could not be established in the present study, and further investigation is needed to clarify this issue.