PLATELET SEROTONIN TRANSPORTER DENSITY AND RELATED PARAMETERS IN ENDURANCE-TRAINED AND SEDENTARY MALE-SUBJECTS

A number of peripheral indices of serotonergic function were examined in endurance-trained (ET) and sedentary males using the blood platelet as a model of the serotonergic neurone. The aim of the study was to i nvestigate possible involvement and adaptation of the central serotone rgic system in exercise-induced fatigue. The [H-3] paroxetine-defined density of platelet serotonin transporters, platelet serotonin content and the plasma concentration of amino acids were determined in 10 ET and eight sedentary males. The mean (standard deviation) density oi th e serotonin transporter in the platelet membranes of the ET subjects w as greater [1237 (182) fmol mg protein(-1)] than that of the sedentary subjects [910 (119) fmol mg protein(-1); P = 0.013]. No difference (P = 0.51) could be seen between the median (range) platelet serotonin c ontent of the ET subjects [0.98 (0.37-3.04) nmol platelet(-10)] and th at of the sedentary subjects [0.82 (0.18-1.49) nmol platelet(-10)]. Th e platelet poor plasma concentrations oi tryptophan and tyrosine were lower in the ET subjects (P = 0.028 and 0.015, respectively). The pres ent study suggests that the platelet membrane of the ET subjects has a greater density of the serotonin transporter and that this is inverse ly related to the circulating concentration of the serotonin precursor , tryptophan. it remains to be resolved whether the increase in seroto nin transporter density in the platelet membrane of ET subjects is ref lected centrally and whether the ET platelet population may be suffici ently different from that oi sedentary individuals to alter serotonin transporter density.