Kinetics of Platelet 5-Hydroxytryptamine Uptake in Headache Patients

Platelet 5-hydroxytryptamine (5-HT) uptake was measured in asymptomatic headache patients attending a specialist migraine clinic, and in hospital staff who did not suffer from regular or severe headache. Current levels of anxiety and depression were assessed in all subjects using the Hospital Anxiety and Depression (HAD) scale and their possible influence on the uptake kinetics taken into account during the analysis of results. The Michaelis-Menten constant (K _m ) was significantly raised in common migraine and tension headache compared with controls (p < 0.001 and p < 0.01, respectively), but not in classical migraine or cluster headache. The increase remained significant after adjusting for differences in age, sex, presence of anxiety or depression (HAD sub-scale score ³ 8), drug intake during the week before testing, time elapsed since last attack and time of assay (am or pm). No differences were observed between patients and controls in the maximal rate of uptake (V _max) or platelet count, and previous reports of a reduction in V _max in patients experiencing attack within 5 days prior to testing could not be confirmed. The cause and significance of an increased K _m are not clear, but plasma factors acting as competitive inhibitors for the uptake site or an alteration in the configuration of the uptake site are possible explanations. If confirmed, the shared biochemical abnormality may suggest that common migraine and tension headache have a common pathogenesis.