Defective serotonin (5-HT) transport mechanism in platelets from patients with endogenous and allergic asthma

The kinetics of the 5-HT-uptake by platelets in platelet-rich plasma (PRP) and PRP diluted with autologous platelet-poor plasma (PRP/PPP) were determined in normal subjects, patients with asymptomatic exogenous asthma and those with symptomatic endogenous asthma. In normal subjects the 5-HT-uptake by platelets strictly obeyed Michaelis-Menten's kinetics. In patients with asymptomatic exogenous asthma, the active 5-HT-transport was moderately distorted in PRP and severely altered in PRP/PPP. Patients with symptomatic endogenous asthma exhibited already in PRP a dramatic transport disturbance. The alteration of the active 5-HT-transport was characterized by increasing uptake inhibition by rising 5-HT concentrations in plasma. This phenomenon could be due to changes in the platelet environment, defects in the platelet membrane or intrinsic platelet disorders. It is concluded that asthmatics have genetically or later acquired platelet disorder, which is more clearly observed in patients with symptomatic endogenous asthma than in those with asymptomatic exogenous asthma.