Hyperoxia alters platelet disposition of serotonin

Exposure of mice to normobaric 100% oxygen for 24-96 h is known to damage the pulmonary capillary endothelium and alter the disposition of serotonin (5-hydroxytryptamine, 5-HT). We now report that such exposure increased the concentration of platelets and decreased the platelet content of 5-HT and a tracer dose of [3H]5-HT. After 48 h of hyperoxia exposure, the platelet concentration was elevated to 121% of air-exposed control values and the content of 5-HT and [3H]5-HT/10(9) platelets was decreased 76% and 57%, respectively. Kinetic analysis of the platelet 5-HT uptake process indicated that hyperoxia exposure caused an increased affinity and decreased velocity of transport. After 48 h of oxygen exposure the Km for platelet 5-HT uptake was 1.91 +/- 0.67 X 10(-7) M and the Vmax 30.1 +/- 4.6 pmol/10(8) platelets/4 min compared to air-exposed control values of Km 3.37 +/- 0.32 X 10(-7) M and Vmax 46.7 +/- 3.5 pmol/10(8) platelets/4 min, respectively. These changes in platelet 5-HT uptake and disposition may contribute to the pathophysiology of the pulmonary microvascular response to hyperoxia-induced injury.