Reduced serotonin content and uptake in platelets from patients with essential hypertension: is a ouabain-like factor involved?

Platelet serotonin (5-HT) content was investigated in 35 essential hypertensive patients and in 58 normotensive subjects. A significant decrease of platelet 5-HT content was observed in both hypertensive men and women in respect to normotensive controls. This decreased platelet 5-HT content appears to be linked to a reduced capacity of platelets to take up 5-HT. Maximal velocity of 5-HT uptake was shown to be reduced in platelets from hypertensive patients and significantly correlated to platelet 5-HT content. No concomitant change of uptake Michaelis constant (KM) was observed. The great sensitivity of human platelets to very low concentrations of ouabain was demonstrated when incubation times were prolonged. The decreased Vmax observed in platelets from hypertensive patients and reproduced by ouabain inhibition could conceivably be linked to the presence of a circulating ouabain-like factor in hypertension.