Decrease of platelet serotonin content in ovariectomized female rats.

Platelet serotonin (5-HT) concentration was determined in ovariectomized and sham-operated rats by high-pressure liquid chromatography. A 23% decrease in platelet 5-HT levels was found in ovariectomized rats. Platelet 5-HT uptake mechanism was studied by incubating platelet-rich plasma with increasing concentrations of [3H]-5-HT at 37 C and 4 C for 10 sec. Kinetics parameters (Km, Vmax) characterizing active 5-HT uptake were found to be identical in both groups of rats. In vitro preincubation of platelets with 17 beta-estradiol and progesterone did not modify the 5-HT uptake levels. The platelet 5-HT decrease observed in ovariectomized rats may reflect a physiological modulation of peripheral 5-HT metabolism by ovarian hormones, which is not linked to a modification of the membranal uptake mechanism.