Mianserin-induced up-regulation of serotonin receptors on normal human platelets _{in vivo}

The antidepressant, mianserin, is a serotonin receptor (5-HT₂) antagonist and produces down-regulation of 5-HT₂ and 5-HT_1c receptors in the cerebral cortex of rats. In preparation for testing the validity of platelets as a model system for changes in 5-HT₂ receptors during antidepressent drug treatment, mianserin (40 mg daily), was given to five human volunteers for five days, and platelets were collected on days 0, 1, 6, and 8. 5-HT₂ receptor affinity and density were measured by specific binding of ¹²⁵I-LSD, with and without an excess of spiperone. 5-HT uptake site affinity and density were determined by ³H-paroxetine binding, with and without an excess of fluoxetine. Platelet serotonin content was measured using high pressure liquid chromatography and electrochemical detention. Platelet 5-HT₂ receptor density was increased and the ligand affinity was decreased during mianserin administration. In contrast, platelet 5-HT content was not altered significantly by mianserin administration, nor was platelet uptake site density and ligand affinity.