In depressed patients, high-lethality suicidal acts are accompanied by serotonin system abnormalities analogous to those seen in completed suicides. We have previously reported greater platelet 5-HT2A receptor density, and impaired serotonin enhancement of ADP-induced platelet aggregation, an indirect measure of signal transduction, in high-lethality suicide attempters. We hypothesized that serotonin-activated phosphoinositide (PI) hydrolysis, a direct measure of platelet serotonin 5-HT2A receptor responsivity would be lower in depressed high-lethality suicide attempters. Twenty-three depressed in-patients that had previously made suicide attempts (low-lethality, n=6; high-lethality, n=17) had platelet 5-HT2A-mediated serotonin-simulated PI hydrolysis assayed. Platelet 5-HT2A receptor responsivity in high-lethality suicide attempters was 41% that of low-lethality suicide attempters (p<0.05). A seasonal effect was also observed. High-lethality suicidal acts are associated with more 5-HT2A receptors but impaired signal transduction.
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