Increased 5-HT-2 receptor function as measured by serotonin-stimulated phosphoinositide hydrolysis in platelets of depressed patients.
1. The present study was undertaken to examine whether or not 5-HT-induced inositol monophosphate (IP-1) accumulation in human platelets is mediated by 5-HT-2 receptors and to assess 5-HT-2 receptor function as measured by 5-HT-stimulated IP-1 accumulation in platelets from normal controls and depressed patients before drug treatment. 2. In platelets prelabeled with 3H-myo-inositol, in Ca ion free HEPES buffer containing 10 mM LiCl, 5-HT caused a dose-dependent accumulation of IP-1 during 15 min incubation. A maximal increase in IP-1 formation was observed at 30 microM of 5-HT and its EC50 value was 4 microM. 3. Ketanserin, a selective 5-HT-2 antagonist, was a potent inhibitor of 5-HT-stimulated IP-1 accumulation with a Ki value of 12 nM, but (-)propranolol (10 microM), a 5-HT-1 antagonist, failed to block the 5-HT response. 4. The potencies of various compounds tested to inhibit 5-HT-stimulated IP-1 accumulation in human platelets correlated positively with the affinities to 5-HT-2 receptor as defined by radioligand binding in rat cerebral cortex. 5. In a group of unmedicated patients with major depressive disorder matched for age with normal control group, we found a significant increase in 5-HT (100 microM)-induced accumulation of IP-1 (150 +/- 7% of basal for depressed patients, 132 +/- 3% for controls).
Mikuni
M
M
Division of Mental Disorder Research, National Institute of Neuroscience, Tokyo, Japan.
Kusumi
I
I
Kagaya
A
A
Kuroda
Y
Y
Mori
H
H
Takahashi
K
K
D000328:Adult; D000368:Aged; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D003866:Depressive Disorder / Q000097:blood*; D006801:Humans; D006868:Hydrolysis; D066298:In Vitro Techniques; D007291:Inosine Monophosphate / Q000097:blood; D007650:Ketanserin / Q000494:pharmacology; D008875:Middle Aged; D010716:Phosphatidylinositols / Q000097:blood*; D011985:Receptors, Serotonin / Q000378:metabolism*; D012701:Serotonin / Q000494:pharmacology*
D010716:Phosphatidylinositols; D011985:Receptors, Serotonin; D007291:Inosine Monophosphate; D012701:Serotonin; D007650:Ketanserin