Effects of type 1A serotonin receptor agonist 8-OH-DPAT on immune response

The platelet of the patients with ischemic cardiopathy and cardiac valve disease showed a reduction of 8OH-DPAT binding sites

Depression is prospectively associated with increased risk of coronary artery disease in individuals initially free of clinical cardiovascular disease probably by an increased platelet activity. The serotonergic receptors mainly implied in depression are 5-HT1A and 5-HT2 receptors. Activation of 5HT2 receptor induces platelet aggregation. Drugs with 5-HT1A receptor agonist and 5-HT2A receptor antagonist effects reduced the receptor-mediated platelet aggregation. There are only indirect data about 5-HT1A receptors presence in platelet membranes, thus our aims were to study the characteristics of the platelet membranes 5-HT1A binding sites of both healthy volunteers and patients with cardiac valve disease and ischemic cardiopathy. The bound of the 5-HT1A selective agonist 3H-8OH-DPAT to the platelet membranes 5-HT1A binding sites of patients with cardiac valve disease and ischemic cardiopathy were compared with a control group of healthy voluntaries using radioligand binding methods. The patients with cardiovascular disease showed a reduction (-50.40%) (p<0.01) of the 3H-8OH-DPAT bound to the platelet membranes 5-HT1A receptors (1.652+/-0.79 fmol/mg protein) with respect to the control group (3.331+/-0.16 fmol/mg protein). 3H-8OH-DPAT binding to human platelet membranes is saturable, of high affinity, and seems selective for 5-HT1A receptors, and similar to that described in animal brain and in other human cells. Patients with ischemic cardiopathy and cardiac valve disease showed a reduction of the 8OH-DPAT bound to the platelet membranes. Taken together, these findings suggest that the 8OH-DPAT bound to the human platelet membranes is modulated by modifications produced by cardiovascular disease conditions.

Serotonin, 5-HT1A serotonin receptors and proliferation of lymphocytes in major depression patients

Serotonin receptors are present in lymphocytes and might be related to the functionality of these cells in health and in pathology. The serotonergic system is affected in the brain and in peripheral immune cells of depressed patients. The objectives of this work were to evaluate the basal proliferation of lymphocytes, the response to the mitogen concanavalin A, and the role of serotonin 5-HT(1A) receptors. Twenty-nine patients, 19-52 years old, were diagnosed for a major depression episode with the Statistical and Diagnostic Manual-IV of the American Psychiatric Association, approved by ethic committees and gave written consent. The Hamilton depression score was 30.60 +/- 2.65. An apparently healthy group without a family history of psychiatric illness was included. Blood peripheral lymphocytes were isolated by density gradients with Ficoll/Hypaque and differential adhesion to plastic, cultured in 96-well plaques with RPMI-1640 medium with or without 4 mug/ml of concanavalin A. 8-Hydroxy-2-(di-n-propylamino)tetralin (5-40 nM) and WAY-100,478 (0.1-100 microM), agonist and antagonist of 5-HT(1A) receptors, serotonin (12.5-100 nM) or imipramine (0.1-100 microM) were also added. Proliferation was evaluated at 72 h with 3-[4,5-dimethythiazol-2-yl]-2,5-diphenyltetrazolium bromide, and the optical density was 570 nm. Basal proliferation was three times higher in depressed patients than in controls, whereas no response to mitogen was obtained, and 5-HT(1A) receptors significantly reacted to the agonist, with increases of about 31-54% at 10, 20 and 40 nM of the specific agonist, indicating initial activation probably in relation to autoimmunity and overreactivity of these receptors in depression. The antagonist reduced proliferation in mitogen-stimulated lymphocytes, 50% in controls and 70% in depressed patients, with a differential concentration dependency; probably, these receptors are more sensitive in depression due to increased 5-HT(1A) receptor transduction. The antagonist also reduced the stimulation produced by the 5-HT(1A) agonist. Imipramine caused biphasic effects according to concentrations, showing a possible dual role for serotonin, although all values were significantly higher in depressed subjects. The described alterations might be of relevance in the pathophysiology of depression.

Serotonin, serotonin 5-HT(1A) receptors and dopamine in blood peripheral lymphocytes of major depression patients

There are increasing evidences of cell markers present in the immune and the nervous systems. These include neurotransmitter receptors and transporters. Serotonin receptor subtypes are related to depression and also have been shown to be present in certain cells of the immune system. In the present report, we determined the presence of 5-HT(1A) receptors by the binding of the selective agonist 8-hydroxy-2-(di-n-propyl-amino)tetralin in lymphocytes of peripheral blood isolated by Ficoll/Hypaque gradients from controls and depressed patients. The capacity of these receptors was around 24 fmol/10(6) cells in both groups of subjects, without significant difference among them. The affinity was in the nM range and either differ between controls and patients. Serotonin, 5-hydroxyindoleacetic acid, dopamine and 3,4-dihydroxyphenylacetic acid were determined by HPLC with electrochemical detector. There were no significant differences between controls and major depression patients in the values obtained for rich and poor platelet plasma or in the isolated cells. However, there was a reduction in serotonin turnover rate indicated by an increase in the ratio serotonin/5-hydroxyindoleacetic acid, but not in that of dopamine, in lymphocytes of major depression patients. Thus, there is a serotonergic dysfunction in immune circulating cells of major depression patients, without changes in the number of 5-HT(1A) receptors, although the coupling of these receptors to transduction mechanisms could be affected and may be related to the alteration of 5-HT turnover rate.