Fluoxetine treatment to rats modifies serotonin transporter and cAMP in lymphocytes, CD4+ and CD8+ subpopulations and interleukins 2 and 4.

Several lines of evidences indicate that antidepressants produce various immunomodulatory effects. Fluoxetine, an antidepressant and selective serotonin reuptake inhibitor, modulates immune cells in vitro. To explore the in vivo influence of fluoxetine on lymphocytes, male Sprague-Dawley rats were treated daily, 10 mg/kg, or with saline solution for 1, 2 and 3 weeks. The presence of serotonin transporter in CD3+, CD4+ and CD8+ subpopulations of T lymphocytes was determined by immunofluorescence. Serotonin transporter was also labeled with [(3)H]paroxetine, specific binding defined with imipramine. Plasma levels of pro-inflammatory interleukin 2 (IL-2), and anti-inflammatory interleukin 4 (IL-4), were measured by ELISA; and cAMP concentration by radioimmunoassay. Fluoxetine significantly increased the number of lymphocytes expressing serotonin transporter and elevated the binding of [(3)H]paroxetine. The percentage of CD4+ cells decreased, that of CD8+ increased, and CD3+ did not change. The ratio CD4+/CD8+ was significantly lowered. Fluoxetine administration elevated the levels of IL-4 at 1, 2 and 3 weeks; and of IL-2, at 2 and 3 weeks. IL-4/IL-2 ratio was significantly increased in fluoxetine group respecting the controls and was similar during the 3 weeks of treatment. Fluoxetine produced a significant decrease in cAMP concentrations in lymphocytes, probably by secondary activation of serotonin receptors. Treatment with fluoxetine modified immune parameters in plasma and lymphocytes of rats, which might be relevant for its systemic therapeutic action as an antidepressant.

Characterization of serotonin transporter in blood lymphocytes of rats. Modulation by in vivo administration of mitogens.

Serotonin transporter sites were characterized in blood lymphocytes of rats. Pharmacological characteristics of drug interactions were in concordance with recent studies in nervous and human immune cells. The potency order of inhibition of [(3)H]paroxetine binding was imipramine>citalopram>alaproclate>serotonin. Selective inhibitors of dopamine or noradrenaline transporters did not inhibit it. The specific binding of [(3)H]paroxetine was higher at intermediate than at low concentrations, and the plot of free vs. specific binding had a sigmoid shape. The affinity constant or K(d), 1.77 nM, was in close agreement with data obtained from kinetic studies (K(d)=1.33 nM), which evidences that the equilibrium was reached. In addition, serotonin transporter was evaluated by lipopolysaccharide or concanavalin A administration in vivo (0.1 mg/kg, i.p., 18 h). After the treatment with lipopolysaccharide, no changes were observed in the numbers of sites or B(max) or in the affinity, K(d). The treatment with concanavalin A showed a significant reduction in B(max) and reduction in K(d). Additionally, serotonin and 5-hydroxyindoleacetic acid levels were determined in plasma and lymphocytes by high-performance liquid chromatography. Treatment with lipopolysaccharide produced a significant increased of serotonin levels in lymphocytes without changes in 5-hydroxyindoleacetic acid level; in plasma, it produced an increase in serotonin and 5-hydroxyindolacetic acid levels. In addition, serotonin synthesis was evaluated by adding 300 microM of tryptophan in the medium, which significantly increased serotonin levels in control lymphocytes. Moreover, the concentrations of 5-hydroxyindoleacetic acid was enhanced significantly, both in plasma and lymphocytes in the presence of tryptophan after treatment with lipopolysaccharide. The administration of concanavalin A significantly decreased plasma levels of serotonin, as well as the concentrations of serotonin and 5-hydroxyindoleacetic acid in lymphocytes. These results demonstrate the presence of serotonin transporter in lymphocytes of rat blood, the capacity for serotonin synthesis in lymphocytes, and the modulation of these parameters by systemic administration of mitogens. The findings of this work contribute to understanding the immunological role of serotonin and the communication of immune and nervous systems.

8-[3H]-hydroxy-2-(di-n-propylamino)tetralin binding sites in blood lymphocytes of rats and the modulation by mitogens and immobilization.

Serotonin 5-HT(1A) receptors were characterized in rat resting lymphocytes obtained by cardiac puncture with the use of the ligand [3H]8-hydroxy-2-(di-n-propylamino)tetralin. Selectivity of the specific binding was demonstrated by inhibition experiments with various serotonergic and nonserotonergic drugs. The rank order of potency for inhibition was WAY-100478>pindobind>NAN-190>buspirone>imipramine>serotonin. While pimozide, desipramine, nomifensine, haloperidol and sulpiride did not inhibit the binding. Kinetic parameters calculated from saturation experiments indicated one site of interaction, with an equilibrium dissociation constant of 2.50 nM and maximum binding capacity of 487.21 nmol/10(6) cells. Complete dissociation was obtained with serotonin as the displacement agent, and equilibrium dissociation constant calculated by association and dissociation experiments was 2.03 nM. Thus, serotonin 5-HT(1A) receptors are present in resting lymphocytes. The in vivo administration of the mitogens lipopolysacharide (0.1 mg/kg, 18 h) or concanavalin A (0.2 mg/kg, 18 h) increased the number of sites. The elevation produced by the latter was of higher magnitude than that of lipopolysacharide, and two sites of the binding were determined by isotopic dilution. Immobilization stress (1 h daily for 7 days) also resulted in a significant increase of binding capacity, but was smaller than that produced by the mitogens. The affinity of binding was not affect by the treatments. The results indicate that serotonin 5-HT(1A) receptors are modulated by unspecific and specific immune system activation, as well as by a potent stress condition, which might result in relevant functional modifications in the response of rat lymphocytes.