Platelet Serotonin Uptake Research Articles

S1R agonist modulates rat platelet eicosanoid synthesis and aggregation

Sigma-1 receptor (S1R) is detected in different cell types and can regulate intracellular signaling pathways. S1R plays a role in the pathomechanism of diseases and the regulation of neurotransmitters. Fluvoxamine can bind to S1R and reduce the serotonin uptake of neurons and platelets. We therefore hypothesized that platelets express S1R, which can modify platelet function. The expression of the SIGMAR1 gene in rat platelets was examined with a reverse transcription polymerase chain reaction and a quantitative polymerase chain reaction. The receptor was also visualized by immunostaining and confocal laser scanning microscopy. The effect of S1R agonist PRE-084 on the eicosanoid synthesis of isolated rat platelets and ADP- and AA-induced platelet aggregation was examined. S1R was detected in rat platelets both at gene and protein levels. Pretreatment with PRE-084 of resting platelets induced elevation of eicosanoid synthesis. The rate of elevation in thromboxane B2 and prostaglandin D2 synthesis was similar, but the production of prostaglandin E2 was higher. The concentration-response curve showed a sigmoidal form. The most effective concentration of the agonist was 2 µM. PRE-084 increased the quantity of cyclooxygenase-1 as detected by ELISA. PRE-084 also elevated the ADP- and AA-induced platelet aggregation. S1R of platelets might regulate physiological or pathological functions.

Platelet FcγRIIA-induced serotonin release exacerbates the severity of transfusion-related acute lung injury in mice

AbstractTransfusion-related acute lung injury (TRALI) remains a major cause of transfusion-related fatalities. The mechanism of human antibody-mediated TRALI, especially the involvement of the Fcγ receptors, is not clearly established. Contrary to mice, human platelets are unique in their expression of the FcγRIIA/CD32A receptor, suggesting that our understanding of the pathogenesis of antibody-mediated TRALI is partial, as the current murine models incompletely recapitulate the human immunology. We evaluated the role of FcγRIIA/CD32A in TRALI using a humanized mouse model expressing the FcγRIIA/CD32A receptor. When challenged with a recombinant chimeric human immunoglobulin G1/mouse anti–major histocompatibility complex class I monoclonal antibody, these mice exhibited exacerbated alveolar edema and higher mortality compared with wild-type (WT) mice. Unlike in WT mice, monocytes/macrophages in CD32A+ mice were accessory for TRALI initiation, indicating the decisive contribution of another cell type. Platelet activation was dramatically increased in CD32A+ animals, resulting in their increased consumption and massive release of their granule contents. Platelet depletion prevented the exacerbation of TRALI in CD32A+ mice but did not affect TRALI in WT animals. By blocking platelet serotonin uptake with fluoxetine, we showed that the severity of TRALI in CD32A+ mice resulted from the serotonin released by the activated platelets. Furthermore, inhibition of 5-hydroxytryptamine 2A serotonin receptor with sarpogrelate, before or after the induction of TRALI, abolished the aggravation of lung edema in CD32A+ mice. Our findings show that platelet FcγRIIA/CD32A activation exacerbates antibody-mediated TRALI and provide a rationale for designing prophylactic and therapeutic strategies targeting the serotonin pathway to attenuate TRALI in patients.

The Impact of Serotonin Transporter Binding Affinity on the Risk of Bleeding Related to Antidepressants.

The alleged primary mechanism underlying bleeding events associated with antidepressants is inhibition of serotonin uptake in platelets resulting in reduced platelet aggregability and activity, and prolonged bleeding time. There is some evidence that a substance's degree of serotonin reuptake inhibition in terms of its binding affinity to the serotonin transporter (SERT) affects the magnitude of bleeding risk increase. To test this hypothesis, we performed data mining in the worldwide largest pharmacovigilance database (VigiBase) and conducted pharmacodynamically informed quantitative signal detection. Reporting odds ratios related to the standardized Medical Dictionary of Regulatory Activities query term "haemorrhages" and 24 antidepressants were calculated, and SERT binding affinities (pKi) were obtained and correlated (Pearson correlation). A strong and statistically significant correlation between substance-related reporting odds ratios and SERT binding affinities was found (r = 0.63; 95% confidence interval, 0.30-0.82; P = 0.00097). Our findings strengthen the hypothesis that inhibition of serotonin uptake contributes to the antidepressant-related bleeding risk and suggest an association between the degree of the SERT binding affinity and the bleeding risk. This supports the preferential use of antidepressants with low or no SERT binding affinity in depressed patients at risk of bleeding.

Development of a Nonradioactive Platelet Serotonin Uptake and Release Assay by Micro-Liquid Chromatography Tandem Mass Spectrometry Using Minimal Blood Volume.

Analysis of platelet functional responses to stimuli is presently quite limited with respect to measurement of dense granule secretion. We sought to develop a nonradioactive assay of stimulated serotonin release using liquid chromatography tandem mass spectrometry (LC-MS/MS). Citrated whole blood (200 μL) was incubated with deuterated serotonin (d45-HT). Following uptake by platelets, blood was diluted 10-fold and aliquots were incubated with platelet stimuli. Following stimulation, blood was further diluted, centrifuged, and supernatant was assayed for released d45-HT by micro-LC-MS/MS. This study demonstrated a broad linear range of 50 to 2,000 pg/mL d45-HT, with a total precision of less than 15.0% coefficient of variation at all quality control levels and a limit of quantitation of 50 pg/mL. Quantification of d45-HT by micro-LC-MS/MS assay offers a highly sensitive, nonradioactive methodology for quantitating platelet serotonin uptake and dense granule secretion, requiring only small volumes of patient blood.

SSRI‐associated gastrointestinal bleeding

Patients with chronic kidney disease (CKD) are often prescribed antidepressants, including selective serotonin reuptake inhibitors (SSRIs), for management of depression. The SSRIs have a very favorable safety profile overall but have been associated with bleeding risk as a result of their blocking serotonin uptake in platelets and the resultant inhibition of platelet aggregation.

Platelet Serotonin Signaling in Patients With Cardiovascular Disease and Comorbid Depression.

Depression in patients with cardiovascular disease is associated with increased risk of adverse clinical outcomes. Investigators have searched for potential biobehavioral explanations for this increased risk. Platelet activation and response to serotonin is an attractive potential mechanism. The aim of the study was to examine platelet serotonin signaling in a group of patients with coronary artery disease (CAD) and comorbid depression to define the relationship between platelet serotonin signaling and cardiovascular complications. A total of 300 patients with CAD were enrolled (145 with acute coronary syndrome and 155 with stable CAD). Depression was assessed using the Structured Clinical Interview for DSM-IV as well as Beck Depression Inventory II in a dichotomous and continuous manner. Platelet serotonin response was measured by serotonin augmented aggregation, direct platelet serotonin activation, platelet serotonin receptor density, and platelet serotonin uptake. Cardiovascular outcomes were assessed at 12-month follow-up. One third of enrolled participants had at least minimal depressive symptoms and 13.6% had major depressive disorder. Depressed cardiovascular patients had significantly higher incidence of major (odds ratio = 3.43, 95% confidence interval = 1.49-7.91, p = .004) and minor (odds ratio = 2.42, 95% confidence interval = 1.41-4.13, p = .001) adverse cardiac events. Platelet serotonin response was not significantly different in patients with depression. Participants with major depressive disorder had higher serotonin receptor density (997.5 ± 840.8 vs 619.3 ± 744.3 fmol/ug, p = .009) primarily found in ACS patients. Depressed patients with minor adverse cardiac events had increased platelet response to serotonin. Depressed cardiovascular patients had higher serotonin receptor density and significantly higher incidence of major and minor cardiac adverse events. Future studies with larger sample sizes including patients with more severe depression are needed to expand on the present hypothesis-generating findings.

The effect of prolonged simvastatin application on serotonin uptake, membrane microviscosity and behavioral changes in the animal model

Simvastatin and other statins (HMG-CoA (3-hydroxy-3-methylglutaryl coenzyme A) reductase inhibitors) are extensively used in clinical practices and are very effective in decreasing serum low-density lipoprotein cholesterol. However, their effect on cholesterol synthesis in central nervous system and its behavioral consequences have not been fully understood yet. We have studied selected biologic traits potentially affected by statin treatment — serotonin (5-HT) uptake in platelets, membrane microviscosity in erythrocytes, cholesterol level in the brain (amygdala; hippocampus and prefrontal cortex), as well as behavioral changes in an elevated plus maze and open field test in male Long-Evans rats, which were treated by simvastatin (30mg/kg per day) for 2 or 4weeks.We demonstrated: 1) a decrease in both serotonin transporter (SERT) activity and membrane microviscosity after treatment with simvastatin, 2) lower cholesterol content in all tested brain regions in animals from the simvastatin treated group, and 3) longer time spent in the open arms and a higher number of entrances to the closed arms in the elevated plus maze by animals from the simvastatin group compared to animals from the control group, but no differences in behavior in the open field test.Taken together, our results confirmed complex alterations, including behavioral changes, after the cholesterol lowering treatment. Furthermore, we discuss the possibility that the behavioral changes, traditionally interpreted as an anxiolytic effect, may be interpreted as increased impulsivity. We also confirmed that such behavioral changes may be attributed to changes in serotonergic neurotransmission.

Sleep bruxism frequency and platelet serotonin transporter activities in young adult subjects.

To evaluate correlations between serotonin transporter (SERT) uptake ability in human peripheral platelets and sleep bruxism (SB) frequency. Subjects were consecutively recruited from sixth-year students at Okayama University Dental School. Subjects were excluded if they (1) were receiving orthodontic treatment, (2) had a dermatological disease, (3) had taken an antidepressant within 6 months, or (4) had used an oral appliance within 6 months. SB frequency was determined as the summary score of three consecutive night assessments using a self-contained electromyography detector/analyzer in their home. Fasting peripheral venous blood samples were collected in the morning following the final SB assessment. SERT amount and platelet number were quantified via an ELISA assay and flow cytometry, respectively. Functional SERT characterization, 5-hydroxytryptamine (5-HT) uptake, maximum velocity (V max), and an affinity constant (K m ) were assessed with a [(3)H] 5-HT uptake assay. The correlations between these variables and SB level were evaluated. Among 50 eligible subjects (26 males, mean age 25.4 ± 2.41 years), 7 were excluded because of venipuncture failure, smoking, and alcohol intake during the experimental period. A small but significant negative correlation between SB level and [(3)H] 5-HT uptake was observed (Spearman's correlation R (2) = 0.063, p = 0.04). However, there were no significant correlations between SB level and total platelet amount, SERT, V max, and K m values (p = 0.08, 0.12, 0.71, and 0.68, respectively). Platelet serotonin uptake is significantly associated with SB frequency, yet only explains a small amount of SB variability.

Association between haemorrhages and treatment with selective and non-selective serotonergic antidepressants: Possible implications of quantitative signal detection

Inhibition of serotonin uptake in platelets seems to be the crucial mechanism underlying SSRI-associated haemorrhages. This effect is also present in antidepressants featuring non-selective serotonin reuptake inhibition (non-SSRI). Impact of selectivity of serotonin reuptake and/or affinity to the serotonin reuptake transporter on the bleeding risk have not yet been studied sufficiently. We retrieved country- and SSRI-/non-SSRI-specific data from the Uppsala Monitoring Centre and used a case/non-case approach to calculate substance-specific reporting odds ratios (ROR) to evaluate the statistical association of treatment with SSRI/non-SSRI and haemorrhages. Country-specific analysis revealed no clear trends towards an increased risk of bleeding related to particular agents of group SSRI/non-SSRI (sporadically ROR>1 for citalopram, duloxetine, escitalopram, fluvoxamine, paroxetine, sertraline, St. John's wort). There was a clear trend in the total dataset towards a “reduced protective effect” (suggested by ROR<1) on the development of haemorrhages with agents featuring comparatively high affinity to the 5-HTT and/or selective serotonin reuptake inhibition (as with escitalopram, citalopram, duloxetine or venlafaxine) in comparison to agents with lower affinity or non-selective serotonin reuptake inhibition (as with mirtazapine or doxepin). Comparison of group-specific aggregated data (SSRI vs. non-SSRI) revealed significant differences regarding the “protective effect” on the development of haemorrhages between groups SSRI vs. non-SSRI in favour of non-SSRI in nearly all countries as well as in the total dataset. Our findings provide preliminary evidence that agents with increased affinity to the 5-HTT and/or selective serotonin reuptake inhibition may be associated with an increased risk of bleeding.

Simvastatin Effects On Brain and Behavior in Animal Model

Introduction Simvastatin and other HMG-CoA (3-hydroxy-3-methylglutaryl coenzyme A) reductase inhibitors (statins) have been demonstrated to reduce mortality and the risk of major cardiovascular events. However, their neuropsychiatric adverse effects have not been sufficiently studied. The aim of our study is to elucidate effect of long term application of simvastatin on cholesterol level in the brain, serotonin uptake, microviscosity of membranes, and behavior in animal model. Methods We have studied cholesterol content in amygdala; hippocampus and prefrontal cortex, serotonin (5-HT) uptake and mitochondrial respiration in platelets, membrane microviscosity in erythrocytes, and behavioral changes in elevated plus maze in 6 male Long Evans rats in the control group and 6 rats in the simvastatin-treated group (30 mg/kg per day) after 2 and 4 weeks of treatment. Results Our results show: 1) lower cholesterol content in all tested brain regions in simvastatin treated group 2) decrease of SERT aktivity after 2 weeks of treatment compared to 4 weeks treatment 3) disturbed mitochondrial respiration and 4) higher number of entrances and the time spent in the closed arms in simvastatin group. Conclusion These results confirmed cholesterol-lowering effect of simvastatin in brain and harmful effect on cellular energy metabolism and further supported the hypothesis that lowering of plasma cholesterol after simvastatin treatments affects membrane fluidity and transmembrane transport of serotonin. Effects on behavior require additional testing to better explain observed changes in experimental tasks.

Risk of bleeding related to selective and non-selective serotonergic antidepressants: a case/non-case approach using data from two pharmacovigilance databases.

There is increasing evidence for an association between treatment with selective serotonin reuptake inhibitors (SSRI) and an increased risk of bleeding events. The most important underlying mechanism appears to be inhibition of serotonin uptake in platelets, an effect that is also present in antidepressants with non-selective serotonin-reuptake inhibition (NSRI). Accordingly, also NSRI may be associated with an increased risk of bleeding. However, there is little data in this regard. Based on data (spontaneous reports of adverse drug reactions) from 2 pharmacovigilance databases (WHO-database/Vigibase™; BfArM/AkdÄ-database in Germany) we used a case/non-case approach and calculated reporting odds ratios (ROR) as measures for disproportionality regarding the association of treatment with an agent of the group SSRI/NSRI and haemorrhages. Whereas both positive control agents (ASS and diclofenac) were statistically associated with haemorrhages in both databases (ASS: BfArM/AkdÄ, ROR 13.62 [95% CI 12.76-14.53]/WHO, ROR 12.96 [95% CI 12.75-13.16]; diclofenac: BfArM/AkdÄ, ROR 3.01 [95% CI 2.71-3.21]/WHO, ROR 2.11 [95% CI 2.05-2.16]), none of the agents of the group SSRI (ROR<1) was associated with haemorrhages. In group NSRI, only St. John's wort/hypericum was associated with haemorrhages (WHO-database, ROR 1.31 [95% CI 1.06-1.63]). Signal detectioning in 2 pharmacovigilance databases suggest that serotonin reuptake inhibition is not associated with an increased risk of bleeding. However, underreporting may have accounted for the evaluated absent associations, particularly concerning SSRI. Regarding the detected increased risk of bleeding associated with hypericum, pharmacokinetic drug-drug interactions may be relevant independent of serotonin reuptake inhibition.

Embryonic exposure to corticosterone modifies aggressive behavior through alterations of the hypothalamic pituitary adrenal axis and the serotonergic system in the chicken

Exposure to excess glucocorticoids (GCs) during embryonic development influences offspring phenotypes and behaviors and induces epigenetic modifications of the genes in the hypothalamic–pituitary–adrenal (HPA) axis and in the serotonergic system in mammals. Whether prenatal corticosterone (CORT) exposure causes similar effects in avian species is less clear. In this study, we injected low (0.2μg) and high (1μg) doses of CORT into developing embryos on day 11 of incubation (E11) and tested the changes in aggressive behavior and hypothalamic gene expression on posthatch chickens of different ages. In ovo administration of high dose CORT significantly suppressed the growth rate from 3weeks of age and increased the frequency of aggressive behaviors, and the dosage was associated with elevated plasma CORT concentrations and significantly downregulated hypothalamic expression of arginine vasotocin (AVT) and corticotropin-releasing hormone (CRH). The hypothalamic content of glucocorticoid receptor (GR) protein was significantly decreased in the high dose group (p<0.05), whereas no changes were observed for GR mRNA. High dose CORT exposure significantly increased platelet serotonin (5-HT) uptake, decreased whole blood 5-HT concentration (p<0.05), downregulated hypothalamic tryptophan hydroxylase 1 (TPH1) mRNA and upregulated 5-HT receptor 1A (5-HTR1A) and monoamine oxidase A (MAO-A) mRNA, but not monoamine oxidase B (MAO-B). High dose CORT also significantly increased DNA methylation of the hypothalamic GR and CRH gene promoters (p<0.05). Our findings suggest that embryonic exposure to CORT programs aggressive behavior in the chicken through alterations of the HPA axis and the serotonergic system, which may involve modifications in DNA methylation.

Relations between peripheral and brain serotonin measures and behavioural responses in a novelty test in pigs

Pigs differ in their behavioural responses towards environmental challenges. Individual variation in maladaptive responses such as tail biting, may partly originate from underlying biological characteristics related to (emotional) reactivity to challenges and serotonergic system functioning. Assessing relations between behavioural responses and brain and blood serotonin parameters may help in understanding susceptibility to the development of maladaptive responses. The objective of the current study was, therefore, to assess the relationship between the pigs' serotonergic parameters measured in both blood and brain, and the behaviour of pigs during a novelty test.Pigs (n=31) were subjected to a novelty test at 11weeks of age, consisting of 5-min novel environment exposure after which a novel object (a bucket) was introduced for 5min. Whole blood serotonin, platelet serotonin level, and platelet serotonin uptake were determined at 13weeks of age. Levels of serotonin, its metabolite and serotonin turnover were determined at 19weeks of age in the frontal cortex, hypothalamus and hippocampus.The behaviour of the pigs was different during exposure to a novel object compared to the novel environment only, with more fear-related behaviours exhibited during novel object exposure. Platelet serotonin level and brain serotonergic parameters in the hippocampus were interrelated. Notably, the time spent exploring the test arena was significantly correlated with both platelet serotonin level and right hippocampal serotonin activity (turnover and concentration). In conclusion, the existence of an underlying biological trait – possibly fearfulness – may be involved in the pig's behavioural responses toward environmental challenges, and this is also reflected in serotonergic parameters.

Platelet serotonin promotes the recruitment of neutrophils to sites of acute inflammation in mice

AbstractThe majority of peripheral serotonin is stored in platelets, which secrete it on activation. Serotonin releases Weibel-Palade bodies (WPBs) and we asked whether absence of platelet serotonin affects neutrophil recruitment in inflammatory responses. Tryptophan hydroxylase (Tph)1–deficient mice, lacking non-neuronal serotonin, showed mild leukocytosis compared with wild-type (WT), primarily driven by an elevated neutrophil count. Despite this, 50% fewer leukocytes rolled on unstimulated mesenteric venous endothelium of Tph1−/− mice. The velocity of rolling leukocytes was higher in Tph1−/− mice, indicating fewer selectin-mediated interactions with endothelium. Stimulation of endothelium with histamine, a secretagogue of WPBs, or injection of serotonin normalized the rolling in Tph1−/− mice. Diminished rolling in Tph1−/− mice resulted in reduced firm adhesion of leukocytes after lipopolysaccharide treatment. Blocking platelet serotonin uptake with fluoxetine in WT mice reduced serum serotonin by > 80% and similarly reduced leukocyte rolling and adhesion. Four hours after inflammatory stimulation, neutrophil extravasation into lung, peritoneum, and skin wounds was reduced in Tph1−/− mice, whereas in vitro neutrophil chemotaxis was independent of serotonin. Survival of lipopolysaccharide-induced endotoxic shock was improved in Tph1−/− mice. In conclusion, platelet serotonin promotes the recruitment of neutrophils in acute inflammation, supporting an important role for platelet serotonin in innate immunity.

Hyperreactive platelet phenotypes: Relationship to altered serotonin transporter number, transport kinetics and intrinsic response to adrenergic co-stimulation

The mechanism underlying a hyperreactive platelet phenotype remains unknown. Since serotonin has been shown to influence platelet biology and atherothrombosis, we sought to investigate the association of platelet serotonin transporter number, binding affinity, and uptake kinetics with platelet aggregation. A total of 542 healthy volunteers had light transmittance platelet aggregometry measured in response to varying concentrations of epinephrine, serotonin, epinephrine plus serotonin, ADP and collagen. Transporter-dependent serotonin uptake rate was determined (Vmax), as were serotonin transporter number (Bmax) and binding affinity (Kd) using 3H paroxetine binding in a homologous displacement assay, nonlinear regression and validated algorithms for kinetic modelling. Stimulation with submaximal (2μM) epinephrine concentration elicited a distinct, bimodal pattern of platelet aggregation in this population. In contrast, subjects exhibited minimal aggregation in response to serotonin alone. Co-stimulation with submaximal epinephrine and serotonin induced platelet aggregation to a level beyond that observed with either agonist alone and maintained a bimodal response distribution. Subjects with heightened (>60%) platelet aggregation to both epinephrine alone and epinephrine plus serotonin exhibited increased platelet serotonin uptake, and transporter number and affinity. In a population of healthy subjects, co-stimulation with submaximal concentrations of epinephrine and serotonin identifies a subset of individuals with a hyperreactive platelet aggregation profile that is associated with changes in platelet serotonin function.

Biological characterization of THRX‐956485, a peripherally‐selective serotonin transport reuptake inhibitor

Peripheral serotonin has been implicated in many therapeutic indications including thrombosis, pulmonary hypertension and osteoporosis. A peripheral selective serotonin reuptake inhibitor (SSRI) without CNS activity could provide a therapeutic index exceeding standard SSRIs. We describe a novel compound that selectively inhibits peripheral serotonin reuptake.THRX‐956485 is a potent (hSERT uptake IC50/binding Ki = 2.5nM/1.0nM) and selective SERT inhibitor in vitro and is &gt;2500‐ fold selective over other reuptake transporters and serotonin receptors. In rat PK studies (single 5 mg/kg PO), or 14‐day osmotic mini‐pump infusions (0.3, 0.7 and 1.6 mg/kg/day), THRX‐956485 showed pronounced peripheral selectivity compared to a CNS‐penetrant SSRI, fluoxetine. Based on unbound CNS vs. plasma exposures and measured SERT occupancy ex vivo, THRX‐ 956485 was &gt;20‐fold peripherally selective (CSF:unbound plasma concentration ratios varied from 1–5%). Additionally, THRX‐956485 demonstrated a dose‐dependent reduction in blood serotonin concentrations in rats. Following 14‐day infusions, blood serotonin concentrations decreased from 94 ng/mL (vehicle) to 43, 25, and 11 ng/mL at 0.3, 0.7 and 1.6 mg/kg/day, respectively. These findings are consistent with inhibition of platelet serotonin uptake, and suggest that THRX‐956485 is a peripherally selective SSRI.

Inhibition of human platelet 5-hydroxytryptamine uptake by beta-phenethylamine derivatives.

Abstract Forty-eight derivatives of ß-phenethylamine have been studied as inhibitors of 5-hydroxytryptamine uptake by human blood platelets in vitro. Inhibitory potency was found to be increased by para-substitution with electronegative groups, by α-methylation in the D-configuration and by addition of N-alkyl groups, and to be reduced by saturation of the ring, by ortho-methoxylation, meta- or ß-hydroxylation and by hydrazine formation. It is suggested that optimal affinity involves folding of the molecule to fit a cleft-like carrier site. The structural requirements for activity show features of similarity to those of tryptamine and tricyclic antidepressant derivatives and some resemblance with requirements for inhibition of the adrenergic uptake1 mechanism of the heart. No obvious correlation exists between the activity of these drugs as inhibitors of platelet 5-HT uptake and their ability to exert effects thought to involve central tryptaminergic mechanisms.

The inhibition of human platelet 5-hydroxytryptamine uptake by tricyclic antidepressive drugs. The relation between structure and potency.

Abstract Thirty-five compounds related to the antidepressive drug imipramine in chemical structure have been examined for their capacity to inhibit the uptake of 5-hydroxytryptamine by human platelets in vitro. Substitution by small-sized electropositive groups in positions 2 or 3 of a benzene ring gave compounds more active than the prototype, 3-chloroimipramine being five times as potent on this test. Alteration of the characteristic seven-membered ring of the antidepressive drugs reduced the activity while substitution in the basic side-chain destroyed it. The tertiary amines were more potent inhibitors than their demethylated derivatives. In this and other ways the active structure for the inhibition of 5-ht uptake by human blood platelets differs from that for the inhibition of noradrenaline uptake by the rat heart.

Candidate Molecule for Premature Ejaculation, DA-8031: In Vivo and In Vitro Characterization of DA-8031

To evaluate the efficacy of DA-8031 against premature ejaculation, we performed in vitro and in vivo pharmacologic studies. We used a monoamine transporter binding affinity assay, receptor binding affinity assay, monoamine reuptake inhibition assay, and serotonin uptake inhibition assay in platelets and chemically induced ejaculation models in rats. The present study reports on the pharmacologic profile of the putative antipremature ejaculation drug, DA-8031. DA-8031 exhibits high affinity and selectivity to the serotonin transporter (Ki value 1.94 nM for 5-hydroxytryptamine transporter, 22 020 nM for norepinephrine transporter, and 77 679 nM for dopamine transporter) and potency to inhibit serotonin reuptake into the rat brain synaptosome in vitro (half maximal inhibitory concentration 6.52 nM for 5-hydroxytryptamine, 30.2 μM for norepinephrine, and 136.9 μM for dopamine). In the platelet serotonin uptake study, DA-8031 exhibited significant inhibition at oral doses of 10 and 30 mg/kg in a dose-dependent manner. In the sexual response studies, after oral and intravenous administration of DA-8031, ejaculation was significantly inhibited in both para-chloroamphetamine- and meta-chlorophenylpiperazine-mediated ejaculation models in rats. The pharmacologic profiles observed in the present study suggest the potential for DA-8031 as a therapeutic agent useful in the treatment of premature ejaculation.

Serotonin level and serotonin uptake in human platelets: A variable interrelation under marked physiological influences

Background Although it is known that platelet serotonin level (PSL) depends directly on platelet serotonin uptake (PSU) through the plasma membrane, reports on their interrelation are inconsistent. The aim of this study was to systematically explore the relationship between these two platelet serotonin parameters in large human population. Methods PSL and full-kinetics of PSU were determined on 318 blood donors (276 males, 42 females; 20–67 years). Results The overall correlation coefficient between PSL and maximal velocity of PSU was highly significant but unexpectedly low ( r = 0.269). Further analyses revealed lack of correlation among females, and variable association among males, depending on the subject age and season of measurements. Highly significant correlations were observed in spring–winter, while association was absent during summer–autumn. Lowering of PSL–PSU correlation with increased age was also demonstrated, showing modest interrelation among younger men and no interrelation in older population. By multiple regression analyses season was identified as the only independent predictor of PSL–PSU relationship. Conclusions The results show prominent influence of biological (sex, age) and, especially, environmental (seasons) physiology on the intraindividual relationship between PSL and PSU. Although serotonin transporter activity plays an important role in determining PSL, the observed correlations indicate that other factors may predominate.