Blood noradrenaline and 5-HT levels in depressed women during amitriptyline or lithium treatment

Noradrenaline levels and platelet and free serotonin concentrations were studied in depressed women in-patients (n=78) before and during amitriptyline (n=41) or lithium treatment (n=37). Pronounced monthly differences in platelet serotonin level have been shown in these subjects before treatment. In all clinical subgroups (neurotic, involutional, manic-depressive patients) a significant fall in platelet serotonin level was observed with amitriptyline medication while an increase was noted with lithium. No significant correlations between serotonin concentrations and clinical outcome were found. Amitriptyline treatment also produced a decrease in peripheral noradrenaline concentration in all subgroups, while an increase was observed with lithium. Some correlations between noradrenaline level and degree of depression were noted in patients treated with amitriptyline or lithium. A more extended analysis of blood amine levels could supply meaningful information on the peripheral action of antidepressive drugs on noradrenaline and serotonin concentrations in depression.     

FURTHER STUDIES ON THE EFFECTS OF ADRENAL STEROIDS IN THE ACTIVE TRANSPORT OF SEROTONIN INTO RAT PLATELETS

Male rats were treated with a fixed dose of aminoglutethimide (50 mg/kg s.c.) or with progressively increasing doses (50-100 mg/kg s.c.) for 3 days. Corticosterone levels were found to be decreased in the latter group. Platelet uptake of serotonin as well as the apparent Vmax were decreased, whereas the Km of uptake were increased when compared with that of the control group. Addition of ACTH (10 iu/dl) to control rat platelet and corticosterone (10-80 micrograms/dl) or triamcinolone (0.5-5.0 micrograms/dl) to adrenalectomized rat platelet suspension in vitro did not increase the serotonin uptake of the preparation. Administration of exogenous dexamethasone (0.05-0.2 mg/kg i.m.) or triamcinolone (0.05-5.0 mg/kg i.m.) to adrenalectomized rats, caused a dose related increase in active uptake of serotonin by the platelets. Deoxycorticosterone (0.1-1.0 mg/kg i.m.) did not have this effect. The time course of response to, and the maximum percentage increase in platelet serotonin uptake by, exogenous corticosteroids are related to their glucocorticoid potency. The possible role of glucocorticoids on platelet serotonin uptake process is discussed.     

Exogenous GTP increases cyclic GMP and inhibits thrombin-induced aggregation of washed human platelets: comparison with ATP, adenosine and guanosine.

The effects of exogenous guanosine 5'-triphosphate (GTP), guanosine, adenosine 5'-triphosphate (ATP) and adenosine on platelet aggregation, serotonin secretion and cyclic nucleotide accumulation were studied using thrombin-stimulated washed human platelets. GTP (10 microM-1 mM) dose-dependently inhibited thrombin-induced aggregation and serotonin secretion. The inhibition of aggregation was accompanied by an increase in platelet cyclic GMP. GTP did not affect cyclic AMP concentration. Adenosine (1 microM-1 mM) dose-dependently inhibited thrombin-induced aggregation and serotonin secretion, and increased cyclic AMP. ATP at high concentrations (100 microM-1 mM) inhibited aggregation and serotonin secretion, and 1 mM ATP increased cyclic AMP. Guanosine was relatively ineffective in preventing aggregation and serotonin secretion and did not affect cyclic GMP. The rank order of inhibition of thrombin-induced aggregation of washed human platelets was adenosine > GTP > ATP > guanosine. In conclusion, exogenous GTP inhibits thrombin-induced aggregation and serotonin secretion of washed human platelets by increasing cyclic GMP. The results raise the possibility of a cell membrane site of action for GTP in platelets which mediates the activation of soluble guanylate cyclase suggesting that GTP may have a local antithrombotic effect also in vivo.     

Exogenous GTP Increases Cyclic GMP and Inhibits Thrombin-Induced Aggregation of Washed Human Platelets: Comparison with ATP,Adenosine and Guanosine

Abstract: The effects of exogenous guanosine 5′-triphosphate (GTP), guanosine, adenosine 5′-triphosphate (ATP) and adenosine on platelet aggregation, serotonin secretion and cyclic nucleotide accumulation were studied using thrombin-stimulated washed human platelets. GTP (10 μM-1 mM) dose-dependently inhibited thrombin-induced aggregation and serotonin secretion. The inhibition of aggregation was accompanied by an increase in platelet cyclic GMP. GTP did not affect cyclic AMP concentration. Adenosine (1 μM-1 mM) dose-dependently inhibited thrombin-induced aggregation and serotonin secretion, and increased cyclic AMP. ATP at high concentrations (100 μM-1 mM) inhibited aggregation and serotonin secretion, and 1 mM ATP increased cyclic AMP. Guanosine was relatively ineffective in preventing aggregation and serotonin secretion and did not affect cyclic GMP. The rank order of inhibition of thrombin-induced aggregation of washed human platelets was adenosine > GTP > ATP > guanosine. In conclusion, exogenous GTP inhibits thrombin-induced aggregation and serotonin secretion of washed human platelets by increasing cyclic GMP. The results raise the possibility of a cell membrane site of action for GTP in platelets which mediates the activation of soluble guanylate cyclase suggesting that GTP may have a local antithrombotic effect also in vivo.     

Serotonin transport and storage in rabbit blood platelets—The effects of reserpine and imipramine

Serotonin transport and storage in suspensions of washed rabbit platelets were investigated by following the exchange of platelet-bound [³H]serotonin and [¹⁴C]serotonin added to the suspending medium. Assuming a three-compartment system (suspending medium, platelet cytoplasm and platelet storage organelles), the transfer rates between the different compartments were calculated from the exchange data by statistical analysis. Reserpine reduced the storage organelle serotonin content by inhibiting the transfer of serotonin from the cytoplasm into the amine storage organelles. It also reduced the fraction of serotonin in the cytoplasm transferred per unit of time into the suspending medium. Imipramine (20 μM) inhibited the uptake of serotonin across the platelet plasma membrane into the cytoplasm and reduced the fraction of cytoplasmic serotonin transferred per unit of time into the suspending medium. At this concentration it had no effect on serotonin transport across the amine storage organelle membrane in either direction. The method used allows the serotonin transfer rates across the platelet plasma membrane to be distinguished from those across the amine storage organelle membrane in intact cells, and permits these transfer rates to be estimated simultaneously. The method may be used for determining the effects of drugs that interfere with transport and storage of biogenic amines and in defining the defects in diseases with abnormal transport or storage of biogenic amines.     

Active translocation of platelets into sinusoidal and Disse spaces in the liver in response to lipopolysaccharides,interleukin-1 and tumor necrosis factor

1. Injection of lipopolysaccharides (LPS) or endotoxin into mice and rats induces a prolonged increase in serotonin (5-hydroxytryptamine: 5HT), predominantly in the liver.2. The 5HT increase reflects the accumulation of platelets in the sinusoidal and perisinusoidal Disse spaces (spaces between endothelial cells and hepatocytes) in the liver.3. Most of the platelets which accumulated in these spaces still retained their intact structure and a large amount of 5HT.4. Interleukin-1 and/or tumor necrosis factor also induce the platelet response.5. Kupffer's cells play a key role in this platelet response.6. Anti-platelet drugs currently used, except for anti-inflammatory steroids, were ineffective in preventing the platelet response.7. This platelet response is different from the well known platelet aggregation.8. The possible involvement of this platelet response in insulin-independent hypoglycaemia, disseminated intravascular coagulation, septic shock, hepatitis, Shwartzman type reactions or self-defense mechanisms is discussed.     

The potentiation of adrenaline-induced in vitro platelet aggregation by ADP, collagen and serotonin and its inhibition by naftopidil and doxazosin in normal human subjects.

1. Aggregation in platelet-rich plasma from normotensive men was induced by adrenaline (0.25-16 microM), ADP (0.25-16 microM), collagen (0.25-8 micrograms ml-1) or serotonin (10 microM) alone, or by previously sub-threshold concentrations of adrenaline (0.03-1 microM) in combination with sub-threshold concentrations of serotonin (2.5 microM), ADP (0.5 microM) or collagen (0.125 micrograms ml-1). The effects of the alpha 1-adrenoceptor blockers naftopidil and doxazosin on platelet aggregation were investigated. 2. The dose-response curves for collagen and ADP were unaffected by either drug. However, naftopidil (40 microM) inhibited serotonin-induced platelet aggregation (23.9%, 95% confidence interval (CI) 10.7 to 37.1%; P < 0.01) and caused a slight shift to the right of the adrenaline dose-response curve with a mean increase in the EC50 value of 0.5 microM (95% CI 0.07 to 0.93 microM; P < 0.05). Doxazosin had no effect on serotonin or adrenaline-induced aggregation. 3. A marked potentiation of the aggregation induced by subthreshold concentrations of adrenaline resulted from the prior addition of low concentrations of ADP, collagen or serotonin. 4. These potentiated responses were inhibited in a dose-dependent manner by naftopidil and to a lesser extent doxazosin. The maximum inhibitions (%) produced by naftopidil (40 microM) on the responses of adrenaline potentiated by ADP were 58.3% (95% CI 36.8 to 79.8%; P < 0.001), serotonin 58.9% (95% CI 40.0 to 77.8%; P < 0.001), and collagen 70.9% (95% CI 52.5 to 89.3%; P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Early effects of paroxetine on serotonin storage, plasma levels, and urinary excretion: a randomized, double-blind, placebo-controlled trial

Selective serotonin reuptake inhibitors efficiently decrease intraplatelet concentrations of the platelet activator and potent vasoconstrictor serotonin within 2 weeks of treatment. As elevated plasma serotonin levels potentially lead to vascular adverse events, like vasoconstriction, it is of interest to examine whether selective serotonin reuptake inhibitors may acutely increase plasma serotonin levels. Twenty healthy male smoking volunteers received the selective serotonin reuptake inhibitors paroxetine 20 mg/d for 18 days in a double-blind, placebo-controlled, block-randomized, 2-way crossover study to characterize the acute effect of paroxetine on serotonin plasma levels and urinary excretion. Paroxetine decreased intraplatelet serotonin concentrations by a median of 16% after 24 hours and by -93% after 18 days (P < 0.001). After 24 hours, there was a slight transient rise in plasma serotonin concentration by 36%-which ranged within physiologic concentrations of the control period. Concomitantly, urinary serotonin excretion increased by 89% after 24 hours.In conclusion, initiation of paroxetine treatment does not increase plasma concentrations of the potent vasoconstrictor serotonin to a pathologically relevant extent.     

Platelet 5-HT2A receptor subresponsivity and lethality of attempted suicide in depressed in-patients

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.     

Serotonin in panic disorder: platelet uptake and concentration

Platelet serotonin uptake and platelet serotonin concentrations were measured in 17 patients (5 males, 12 females) with panic attacks and 15 controls (8 males, 7 females). Higher Vmax values were found in the patient group compared with controls (65 +/- 7 vs. 47 +/- 3 pmol/10(8) platelets/min; p less than 0.05) while the affinity constant Km was not significantly different (0.6 +/- 0.1 vs. 0.5 +/- 0.1 microM). Platelet serotonin concentrations were not significantly different between the two groups (38 +/- 4 vs. 41 +/- 4 ng/10(8) platelets). These results confirm our earlier finding of increased serotonin uptake in patients with panic attacks and suggest that platelet serotonin levels are normal.     

Involvement of catecholamines and serotonin in human hypertension

Lumber cerebrospinal fluid (CSF) concentrations of metabolites of noradrenaline, adrenaline and serotonin were estimated in patients of sustained hypertension (n = 20), and healthy controls (n = 15). Platelet uptake of serotonin and its basal contents were also estimated in the same individuals. CSF 5-hydroxy indole acetic acid level (5-HIAA) (major metabolite of serotonin) was significantly higher in hypertensives than controls (p less than .01). CSF 3-methoxy, 5-hydroxy phenyl glycol (MHPG) (major metabolite of adrenaline and noradrenaline) level was also raised significantly in cases of hypertension (p less than .01). However, platelet uptake of serotonin as well as its basal contents in hypertension were significantly lower than controls (p less than .01). It can thus be postulated that there exists an increased central serotonergic and catecholaminergic activity in hypertension. Furthermore, alterations observed in platelet serotonin uptake and its basal content suggest the involvement of platelet serotonergic system in hypertension.     

Platelet serotonin uptake in men with family histories of alcoholism

Platelet serotonin uptake kinetics were examined in a carefully screened group of 28 male subjects, half of whom had an alcoholic father. Paired subjects were matched for a variety of characteristics, including age, race, sex, substance use history, height/weight ratio, season, and time of day for platelet serotonin uptake assays. The family history positive group had a significantly (p = 0.01) higher mean Vmax for platelet serotonin uptake (64.1 +/- 19, SD) compared to the control group without family histories of first-degree relatives with alcoholism (53.8 +/- 19). No significant differences in the affinity constant (Km) or in the Hill constant were found between groups. The results are consistent with the possibility that a higher Vmax of platelet serotonin uptake indicates a biologic factor associated with alcoholism risk.     

Plasma components are required for platelet activation by the toxin of Loxosceles reclusa

We have used a partially purified toxin from the venom of the brown recluse spider, Loxosceles reclusa, to study its effects on human platelets isolated from plasma proteins. This toxin, which produced skin necrosis in rabbits, contained sphingomyelinase D activity. The toxin induced platelet aggregation and secretion of [3H]serotonin in human plasma but not in buffer or in human neonate plasma. Ca2+ was required for the interaction of toxin, platelets, and plasma factor(s). The addition of C-reactive protein restored aggregation and serotonin release of platelets incubated in human neonate plasma. The ADP-degrading enzyme, apyrase, and the non-steroidal, anti-inflammatory drug, indomethacin, inhibited platelet aggregation, suggesting that ADP secreted from platelet storage granules and indomethacin-sensitive pathway(s) are involve in the toxin-induced human platelet activation (aggregation and serotonin release). Generation of platelet activating factor (PAF) from the platelet by brown recluse toxin is not likely since the PAF receptor antagonist, BN 52021, did not inhibit platelet aggregation induced by the brown recluse toxin.     

Possible Regulatory Role of Histamine in Human Platelet Function Examined by Thrombin-induced Serotonin Release

Abstract: The influence of histamine on human platelet function was studied by thrombin-induced serotonin release. The thrombin-induced ³H-serotonin release was confirmed to be a rapid process which does not require external calcium. Histamine was found to reduce the release of serotonin and the inhibition was abolished when H₁-plus H₂-antagonists were added together with histamine. H₁- and H₂-receptor stimulation was examined in two ways, by a combination of histamine with cimetidine or diphenhydramine and by the selective agonists 2-(2-pyridyl)-ethylamine and impromidine. In both instances H₁- and H₂-stimulation was found to reduce the platelet serotonin release. These results suggest a regulatory role of histamine in the platelet function by stimulation of platelet H₁- and H₂-receptors.     

Seasonal variations in the binding of [3H]paroxetine to the platelet serotonin transporter sites in African-American cocaine-dependent patients and healthy volunteers

Although seasonal fluctuations in several indices of serotonin function have been described, little is known about seasonality and serotonergic activity in substance abusers. We investigated whether there were seasonal differences in platelet serotonin transporter sites among cocaine dependent patients and controls. Platelet [(3)H]paroxetine binding, a measure of serotonin transporter sites, was assayed in 141 African-American cocaine-dependent subjects and in 60 race matched healthy volunteers who served as the control group. B(max) (density of serotonin transporter) and K(d) (affinity constant) values of [(3)H]paroxetine binding were compared during spring, summer, fall and winter. Consistent with our previous findings B(max) values were significantly lower in cocaine patients (639 +/- 234) than in controls (906 +/- 225) (t = 7.12, p < 0.001). Moreover, B(max) values showed a significant seasonal variation in controls with the highest values in summer and spring compared with fall and winter (F = 4.47, p < 0.01). However, there were no significant seasonal differences in B(max) values in cocaine patients. K(d) values did not show any seasonal changes in either group. There were no effects of age or gender on seasonal variations in B(max). The study demonstrates a seasonal effect on platelet serotonin uptake in healthy African-American volunteers. The lack of seasonal differences in transporter availability in cocaine patients indicates that the normal seasonal rhythm of serotonergic activity may be disturbed in cocaine abusers. Biological studies that employ platelet serotonin transporter sites as a marker of serotonin function should consider seasonal variations in these markers as a potential source of variance.     

痴呆病人血小板5-羟色胺浓度初探

目的：探讨痴呆病人5-羟色羟(5-HT,血清素)水平与病情严重程度、精神行为症状之间的关系。方法：将痴呆病人分为阿尔采末病(AD)组、血管性痴呆(VaD)组,对照组为无明显认知损害的精神分裂症老年病人,采集病人外周血4mL测定血小板5-HT浓度。同时采用简易智力状态检查(MMSE)、神经精神科问卷(NPI)和临床大体印象评定量表(CGI)等对病人进行评估。结果：共入组AD病人22例、VaD病人10例及精神分裂症病人10例；3组病人血小板5-HT浓度比较无显著差异(P＞0．05)；血小板5-HT浓度与年龄、性别、用药情况、MMSE和NPI评分不相关(P＞0．05)。结论：总体5-HT水平与认知损害不直接相关,不能作为痴呆病人的精神行为与疾病严重程度的生物学标志。     

蛋白酪氨酸磷酸化在血小板激活因子诱导血小板信号传导中的调节 …

AIM: To study the role of protein tyrosine phosphorylation (PTP) in platelet activating factor (PAF)-induced platelet signal transduction cascade. METHODS: Washed rabbit platelets were used to test the inhibitory effect of genistein (Gen) on platelet aggregation and serotonin secretion. Intracellular Ca2+ ([Ca2+]i) and pH (pHi) were measured by a dual wavelength fluorophotometer with Fura 2-AM and BCECF-AM. PTP was determined with a specific anti-phosphotyrosine monoclonal antibody by Western blotting. RESULTS: Pretreatment with Gen (100 and 200 mumol.L-1) inhibited PAF (20 nmol.L-1)-stimulated platelet serotonin release by 23.7% +/- 2.0% and 41% +/- 8%, respectively. Similar inhibitory effects of Gen were observed on PAF-evoked increase of [Ca2+]i and intracellular alkalization. PAF also elicited a pronounced increase in PTP of several bands with M(r) 70,000, 60,000, 50,000, 42,000/40,000, and 34,000, which were suppressed markedly by Gen 200 and 400 mumol.L-1. Pretreatment with staurosporine (Sta) 20 nmol.L-1, BAPTA 200 mumol.L-1, and egtazic acid 2 mmol.L-1 to inhibit PKC activation, [Ca2+]i elevation, and Ca2+ influx respectively, also showed an inhibitory effects on the formation of PTP. CONCLUSION: PTP is involved in multiple signal transduction pathways induced by PAF, on which PKC activation and calcium mobilization play a regulatory role.     

Effects of clofibrate and 6-substituted chroman analogs on human platelet function:: Mechanism of inhibitory action

The effects of cloflbrate (CPIB) and two related cyclic analogs, 6-chlorochroman-2-carboxylic acid (CCCA) and 6-phenylchroman-2-carboxylic acid (PCCA), on human platelet function were evaluated. CPIB, CCCA and PCCA all inhibited platelet activation, i.e. aggregation and secretion of [¹⁴C]serotonin induced by ADP, epinephrine, collagen and thrombin, in a concentration-dependent manner. PCCA was at least fifty-two times more effective as an inhibitor of ADP-, epinephrine- and collagen-induced platelet activation and only 2-fold more effective as an inhibitor of thrombin-induced platelet activation when compared with CPIB or CCCA. Only PCCA inhibited platelet aggregation and [¹⁴C]serotonin secretion induced by arachidonic acid (AA) in a concentration-dependent manner. CPIB and CCCA did not inhibit AA-induced platelet activation. In fact, both of these agents had a potentiating effect on the onset of platelet aggregation by AA. All three compounds inhibited thrombin-induced release of [³H]arachidonic acid ([³H]AA) from platelet phospholipids and thrombin-mediated malondialdehyde (MDA) production. Only PCCA, however, inhibited AA-induced MDA production. These results indicate that CPIB, CCCA and PCCA all inhibit platelet activation by inhibiting prostaglandin biosynthesis. PCCA blocked AA-induced platelet activation, and this additional inhibitory action of PCCA appears to be responsible for its comparatively higher inhibitory potency. A comparison of the structure-activity relationship of the inhibitors indicated that replacement of the chloro group by a phenyl group produced a compound (PCCA) that was a potent inhibitor of prostaglandin biosynthesis and was thereby a more effective antiaggregatory agent than either CPIB or CCCA.     

Serotonergic responsivity in eating disorders.

Evidence suggests that serotonin may play a role in the pathogenesis of eating disorders. In this ongoing study, serotonin-mediated physiological responses and whole-blood serotonin content are measured in young women with an eating disorder during the active phase of the illness and at the conclusion of inpatient treatment. The responsivity of central nervous system (CNS) serotonergic pathways is assessed by neuroendocrine challenge with a 60-mg oral dose of dl-fenfluramine, an indirect serotonin agonist, whereas the responsivity of the platelet serotonin2 (5-HT2) receptor complex is evaluated by measurement of the magnitude of serotonin-amplified platelet aggregation. Compared with normal controls, eating-disorder patients have exhibited a trend toward reduced prolactin responses to fenfluramine challenge at both the initial and followup assessments. Patients also have exhibited a substantially wider range of serotonin-amplified platelet aggregation responses than have controls; normal-weight bulimic patients have had significantly greater responses than both anorexic restrictors and normal subjects. These preliminary results suggest potential alterations in serotonin-mediated responses in eating-disorder patients that may vary with the diagnostic subgroup.     

Circadian rhythm of serotonin transport in human platelets

The circadian rhythm of serotonin active transport in human platelets was investigated in ten healthy men, aged 27–35 years. Blood was collected at 08.00, 14.00, 20.00, 02.00 and 08.00 hours the next morning. Simultaneous evaluation of the mean platelet volume, platelet distribution width, platelet distribution skewness and platelet number in whole blood was performed. K _m and V _max for serotonin transport varied considerably among individuals over 24 h. However, the mean values and distribution of these kinetic parameters were reduced at 02.00 hours. All platelet size or number parameters were stable and normal over 24 h; therefore, the reduction in mean K _m and V _max values at 02.00 h is not related to morphological platelet differences but either to platelet intrinsic factors or plasmatic variables. Knowledge of the affinity and capacity of serotonin transport throughout the diurnal cycle is important for future comparisons with depressed patients as well as other hormonal rhythms in patients and healthy humans.