Platelets inhibit the induction of nitric oxide synthesis by interleukin-1 beta in vascular smooth muscle cells

We have investigated the role of platelets in regulating the hemostatic and vasomotor properties of vascular smooth muscle. Experiments were performed to examine the effect of the releasate from activated platelets on the production of nitric oxide from interleukin-1 beta (IL-1 beta)-treated cultured rat aortic smooth muscle cells. Treatment of vascular smooth muscle cells with IL-1 beta resulted in significant accumulation of nitrite in the culture media and in marked elevation of intracellular cyclic guanosine monophosphate (GMP) levels. The releasate from collagen-aggregated platelets blocked the IL-1 beta-mediated production of nitrite and the accumulation of cyclic GMP in smooth muscle cells in a platelet number-dependent manner. In functional assays, the perfusates from columns containing IL-1 beta-treated smooth muscle cells relaxed detector blood vessels without endothelium and the addition of IL-1 beta-treated smooth muscle cells to suspensions of platelets inhibited their thrombin-induced aggregation. The simultaneous treatment of smooth muscle cells with IL-1 beta and the platelet releasate abolished both the vasorelaxing activities of the perfusates and the inhibition of platelet aggregation. Platelet releasates treated with a neutralizing antibody to platelet-derived growth factor (PDGF) failed to block IL-1 beta-induced nitric oxide production by the smooth muscle cells, as measured by both biochemical and functional assays. The platelet releasate from a patient with gray platelet syndrome likewise failed to block IL-1 beta-induced nitrite release by smooth muscle cells. These results demonstrate that platelets downregulate the production of nitric oxide by IL-1 beta-treated vascular smooth muscle cells through the release of PDGF. This effect may represent a novel mechanism by which platelets regulate vasomotor tone and thrombus formation at sites of vascular injury.     

The effect of tricyclic antidepressants and neuroleptics on the peripheral and central action of norepinephrine in reserpine-treated mice

The effect of exogenous norepinephrine on the ptosis induced by reserpine and its modification by tricyclic antidepressants and neuroleptics were studied in reserpine-pretreated mice. S.c injection of norepinephrine (0.3-5 mg/kg) reversed dose-dependently the ptosis induced by reserpine. The maximal effect was obtained 15 min after norepinephrine administration. Tricyclic antidepressants (2.5 and 5 mg/kg i.p.) potentiated the effect of norepinephrine. In contrast neuroleptics (1 and 5 mg/kg i.p.) antagonized it. Intracerebral injection of norepinephrine (5-20 mug) also reversed dose-dependently the ptosis induced by reserpine, and the maximal effect was obtained within 5 min. Tricyclic antidepressants potentiated the effect of norepinephrine, but neuroleptics antagonized it. Among tricyclic antidepressants, the potentiating action of secondary amines was stronger than that of tertiary amines. Chlorpromazine blocked the action of norepinephrine more strongly than did the same dose of haloperidol.     

The difference in the inhibitory mechanisms of papaverine on vascular and intestinal smooth muscles

Papaverine (0.3-100 microM) more potently inhibited phenylephrine (1 microM)-induced contraction than 65 mM K+-induced contraction of the aorta, while it equally inhibited contractions induced by 65 mM K+ and carbachol (1 microM) in ileal smooth muscle. In phenylephrine-treated aorta, papaverine (1-10 microM) increased the cAMP and cGMP content. However, in carbachol-treated ileum, 30 microM papaverine partially increased the cAMP content while it maximally relaxed the preparation. In fura2-loaded aorta, papaverine (0.3-10 microM) inhibited both the contraction and the increase in intracellular Ca2+ level ([Ca2+]i) induced by phenylephrine in parallel. However, papaverine inhibited carbachol-induced contraction with only a small decrease in [Ca2+]i. Papaverine (1-30 microM) inhibited the carbachol-induced increase in oxidized flavoproteins, an indicator of increased mitochondrial oxidative phosphorylation, in ileal smooth muscle whereas it did not change the phenylephrine-induced increase in the aorta. These results suggest that papaverine inhibits smooth muscle contraction mainly by the accumulation of cAMP and/or cGMP due to the inhibition of phosphodiesterase in the aorta whereas, in ileal smooth muscle, papaverine inhibits smooth muscle contraction mainly by the inhibition of mitochondrial respiration.     

Effects of viloxazine, an antidepressant agent, on biogenic amine uptake mechanisms and related activities

The effects of viloxazine, a clinically effective antidepressant, on noradrenaline (NA) and 5-hydroxytryptamine (5-HT) uptake and various related pharmacological activities were determined and compared to those of the tricyclic antidepressants desimipramine, imipramine, and amitriptyline. Viloxazine inhibitied [3H]NA uptake in the mouse and rat heart, being maximally about one half as potent as imipramine with a similar onset, but shorter duration of action than imipramine. The drug did not inhibit [3H]NA uptake in rat medulla or hypothalamus in contrast to desimipramine and imipramine, but it did alter [3H]NA metabolites in a similar manner. Viloxazine, like desimipramine, was a weak blocker of mouse brain 5-HT uptake, but differed from desimipramine as it poteniated 5-HT-mediated functions in the mouse and rat, as did imipramine and amitriptyline, the latter drugs being relatively potent blockers of 5-HT uptake. Viloxazine potentiated the L-DOPA behavioural syndrome in the mouse, antagonized reserpine-induced ptosis and hypothermia in the mouse, and inhibited gastric acid secretion in the rat, but was less potent than the tricyclic antidepressants. No appreciable in vivo inhibition of monoamine oxidase (EC 1.4.3.4.) activity in the mouse was exhibited. Like imipramine, the drug potentiated the ocular effects of L-adrenaline in the rabbit. It was similar to imipramine in potency in potentiating the apomorphine-induced gnawing in the mouse. The drug antagonized oxotremorine-induced hypothermia in the mouse but differed from the tricyclic antidepressants in not exhibiting the anticholinergic effects of blocking the tremors, salivation and lacrimation. Thus, viloxazine exhibits activities related to the biogenic amines both similar to and different from the tricyclics desimipramine, imipramine, and amitriptyline. These actions appear to be of relevance with respect to the antidepressant action of this drug.     

Nitric oxide and regulation of vascular tone: pharmacological and physiological considerations

The endothelial cells of the vascular system are responsible for many biological activities that maintain vascular homeostasis. Responding to a variety of chemical and physical stimuli, the endothelium elaborates a host of vasoactive agents. One of these agents, endothelium-derived relaxing factor, now accepted as nitric oxide, influences both cellular constituents of the blood and vascular smooth muscle. A principal intracellular target for nitric oxide is guanylate cyclase, which, when activated, increases the intracellular concentration of cyclic guanosine monophosphate, which in turn activates protein kinase G. Acting by this pathway, nitric oxide induces relaxation of vascular smooth muscle and inhibits platelet activation and aggregation. Derangements in endothelial production of nitric oxide are implicated as both cause and consequence of vascular diseases, including hypertension, atherosclerosis, and coronary artery disease.     

Comparison of the effects of various spasmolytic drugs on isolated human and porcine detrusor smooth muscle

The spasmolytic activity of flavoxate (CAS 15301-69-6), anticholinergic agents oxybutynin (CAS 5633-20-5), and trospium chloride (CAS 10405-02-4), drugs commonly utilized in the therapy of hyperactive bladder, and phosphodiesterase (PDE) inhibitors papaverine (CAS 58-74-2) and vinpocetine (CAS 42971-09-5) on muscarinic contractions of detrusor smooth muscle strips isolated from human and porcine urinary bladder was studied in vitro using the organ bath technique. Trospium chloride was most effective in relaxing contractions elicited by muscarinic stimulation, while flavoxate was significantly less effective than all other drugs tested. The relaxing potency of oxybutynin was greater than those of PDE-inhibitors papaverine and vinpocetine but 3,000 fold less significant than those of trospium chloride. The effects of the individual drugs on muscarinic tension of both human and porcine detrusor muscle strips were nearly equal. The present results suggest that the pig might be an appropriate animal model for the study of effects of spasmolytic substances on the contractility of urinary bladder smooth muscle in vitro.     

Red-wine polyphenols and inhibition of platelet aggregation: possible mechanisms, and potential use in health promotion and disease prevention

Correction of uremic platelet serotonin (5-HT) storage pool deficiency is one of the very early hemostatic effects of erythropoietin (Epo) therapy. In this work, platelet 5-HT with relation to primary hemostasis was studied in 15 hemodialysis patients treated with Epo for 8 months. Moreover, effects of ketanserin, a blocker of platelet and vascular smooth muscle cell 5-HT2A receptors, in these patients were followed. The parameters studied were compared with relevant values in healthy controls and in hemodialysis patients not treated with Epo, and remeasured in the long-term Epo patients after a 14-day oral ketanserin trial. Platelet 5-HT content in the eighth month of Epo therapy was not different from the one in untreated patients. Ristocetin- and collagen-induced platelet aggregation were enhanced in comparison with both control groups, as opposed to unaltered response to ADP and arachidonic acid. Fibrinogen concentration was lower than in the untreated group. An inverse correlation between ADP-induced platelet aggregation and the skin bleeding time (r=-0.536, p<0.05) and a positive one between the former and platelet 5-HT (r=0.644, p<0.01) were found. Platelet count correlated positively with both platelet 5-HT (r=0.823, p<0.0002) and ADP-induced platelet aggregation (r=0.596, p<0.02). Ketanserin produced a decrease in ristocetin-induced platelet aggregation, fibrinogen, and prolongation of the bleeding time. The first two of the changes correlated positively with their pre-ketanserin values (r=0.923, p<0.00001 and r=0.839, p< 0.0001, respectively). Post-ketanserin, positive correlations between depressed ristocetin- and arachidonic acid-induced platelet aggregation (r=0.760, p<0.005), and between collagen- and corresponding values of arachidonic acid- (r=0.622, p<0.02), ADP-induced platelet aggregation (r=0.396, p<0.01), and platelet 5-HT (r=0.654, p<0.05) were found. Efficient hemostasis in hemodialysis patients on protracted Epo therapy is, in part, dependent on enhanced platelet aggregability. Correction of platelet 5-HT storage pool deficiency is not evident in this stage but 5-HT still influences complex mechanisms of primary hemostasis. Ketanserin is of anticoagulant value in these patients but its effects must be weighted against possible exacerbation of the anemia.     

Effects of mianserin, a new antidepressant, on the in vitro and in vivo uptake of monoamines

1 The effects of mianserin and of selected tricyclic antidepressants were compared in a number of monoamine uptake models. 2 The ability of mianserin to block the noradrenergic neurone membrane amine pump of rabbit brain stem slices was comparable to that of imipramine and amitriptyline and less than that of desipramine and nortriptyline. Both mianserin and desipramine were competitive inhibitors of noradrenaline uptake in vitro. The effect of mianserin on noradrenaline uptake in vivo was studied both peripherally and centrally. The ability of 6-hydroxydopamine to lower rat heart noradrenaline levels was found to be very sensitive to inhibition by tricyclic antidepressants. Mianserin was active in this model. However, its ability to block the 6-hydroxydopamine-induced fall in rat heart noradrenaline concentration was appreciably less than that of the tricyclics studied. 3 Mianserin, like tricyclic antidepressants, was essentially devoid of effect on dopamine uptake both in vitro and in vivo. 4 The ability of mianserin to inhibit [3H]-5-hydroxytryptamine uptake by rat hypothalamic synaptosomes was appreciably less than that of the tricyclic antidepressants studied. Mianserin was essentially devoid of effect on rat brain 5-hydroxytryptamine uptake in vivo. 5 It is concluded that in certain situations large doses of mianserin may block noradrenaline uptake in vivo. However, in no way does mianserin rival tricyclic antidepressants in blocking monoamine uptake in vivo. The clinical efficacy of mianserin cannot be attributed to inhibition of monoamine uptake.     

Specific interaction of HLA antibodies (eluates) with washed platelets

The mechanism of complement-independent action of HLA-A2 antibodies (eluates) on washed platelets was investigated. HLA-specific alteration was confirmed by serological (platelet micro-complement fixation), morphological (platelet spreading) and functional parameters (platelet aggregation, inhibition of collagen-induced platelet aggregation, [14C]serotonin release). In the presence of fibrinogen and calcium ions, HLA antibodies induced instantaneous platelet aggregation and release. Although no morphological (spreading) and functional changes (collagen-induded aggregation) were seen, these platelets did not aggregate or release when fibrinogen was subsequently added. When platelets--in the presence of fibrinogen--were incubated with antibody concentrations too low to induce platelet aggregation or release, specific reduction of platelet reactivity was observed by subsequent collagen aggregation. HLA-specific action of antibodies on washed platelets was inhibited by apyrase and acetyl-salicylic acid, indicating an active participation of platelets in HLA antibody-induced platelet alteration.     

Vitamin E and atherosclerosis

Vitamin E was advocated as an effective treatment for heart disease by Dr. Even Shute of London, Ontario more than 50 years ago. His pioneering claims, which were unacceptable to the medical community at large, have been confirmed by recent findings from epidemiologic studies and clinical trials. This review integrates our current knowledge of atherogenesis with the biological functions of vitamin E. The response-to-injury hypothesis explains atherosclerosis as a chronic inflammatory response to injury of the endothelium, which leads to complex cellular and molecular interactions among cells derived from the endothelium, smooth muscle and several blood cell components. Inflammatory and other stimuli trigger an overproduction of free radicals, which promote peroxidation of lipids in LDL trapped in the subendothelial space. Products of LDL oxidation are bioactive, and they induce endothelial expression and secretion of cytokines, growth factors and several cell surface adhesion molecules. The last-mentioned are capable of recruiting circulating monocytes and T lymphocytes into the intima where monocytes are differentiated into macrophages, the precursor of foam cells. In response to the growth factors and cytokines, smooth muscle cells proliferate in the intima, resulting in the narrowing of the lumen. Oxidized LDL can also inhibit endothelial production of prostacyclin and nitric oxide, two potent autacoids that are vasodilators and inhibitors of platelet aggregation. Evidence is presented that vitamin E is protective against the development of atherosclerosis. Vitamin E enrichment has been shown to retard LDL oxidation, inhibit the proliferation of smooth muscle cells, inhibit platelet adhesion and aggregation, inhibit the expression and function of adhesion molecules, attenuate the synthesis of leukotrienes and potentiate the release of prostacyclin through up-regulating the expression of cytosolic phospholipase A2 and cyclooxygenase. Collectively, these biological functions of vitamin E may account for its protection against the development of atherosclerosis.     

On-line nonaqueous capillary electrophoresis and electrospray mass spectrometry of tricyclic antidepressants and metabolic profiling of amitriptyline by Cunninghamella elegans

An on-line nonaqueous capillary electrophoresis-electrospray mass spectrometry (ESI-MS) technique was developed using a commercial ion spray interface. The nonaqueous capillary electrophoresis ESI-MS system was used to profile tricyclic antidepressants of similar structures and mass-to-charge ratios. We found that pure methanol can be used as a sheath liquid to obtain stable ion spray from nonaqueous capillary electrophoresis. The flow rate of the coaxial nebulizing gas affected baseline signals, separation efficiency, and migration times. Other nonaqueous capillary electrophoresis operating conditions and electrospray parameters were optimized for enhanced baseline separation and high sensitivity detection. The effect of sample stacking on separation and detection was evaluated. The calculated detection limits were approximately 3 pg injected onto the capillary. ESI mass spectra of tricyclic antidepressants from a single quadrupole MS were obtained and elucidated. The information was used to propose fragmentation pathways of the tricyclic antidepressants. The method was also used to analyze the metabolites of amitriptyline produced by the fungus Cunninghamella elegans. Sixteen metabolites were detected and most of them were tentatively identified as demethylated and/or hydroxylated, and/or N-oxidized products.     

Eicosapentaenoic acid potentiates the production of nitric oxide evoked by interleukin-1 beta in cultured vascular smooth muscle cells

Experiments were designed to determine whether the omega 3-unsaturated fatty acid eicosapentaenoic acid affects the production of nitric oxide evoked by interleukin-1 beta in cultured vascular smooth muscle cells. Incubation of cultured rat or human aortic smooth muscle cells with interleukin-1 beta evoked a time- and concentration-dependent release of nitrite, an oxidation product of nitric oxide. The exposure of cells to interleukin-1 beta in combination with eicosapentaenoic acid caused a significantly larger production of nitrite than that evoked by the cytokine alone. The potentiation by eicosapentaenoic acid was concentration-dependent. The production of nitrite evoked by equieffective concentrations of interleukin-1 beta in the presence and absence of eicosapentaenoic acid were inhibited to a similar extent by nitro L-arginine (an inhibitor of nitric oxide synthase), transforming growth factor beta 1, platelet-derived growth factorAB and thrombin. The addition of interleukin-1 beta-activated smooth muscle cells to suspensions of washed and indomethacin-treated platelets inhibited the aggregation caused by thrombin. The inhibitory effect was enhanced when the smooth muscle cells were exposed to the cytokine in the presence of eicosapentaenoic acid prior to the experiment. Smooth muscle cells exposed to interleukin-1 beta and eicosapentaenoic acid did not affect platelet aggregation in the presence of oxyhemoglobin or methylene blue. Untreated cells or cells exposed to the fatty acid alone did not have such effects. These observations suggest that eicosapentaenoic acid potentiates the production of nitric oxide evoked by interleukin-1 beta in vascular smooth muscle.     

The efficacy, safety and tolerability of antidepressants in late life depression: a meta-analysis

BACKGROUND: To determine the efficacy, safety and tolerability of antidepressants in depressed elderly patients. METHODS: Search for randomized controlled double-blind studies evaluating atypical antidepressants (ATYPs), reversible inhibitors of monoamine oxidase-A, selective serotonin reuptake inhibitors (SSRIs) and tricyclic antidepressants in moderate/severe depressed patients > or = 60 years for > or = four weeks. The random effects model (single-arm; comparative) was used to aggregate efficacy, safety and dropout. RESULTS: No difference in single-arm aggregation of outcomes for four antidepressant classes. Comparative analyses showed no statistical difference between outcomes, except SSRIs had a higher response rate than ATYPs. CONCLUSION: Elderly show no differences in antidepressant class outcomes. LIMITATIONS: Heterogeneity and lack of power. CLINICAL RELEVANCE: There is little advantage for antidepressant classes over another in the aged.     

Conditions that lithium inhibits or potentiates vasopressin V1-receptor-mediated platelet aggregation and [Ca++]i mobilization

1. Besides clinical use, there are many explanations for the mechanism of action of lithium. Although it is shown that lithium may reduce the supply of inositol that is required to sustain phosphoinositide synthesis, evidence exists concerning the potentiating effect of lithium on this pathway. We therefore decided to evaluate conditions in which lithium inhibits or potentiates platelet aggregation and calcium response induced by vasopressin. 2. Platelet aggregation was measured by the photometric method, and changes in intracellular free calcium were measured using fura-2/AM. 3. We show an inhibitory action of neomycin on vasopressin-induced platelet aggregation. Lithium, according to the preincubation time, could both potentiate or inhibit platelet aggregation and calcium responses induced by vasopressin. The inhibitory effect of lithium on platelet aggregation is dependent on concentrations of both lithium and vasopressin and also the presence of indomethacin, for example, in the absence of indomethacin there was no clear inhibitory action of lithium on vasopressin-induced platelet aggregation. 4. These results show the importance of arachidonate metabolites concerning lithium effects on platelet V1-receptor signaling. In conclusion, because the arachidonate metabolites are responsible for the release of other active substances from platelets' granules, the aggregatory responses in the absence of indomethacin may be amplified, and this subsequently may change the net inhibitory action of lithium.     

Chondrosarcoma of the thoracic wall

In this paper, three placebo-controlled trials of moclobemide, and four three-way comparison trials of moclobemide, placebo and one of the standard tricyclic antidepressants, imipramine, clomipramine, or amitriptyline, are reviewed. The results of the placebo-controlled trials indicate that about twice as many of the patients receiving moclobemide showed a marked improvement during a four-week treatment period, as compared with patients receiving placebo. Of the three-way trials, two studies indicated that the efficacy of moclobemide was significantly greater than that of placebo and similar to that of other antidepressants (imipramine or amitriptyline). Tolerance of moclobemide was good and better than that of the tricyclic antidepressants. In the other three-way comparison trials, the differences in efficacy between the placebo, moclobemide, and the tricyclic antidepressant were not significant.     

A comparison of antrafenine and aspirin on platelet aggregation and frusemide-induced diuresis

The effects of antrafenine were compared with aspirin and placebo on platelet aggregation and on the diuretic action of frusemide in normal volunteers. Aspirin significantly reduced platelet aggregation at 3 and 6 hr after administration, but antrafenine only at 3 hr. Only aspirin significantly reduced the increase in urine sodium and potassium produced by frusemide.     

A novel surface-active peptide derivative exhibits in vitro inhibition of platelet aggregation

A tetrapeptide corresponding to a region of the N-terminal portion of lactotransferrin with hydrophobic alkyl groups at the terminal ends was synthesized and its physicochemical properties as well as its effect on thrombin-stimulated platelet aggregation were examined. The tetrapeptide derivative, in the aggregated state, produced inhibitory effect on platelet aggregation. The concentration dependent activity of the peptide was analyzed in the light of micelle formation, with the micellar aggregate comprising four tetrapeptide units. The unique action of this peptide derivative on the inhibition of platelet aggregation might be useful in the development of potent antithrombotic drugs.     

Critical evaluation of measurement of platelet monoamine oxidase in man

Some biochemical characteristics such as substrate specificity, substrate affinity and inhibitor sensitivity of monoamine oxidase of human blood platelets were investigated. Tyramine, tryptamine and beta-phenylethylamine were used as substrates. The apparent Michaelis constants, maximal velocity rates and I50 for the inhibitor tranylcypromine were determined. The data were analyzed according to Lineweaver-Burk and Dixon. The influence of amitriptyline, a prototype of tricyclic antidepressants, on the selected variables (Km, V, I50), was studied. The parameters investigated showed remarkably low interindividual differences when healthy volunteers were tested. The inhibitor activity of amitriptyline towards platelet monoamine oxidase depends on the substrate used. Amitriptyline concentrations which showed a pronounced effect on the enzyme characteristics are significantly higher than plasma levels of the drug found under therapeutic conditions.     

General practitioners' perceptions of the tolerability of antidepressant drugs: a comparison of selective serotonin reuptake inhibitors and tricyclic antidepressants

OBJECTIVE: To examine inceptions and discontinuations of antidepressants in general practice. DESIGN: An observational study analysing data from an ongoing cross sectional postal survey. Every three months a representative sample of 250 doctors recorded prescribing activity for four weeks. This provided 4000 general practitioner weeks of recording per year. SETTING: A representative panel of general practitioners in England, Wales, and Scotland. SUBJECTS: Patients who began a new course of an antidepressant or had their treatment stopped or changed by the general practitioner between 1 July 1990 and 30 June 1995. MAIN OUTCOME MEASURES: Numbers of patients prescribed a new course of antidepressant; numbers discontinuing treatment; the ratio of antidepressant discontinuations to antidepressant inceptions; reasons for discontinuation; proportion of switches to another antidepressant. RESULTS: There were 13,619 inceptions and 3934 discontinuations of selective serotonin reuptake inhibitors and tricyclic antidepressants during the study. The number of newly prescribed courses of antidepressants increased by 116%, mostly due to an increase in prescribing of serotonin reuptake inhibitors. The ratio of total discontinuations to inceptions was significantly lower for serotonin reuptake inhibitors (22%) than for tricyclic antidepressants (33%). Differences persisted when controlled for age and sex of patients and severity of depression. However, there was more switching away from selective serotonin reuptake inhibitors when they failed (72%) than from tricyclic antidepressants (58%). CONCLUSIONS: Selective serotonin reuptake inhibitors are less likely than tricyclic antidepressants to be discontinued. A prospective study is needed in general practice to assess the implications of differences in discontinuation rates and switches on clinical and economic outcomes.     

Column liquid chromatography of tricyclic antidepressants

A column liquid chromatographic system for the analysis of tricyclic antidepressants in serum is described. A high separation efficiency can be obtained with a mixture of ethyl acetate, n-hexane and methylamine as eluent on a silica gel column. The retention is easily regulated by varying the concentration of n-hexane, the modifier methylamine and the water content of the ethyl acetate. Examples are given of separation of test mixtures of tricyclic antidepressants and of some of these drugs in serum. UV detection permits determinations down to the 10-ng level in serum.