Nonexocytotic noradrenaline release and ventricular fibrillation in ischemic rat hearts

In myocardial ischemia, nonexocytotic noradrenaline release has been identified as underlying mechanism of ischemia-evoked noradrenaline release. Nonexocytotic noradrenaline release can be suppressed by inhibitors of the neuronal noradrenaline carrier (uptake), such as desipramine. Utilizing this pharmacological intervention the role of local noradrenaline release in the genesis of ischemia-induced ventricular arrhythmias was studied. Regional ischemia was induced in rat isolated perfused hearts by ligature of the left anterior descending coronary artery, and the venous effluent obtained during the first 2 min of reperfusion was used to measure the release of endogenous noradrenaline by high-performance liquid chromatography methods. Coronary occlusion caused ventricular fibrillation in a well reproducible manner with an incidence of 70 to 80% during a 30 min observation period. Blockage of uptake1 by desipramine decreased the occurrence of ischemia-induced ventricular fibrillation to 60% (0.01 mumol/l) or 20% (0.1 mumol/l), and ventricular fibrillation was completely suppressed by 1 mumol/l desipramine. Likewise, desipramine (0.01-1 mumol/l) concentration-dependently reduced endogenous noradrenaline release during 30 min of regional myocardial ischemia. Nisoxetine, a structurally unrelated inhibitor of uptake1, also suppressed ischemia-evoked ventricular fibrillation. In contrast to its antifibrillatory effect during regional myocardial ischemia, desipramine precipitated arrhythmias when ventricular fibrillation was induced by perfusing normoxic hearts with exogenous noradrenaline. Combination of desipramine (0.1 mumol/l) with exogenous noradrenaline (0.01 to 1 mumol/l) increased the incidence of ventricular fibrillation compared to noradrenaline perfusion alone. Under these conditions, uptake1-blockade is known to increase the extracellular concentration of the perfused noradrenaline. Finally, in the isolated, spontaneously beating papillary muscle of the left rat heart, desipramine (0.1 and 1.0 mumol/l) had no effect on the upstroke velocity of action potentials, the action potential duration and the effective refractory period. In conclusion, the findings demonstrate that nonexocytotic noradrenaline release is an important mediator of ischemia-induced ventricular fibrillation in isolated hearts of the rat. It is also documented that uptake1 inhibitors such as desipramine reveal their effects on ventricular fibrillation secondary to their action on transmembrane noradrenaline transport.     

Evidence from microdialysis and synaptosomal studies of rat cortex for noradrenaline uptake sites with different sensitivities to SSRIs

1. Microdialysis of the frontal cortex of freely-moving rats and uptake of [3H]noradrenaline into cortical synaptosomes were used to evaluate changes in efflux of noradrenaline in vivo and uptake of [3H]noradrenaline in vitro, respectively, induced by the selective serotonin reuptake inhibitors (SSRIs), fluoxetine and citalopram, and the tricyclic antidepressant, desipramine. 2. Noradrenaline efflux was increased during local infusion into the cortex of each of these drugs. All three agents also inhibited synaptosomal uptake of [3H]noradrenaline; this inhibition was unaffected by a substantial (50%) lesion of central 5-hydroxytrytaminergic neurones induced by intracerebroventricular infusion of 5,7-DHT (150 microg). 3. A noradrenergic lesion (70%), induced by pretreatment with the selective neurotoxin, N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4, 40 mg kg(-1) i.p.), 5 days earlier, abolished the increase in noradrenaline efflux caused by local infusion of fluoxetine. In contrast, the desipramine-induced increase in efflux was greater than in non-lesioned rats whereas the effect of citalopram on noradrenaline efflux was unaffected by DSP-4 pretreatment. 4. The combined results of all these experiments suggest that there could be more than one, functionally distinct, noradrenaline uptake site in rat frontal cortex which can be distinguished by their different sensitivities to desipramine and the SSRIs, fluoxetine and citalopram.     

Vasopressin reduces taurochenodeoxycholate-induced hepatotoxicity by lowering the hepatocyte taurochenodeoxycholate content

BACKGROUND/AIMS: Vasopressin has been reported to reduce bile flow, but its effects on bile acid secretion and bile acid-related hepatotoxicity are still unclear. We therefore investigated the influence of vasopressin on the hepatotoxicity and biliary excretion of taurochenodeoxycholic acid in primary cultured rat hepatocytes and isolated perfused rat liver models. METHODS/RESULTS: 1) Addition of vasopressin to hepatocyte cultures significantly decreased lactate dehydrogenase release as compared to cultures exposed to 1 mM taurochenodeoxycholic acid alone, and also reduced intracellular taurochenodeoxycholic acid content from 19.3 +/- 2.2 to 13.0 +/- 1.6 nmol/mg protein. After 30 min of preincubation with 1 mM taurochenodeoxycholic acid, rinsing and reculture of hepatocytes in bile acid-free medium resulted in gradual decrease in the intracellular level of the bile acid, and addition of vasopressin (10(-9) M) to the reculture medium accelerated this process. 2) Superimposition of vasopressin (330 pmol/l) for 10 min on taurochenodeoxycholic acid infusion (1.0 mumol/min: 25 mumol/l) caused a rapid increase in bile flow and biliary excretion of taurochenodeoxycholic acid (697 +/- 42 vs 584 +/- 27 nmol/10 min per g liver) from perfused rat livers, and significantly reduced lactate dehydrogenase release. 3) Superimposition of the PKC blocker H-7 (5 mumol/l) on taurochenodeoxycholic acid infusion (1.0 mumol/min: 25 mumol/l) caused a gradual increase in bile flow and biliary excretion of taurochenodeoxycholic acid. Furthermore, an additional infusion of vasopressin (100 pmol/l) for 10 min in the presence of H-7 produced a greater increase in bile flow and biliary excretion of taurochenodeoxycholic acid as compared with H-7 alone (754 +/- 71 vs. 657 +/- 26 nmol/g liver). 4) Continuous infusion of vasopressin (330 pmol/l) significantly increased the late peak (10-50 min) of horseradish peroxidase excretion from perfused livers (from 8.48 +/- 1.02 to 21.7 +/- 6.02 ng/g liver). CONCLUSIONS: These findings suggest that vasopressin exerts a protective effect against taurochenodeoxycholic acid-induced hepatotoxicity by stimulating the secretion of this bile acid via intracellular vesicular transport systems.     

Effects of iodoproxyfan, a potent and selective histamine H3 receptor antagonist, on alpha 2 and 5-HT3 receptors

We determined the affinity and/or potency of the novel H3 receptor antagonist iodoproxyfan at alpha 2 and 5-HT3 receptors. Iodoproxyfan and rauwolscine (a reference alpha 2 ligand) (i) monophasically displaced 3H-rauwolscine binding to rat brain cortex membranes (pKi 6.79 and 8.59); (ii) facilitated the electrically evoked tritium overflow from superfused mouse brain cortex slices preincubated with 3H-noradrenaline (pEC50 6.46 and 7.91) and (iii) produced rightward shifts of the concentration-response curve (CRC) of (unlabelled) noradrenaline for its inhibitory effect on the evoked overflow (pA2 6.65 and 7.88). In the guinea-pig ileum, iodoproxyfan 6.3 mumol/l failed to evoke a contraction by itself but depressed the maximum of the CRC of 5-hydroxytryptamine (pD'2 5.24). Tropisetron (a reference 5-HT3 antagonist) produced rightward shifts of the CRC of 5-hydroxytryptamine (pA2 7.84). In conclusion, the affinity/potency of iodoproxyfan at H3 receptors (range 8.3-9.7 [1]) exceeds that at alpha 2 receptors by at least 1.5 log units and that at 5-HT3 receptors by at least 3 log units.     

Transport of monoamine transmitters by the organic cation transporter type 2, OCT2

The recently cloned apical renal transport system for organic cations (OCT2) exists in dopamine-rich tissues such as kidney and some brain areas (Gründemann, D., Babin-Ebell, J., Martel, F., Ording, N., Schmidt, A., and Sch?mig, E. (1997) J. Biol. Chem. 272, 10408-10413). The study at hand was performed to answer the question of whether OCT2 accepts dopamine and other monoamine transmitters as substrate. 293 cells were stably transfected with the OCT2r cDNA resulting in the 293OCT2r cell line. Expression of OCT2r in 293 cells induces specific transport of tritiated dopamine, noradrenaline, adrenaline, and 5-hydroxytryptamine (5-HT). Initial rates of specific 3H-dopamine, 3H-noradrenaline, 3H-adrenaline, and 3H-5-HT transport were saturable, the Km values being 2.1, 4.4, 1.9, and 3.6 mmol/liter. The corresponding Vmax values were 3.9, 1.0, 0. 59, and 2.5 nmol min-1.mg of protein-1, respectively. 1, 1'-diisopropyl-2,4'-cyanine (disprocynium24), a known inhibitor of OCT2 with a potent eukaliuric diuretic activity, inhibited 3H-dopamine uptake into 293OCT2r cells with an Ki of 5.1 (2.6, 9.9) nmol/liter. In situ hybridization reveals that, within the kidney, the OCT2r mRNA is restricted to the outer medulla and deep portions of the medullary rays indicating selective expression in the S3 segment of the proximal tubule. These findings open the possibility that OCT2r plays a role in renal dopamine handling.     

Bradykinin B2-receptor-mediated stimulation of exocytotic noradrenaline release from cardiac sympathetic neurons

Myocardial ischemia, as well as angiotensin-converting-enzyme-inhibitors, increase cardiac concentrations of the non-apeptide bradykinin. Cardiac effects of bradykinin are potentially mediated by modulation of sympathoadrenergic neurotransmission. Accordingly, the present study was designed to examine the influence of bradykinin on exocytotic noradrenaline release from rat isolated perfused heart. Exocytotic noradrenaline release was induced by electrical field stimulation (1 min, 5 V, 6 Hz) twice to compare the effect of intervention (S2) with respective control stimulation (S1). The overflow of endogenous noradrenaline was determined by high pressure liquid chromatography and electrochemical detection. The results are expressed as the mean S2/S1 ratio+/-S.E.M. Bradykinin (1 micromol/l) evoked a significant increase in noradrenaline release (S2/S1: 1.60+/-0.12; P<0.01), which was even more pronounced after inhibition of neuronal reuptake of noradrenaline by desipramine (0.1 micromol/l: S2/S1: 1.83+/-0.15; P<0.01) excluding interference of bradykinin with the noradrenaline uptake1 carrier. The concentration-response curve for bradykinin (0.1 nmol/l to 10 micromol/l) revealed a maximum effect at 1 micromol/l and an EC50-value of 7.5 nmol/l. The effect of bradykinin was unaltered by the B1-receptor antagonist des-Arg9 (Leu8)-bradykinin (1 micromol/l; S2/S1: 1.69+/-0.17), whereas it was reduced significantly by the B2-receptor antagonist Hoe 140 (1 micromol/l; S2/S1: 1.14+/-0.11; P<0.05). Des-Arg9-bradykinin (1 micromol/l), a specific B1-agonist, had no effect on stimulation-induced noradrenaline release (S2/S1: 0.94+/-0.08). Utilizing pharmacological interventions, we attempted to characterize the intraneuronal signal transduction pathway mediating the effect of bradykinin on exocytosis. Neither inhibition of cyclooxygenase nor blockade of nitric oxide synthesis affected bradykinin-induced stimulation of noradrenaline release. Likewise, inhibition of protein kinase C by bisindolylmaleimide (1 micromol/l) or tyrosine kinase by genistein (10 micromol/l) had no effect on the promoting action of bradykinin. In contrast, inhibition of cytosolic phospholipase A2 activity by the specific inhibitor AACOCF3 (1 micromol/l) prevented bradykinin-induced increase in noradrenaline release (S2/S1: 1.09+/-0.15; P<0.01). In conclusion, bradykinin increases exocytotic release of endogenous noradrenaline from cardiac sympathetic neurons via activation of presynaptic B2-receptors. Intraneuronal coupling of B2-receptors to phospholipase A2 appears to mediate the facilitatory effect of bradykinin on noradrenaline release in rat heart.     

Serotonin efflux in the rat ventral lateral geniculate nucleus assessed by fast cyclic voltammetry is modulated by 5-HT1B and 5-HT1D autoreceptors

Fast cyclic voltammetry (FCV) was used to measure electrically stimulated monoamine efflux in the rat ventral lateral geniculate nucleus (vLGN). The electrochemical characteristics of the released species resembled 5-HT but not dopamine or noradrenaline. Amine efflux was abolished by the sodium channel blocker tetrodotoxin (0.1 microM), Ro 4-1284 (1.0 microM), the fast-acting reserpine analogue, and removal of Ca2+ from the superfusate. Amine efflux was unaffected by the monoamine oxidase inhibitor clorgyline (0.1 microM). Of paroxetine (0.1 microM), desipramine (50 nM) and vanoxerine (0.5 microM), selective blockers of 5-HT, noradrenaline and dopamine uptake respectively, only paroxetine increased monoamine efflux (to 194 +/- 25%, mean +/- SEM) and prolonged the removal half-life (to 638 +/- 105%). The non-specific 5-HT1 antagonist methiothepin (0.2 microM) increased 5-HT efflux on long (20 pulses at 20 Hz) but not short trains (20 pulses at 100 Hz). When tested on pseudo-one-pulse stimulations (5 pulses, 100 Hz), the selective 5-HT1A agonist 8-OHDPAT (1.0 microM) had no effect. CP 93129 (0.3 microM), the selective 5-HT1B agonist, decreased 5-HT efflux to 37 +/- 4% of control and was antagonised by the 5-HT1B blocker isamoltane (0.5 microM) and by the 5-HT1D/B antagonist GR 127935 (50 nM). The preferential 5-HT1D agonist sumatriptan (0.5 microM) also decreased 5-HT efflux, to 55 +/- 6% and was antagonised by GR 127935 (50 nM) but not isamoltane (0.5 microM). These results suggest that 5-HT released in the vLGN can be measured by FCV. Furthermore, released 5-HT is taken up by the 5-HT transporter and may be under the influence of 5-HT1B and 5-HT1D autoreceptors.     

Effects of ginkgolides on interleukin-1, tumor necrosis factor-alpha and nitric oxide production by rat microglia stimulated with lipopolysaccharides in vitro

The effects of ginkgolide A (CAS 15291-75-5, BN52020, GA) and B (CAS 15291-77-7, BN52021, GB) on interleukin (IL)-1, tumor necrosis factor-alpha (TNF-alpha) and nitric oxide (NO) production in resting and lipopolysaccharide (LPS)-stimulated neonatal rat microglia were studied. Apafant (CAS 105219-56-5), a platelet activating factor (PAF) antagonist of triazolobenzodiazepine type was used as control. The biological activities of IL-1 and TNF-alpha were tested by mouse thymocyte proliferation and L929 cytotoxicity assay, respectively. NO concentration was represented by nitrite and determined by Griess reaction. GA 1 nmol/1-10 mumol/l inhibited IL-1 production, and 100 nmol/l-10 mumol/l decreased TNF-alpha and NO production in dose-dependent manner. GB inhibited IL-1, TNF-alpha and NO production at the concentrations 10 nmol/l-10 mumol/l, 100 nmol/l-10 mumol/l and 10 nmol/l-10 mumol/l, respectively. Apafant inhibited IL-1, but not TNF-alpha and NO production. GB plus apafant (50 mumol/l) showed IL-1 and NO inhibitory effects, but not on TNF-alpha. The manner was different from that of GB or apafant alone. The results suggested that GA and GB inhibited proinflammatory cytokines and NO production from LPS-stimulated rat microglia, however, apafant inhibited IL-1 production only. The effects of GA and GB on proinflammatory cytokines and NO production from rat microglia do not seem to be based on PAF receptor antagonism. In addition, GA and GB are regarded as promising agents for the treatment of some neurodegenerative diseases in the central nervous system.     

Studies of the biogenic amine transporters. IV. Demonstration of a multiplicity of binding sites in rat caudate membranes for the cocaine analog [125I]RTI-55

The drug 3 beta-[4'-iodophenyl]tropan-2 beta-carboxylic acid methyl ester (RTI-55) is a cocaine congener with high affinity for the dopamine transporter (Kd < 1 nM). The present study characterized [125I]RTI-55 binding to membranes prepared from rat, monkey and human caudates and COS cells transiently expressing the cloned rat dopamine (DA) transporter. Using the method of binding surface analysis, two binding sites were resolved in rat caudate: a high-capacity binding site (site 1, Bmax = 11,900 fmol/mg of protein) and a low-capacity site (site 2, Bmax = 846 fmol/mg of protein). The Kd (or Ki) values of selected drugs at the two sites were as follows: (Ki for high-capacity site and Ki for low-capacity site, respectively): RTI-55 (0.76 and 0.21 nM), 1-[2-diphenyl-methoxy)ethyl]-4-(3-phenylpropyl)piperazine (0.79 and 358 nM), mazindol (37.6 and 631 nM), 2 beta-carbomethoxy-3 beta-(4-fluorophenyl)tropane (45.0 and 540 nM) and cocaine (341 and 129 nM). Nisoxetine, a selective noradrenergic uptake blocker, had low affinity for both sites. Serotonergic uptake blockers had a high degree of selectivity and high affinity for the low-capacity binding site (Ki of citalopram = 0.38 nM; Ki of paroxetine = 0.033 nM). The i.c.v. administration of 5,7-dihydroxytryptamine to rats pretreated with nomifensine (to protect dopaminergic and noradrenergic nerve terminals) selectively decreased the Bmax of site 2, strongly supporting the idea that site 2 is a binding site on the serotonin (5-HT) transporter. This serotonergic lesion also increased the affinity of [125I]RTI-55 for the DA transporter by 10-fold. The ligand selectivity of the caudate 5-HT transporter was different from the [I125]RTI-55 binding site on the 5-HT transporter present in membranes prepared from whole rat brain minus caudate. The [125I]RTI-55 binding to the DA transporter was further resolved into two components, termed sites 1a and 1b, by using human and monkey (Macaca mulatta) caudate membranes but not the membranes prepared from rat caudate or COS cells that transiently expressed the cloned cocaine-sensitive DA transporter complementary DNA. Similar experiments also resolved two components of the caudate 5-HT transporter. Viewed collectively, these data provide evidence that [125I]RTI-55 labels multiple binding sites associated with the DA and 5-HT transporters.     

Acute and chronic citalopram treatment differently modulates rat exploratory behavior in the exploration box test: no evidence for increased anxiety or changes in the [3H]raclopride binding

The effect of acute and chronic desipramine (10 mg/kg) and citalopram (10 mg/kg) treatment on rat exploratory behavior in the recently developed exploration box test was studied on 5 consecutive days. Acute desipramine but not citalopram treatment decreased the time spent exploring, the number of line crossings, rears, investigative approaches, entries into the large arena, and sum of exploratory events. After 3 weeks of pretreatment, both desipramine and citalopram attenuated rat exploratory behavior, whereas the number of entries into the large arena was unchanged. In the open field test, acute desipramine or citalopram treatment (5, 10, 15 mg/kg) attenuated rat exploratory behavior in a dose-dependent manner. In the subsequent rota-rod test, neither desipramine nor citalopram treatment (0-20 mg/kg) impaired motor performance capacity. In an additional experiment, [3H]raclopride binding was unchanged after single as well as 3 weeks of desipramine or citalopram treatment in the rat brain neostriatum. Our experiments demonstrate that acute citalopram treatment in the open field test and chronic citalopram treatment in the exploration box test attenuate rat exploratory behavior, but these effects may not be implicated with enhanced anxiety or changed dopamine D2 receptor characteristics.     

The diagnostic value of hyperostosis in midline subfrontal meningioma

In vivo blockade of 5-HT uptake was studied by investigating the effect of drug pretreatment on the ability of p-chloramphetamine to lower rat brain 5-HT levels. Org 6582 was approximately twice as potent as fluoxetine, five times more potent than chlorimipramine and 14 times more potent than desipramine in blocking the ability of p-chloroamphetamine to lower rat brain 5-HT content. Org 6582 also had a longer duration of action than either fluoxetine or chlorimipramine. Org 6582, whilst having no effect on amine steady state levels, decreased rat brain 5-HT turnover and also lowered rat brain levels of 5-HIAA. In contrast to both desipramine and chlorimipramine, Org 6582 was devoid of effect on the ability of 1-metaraminol and 6-hydroxydopamine to lower rat heart NA levels. The ability of intraventricularly administered 6-hydroxydopamine to lower rat brain NA levels was unaltered by Org 6582 pretreatment. The corresponding i.p. ED50 values for desipramine and chlorimipramine were 7.3 mg/kg and 28.8 mg/kg respectively. Like desipramine and chlorimipramine, Org 6582 had no effect on the ability of intraventricular 6-hydroxydopamine to lower rat brain DA content. Org 6582 had no effect on steady state levels or on the turnover of NA and DA in the rat brain. It is concluded that Org 6582 is a potent long acting selective inhibitor of 5-HT uptake in vivo.     

Heart failure: the Cinderella of cardiology?

Ergotamine contracted isolated rat aorta rings with an intrinsic activity of 50% of that of 5-hydroxytryptamine. (5-HT, 0.1 mmol/l). Dihydroergotamine did not contract the tissue, but insurmountably blocked contraction in response to ergotamine and 5-HT. The 5-HT2A receptor antagonist, ketanserin (0.1 mumol/l), inhibited ergotamine (pKB 8.0) and 5-HT (pKB 8.1) induced contractions. These results indicate that in the rat aorta ergotamine is a partial 5-HT2A receptor agonist, whilst dihydroergotamine is an insurmountable 5-HT2A receptor antagonist. The present data could explain why ergotamine displays more cardiovascular and uterotonic side effects than dihydroergotamine.     

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.     

Sarcoplasmic reticulum Ca2+ uptake and thapsigargin sensitivity in permeabilized rabbit and rat ventricular myocytes

Ca2+ uptake by the sarcoplasmic reticulum (SR) and free [Ca2+] were measured simultaneously with indo 1 and a Ca(2+)-selective minielectrode in suspensions of permeabilized rabbit or rat ventricular myocytes (approximately 10 mg/mL protein). In the presence of 25 mumol/L ruthenium red and 10 mmol/L oxalate, the Km for Ca2+ uptake by the SR was approximately 250 nmol/L in rabbit and rat ventricular myocytes. The maximal Ca2+ uptake rate was 2.4 times higher in rat than in rabbit. Addition of 5 nmol thapsigargin (TG) per milligram cell protein abolished Ca2+ uptake completely in both species. The [TG] necessary for a half-maximal reduction of the uptake rate (K1/2) was 55 pmol/mg cell protein for rabbit and 390 pmol/mg cell protein for rat. Assuming that the number of pump sites is two times the concentration of TG necessary to inhibit half of the Ca2+ pump activity (ie, the TG affinity is very high), the density of pump sites is 7.7 mumol/kg wet wt for rabbit and 54.6 mumol/kg wet wt for rat. Despite a fivefold decrease of the Ca2+ uptake rate by a submaximal [TG], the permeabilized myocytes were still able to lower the free [Ca2+] to < 150 nmol/L from a peak value > 10 mumol/L. The relative inhibition of Ca2+ uptake by TG did not depend on the free [Ca2+]. Addition of more than 5 nmol TG per milligram cell protein abolished Ca2+ uptake by the SR completely in < 15 seconds and reduced the uptake rate by 95% in 5 seconds.(ABSTRACT TRUNCATED AT 250 WORDS)     

Investigation of the presynaptic effects of quinine and quinidine on the release and uptake of monoamines in rat brain tissue

Quinine and quinidine are reported to potentiate the behavioural effects of serotonergic agents and monoamine uptake inhibitors. We have therefore investigated the presynaptic actions of quinine and quinidine on monoamine uptake and release in rat brain tissue in vitro. Quinidine evoked the release of [3H]5-HT, [3H]noradrenaline and [3H]dopamine from pre-loaded rat brain slices in a concentration dependent manner with EC50 values of 175, 486 and 150 microM, respectively. Quinine induced [3H]monoamine release with similar potencies. Both quinine and quinidine also inhibited the active uptake of [3H]5-HT, [3H]noradrenaline and [3H]dopamine into rat brain synaptosomes with IC50 values in the range 0.13-12.4 microM. The potency of each drug to inhibit [3H]5-HT uptake was significantly higher than that for [3H]noradrenaline or [3H]dopamine. The relative potency of quinidine compared to quinine was more marked in the case of [3H]5-HT (58-fold) than for [3H]noradrenaline (3-fold) or [3H]dopamine (4-fold). The inhibition of [3H]5-HT uptake by quinine and quinidine was competitive in nature and corresponded with the potencies of these drugs to inhibit [3H]paroxetine binding. No correlation was observed between the potencies of quinine and quinidine to induce the release of [3H]monoamines and to inhibit their uptake, suggesting that these effects are mediated by two distinct mechanisms. We conclude that the presynaptic actions of quinine and quinidine on monoamine uptake and release may be implicated in their potentiation of the effects of serotonergic agents and uptake blockers.     

Adaptive abilities of hospitalized alcoholics and matched controls. The brain-age quotient

1 The effect of a series of antidepressant drugs on noradrenaline accumulation was studied in the isolated anococcygeus muscle of the rat. 2 The most potent inhibitors of noradrenaline accumulation were nortriptyline, desipramine and protriptyline. Opipramol, trimipramine and iprindole were active only in high concentrations. 3 Contractions of the anococcygeus muscle produced by noradrenaline were strongly potentiated by nortriptyline, desipramine and protriptyline. Other uptake inhibitors were less active in potentiating the noradrenaline response. 4 Nortriptyline, in concentrations that potentiated the action of noradrenaline, reduced or abolished the response to tyramine.     

Down-regulation of the noradrenaline transporter by interferon-alpha in cultured bovine adrenal medullary cells

The aim of this study was to investigate the effect of long-term treatment with interferon (IFN)-alpha on the noradrenaline transporter of bovine adrenal medullary cells. Treatment of cultured adrenal medullary cells with IFN-alpha caused a decrease in uptake of [3H]noradrenaline by the cells in time (4-48 h)- and concentration (300-1,000 U/ml)-dependent manners. IFN-beta also inhibited [3H]noradrenaline uptake to a lesser extent than did IFN-alpha, whereas IFN-gamma had little effect. An anti-IFN-alpha antibody reduced the effect of IFN-alpha on [3H]noradrenaline uptake. Saturation analysis of [3H]noradrenaline uptake showed that the inhibitory effect of IFN-alpha was due to a reduction in the maximal uptake velocity (Vmax) values without altering apparent Michaelis constant (Km) values. Incubation of cells with IFN-alpha caused a translocation of protein kinase C from the soluble to the particulate fraction in the cells. The effect of IFN-alpha on [3H]noradrenaline uptake was diminished in protein kinase C-down-regulated cells. Incubation of cells with IFN-alpha for 48 h significantly reduced the specific binding of [3H]desipramine to crude plasma membranes isolated from cells. Scatchard analysis of [3H]desipramine binding revealed that IFN-alpha decreased the maximal binding (Bmax) values without any change in the dissociation constant (K(D)) values. These findings suggest that IFN-alpha suppresses the function of noradrenaline transporter by reducing the density of the transporter in cell membranes through, at least in part, a protein kinase C pathway.     

Role of 5-ht7 receptors in the long-lasting hypotensive response induced by 5-hydroxytryptamine in the rat

1. The receptor mediating the long-lasting hypotensive effect of intravenous (i.v.) 5-hydroxytryptamine (5-HT) in the rat was originally classified as 5-HT1-like. Since some pharmacological properties of this receptor are closely similar to those for the cloned 5-ht7 receptor, the present study investigated the effects of several 5-HT receptor agonists and antagonists showing high affinity for the cloned 5-ht7 receptor in pithed rats with artificially raised blood pressure. 2. I.v. bolus administration of 5-HT, 5-carboxamidotryptamine (5-CT), 5-methoxytryptamine, lisuride and sumatriptan to bilaterally vagotomized pithed rats pretreated with ketanserin (0.18 mumol kg-1, i.v.), the diastolic blood pressure of which had been raised by a continuous i.v. infusion of methoxamine (60-80 nmol kg-1 min-1), produced dose-dependent hypotensive responses; only 5-HT and 5-CT displayed similar maximum effects. In addition to mimicking the hypotensive action of 5-HT with a lower maximum effect, lisuride strongly antagonized the 5-CT-induced hypotensive responses thus suggesting a partial agonist effect. The rank order of hypotensive agonist potency was 5-CT > > 5-HT > or = 5-methoxytryptamine > or = lisuride > > sumatriptan. 3. In experiments with antagonists, i.v. treatment with metergoline (2.48 mumol kg-1), mesulergine (2.76 mumol kg-1), methysergide (2.13 mumol kg-1), lisuride (0.22 mumol kg-1), methiothepin (0.68 mumol kg-1), mianserin (10.6 mumol kg-1), or the atypical antipsychotic drugs, clozapine (11.0 mumol kg-1) or risperidone (78.0 nmol kg-1), produced significant rightward displacements of the dose-response curve for 5-CT in methoxamine-infused pithed animals pretreated with ketanserin (0.18 mumol kg-1, i.v.); lisuride, methiothepin and risperidone behaved as non-competitive antagonists as they elicited a significant reduction of the maximum effect to 5-CT. In contrast, blockade of 5-HT1, 5-HT3 and 5-HT4 receptors with i.v. propranolol (3.38 mumol kg-1), MDL-72222 (1.59 mumol kg-1) and GR125487 (1.91 mumol kg-1), respectively, did not alter 5-CT-induced hypotensive responses; ketanserin (0.18 mumol kg-1, i.v.) failed to modify the dose-response curve for 5-CT in saline-pretreated animals. Lastly, inhibition of the prostaglandin-forming cyclo-oxygenase and nitric oxide synthase with indomethacin (14 mumol kg-1, i.v.) and NG-nitro-L-arginine methyl ester (L-NAME, 120 mumol kg-1, i.v.), respectively, had no significant effects on 5-CT-induced hypotensive effects. 4. Taken together, the present pharmacological data suggest that the long-lasting vasodepressor action of 5-HT in the rat involves activation of receptors closely similar to the cloned 5-ht7 subtype. Since no evidence for an indirect mechanism could be obtained, these receptors may be primarily located in the vascular smooth muscle of the systemic resistance vessels. These findings represent further evidence favouring the functional role of the 5-ht7 receptor.     

Poly(ethylene glycol) on the liposome surface: on the mechanism of polymer-coated liposome longevity

The mode of action of muramyl dipeptide (MDP), a compound with immunopharmacological properties, was studied in isolated nerve smooth muscle preparations with different receptor systems. The amplitudes of contractions evoked directly by stimulants as well as neurogenic twitches or relaxations were registered. In the rat stomach strip EC50 of acetylcholine, serotonin (5-HT) and KCl was estimated. MDP (50 nmol/l) but not levamisole potentiated selectively the contractions evoked by 5-HT and significantly (p < 0.01) lowered the respective EC50. In the rat vas deferens MDP selectively potentiated the twitches enhanced by 5-HT but not those enhanced by noradrenaline. Such potentiation was blocked by 5-HT3 antagonists tropisetron and MDL 72,222 (1 alpha H,3 alpha,5 alpha-H-tropan-3-yl 3,5-dichlorobenzoate) but not by the 5-HT2 antagonist ketanserin. The antagonist methiothepin nonselectively abolished the potentiation by MDP as well as the enhancement of twitches by 5-HT and noradrenaline, whereas l-propranolol and isamoltan influenced neither the enhancement of twitches by 5-HT nor the potentiation by MDP. In the isolated longitudinal muscle of guinea pig proximal colon, 5-HT caused a biphasic response in the presence of atropine; the initial neurogenic relaxation was potentiated in the presence of MDP and was suppressed in the presence of tropisetron. Thus, the potentiating effect of MDP in the isolated organs studied was selective with respect to the serotoninergic system and might be mediated by 5-HT3 receptors.