Inhibition Of Amine Uptake Research Articles

Indanes--Properties, Preparation, and Presence in Ligands for G Protein Coupled Receptors.

The indane (2,3-dihydro-1H-indene) ring system is an attractive scaffold for biologically active compounds due to the combination of aromatic and aliphatic properties fused together in one rigid system. This bicyclic structure provides a wide range of possibilities to incorporate specific substituents in different directionalities, thus being an attractive scaffold for medicinal chemists. Notably, many indane-based compounds are being used in the clinic to treat various diseases, such as indinavir, an HIV-1 protease inhibitor; indantadol, a potent Monoamine Oxidase (MAO)-inhibitor; the amine uptake inhibitor indatraline; and the ultra-long-acting β-adrenoceptor agonist indacaterol. Given the diversity of targets these drugs act on, one could argue that the indane ring system is a privileged substructure. In the present review, the synthetic and medicinal chemistry of the indane ring system is described. In more detail, it contains a comprehensive overview of compounds bearing the indane substructure with G protein coupled receptor (GPCR) activity, with particular emphasis on their structure-activity relationships (SAR).

The Triple Uptake Inhibitor (1R,5S)-(+)-1-(3,4-Dichlorophenyl)-3-azabicyclo[3.1.0] Hexane Hydrochloride (DOV 21947) Reduces Body Weight and Plasma Triglycerides in Rodent Models of Diet-Induced Obesity

Selective inhibitors of biogenic amine (e.g., serotonin, norepinephrine, and dopamine) uptake exhibit varying degrees of safety and efficacy as antiobesity agents. Moreover, preclinical findings suggest that the combined inhibition of monoamine neurotransmitter transporters synergistically enhances antiobesity activity. (1R,5S)-(+)-1-(3,4-Dichlorophenyl)-3-azabicyclo-[3.1.0] hexane hydrochloride (DOV 21947) inhibits norepinephrine, 5-hydroxytryptamine, and dopamine uptake, and it reduces body weight in rodent models of diet-induced obesity (DIO). DIO rats treated orally with DOV 21947 for 1 to 24 days showed significantly lower body weights than vehicle-treated DIO rats. The decrease in body weight resulted specifically from a loss of retroperitoneal and mesenteric depots of white adipose tissue. DOV 21947 also reduced daily food intake in DIO rats, but consumption returned to control levels after 11 days of treatment. With the exception of a decrease in triglyceride levels, blood chemistry was unaltered after 24 days of DOV 21947 treatments. DOV 21947 had no effect on motor activity. Although DOV 21947 increased respiratory rate and decreased the tidal volume of normal rats, it did not alter the minute volume. In addition, DOV 21947 did not significantly affect blood pressure, heart rate, electrocardiographic indices or body temperature in telemeterized dogs. However, it caused a sustained, but reversible reduction in the rate of body weight gain for as long as 6 months in normal rats, and for up to 1 year in normal dogs. In summary, DOV 21947 is effective in causing a sustained and selective reduction in fat content and triglyceride levels in animal models of obesity without significantly altering vital organ function.

Design and Synthesis of Promiscuous High-Affinity Monoamine Transporter Ligands: Unraveling Transporter Selectivity

A series of 4-[2-[bis(4-fluorophenyl)methoxy]ethyl]-piperidines and 4-[2-[(bisphenyl)methoxy]ethyl]-piperidines with different types of substituents in the phenylpropyl side-chain were synthesized and examined for their ability to bind to the dopamine transporter (DAT), the serotonin transporter (SERT), and the norepinephrine transporter (NET). All of the compounds showed high binding affinities for the DAT in the low to subnanomolar range. Their ability to bind to the SERT and the NET, while maintaining their high affinity for the DAT, could be altered by substitution in positions C2 and C3 of the phenylpropyl side-chain. This approach gave rise to a new set of compounds with selectivity for the DAT, the DAT and the SERT, or the DAT and the NET. Six compounds (7, 9, 11, 12, 14, and 20) with relatively low SERT/DAT ratios were selected for additional study in biogenic amine uptake inhibition assays based on the biogenic amine transporter binding results. Some of the new ligands can serve as pharmacological tools to block DAT or DAT and another transporter simultaneously.

Tolerability of Amine Uptake Inhibitors in Urologic Diseases

Inhibitors of serotonin (5-HT) and/or noradrenaline (NA) reuptake have been developed for pharmacological treatment of major depressive disorder. Insights in the role of 5-HT and NA in the neurological control of the lower urinary tract have also led to their application in common urological conditions such as stress urinary incontinence (SUI), nocturnal enuresis and ejaculatory disorders. The European approval of the 5-HT and NA reuptake inhibitor (SNRI) duloxetine for treatment of SUI underlines the importance of a new approach in SUI, but has also given rise to questions about the safety of antidepressants in urology. This paper reviews the safety of 5-HT and NA reuptake inhibitors in their on- and off-label use in urology. A systematic Medline search was performed for randomised controlled trials, meta-analyses and practice guidelines dealing with antidepressants in urology. The safety profiles of the drugs in the urological population were compared with data from psychiatric populations. Tricyclic antidepressants are associated with serious cardiovascular side effects. In addition, anticholinergic and antihistaminic side effects are common. Although recently questions have been raised regarding the cardiovascular safety profile of venlafaxine, most selective 5-HT reuptake inhibitors and SNRI have not been associated with serious cardiovascular effects. Their most common side effect is nausea. However, nausea tends to be mild and, importantly, transient. Patient counselling about side effects and up-titrating doses may be useful strategies for minimising discomfort and withdrawals.

A new hypertrophic mechanism of serotonin in cardiac myocytes: receptor‐independent ROS generation

Reactive oxygen species (ROS) play a critical role in cardiac hypertrophy. We have recently shown that the serotonin-degrading enzyme monoamine oxidase A (MAO A) is an important source of hydrogen peroxide in rat heart. In the present study, we investigated the potential role of hydrogen peroxide generated by MAO A in cardiomyocyte hypertrophy by serotonin. Serotonin (5 microM, 48 h) induced hypertrophy in cultured adult rat ventricular myocytes, as reflected by increased 3H-leucine incorporation (+43%, P<0.001) and total protein content (+22%, P<0.001). Serotonin also increased intracellular hydrogen peroxide and oxidative stress production, measured respectively by DCF fluorescence intensity and GSH/GSSG ratio, and promoted ERK1/2 phosphorylation (P<0.001). Serotonin effects were only partially inhibited by the 5-HT2B receptor antagonist SB 206553. In contrast, they were extensively (>80%) prevented by the amine uptake inhibitor imipramine, the MAO inhibitor pargyline and the MEK inhibitor PD 98059. Cardiomyocyte hypertrophy and ERK activation were also inhibited by decreasing intracellular ROS by adenoviral overexpression of catalase or cardiomyocytes treatment with the iron chelator deferoxamine. These data suggest that part of cardiac hypertrophic effect of serotonin requires hydrogen peroxide production by MAO A and ERK1/2 activation. This newly recognized, receptor-independent mechanism of serotonin may contribute to myocardial remodeling and failure.

Brain tyramine and reproductive states of workers in honeybees

To explore the role of tyramine in the transformation of reproductive states of honeybee workers, brain levels of tyramine and N-acetyltyramine were measured in both normal and queenless workers. Queenless workers had higher tyramine levels and lower N-acetyltyramine levels than normal workers did. Intermediate reproductive workers that were transferred into a normal colony from a queenless colony had intermediate levels of tyramine and N-acetyltyramine. Elevation of tyramine in the queenless workers occurred at an earlier adult stage than elevation of dopamine. Tyramine levels in intermediate reproductive workers returned to the levels seen in normal workers, but dopamine levels in intermediate reproductive workers remained elevated at the same level as in queenless workers. Thus, brain tyramine may be regulated by the colony condition with or without a queen. Injection of an amine uptake inhibitor, reserpine, depleted tyramine and elevated N-acetyltyramine. Distributions of tyramine and dopamine within the brain were distinctively different, whereas distributions of N-acetyltyramine and N-acetyldopamine were similar, suggesting that each functional amine is stored in specific neurosecretory cells and released to the relevant receptor sites but that metabolism into each N-acetylmetabolite is determined by diffusion.

PACAP enhances stimulation-induced norepinephrine release in canine pancreas in vivo

The present study was to investigate whether pituitary adenylate cyclase activating polypeptide (PACAP) can modify norepinephrine (NE) release in response to pancreatic nerve stimulation in anesthetized dogs. Plasma catecholamine concentrations in aortic and superior pancreaticoduodenal (SPD) venous blood were determined by a high performance liquid chromatography method. SPD venous blood flow was measured with an electromagnetic flowmeter. Pancreatic nerves were directly stimulated for 1 min (2 ms, 12 V) at various frequencies at the level of the SPD artery. Various doses of PACAP1-27 (PACAP27) were locally infused into the pancreas through the SPD artery. Nerve stimulation significantly increased both SPD venous NE concentration and its output from the pancreas in a frequency-dependent manner. With PACAP27 alone, neither SPD venous NE concentration nor its output changed significantly following the local administration of PACAP27 at any dose tested. In the presence of PACAP27, however, the net increases in NE concentration and its output in response to nerve stimulation at 2 Hz were significantly enhanced in a dose-dependent manner. The enhanced NE responses to nerve stimulation by PACAP27 were thus significantly greater than those obtained from the group receiving either PACAP27 or stimulation alone. Increases in NE concentration and its output induced by local administration of tyramine were virtually abolished by desipramine, a neural amine uptake inhibitor. However, the NE response to tyramine was not diminished by PACAP27. The results indicate that PACAP27 enhances the stimulation-induced NE release in the pancreas, and that this facilitatory effect of PACAP27 does not result from an inhibition of the neural amine uptake mechanism. The study suggests that PACAP receptor-mediated mechanisms may be involved either directly or indirectly in the local modulation of neural NE release in the canine pancreas in vivo.Key words: presynaptic, sympathetic nerve, neuropeptide, tyramine, reuptake, anesthetized dog.

Studies of the biogenic amine transporters. VII. Characterization of a novel cocaine binding site identified with [125I]RTI-55 in membranes prepared from human, monkey and guinea pig caudate

[125I]RTI-55 is a cocaine analog with high affinity for dopamine (DA) and serotonin (5-HT) transporters. Quantitative ligand binding studies revealed a novel high affinity [125I]RTI-55 binding site assayed under 5-HT transporter (SERT) conditions which has low affinity for almost all classic biogenic amine transporter ligands, including high affinity 5-HT transporter inhibitors such as paroxetine, but which retains high affinity for cocaine analogs. This site, termed SERT(site2) for its detection under 5-HT transporter conditions (not for an association with the SERT) occurs in monkey caudate, human caudate, and guinea pig caudate membranes, but not in rat caudate membranes. SERT(site2) is distinguished from the DA transporter (DAT) and SERT by several criteria, including a distinct ligand-selectivity profile, the inability to detect SERT(site2) in cells stably expressing the cloned human DAT, and insensitivity to irreversible ligands which inhibit [125I]RTI-55 binding to the DAT and SERT. Perhaps the most striking finding about SERT(site2) is that a wide range of representative antidepressant agents have very low affinity for SERT(site2). The affinity of cocaine for this site is not very different from the concentration cocaine achieves in the brain at pharmacological doses. Viewed collectively with the observation that ligands with high affinity for SERT(site2) are mostly cocaine analogs, these data lead us to speculate that actions of cocaine which differ from those of classic biogenic amine uptake inhibitors may be mediated in part via SERT(site2).

The neuroprotective and neuronal rescue effects of (-)-deprenyl.

The pharmacological effects of (-)-deprenyl is multi-fold in its nature (dopamine sparing activity, neuroprotective and neuronal rescue effects), which cannot be explained solely by the irreversible MAO-B inhibitory action of the substance. Deprenyl slightly inhibits the re-uptake of noradrenaline and dopamine, but methylamphetamine, the metabolite of the inhibitor, by one order of magnitude is more potent in this respect, than the parent compound. Neither the metabolite nor (-)-deprenyl acts on the uptake of serotonin. The inhibitor has an intensive first pass metabolism after oral treatment. The in vivo pharmacokinetic studies with (-)-deprenyl, using the double labelled radioisotope technique (1.5 mg/kg; orally) in rats revealed that the molar concentration of methylamphetamine can reach the level suitable to induce a significant inhibition of amine uptake. Deprenyl, but especially methylamphetamine pre-treatment can prevent the noradrenaline release induced by the noradrenergic neurotoxin DSP-4. The uptake inhibitory effect of (-)-deprenyl and the metabolites is reversible. After repeated administration of (-)-deprenyl (1.5 mg/kg daily, for 8 days) sustained concentration of its metabolites was detected, compared to that of the acute studies. This can at least partly explain why (-)deprenyl should be administered daily to evoke therapeutic effects in Parkinson's disease. Administration of (-)-deprenyl in a low dose, following the toxic insult, can rescue the damaged neurones. The neuronal rescue effect of the drug was studied on M-1 human melanoma cells in tissue culture. The inhibitor reduced the apoptosis of serum-deprived M-1 cells, but the (+)-isomer failed to exert this effect. The (+/-)-desmethyl-deprenyl almost lacks the property to inhibit apoptosis. For neuroprotection and neuronal rescue an optimal dose of (-)-deprenyl should be administered, because to reach a well balanced concentration of the metabolites in tissues is critical.

PACAP enhances stimulation-induced norepinephrine release in canine pancreas in vivo.

The present study was to investigate whether pituitary adenylate cyclase activating polypeptide (PACAP) can modify norepinephrine (NE) release in response to pancreatic nerve stimulation in anesthetized dogs. Plasma catecholamine concentrations in aortic and superior pancreaticoduodenal (SPD) venous blood were determined by a high performance liquid chromatography method. SPD venous blood flow was measured with an electromagnetic flowmeter. Pancreatic nerves were directly stimulated for 1 min (2 ms, 12 V) at various frequencies at the level of the SPD artery. Various doses of PACAP1-27 (PACAP27) were locally infused into the pancreas through the SPD artery. Nerve stimulation significantly increased both SPD venous NE concentration and its output from the pancreas in a frequency-dependent manner. With PACAP27 alone, neither SPD venous NE concentration nor its output changed significantly following the local administration of PACAP27 at any dose tested. In the presence of PACAP27, however, the net increases in NE concentration and its output in response to nerve stimulation at 2 Hz were significantly enhanced in a dose-dependent manner. The enhanced NE responses to nerve stimulation by PACAP27 were thus significantly greater than those obtained from the group receiving either PACAP27 or stimulation alone. Increases in NE concentration and its output induced by local administration of tyramine were virtually abolished by desipramine, a neural amine uptake inhibitor. However, the NE response to tyramine was not diminished by PACAP27. The results indicate that PACAP27 enhances the stimulation-induced NE release in the pancreas, and that this facilitatory effect of PACAP27 does not result from an inhibition of the neural amine uptake mechanism. The study suggests that PACAP receptor-mediated mechanisms may be involved either directly or indirectly in the local modulation of neural NE release in the canine pancreas in vivo.

"In vitro" effect of some 5-hydroxy-indolalkylamine derivatives on monoamine uptake system.

Three different indolalkylamine derivatives (FA 102, FA 69, FA 70) having in common an -OH group at 5 position of the indole ring and differing in the presence of a methyl group at the N or the acetylenic group of the side chain, have been synthesized and assayed as monoamine oxidase-A (MAO-A) [E.C.1.4.3.4] inhibitors. They were effective inhibitors with, in some cases, similar potencies to clorgyline. "In vitro" experiments were performed on rat brain synaptosomes to investigate whether these MAO-A inhibitors had any effect on noradrenaline (NA), dopamine (DA) and 5-hydroxytryptamine (5-HT) transport systems in different rat brain regions. The effect of these drugs were compared with those of clorgyline and 1-deprenyl. FA 102, FA 69, FA 70 behaved as inhibitors of 3H-monoamine uptake with similar rank of order of potency for amine uptake inhibition: 5-HT > DA > NA. The IC50 values for FA 102, FA 69, FA 70, respectively, were: 17 microM, 60 microM, 18 microM for 5HT uptake in cortex and 37 microM, 55 microM and 20 microM in hippocampus; 70 microM, 385 microM for NA uptake in cortex and 315 microM, 255 microM and 600 microM in hypothalamus; 270 microM, 160 microM, 40 microM for DA uptake in striatum. 1-Deprenyl was a very poor inhibitor of monoamine uptake, whereas clorgyline behaved similarly to these indolalkylamine derivatives. Comparing these results with the IC50 values of citalopram, nisoxetine and GBR12909, specific and selective inhibitors of 5-HT, NA and DA transport systems respectively, indicated that these indolalkylamine derivatives interact more strongly with the 5HT uptake system.

α1A‐Adrenoceptor‐mediated contractile responses of the human vas deferens

1. The predominant alpha 1-adrenoceptor mediating contractions of the human vas deferens has been characterised in vitro by use of subtype selective antagonists. 2. Responses of human epididymal vas deferens were obtained to phenylephrine in the presence of amine uptake inhibitors and propranolol. The effects of the alpha 1-adrenoceptor antagonists, 5-methylurapidil, oxymetazoline, WB4101, prazosin and chloroethylclonidine were examined and also the L-type calcium channel blocker, nifedipine. 3. 5-Methylurapidil, WB4101, oxymetazoline and prazosin acted as competitive antagonists of the responses to phenylephrine, yielding pA2 values of 8.8, 9.2, 7.7 and 8.8 respectively. All four antagonists produced Schild plots with slopes similar to unity and maximum responses to phenylephrine were not altered in the presence of any of the antagonists. 4. Tamsulosin (1 nM) caused rightward shifts of phenylephrine concentration-response curves yielding an apparent pKB value of 10.0. However, maximum responses were also reduced by 51% with this concentration of antagonist. 5. Incubation of tissues with chloroethylclonidine (100 microM for 40 min) failed to alter responses significantly but the presence of nifedipine (1 microM) reduced maximum responses to phenylephrine by 32%. 6. The high affinity of 5-methylurapidil, oxymetazoline and WB4101, together with the failure of chloroethylclonidine to antagonize responses, indicate that the predominant alpha 1-adrenoceptor mediating contraction of the human vas deferens has the characteristics previously described for the pharmacologically-defined alpha 1A-adrenoceptor. The data are also consistent with those described for the cloned alpha 1c-adrenoceptor subtype thereby supporting the hypothesis that the two receptors are identical. The human vas deferens therefore represents a readily accessible preparation for functional studies of the human alpha 1A-adrenoceptor.

In vitro effects on monoamine uptake and release by the reversible monoamine oxidase-B inhibitors Lazabemide and N-(2-aminoethyl)- p-chlorobenzamide: A comparison with l-deprenyl

To investigate whether the reversible monoamine oxidase-B (MAO-B) inhibitors lazabemide and Ro 16–6491 have any additional effect on monoamine uptake and release, in vitro experiments were performed on rat forebrain synaptosomes and blood platelets. The effects of the two drugs were compared with those of l-deprenyl, the well-known irreversible MAO-B inhibitor which is reported to affect amine uptake. Both lazabemide and Ro 16–6491 behaved as weak inhibitors of [ 3H]monoamine uptake by synaptosomes, with a similar rank order of potency for amine uptake inhibition (noradrenaline (NA) ⩾ 5-hydroxytryptamine (5 HT) dopamine (DA)). The ic 50 values for lazabemide and Ro 16–6491, respectively, were: 86 μM and 90 μM for NA uptake; 123 μM and 90 μM for 5HT uptake; > 500 μM and > 1000 μM for DA uptake. l-Deprenyl (rank order of inhibitory potency: NA > DA > 5 HT) was four to 10 times more potent than either compound in inhibiting [ 3H]catecholamine uptake (IC 50 = NA 23 μM, DA 109 μM), and two to three times less potent in inhibiting 5 HT uptake ( ic 50 233 μM). Lazabemide and Ro 16–6491 also differed from l-deprenyl in their ability to induce release of endogenous monoamines from synaptosomes. Thus, Ro 16–6491 (500 μM) induced a greater 5 HT release than did l-deprenyl, but was less effective than l-deprenyl in releasing DA. On the contrary, lazabemide was almost completely inactive on either 5 HT and DA release. The differential effect of the three MAO-B inhibitors on synaptosome 5 HT uptake and release was confirmed by [ 14C]5HT uptake and liberation experiments with isolated rat platelets. The data indicate that the reversible MAO-B inhibitors lazabemide and Ro 16–6491 at relatively high concentrations possess amine uptake-inhibiting properties. With regard to the effects examined, lazabemide markedly differs from l-deprenyl since it does not interfere with DA uptake nor induce amine release from synaptosomes.

Desmethylimipramine, a potent inhibitor of synaptosomal norepinephrine uptake, has diverse effects on thyroid hormone processing in rat brain. I. Effects on in vivo uptake of 125I-labeled thyroid hormones in rat brain

Several lines of evidence point to an interaction between amine uptake inhibitors (tricyclic antidepressants) and thyroid hormones. To examine this issue under conditions which would minimize secondary effects of drug treatment, desmethylimipramine (DMI), a highly specific norepinephrine uptake inhibitor, was given acutely as a single i.p. dose one hour before i.v. [ 125I]triidothyronine (T 3 *) or [ 125I]thyroxine (T 4 *). Tissues were analysed after rat decapitation at 3, 5, 10, and 20 min intervals thereafter. DMI had a small but significant inhibitory effect on the brain uptake of both T 3 * (7.4%) and T 4 * (19%) over their respective 20-min time courses as indicated by two-way ANOVA. To examine the drug response further and to determine the effect of thyroid status on the response, hypothyroid (HYPO) and T 4-induced hyperthyroid (HYPER) rats, were given i.v. T 3 * and, 5 min later, i.p. DMI or saline. They were killed 3 h later and tissues analysed. Because DMI effects on T 4 * uptake could not be evaluated over a 3 h period without blocking T 4 * to T 3 * conversion, sodium ipodate (60 mg/kg) was given in 2 doses before i.v. T 4 *. Under these conditions, DMI significantly reduced brain concentrations of the administered T 3 * and T 4 * in HYPO (15% and 19%) and HYPER rats (13% and 25%). These results suggest that, as it does in the case of norepinephrine, DMI blocks the uptake site for T 3 and T 4 in rat brain. No information is available regarding the relationship, if any, between the thyroid hormone and norepinephrine uptake sites.

A‐75169 HCI: Pharmacological profile and ocular pharmacology studies of a new α‐2 antagonist

AbstractA‐75169 HCI (1,2,3,4‐tetrahydro‐6‐hydroxy‐1‐[N‐methylamino)‐methyl‐N‐phenethyl]‐naphthalene HCI, a racemate, is derived from a series of compounds that combine selective α‐2 receptor antagonism and amine uptake inhibition in a single molecule. A‐75169 HCI showed high affinity (pK1 = 8.79) for cerebral cortex‐derived α‐2 adrenoceptors assayed with [3H] rauwolscine. The R‐enantiomer showed a tenfold greater affinity (pk1 = 9.09) for these receptors than the S‐enantiomer (pK1 = 8.10). A‐75169 HCI and both enantiomers had potent antagonistic effects at postsynaptic α‐2 adrenoceptors (pA2 values 7.31–7.49, dog saphenous vein). The racemate and the R‐enantiomer were moderately potent as antagonists for presynaptic α‐2 adrenoceptors (pA2 values 7.06 and 7.09, respectively, rat vas deferens), and they were more potent inhibitors (ID50 = 1.50 mg/kg, i.v., and 0.60 mg/kg, i.v., respectively) of clonidine‐induced mydriasis, an α‐2 mediated effect, than the S‐enantiomer. The S‐enantiomer was a more potent inhibitor of norepinephrine synaptosomal uptake than the R‐enantiomer (pIC50 = 6.00 and 5.79, respectively). When applied topically to the eyes of rabbits (3.0% solution) and monkeys (0.3% solution), the racemate significantly reduced intraocular pressure (IOP). The topical administration of A‐75169 HCI (0.5% solution) to dog cornea did not affect blood pressure or heart rate. A‐75169 HCI, a selective α‐2 antagonist possessing amine uptake blocking properties, is a potentially novel antiglaucoma compound. © 1993 Wiley‐Liss, Inc.

Amine uptake inhibition by diosmin and diosmetin in human neuronal and neuroendocrine cell lines

Human neuroblastoma cells of sympathetic origin have been used for studying the effects of diosmin and its metabolite diosmetin (vasotonic agent) on amine reuptake systems. Neuroblastoma cells take up 3H-dopamine in a specific and time-dependent manner. 3H-dopamine uptake was dose-dependently inhibited by the known antagonist desipramine. Diosmin did not affect 3H-dopamine uptake at concentrations as high as I m m. On the other hand the aglycone metabolite of diosmin, diosmetin, inhibited 3H-dopamine uptake in a dose-dependent manner (IC50=4 μm). Diosmetin inhibited 3H-dopamine uptake in control and differentiated neuroblastoma cells, as well as in small-cell lung carcinoma cells. Furthermore diosmetin also inhibited 'H-serotonin uptake in both cell types. These results demonstrate that some flavonoids act as antagonists of plasmamembrane amine transporters at the molecular level and suggest that inhibition of amine reuptake at the level of peripheral sympathetic nerve terminals could be responsible for the increased vascular tone observed in vivo after treatment with these drugs.

The Effects of Tianeptine and other Antidepressants on a Rat Model of Depression

A model of depression based on measurements made after restraining rats for two hours has been developed. The model is associated with elevation in corticosterone, reflects the higher incidence of depression in women, and shows increased post-synaptic 5-HT function with adaptation. The effects of tianeptine and other antidepressants on the model were studied. Chronic pre-treatment with desipramine, sertraline (amine uptake inhibitors), and chlordiazepoxide normalised open field activity after restraint. Single high doses, post-restraint, of 8-OH-DPAT, gepirone (5-HT agonists), and tianeptine normalised open field activity, whereas desipramine, chlordiazepoxide, and diazepam did not. It is of considerable interest that tianeptine decreased the availability of 5-HT to receptors.

Advances in sodium-ion coupled biogenic amine transporters

The sodium-ion coupled transporters for 5-hydroxytryptamine (5HT), noradrenaline and dopamine function to reduce extracellular levels of biogenic amines. Over the past fifteen years selective inhibitors of these transport systems have been developed including fluoxetine, citalopram, paroxetine, litoxetine (for 5HT), nisoxetine, desipramine, maprotiline (for noradrenaline) and GBR-12935 (for dopamine). Some of these inhibitors, including drugs selective for noradrenaline transport and particularly those selective for the 5HT transport system are currently widely used in the clinical management of affective disorders. Selective biogenic amine uptake inhibitors have, in addition, provided tools to undertake molecular pharmacological and biochemical studies of their respective transporters. By this means, the rat brain 5HT and dopamine transporters have been identified as polypeptides with relative molecular masses of 73,000 and 80,000, respectively, using affinity-chromatographic purification and photoaffinity-labelling techniques. Recently, the biogenic amine transporters have been cloned and a comparison of their predicted amino acid sequences reveals that these proteins share a considerable degree of similarity with notably 12–13 transmembrane spanning domains. Perspectives for future fundamental and clinical research on biogenic amine transport systems using molecular biological techniques are discussed.

Binding of [&lt;sup&gt;3&lt;/sup&gt;H]-Dopamine to Human Lymphocytes: Possible Relationship to Neurotransmitter Uptake Sites

Freshly isolated human lymphocytes from 11 healthy subjects had specific binding sites for dopamine which were dependent on time, temperature and sodium, and appeared to follow Michaelis-Menten kinetics. The apparent affinity constant (KD) of human lymphocytes for dopamine and the maximal number of binding sites (Bmax) were 109 +/- 21 nM and 2.66 +/- 1.75 pmol/10(7) cells, respectively. Dopamine binding was markedly affected by cocaine (IC50 = 150 nM) and other inhibitors of biogenic amine uptake. The relatively high potency of cocaine in competing for dopamine binding suggested that human lymphocytes may serve as a readily accessible model to detect changes in the neuronal uptake of dopamine and perhaps other monoamine neurotransmitters.

Pharmacological profile of duodenal alkaline secretion

Stimulation of mucosal alkaline secretion represents an opportunity for discovering novel drugs of potential benefit in maintenance therapy of duodenal ulcer disease. We screened over 200 agents representing the full spectrum of pharmacological categories in order to characterize stimulatory pathways and identify mechanistic leads. A variety of eicosanoids, phospho-diesterase inhibitors and adrenoreceptor agonists together with forskolin, 6-hydroxy-dopamine, 2-chloroadenosine, diazepam, testosterone, dipyridamole and dihydropyridazinone caused a reproducible increase in the metabolism-dependent component of alkaline secretion in bullfrog proximal duodenum. PGE2 (ED50 0.02 microgram/ml) was the most potent agent in vitro and was also the most effective stimulant of duodenal alkalinization in vivo in an anaesthetized cat preparation. Agents without effect on spontaneous alkaline secretion by amphibian duodenum included agonists and antagonists of histamine, 5-hydroxy-tryptamine, gamma-aminobutyric acid, dopamine, muscarinic and nicotinic receptors, inhibitors of amine uptake, monoamine oxidase and cholinesterase, plus various corticoids, diuretics, oestrogens, chemotherapeutic (anticancer) and antimicrobial agents. The major mechanism of stimulating alkaline secretion in the isolated duodenum is by increasing intracellular cyclic AMP levels. This may occur by either inhibiting metabolism of the nucleotide or by stimulating its formation. Additionally, many stimulants appear to act indirectly via liberation of endogenous prostaglandins as judged from the marked attenuation of responses in the presence of indomethacin to all agonists apart from exogenous PGE2, forskolin, ICI 63197 (PDE inhibitor), 2-chloroadenosine and diazepam. Whether purinergic agonists and benzodiazepines act directly on the enterocyte or by releasing other paracrine mediators is unknown.