Role of noradrenergic and dopaminergic systems in the antinociceptive effect of N-(3-(phenylselanyl)prop-2-yn-1-yl)benzamide in mice.

Pain has a negative impact on public health, reducing quality of life. Unfortunately, current treatments are not fully effective and have adverse effects. Therefore, there is a need to develop new analgesic compounds. Due to promising results regarding the antinociceptive effect of N-(3-(phenylselanyl)prop-2-in-1-yl)benzamide (SePB), this study aimed to evaluate the participation of the dopaminergic and noradrenergic systems in this effect in mice, as well as its toxicity. To this, the antagonists sulpiride (D2/D3 receptor antagonist, 5 mg/kg), SCH-23390 (D1 receptor antagonist, 0.05 mg/kg), prazosin (α1 adrenergic receptor antagonist, 0.15 mg/kg), yohimbine (α2-adrenergic receptors, 0.15 mg/kg) and propranolol (non-selective ß-adrenergic antagonist, 10 mg/kg) were administered intraperitoneally to mice 15 min before SePB (10 mg/kg, intragastrically), except for propranolol (20 min). After 26 min of SePB administration, the open field test was performed for 4 min to assess locomotor activity, followed by the tail immersion test to measure the nociceptive response. For the toxicity test, animals received a high dose of 300 mg/kg of SePB. SePB showed an increase in the latency for nociceptive response in the tail immersion test, and this effect was prevented by SCH-23390, yohimbine and propranolol, indicating the involvement of D1, α2 and ß-adrenergic receptors in the antinociceptive mechanism of the SePB effect. No changes were observed in the open field test, and the toxicity assessment suggested that SePB has low potential to induce toxicity. These findings contribute to understanding SePB's mechanism of action, with a focus on the development of new alternatives for pain treatment.

Effects of 071031B, a novel serotonin and norepinephrine reuptake inhibitor, on monoamine system in mice and rats.

Our previous study indicated that 071031B, a novel potential serotonin and norepinephrine reuptake inhibitor, showed robust antidepressant activity in multiple depression models, and could simultaneously inhibit 5-HT and NE reuptake in vitro. The present study was to evaluate the effects of 071031B on monoamine system in vivo, by using pharmacological models, including 5-HTP induced head-twitch test, yohimbine toxicity potentiation test, and reserpine induced hypothermia test, and determining monoamine transmitter levels in reserpine induced monoamine depletion model or chronic unpredictable stress (CUS) model. Results in pharmacological models indicated that acute administration of 071031B at 5-20 mg/kg significantly enhanced 5-HTP induced head-twitch behavior, potentiated yohimbine induced lethal rate, and reversed reserpine induced hypothermia. Further monoamine assays demonstrated that acute or chronic administration of 071031B at 10 or 20 mg/kg increased 5-HT and/or NE levels in various brain regions in reserpine or CUS induced monoamine depletion models, respectively, without effect on DA and its metabolites. Our results revealed that 071031B produces potent inhibition of 5-HT and NE reuptake in vivo.

Behavioral profile of Hypericum perforatum (St. John's Wort) extract. A comparison with standard antidepressants in animal models of depression.

BACKGROUND AND OBJECTIVES: Hypericum (H.) perforatum, popularly called St. John's Wort has been used traditionally for the treatment of anxiety, depression and as a nerve tonic. Large amount of clinical and animal experimental data demonstrate that H. perforatum acts by biochemical mechanisms similar to the tricyclic antidepressants or serotonin reuptake inhibitors. However, its efficacy in comparison to standard antidepressant drugs is not well studied. The present study evaluated H. perfortum extract in animal models of depression compared to clinically used antidepressants. MATERIALS AND METHODS: The effects of standardized extract of H. perforatum was compared with standard antidepressants using animal models of depression such as forced swim test (FST), yohimbine induced lethality test, pnetylenetetrazole (PTZ) induced convulsion and locomotor activity tests. Different doses of the plant extract and standard drugs were administered to rats or mice intraperitoneally (i.p). RESULTS: In the FST, H. perforatum extract (30-90 mg/kg i.p.) caused a dose dependent reduction in immobility time in rats with maximal effect being 53% at 90 mg/kg. This effect was reversed at higher doses (100 mg/kg) showing a U-shaped dose response curve. Fluoxetine and imipramine (30-70 mg/kg i.p.) produced similar reduction in the immobility time in rats. Venlafaxine exhibited weak antidepressant effect. H. perforatum extract (30-100 mg/kg i.p.), dothiepin (10-50 mg/kg i.p.), fluoxetine (30-60 mg/kg i.p.) and venlafaxine (20-40 mg/kg i.p.) potentiated yohimbine induced lethality. PTZ induced toxicity was also enhanced with these agents. In the locomotor activity test H. perforatum decreased the locomotor counts of mice similar to standard antidepressants. CONCLUSIONS: H. perforatum has antidepressant properties similar to standard antidepressants. The antidepressant profile of H. perforatum is closely related to the selective serotonin reuptake inhibitors class of antidepressants.

Yohimbine Directly Induces Cardiotoxicity on Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes.

Yohimbine is a highly selective and potent α2-adrenoceptor antagonist, which is usually treated as an adjunction for impotence, as well for weight loss and natural bodybuilding aids. However, it was recently reported that Yohimbine causes myocardial injury and controversial results were reported in the setting of cardiac diseases. Here, we used human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) as a model system to explore electrophysiologic characterization after exposure to Yohimbine. HiPSC-CMs were differentiated by employment of inhibitory Wnt compounds. For analysis of electrophysiological properties, conventional whole-cell patch-clamp recording was used. Specifically, spontaneous action potentials, pacemaker currents (If), sodium (Na+) channel (INa), and calcium (Ca++) channel currents (ICa) were assessed in hiPSC-CMs after exposure to Yohimbine. HiPSC-CMs expressed sarcomeric-α-actinin and MLC2V proteins, as well as exhibited ventricular-like spontaneous action potential waveform. Yohimbine inhibited frequency of hiPSC-CMs spontaneous action potentials and significantly prolonged action potential duration in a dose-dependent manner. In addition, rest potential, threshold potential, amplitude, and maximal diastolic potential were decreased, whereas APD50/APD90 was prolonged. Yohimbine inhibited the amplitude of INa in low doses (IC50 = 14.2 µM, n = 5) and inhibited ICa in high doses (IC50 = 139.7 µM, n = 5). Whereas Yohimbine did not affect the activation curves, treatment resulted in left shifts in inactivation curves of both Na+ and Ca++ channels. Here, we show that Yohimbine induces direct cardiotoxic effects on spontaneous action potentials of INa and ICa in hiPSC-CMs. Importantly, these effects were not mediated by α2-adrenoceptor signaling. Our results strongly suggest that Yohimbine directly and negatively affects electrophysiological properties of human cardiomyocytes. These findings are highly relevant for potential application of Yohimbine in patients with atrioventricular conduction disorder.

Alpha2-adrenergic dysregulation in congenic DxH recombinant inbred mice selectively bred for a high fear-sensitized (H-FSS) startle response.

Patients with anxiety disorders and posttraumatic stress disorder (PTSD) exhibit exaggerated fear responses and noradrenergic dysregulation. Fear-related responses to α2-adrenergic challenge were therefore studied in DxH C3H/HeJ-like recombinant inbred (C3HLRI) mice, which are a DBA/2J-congenic strain selectively bred for a high fear-sensitized startle (H-FSS). C3HLRI mice showed an enhanced acoustic startle response and immobility in the forced swim test compared to DBA/2J controls. The α2-adrenoceptor antagonist yohimbine (Yoh; 5.0 mg/kg) induced an anxiogenic and the α2-adrenoceptor agonist clonidine (Clon; 0.1 mg/kg) an anxiolytic effect in the open field (OF) in C3HLRI but not DBA/2J mice. In auditory fear-conditioning, Yoh (5.0 mg/kg)-treated C3HLRI mice showed higher freezing during fear recall and extinction learning than DBA/2J mice, and a higher ceiling for the Yoh-induced deficit in fear extinction. No strain differences were observed in exploration-related anxiety/spatial learning or the Clon-induced (0.1 mg/kg) corticosterone surge. A global analysis of the behavioral profile of the two mouse strains based on observed and expected numbers of significant behavioral outcomes indicated that C3HLRI mice showed significantly more often fear- and stress-related PTSD-like behaviors than DBA/2J controls. The analysis of the robustness of significant outcomes based on false discovery rate (FDR) thresholds confirmed significant differences for the strain-Yoh-interactions in the OF center and periphery, the Yoh-induced general extinction deficit, strain differences in conditioned fear levels, and at the dose of 5.0 mg/kg for the Yoh-induced ceiling in freezing levels among others. The current findings are consistent with previous observations showing alterations in the central noradrenergic system of C3HLRI mice (Browne et al., 2014, Stress 17:471-83). Based on their behavioral profile and response to α2-adrenergic stimulation, C3HLRI mice are a valuable genetic model for studying adrenergic mechanisms of anxiety disorders and potentially also of PTSD.

Role for serotonin in the antidepressant-like effect of a flavonoid extract of Xiaobuxin-Tang.

Xiaobuxin-Tang (XBXT), a traditional Chinese herbal decoction, has been used for the treatment of depressive disorders for centuries in China. Herein, we explored the antidepressant-like effect and its monoaminergic mechanism of the total flavonoids (XBXT-2) isolated from the extract of XBXT. In present study, single XBXT-2 (25, 50, 100 mg/kg, p.o.) administration significantly potentiated the mouse head-twitch response induced by 5-hydroxytryptophan (5-HTP, a metabolic precursor to serotonin), and also, decreased the immobility time in mouse tail suspension test, which was completely prevented by p-chlorophenylalanine (PCPA, an inhibitor of serotonin synthesis) pretreatment. However, single treatment with XBXT-2 had no effect on yohimbine toxicity and high dose of apomorphine-induced hypothermia in mice. These results indicated that acute treatment with XBXT-2 produced serotonergic, but not noradrenergic activation. In addition, chronic XBXT-2 (25, 50 mg/kg, p.o., 28 days) treatments significantly reversed the depressive-like behaviors in chronically mildly stressed (CMS) rats, including the reduced sucrose preference, deficient locomotor activity and prolonged latency to novelty-suppressed feeding. Furthermore, XBXT-2 normalized the neurotransmitter changes, including the decreased serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) levels in hippocampus and prefrontal cortex in CMS rats. These findings confirm the antidepressant-like effect of XBXT-2 in CMS model of rats, which may be primarily based on its serotonergic activation.

Synthesis of some tropane derivatives of anticipated activity on the reuptake of norepinephrine and/or serotonin.

A variety of tropane derivatives 14a-g were prepared via the reaction of the alcohol analogs 12a and 12b with substituted fluorobenzenes 13a-f. The prepared compounds were tested for their activity and selectivity toward the norepinephrine transporter (NET) and serotonin transporter (SERT) using yohimbine-induced mortality and 5-hydroxytryptophan-induced neurotoxicity in mice, respectively. All the tested compounds were found to be NE and 5-HT reuptake inhibitors except 14d which exhibited selective 5-HT reuptake inhibition activity.

Influence of pharmacologically-induced experimental anxiety on nociception and antinociception in rats.

Animal studies reveal that diverse environmental stimuli that generate anxiety-like behaviors also induce antinociception; conversely, clinical data show that pain perception is reduced under anxiolysis. This study was conducted to investigate the influence of pharmacologically induced-anxiety on nociception and antinociception. Experimental anxiety levels were measured using the rat burying behavior test. Diazepam (0, 0.5, 1.0 and 2.0 mg/kg, i.p.) or yohimbine (0, 0.5 and 1.0 mg/kg, i.p.) were used as anxiolytic or anxiogenic drugs, respectively. To evaluate the influence of different experimental anxiety levels on nociception, the pain-induced functional impairment in the rat (PIFIR model) was used. Nociception was induced by an intra-articular injection of 15% uric acid into the knee joint of the right hind limb. Diazepam or yohimbine were administered 15 min before uric acid and the ability of the rat to use the injured hind limb was recorded. To analyze the influence of different levels of anxiety on the antinociceptive effects produced by acetylsalicylic acid (0, 31, 100 and 310 mg/kg, p.o.); this analgesic was administered 3.5 h after uric acid. Fifteen min before diazepam (2.0 mg/kg) or yohimbine (1.0 mg/kg) were administered. We found that, in the burying behavior test, diazepam and yohimbine produced a dose-dependent decrease or augment in the cumulative time of burying, effects denoting reduced or increased experimental anxiety, respectively. Diazepam or yohimbine, administered alone, was unable to produce nociception. The results showed an influence of anxiety on nociception since a decreased (by diazepam) or increased (by yohimbine) experimental anxiety prevented nociception. Control experiments showed that acetylsalicylic acid did not modify experimental anxiety in the burying behavior test, but effectively reversed the nociception induced by uric acid (15%) in the PIFIR model. Such antinociceptive effect was unmodified by the anxiolytic or anxiogenic actions of diazepam or yohimbine. Data are discussed on the bases of clinical- and animal-studies revealing interactions between anxiety and nociception.

The anxiogenic drug yohimbine reinstates methamphetamine seeking in a rat model of drug relapse.

BACKGROUND: Brain noradrenaline is involved in footshock stress-induced reinstatement of drug seeking in a rat relapse model. We studied whether yohimbine, an alpha-2 adrenoceptor antagonist that increases noradrenaline release and induces anxiety-like responses in human and nonhuman subjects, would reinstate methamphetamine seeking in rats. METHODS: In experiment 1, the effect of yohimbine (1.25-2.5 mg/kg) on reinstatement was compared with that of intermittent footshock (5 min;.2-.6 mA) in rats that were trained to lever press for intravenous methamphetamine (9-11 days) and subsequently underwent 7 days of extinction training. In experiment 2, the effect of yohimbine on reinstatement of drug seeking was determined during early (1 day) and late (21 or 51 days) withdrawal periods. On the test days, rats were first given 3-hour extinction sessions and were then tested for reinstatement induced by yohimbine. RESULTS: In experiment 1, both yohimbine and footshock stress reinstated methamphetamine seeking after extinction. In experiment 2, extinction responding was higher after 21 or 51 withdrawal days than after 1 withdrawal day. In contrast, no significant time-dependent changes in yohimbine-induced reinstatement were observed. CONCLUSIONS: Results indicate that yohimbine is a potent stimulus for reinstatement of methamphetamine seeking in a rat relapse model.

Pharmacological blockade of alpha2-adrenoceptors induces reinstatement of cocaine-seeking behavior in squirrel monkeys.

Converging evidence suggests a role for noradrenergic mechanisms in stress-induced reinstatement of cocaine seeking in animals. Yohimbine, an alpha(2)-adrenoceptor antagonist, is known to be anxiogenic and induce stress-related responses in humans and animals. Here, we tested the ability of yohimbine to reinstate cocaine-seeking behavior and induce behavioral and physiological signs characteristic of stress in squirrel monkeys. Monkeys were trained to self-administer cocaine under a second-order schedule of i.v. drug injection. Drug seeking subsequently was extinguished by substituting saline for cocaine injections and omitting the cocaine-paired stimulus. The ability of yohimbine and the structurally distinct alpha(2)-adrenoceptor antagonist RS-79948 to reinstate cocaine-seeking behavior was assessed by administering priming injections immediately before test sessions in which the cocaine-paired stimulus was either present or absent. Priming injections of yohimbine (0.1-0.56 mg/kg, i.m.) or RS-79948 (0.01-0.1 mg/kg, i.m.) induced dose-related reinstatement of cocaine-seeking behavior. The magnitude of yohimbine-induced reinstatement was similar regardless of the presence or absence of the cocaine-paired stimulus. Yohimbine also significantly increased salivary cortisol levels, a physiological marker of stress, as well as scratching and self-grooming, behavioral markers of stress in nonhuman primates. In drug interaction experiments, pretreatment with the alpha(2)-adrenoceptor agonist clonidine (0.1-0.3 mg/kg, i.m.) dose-dependently inhibited yohimbine-induced reinstatement of cocaine seeking. In contrast, pretreatment with the dopamine receptor antagonist flupenthixol failed to inhibit yohimbine-induced reinstatement of cocaine seeking. The results show that pharmacological blockade of alpha(2)-adrenoceptors can induce reinstatement of cocaine-seeking behavior and characteristic stress responses in squirrel monkeys, providing a potentially useful model of stress-induced relapse to drug seeking.

Potential antidepressant activity of rolipram and other selective cyclic adenosine 3',5'-monophosphate phosphodiesterase inhibitors.

Following intraperitoneal administration, the selective cAMP phosphodiesterase (PDE) inhibitors rolipram, ICI 63 197 and Ro 20-1724 were investigated in mice in comparison with imipramine for their effectiveness in two classical test models for prediction of clinical antidepressant activity: antagonism of reserpine-induced hypothermia or hypokinesia and potentiation of yohimbine lethality. Rolipram was approximately 15 times more potent than imipramine or Ro 20-1724 and approximately as potent as ICI 63 197 in antagonizing reserpine-induced hypothermia. The antihypothermic effect of the phosphodiesterase inhibitors occurred at a smaller dose than that of imipramine. In contrast to imipramine, the phosphodiesterase inhibitors reversed reserpine-induced hypokinesia. Rolipram was approximately as potent as ICI 63 197 and about 15 times more potent than Ro 20-1724. Rolipram was approx. 5 times more potent than Ro 20-1724 and approx. as potent as imipramine or ICI 63 197 in potentiating the lethality of yohimbine. In both test models the (-)-isomer of rolipram was approx. 10-15 times more potent than the (+)-isomer, indicating a stereospecific mechanism of action. The present data suggest an antidepressant action of selective cAMP phosphodiesterase inhibitors due to enhancement of central noradrenergic transmission. The hypothesis is put forward that the increase of noradrenaline turnover induced by phosphodiesterase inhibitors in conjunction with the inhibitory action of the compounds on cAMP metabolism enables more efficient adaptative changes to occur at central synapses resulting in a rapid onset of the antidepressant activity. Preliminary results with rolipram in patients with endogenous depression seem to support this assumption.

Comparison of imipramine-imipraminium in mice. To elucidate central or peripheral origin of effects of imipramine.

Imipramine hydrochloride shows effects in a battery of tests used for the screening of antidepressant drugs. The central origin of these pharmacological effects of imipramine has not been clearly established. Imipramine methiodide is a quaternary derivative of imipramine which does not cross the blood-brain barrier easily. The effects of the two forms of imipramine have been compared: on an effect known to have a central origin; on two effects known to have a peripheral origin; on a battery of tests used for the screening of antidepressant drugs. It has been demonstrated that imipramine methiodide is as active as imipramine hydrochloride on two effects of peripheral origin, less active than imipramine hydrochloride on an effect considered to have a central origin and less active than imipramine hydrochloride or inactive on the tests which are used for the screening of antidepressant drugs. Consequently, the tests used for the screening of antidepressant drugs represent, primarily or exclusively, effects of central origin.

Yohimbine-induced seizures involve NMDA and GABAergic transmission.

The alpha 2-antagonist, yohimbine has been shown to dose-dependently induce clonic seizures in mice. The convulsant effects of yohimbine are not due to alpha 2-antagonism, as other alpha 2-antagonists, such as rauwolscine and idazoxan, did not produce seizures at doses up to 100 mg/kg. Since GABAmimetic and excitatory amino acid antagonist agents attenuate yohimbine-induced seizures, the respective contribution of these systems to the production of yohimbine seizures was investigated. The CD50 dose of yohimbine (dose required to produce clonic seizures in 50% of the mice) was determined to be 25.5 mg/kg (s.c.). The CD15 dose of N-methyl-DL-aspartic acid (NMDLA), bicuculline and methyl-6,7-dimethoxy-4 ethyl-beta carboline-3-carboxylate (DMCM) significantly potentiated the convulsant effects of yohimbine, such that the CD50 dose was decreased from 25.5 mg/kg to 1.6, 10.9 and 9.9 mg/kg, respectively. Furthermore, the potentiation in the presence of NMDLA was significantly greater than either bicuculline or DMCM. These results suggest that yohimbine-induced seizures are not only mediated through the impairment of GABAergic transmission but moreover, by a possible endogenous enhancement of excitatory amino acid transmission. In addition, the effects of GABAmimetic agents, competitive and non-competitive NMDA receptor antagonists and strychnine-insensitive glycine receptor antagonists were compared in the yohimbine-, bicuculline- and NMDLA-induced seizure assays.

1-Aryl-2-(aminomethyl)cyclopropanecarboxylic acid derivatives. A new series of potential antidepressants.

A series of 1-aryl-2-(aminomethyl)cyclopropanecarboxylic acid derivatives were synthesized and evaluated as potential antidepressants. Compounds with the Z configuration were synthesized from 1-aryl-2-oxo-3-oxabicyclo[3.1.0]hexane and those with the E configuration from (E)-1-phenyl-2-(hydroxymethyl)cyclopropanecarboxylic acid. The compounds were evaluated in animal tests designed to reveal potential antidepressant activity and the existence of undesirable side effects. Several derivatives were more active than imipramine and desipramine. On the basis of its activity in pharmacological animal tests of antidepressant activity and its potential lack of side effects, 1-phenyl-1-[(diethylamino)carbonyl]-2- (aminomethyl)cyclopropane hydrochloride, midalcipran (INN), was selected for further development. This compound is currently in phase III clinical evaluation.

1-(Aminoalkyl)-6-aryl-4-H-s-triazolo[4,3-a][1,4]benzodiazepines with antianxiety and antidepressant activity.

A series of 1-(aminoalkyl)-6-aryl-4H-s-triazolo[4,3-a][1,4]benzodiazepines has been prepared and evaluated for central nervous system activity. We have found that members of this series have activity in pharmacological test systems designed to detect both anxiolytic and antidepressant activity. Each type of activity could be varied independently by appropriate substituent selections.

(+/-)-4-Aryl-4,5-dihydro-3H-1,3-benzodiazepines. 1. Synthesis and evaluation of (+/-)-4,5-dihydro-2,3-dimethyl-4-phenyl-3H-1,3-benzodiazepine and analogues as potential antidepressant agents.

A series of (+/-)-4,5-dihydro-4-phenyl-3H-1,3-benzodiazepines and (+/-)-4,5-dihydro-4-phenyl-1H-1,3-benzodiazepines was synthesized as part of a program to develop novel psychotropics. Of these compounds, (+/-)-4,5-dihydro-2,3-dimethyl-4-phenyl-3H-1,3-benzodiazepine (10a, HRP 543) emerged as a potential antidepressant. In in vivo mouse tests (inhibition of tetrabenazine-induced ptosis and potentiation of yohimbine toxicity) which are predictive of antidepressant-like activity, 10a is comparable to amitriptyline. The similarity is also maintained in vitro, as both 10a and amitriptyline inhibit norepinephrine and serotonin uptake into rat brain synaptosomes. No significant inhibition of rat brain monoamine oxidase A or B was found with 10a, nor did the compound potentiate tryptamine-induced seizures. On chronic administration, the number of cortical beta-adrenergic receptor sites was similarly reduced by 10a and desipramine. The anticholinergic activity of clinically useful antidepressants, such as amitriptyline, is a proposed cause of side effects which reduce patient compliance. In contrast to the tricyclics, 10a apparently lacks anticholinergic activity, as evidenced in vitro by negligible displacement of [3H]quinuclidinyl benzylate from rat brain muscarinic receptors and in vivo by insignificant antagonism of the cholinergic stimulation produced by physostigmine or oxotremorine. These data suggest that 10a may be clinically useful as a novel nontricyclic antidepressant which is devoid of anticholinergic side-effect liability. Further evaluation of 10a in nonrodent species is in progress.

Resolution, absolute stereochemistry, and enantioselective activity of nomifensine and hexahydro-1H-indeno[1,2-b]pyridines.

Nomifensine and three selected compounds from the series of H4a,H5-trans,H4a,H9b-cis-2,3,4,4a,5,9b-hexahydro-1H-in deno[1,2-b]pyridines have been resolved into their enantiomers. All compounds exhibit pronounced enantioselective activity with respect to their inhibition of tetrabenazine-induced ptosis and potentiation of yohimbine toxicity. Nomifensine exhibits the same preference for one enantiomer with respect to dopamine and norepinephrine reuptake, whereas in the indeno[1,2-b]pyridine series in vitro experiments do not discriminate between the optical antipodes. The absolute stereochemistry of the pharmacologically active enantiomers in both series was determined by X-ray analyses and comparative CD spectra. For biological activity the diphenylmethane is an essential structure feature in both series. Its absolute configuration proved to be 4S for nomifensine and 5S for indenopyridines. The similar pharmacological profile of the two chemical entities is therefore reflected in an identical configuration of this pharmacologically important molecular part.

Interaction between yohimbine alkaloids and amphetamine in mice.

The toxicity (LD50) of the isomers yohimbine, beta-yohimbine, and corynanthine was determined in mice. The LD50 of amphetamine in the presence of a constant dose of a yohimbine isomer and that of the isomer in the presence of a constant dose of amphetamine were determined in aggregated mice. Isobolograms were constructed from these data and used to evaluate the interaction of the yohimbine alkaloids and amphetamine. Beta-yohimbine was found to be approximately twice as toxic as yohimbine and corynanthine about one fifth as toxic. There was a mutual potentiation between the toxicities of yohimbine and amphetamine. Potentiation of the toxicity of amphetamine occurred with beta-yohimbine but the effect was not as marked as with yohimbine. In contrast, corynanthine antagonized the toxicity of amphetamine. The interaction between yohimbine and amphetamine is unlikely to be due to noradrenergic mechanisms but could conceivably involve serotonergic or dopaminergic mechanisms.

Adrenergic nonspecific potentiation of yohimbine toxicity in mice by antidepressants and related drugs and antiyohimbine action of antiadrenergic and serotonergic drugs.

Thirteen imipramine-like antidepressants and three anticholinergics potentiated yohimbine toxicity in mice. The strongest potentiation was observed after the nonantidepressant adrenergic compound AW 151129. Monomethyl derivatives were significantly stronger than their parent dimethyl compounds. Quaternary imipramine and amitriptyline, amphetamine, and inhibitors of monoamine oxidase were inactive. Pretreatment with an inhibitor of tyrosine hydroxylase (alpha-methyl-p-tyrosine) or the beta-adrenergic-blocking drug pindolol diminished lethality in mice treated with a combination of desmethylimipramine (AW 151129) and yohimbine. The inhibitor of brain serotonin synthesis p-chlorophenylalanine and a depletor of serotonin and catecholamine synthesis reserpine, enhanced yohimbine toxicity whereas serotonin and its precursors tryptophan and 5-hydroxytryptophan prolonged survival time. Thus, a test of yohimbine potentiation toxicity in mice reveals an adrenergic component of pharmacological activity of antidepressants. The predictive value of this test is limited similarly to antihypothermic tests of antagonism to reserpine and the related drugs apomorphine and 5-hydroxytryptophan.

High prevalence of potentially hepatotoxic herbal supplement use in patients with fulminant hepatic failure.

HYPOTHESIS: The use of potentially hepatotoxic herbal and dietary supplements is highly prevalent in the fulminant hepatic failure (FHF) patient population at our institution, and this subgroup of patients has a worse prognosis. DESIGN: Retrospective case series. Settings An adult tertiary care university hospital and a Veterans Affairs hospital in Oregon. PATIENTS: All patients referred to the liver transplantation service for FHF from January 2001 through October 2002 (N = 20). We defined FHF as onset of encephalopathy within 8 weeks of onset of jaundice in the absence of preexisting liver disease. All patients underwent investigation for potential causes of liver injury. Potentially hepatotoxic supplements were defined as those with previously published reports of hepatic injury related to their use. RESULTS: Ten patients (50%) were recent or active users of potentially hepatotoxic supplements or herbs; 10 had no history of supplement use. In the supplement group, 7 patients (35%) had no other identified cause for hepatic failure. Six patients in the supplement group and 2 patients in the nonsupplement group underwent orthotopic liver transplantation. Five patients in each group died. There were no significant differences in transplantation rate (P =.07) or survival (P>.99) between groups. Supplement use alone accounted for the most cases of FHF during this period, exceeding acetaminophen toxicity and viral hepatitis. CONCLUSIONS: Herbal and dietary supplements were potential hepatotoxins in a high proportion of patients with FHF at our institution. Enhanced public awareness of the potential hepatotoxicity of these commonly used agents and increased regulatory oversight of their use is strongly urged.