Incidence of hyperoxia in trauma patients receiving pre-hospital emergency anaesthesia: results of a 5-year retrospective analysis

Background

Previous studies have demonstrated an association between hyperoxia and increased mortality in various patient groups. Critically unwell and injured patients are routinely given high concentration oxygen in the pre-hospital phase of care. We aim to investigate the incidence of hyperoxia in major trauma patients receiving pre-hospital emergency anesthesia (PHEA) in the pre-hospital setting and determine factors that may help guide clinicians with pre-hospital oxygen administration in these patients.

Methods

A retrospective cohort study was performed of all patients who received PHEA by a single helicopter emergency medical service (HEMS) between 1 October 2014 and 1 May 2019 and who were subsequently transferred to one major trauma centre (MTC). Patient and treatment factors were collected from the electronic patient records of the HEMS service and the MTC. Hyperoxia was defined as a PaO₂ > 16 kPA on the first arterial blood gas analysis upon arrival in the MTC.

Results

On arrival in the MTC, the majority of the patients (90/147, 61.2%) had severe hyperoxia, whereas 30 patients (20.4%) had mild hyperoxia and 26 patients (19.7%) had normoxia. Only 1 patient (0.7%) had hypoxia. The median PaO₂ on the first arterial blood gas analysis (ABGA) after HEMS handover was 36.7 [IQR 18.5–52.2] kPa, with a range of 7.0–86.0 kPa. SpO₂ pulse oximetry readings before handover were independently associated with the presence of hyperoxia. An SpO₂ ≥ 97% was associated with a significantly increased odds of hyperoxia (OR 3.99 [1.58–10.08]), and had a sensitivity of 86.7% [79.1–92.4], a specificity of 37.9% [20.7–57.8], a positive predictive value of 84.5% [70.2–87.9] and a negative predictive value of 42.3% [27.4–58.7] for the presence of hyperoxemia.

Conclusion

Trauma patients who have undergone PHEA often have profound hyperoxemia upon arrival at hospital. In the pre-hospital setting, where arterial blood gas analysis is not readily available a titrated approach to oxygen therapy should be considered to reduce the incidence of potentially harmful tissue hyperoxia.

Increased diaphragm motor unit discharge frequencies during quiet breathing in people with chronic tetraplegia

KEY POINTS

Respiratory muscle strength is compromised in people with tetraplegia, which may be compensated for by an increase in neural drive to the diaphragm. We found that the discharge frequencies of diaphragm motor units are higher in people with chronic tetraplegia compared with able-bodied people during quiet breathing. Furthermore, we found that the area of single motor unit potentials was increased in people with tetraplegia. These results suggest an increased motoneurone output to the diaphragm and remodelling of diaphragm motor units to maintain ventilation in tetraplegia.

ABSTRACT

People with tetraplegia have reduced inspiratory muscle strength, ∼40% of able-bodied individuals. Paralysed or partially paralysed respiratory muscles as a result of tetraplegia compromise lung function, increase the incidence of respiratory infections and can cause dyspnoea. We hypothesised that reduced inspiratory muscle strength in tetraplegia may increase neural drive to the inspiratory muscles to maintain ventilation. We recorded the discharge properties of single motor units from the diaphragm in participants with chronic tetraplegia (8 males, 42-78 years, C3-C6 injury, AIS A-C) and able-bodied control participants (6 males matched for age and body mass index). In each group, 117 and 166 single motor units, respectively, were discriminated from recordings in the costal diaphragm using a monopolar electrode. A linear mixed-effects model analysis showed higher peak discharge frequencies of motor units during quiet breathing in tetraplegia (17.8 ± 4.9 Hz; mean ± SD) compared with controls (12.4 ± 2.2 Hz) (P < 0.001). There were no differences in tidal volume, inspiratory time or mean air flow between groups. Motor unit potentials in tetraplegia, compared with controls, were larger in amplitude (1.1 ± 0.7 mV and 0.5 ± 0.3 mV, respectively, P = 0.007) and area (1.83 ± 1.49 µV ms and 0.69 ± 0.52 µV ms, respectively, P = 0.003). The findings indicate that diaphragm motor unit remodelling is likely to have occurred in people with chronic tetraplegia and that there is an increase in diaphragm motor unit discharge rates during quiet breathing. These neural changes ensure that ventilation is maintained in people with chronic tetraplegia.

Abdominal Functional Electrical Stimulation to Augment Respiratory Function in Spinal Cord Injury

Background: Functional electrical stimulation (FES) is the application of electrical pulses to a nerve to achieve a functional muscle contraction. Surface electrical stimulation of the nerves that innervate the abdominal muscles, termed abdominal FES, can cause the abdominal muscles to contract, even when paralysed after spinal cord injury. As the abdominal muscles are the major expiratory muscles, and commonly partially or completely paralysed in tetraplegia, abdominal FES offers a promising method of improving respiratory function for this patient group. Objective: The aim of the article is to provide readers with a better understanding of how abdominal FES can be used to improve the health of the spinal cord-injured population. Methods: A narrative review of the abdominal FES literature was performed. Results: Abdominal FES can achieve an immediate effective cough in patients with tetraplegia, while the repeated application over 6 weeks of abdominal FES can improve unassisted respiratory function. Ventilator duration and tracheostomy cannulation time can also be reduced with repeated abdominal FES. Conclusion: Abdominal FES is a noninvasive method to achieve functional improvements in cough and respiratory function in acute and chronically injured people with tetraplegia. Potential practical outcomes of this include reduced ventilation duration, assisted tracheostomy decannulation, and a reduction in respiratory complications. All of these outcomes can contribute to reduced morbidity and mortality, improved quality of life, and significant potential cost savings for local health care providers.

EVERSUN: a phase 2 trial of alternating sunitinib and everolimus as first-line therapy for advanced renal cell carcinoma

BACKGROUND

We hypothesised that alternating inhibitors of the vascular endothelial growth factor receptor (VEGFR) and mammalian target of rapamycin pathways would delay the development of resistance in advanced renal cell carcinoma (aRCC).

PATIENTS AND METHODS

A single-arm, two-stage, multicentre, phase 2 trial to determine the activity, feasibility, and safety of 12-week cycles of sunitinib 50 mg daily 4 weeks on / 2 weeks off, alternating with everolimus 10 mg daily for 5 weeks on / 1 week off, until disease progression or prohibitive toxicity in favourable or intermediate-risk aRCC. The primary end point was proportion alive and progression-free at 6 months (PFS6m). The secondary end points were feasibility, tumour response, overall survival (OS), and adverse events (AEs). The correlative objective was to assess biomarkers and correlate with clinical outcome.

RESULTS

We recruited 55 eligible participants from September 2010 to August 2012.

DEMOGRAPHICS

mean age 61, 71% male, favourable risk 16%, intermediate risk 84%. Cycle 2 commenced within 14 weeks for 80% of participants; 64% received ≥22 weeks of alternating therapy; 78% received ≥22 weeks of any treatment. PFS6m was 29/55 (53%; 95% confidence interval [CI] 40% to 66%). Tumour response rate was 7/55 (13%; 95% CI 4% to 22%, all partial responses). After median follow-up of 20 months, 47 of 55 (86%) had progressed with a median progression-free survival of 8 months (95% CI 5-10), and 30 of 55 (55%) had died with a median OS of 17 months (95% CI 12-undefined). AEs were consistent with those expected for each single agent. No convincing prognostic biomarkers were identified.

CONCLUSIONS

The EVERSUN regimen was feasible and safe, but its activity did not meet pre-specified values to warrant further research. This supports the current approach of continuing anti-VEGF therapy until progression or prohibitive toxicity before changing treatment.

AUSTRALIAN NEW ZEALAND CLINICAL TRIALS REGISTRY

ACTRN12609000643279.

1-[(IMIDAZOLIN-2-YL)AMINO]INDOLINE AND 1-[(IMIDAZOLIN-2 YL)AMINO] 1,2,3,4-TETRAHYDROQUINOLINE DERIVATIVES: NEW INSIGHTS INTO THEIR CIRCULATORY ACTIVITIES

N-[(Imidazolin-2-yl)amino]indolines and N-[(imidazolin-2-yl)amino]-1,2,3,4-tetrahydroquinolines, previously described in patent literature as hypertensive agents, were synthesized and tested in viny for their affinities to α1- and α2-adrenoceptors as well as imidazoline I, and I2 receptors. The compounds most potent at either α1- or α2-adrenoceptors were administered intravenously to normotensive Wistar rats to determine their effects on mean arterial blood pressure and heart rate. Upon intravenous administration at dose of 0.1 mg/kg to normotensive male Wistar rats, the initial transient pressor effect was followed by long-lasting hypotension and bradycardia. In view of the above results the 1-[(imidazolin-2-yl)amino]indolines and [(imidazolin-2-yl)amino]-1,2,3,4-tetrahydroquinolines are now found to possess circulatory profile characteristic of the centrally acting clonidine-like hypotensive imidazolines.

Ecstasy, legal highs and designer drug use: A Canadian perspective

Recreational drug use in Canada is not uncommon, but as with most societies, illegal drug use carries harsh penalties resulting in a criminal record when an individual is successfully prosecuted. Popular drugs of use in Canada include ecstasy, cannabis (including some synthetic cannabinoids sold as ‘Spice’ and ‘Incense’) and several emerging psychoactive ‘legal highs’. Surprisingly, Canada is a major manufacturer and exporter of the popular club drug ecstasy, with criminal gangs organising the synthesis and distribution of this club drug worldwide. Over the last 18 months, there has been much interest in and use of alternatives to ecstasy due to contamination of ecstasy during synthesis. One particular contaminant, paramethoxymethamphetamine (PMMA), has resulted in several deaths. Other alternatives include piperazines and mephedrone analogues. With regard to cannabis, some is home grown within people’s properties, but there is also large-scale cultivation in British Columbia where the climate is more temperate. With the introduction of corporate drug screening, there is increasing use of synthetic cannabinoids to avoid detection of marijuana use. This article discusses the problems and trends of synthetic drug use in Canada and reflects on the limited education available to youth in this regard.

Venlafaxine enhances the effect of bupropion on extracellular dopamine in rat frontal cortex

Venlafaxine is recognised as an effective treatment for depression and is known to inhibit the reuptake of serotonin (5-HT) and noradrenaline (NA). Another antidepressant, bupropion, acts to inhibit dopamine (DA) and NA reuptake and is commonly co-administered with other antidepressants to improve the efficacy of the antidepressant effect. The present study was designed to investigate the acute effect of combining the 2 drugs on extracellular levels of 5-HT, DA, and NA in rat frontal cortex using brain microdialysis, with the drugs being administered by intraperitoneal injection (i.p). Bupropion (10 mg/kg body mass, i.p.) alone had no effect on extracellular 5-HT levels, whereas venlafaxine (10 mg/kg, i.p.) alone significantly elevated extracellular 5-HT over basal values. As expected, bupropion alone elevated extracellular dopamine above basal values at 40 min post-drug administration, and this effect lasted for a further 2 h. Venlafaxine alone did not statistically elevate extracellular dopamine. The co-administration of venlafaxine with bupropion resulted in a dramatic increase in extracellular dopamine, and this effect was significantly greater than that seen with bupropion alone. In the frontal cortex, NA was elevated by bupropion alone and venlafaxine alone, relative to the control animals. The combination of bupropion and venlafaxine resulted in a marked elevation of NA.

Evaluation and initial in vitro and ex vivo characterization of the potential positron emission tomography ligand, BU99008 (2-(4,5-dihydro-1H-imidazol-2-yl)-1- methyl-1H-indole), for the imidazoline₂ binding site

The density of the Imidazoline₂ binding site (I₂BS) has been shown to change in psychiatric conditions such as depression and addiction, along with neurodegenerative disorders such as Alzheimer's disease and Huntington's chorea. The presence of I₂BS on glial cells and the possibility that they may in some way regulate glial fibrillary acidic protein has led to increased interest into the role of I₂BS and I₂BS ligands in conditions characterized by marked gliosis. In addition, it has been suggested that I₂BS may be a marker for human glioblastomas. Therefore, the development of a positron emission tomography (PET) radioligand for the I₂BS would be of major benefit in our understanding of these conditions. We now report the successful synthesis and initial pharmacological evaluation of potential PET radioligands for the I₂BS as well as the tritiation and characterization of the most favorable of the series, BU99008 (6), both in vitro and ex vivo in rat. The series as a whole demonstrated excellent affinity and selectivity for the I₂BS, with BU99008 (6) selected as the lead candidate to be taken forward for in vivo assessment. BU99008 (6) showed very good affinity for the I₂BS (K(i) of 1.4 nM; K(d) = 1.3 nM), good selectivity compared with the α₂ -adrenoceptor (909-fold). In addition, following peripheral administration, [³H]BU99008 demonstrated a heterogenous uptake into the rat brain consistent with the known distribution of the I₂BS in vivo. This, and the amenability of BU99008 (6) to radiolabeling with a positron-emitting radioisotope, indicates its potential as a PET radioligand for imaging the I₂BS in vivo.

Favourable involvement of α2A-adrenoreceptor antagonism in the I₂-imidazoline binding sites-mediated morphine analgesia enhancement

Aim of the present study was to obtain novel α(2)-adrenoreceptor (α(2)-AR) antagonists, possibly endowed with subtype-selectivity. Therefore, inspired by the non subtype-selective α(2)-AR antagonist idazoxan, we designed 1,4-dioxane derivatives bearing an aromatic area in position 5 or 6 and the imidazoline nucleus in position 2. Among the novel molecules 1-6, compound 2, with a trans stereochemical relationship between 5-phenyl and 2-imidazoline groups, was able to antagonize the sole α(2A)-subtype. Moreover, 2 showed an affinity at I(2)-imidazoline binding sites (I(2)-IBS) comparable to that at α(2A)-AR. In in vivo studies 2 strongly increased morphine analgesia. This interesting behaviour appeared to be induced by the favourable involvement of α(2A)-AR antagonism in the I(2)-IBS-mediated morphine analgesia enhancement.

Quetiapine and Buspirone Both Elevate Cortical Levels of Noradrenaline and Dopamine In vivo, but Do Not have Synergistic Effects

Decreased cognitive ability is a significant problem in schizophrenia, and it has been proposed that augmentation of antipsychotics with 5HT(1A) receptor agonists may improve cognitive performance. Clinical studies have been mixed but there have been no studies specifically examining the effects of combining the atypical antipsychotic quetiapine with the 5HT(1A) receptor partial agonist, buspirone on monoamine release. This is of interest given previous evidence that monoamine release can alter cognition in schizophrenia. In the present study we measured in vivo levels of monoamines in the frontal cortex of Sprague Dawley rats and examined if buspirone (2.5 mg/kg i.p.), altered monoamine release both when given alone and when combined with quetiapine (10 mg/kg i.p.). We found that serotonin levels were not altered by either drug, either alone or in combination. In contrast, both buspirone and quetiapine monotherapy significantly increased release of noradrenaline (112 and 160% respectively) and dopamine (169 and 191% respectively) compared to controls. However, there were no additional increases in in vivo monoamine release when the combination of these drugs were given. One possible explanation for these negative findings could be that the intrinsic 5HT(1A) agonist activity of quetiapine on its own is of such significance that it is not further enhanced by buspirone. These findings do not support clinical studies combining buspirone and quetiapine, if these were to be used on the basis of enhanced monoamine neurotransmission. These findings may also have implications for the atypical antipsychotic drugs in development which combine dopamine D(2) antagonism with 5HT(1A) partial agonism.

Symptom experience and functional status among HIV-infected women

Irrespective of powerful drug therapies, there has been a slight increase in newly diagnosed cases of AIDS in women. HIV/AIDS-related symptoms develop from the illness itself, treatments or medications. Symptoms and their reoccurrence remain problematic. This study is a secondary analysis of data exploring symptoms, symptom distress and functional status in 104 ethnically diverse HIV-positive women. Measures included the Brief Symptom Inventory, a General Symptom Questionnaire, the Center for Epidemiological Studies Depression Scale, and the Inventory of Functional Status. Findings indicate that this sample of women was distressed, at risk for depression and had a moderate level of physical functioning. These findings support the need for symptom management interventions that enhance emotional wellbeing and self-care activities for HIV-infected women.

2-[(Arylmethoxy)imino]imidazolidines with potential biological activities

A series of 2-[(arylmethoxy)imino]imidazolidines was synthesized by reacting 2-chloro-4,5-dihydroimidazole with corresponding O-arylmethylhydroxylamines and evaluated for their alpha-, alpha2-adrenergic and imidazoline I1, I2 receptor binding affinities. The most potent 2-[(naphthalen-1-ylmethoxy)imino]imidazolidine showed a high selectivity and good affinity for the [3H]prazosin-labeled alpha1-adrenoceptors (K(i) = 107 nM). Representative compounds of this series were also tested in vivo for possible circulatory effects in rats after intravenous administration.

Synthesis and biological activity of some 2-imidazolinylhydrazone derivatives

A series of N-(imidazolidin-2-ylidene)hydrazones and N-(4,5-dihydro-1H-imidazol-2-yl)-N-methylhydrazones were prepared and examined for alpha 1-, alpha 2-adrenergic and imidazoline I1, I2 receptors binding affinities as well as cytotoxic activity against human tumor cell lines. Among the compounds tested, 2-naphthaldehyde N-(imidazolidin-2-ylidene)hydrazone (3e) exhibited a significant affinity for both alpha 2-adrenergic and imidazoline I1 receptors (Ki = 94.3 nM and IC50 = 51.7 nM, respectively). Moreover, pyridine-2-carboxaldehyde N-(imidazolidin-2-ylidene)hydrazone (3l) showed the highest binding affinity to alpha 1-adrenoceptors (Ki = 24.6 nM), while quinoline-2-carboxaldehyde N-(imidazolidin-2-ylidene)hydrazone (3m) displayed the highest I2 affinity with a Ki value of 26.7 nM and a high selectivity with respect to alpha 2-adrenergic and imidazoline I1 receptors (Ki = 22470.0 nM and IC50 = 6145.0 nM, respectively). None of the tested N-(4,5-dihydro-1H-imidazol-2-yl)-N-methylhydrazones 4p-u displayed cytotoxic activity.

Identification of an imidazoline binding protein: creatine kinase and an imidazoline-2 binding site

Drugs that bind to imidazoline binding proteins have major physiological actions. To date, three subtypes of such proteins, I₁, I₂ and I₃, have been proposed, although characterisations of these binding proteins are lacking. I₂ binding sites are found throughout the brain, particularly dense in the arcuate nucleus of the hypothalamus. Selective I₂ ligands demonstrate antidepressant-like activity and the identity of the proteins that respond to such ligands remained unknown until now. Here we report the isolation of a ∼ 45 kDa imidazoline binding protein from rabbit and rat brain using a high affinity ligand for the I₂ subtype, 2-BFI, to generate an affinity column. Following protein sequencing of the isolated ∼ 45 kDa imidazoline binding protein, we identified it to be brain creatine kinase (B-CK). B-CK shows high binding capacity to selective I₂ ligands; [³H]-2-BFI (5 nM) specifically bound to B-CK (2330 ± 815 fmol mg protein^− 1). We predicted an I₂ binding pocket near the active site of B-CK using molecular modelling. Furthermore, B-CK activity was inhibited by a selective I₂ irreversible ligand, where 20 μM BU99006 reduced the enzyme activity by 16%, confirming the interaction between B-CK and the I₂ ligand. In summary, we have identified B-CK to be the ∼ 45 kDa imidazoline binding protein and we have demonstrated the existence of an I₂ binding site within this enzyme. The importance of B-CK in regulating neuronal activity and neurotransmitter release may well explain the various actions of I₂ ligands in brain and the alterations in densities of I₂ binding sites in psychiatric disorders.

Synthesis and biological activities of [7-(azetidine-2-carboxylic acid)]-oxytocin and -lysine-vasopressin

[7-(Azetidine-2-carboxylic acid)]-oxytocin and -lysine-vasopressin have been synthesised by a (6 + 3) strategy using protected hexapeptide acids with preformed disulphide bridges, and their biological activities have been investigated. All activities were reduced but not to the same extent. In assays of pressor and antidiuretic activity it was observed consistently that the responses to the vasopressin analogue were of shorter duration than responses to lysine-vasopressin of the same amplitude.

Bioactive contaminants leach from disposable laboratory plasticware

Disposable plasticware such as test tubes, pipette tips, and multiwell assay or culture plates are used routinely in most biological research laboratories. Manufacturing of plastics requires the inclusion of numerous chemicals to enhance stability, durability, and performance. Some lubricating (slip) agents, exemplified by oleamide, also occur endogenously in humans and are biologically active, and cationic biocides are included to prevent bacterial colonization of the plastic surface. We demonstrate that these manufacturing agents leach from laboratory plasticware into a standard aqueous buffer, dimethyl sulfoxide, and methanol and can have profound effects on proteins and thus on results from bioassays of protein function. These findings have far-reaching implications for the use of disposable plasticware in biological research.

The effect of 1-(4,5-dihydro-1H-imidazol-2-yl) isoquinoline on monoamine release and turnover in the rat frontal cortex

Imidazoline-(2) binding sites (I(2)-BS) are widely distributed in rat brain and our studies have shown that drugs selective for these sites regulate central extrasynaptic monoamine concentrations. Radioligand binding studies have recently shown that BU98008 (1-[4,5-dihydro-1H-imidazol-2-yl] isoquinoline) displays high affinity at I(2)-binding sites. The aim of this study was set to assess the pharmacological actions of BU98008 in a functional in vivo model using the technique of in vivo brain microdialysis. Systemic injection of 20 mg/kg BU98008 produced an 85% rise in extracellular noradrenaline levels compared with basal values in the rat frontal cortex. Further experiments demonstrated that peripheral administration of 10 and 20 mg/kg BU98008 elicited a transient 25% elevation in dopamine overflow compared with basal values and simultaneously produced an 18% decrease in extracellular DOPAC (3-4-dihydroxyphenylacetic acid) levels compared to basal values. In addition, BU98008 did not appear to affect serotonergic neurotransmission in the frontal cortex. In conclusion, the present study demonstrates that BU98008 shares some functional similarities with known selective I(2)-BS ligands.

Pharmacological characterisation of the electrically evoked release of monoamines from chicken brainin vitro

1. A study was conducted to develop an in vitro model for examining the basal and electrical-stimulation-induced release of [3H]monoamines from chicken hyperstriatal neurones in order to demonstrate the presence of presynaptic autoreceptors for the three main monoamine transmitters: noradrenaline, dopamine and 5-HT. 2. Two sets of experiments were carried out: the first was to evaluate the effect of calcium and tetrodotoxin (TTX, sodium channel conductance inhibitor) in order to demonstrate that evoked release of monoamines was a consequence of exocytotic processes; the second to investigate the effect of selective agonists and antagonists on neurotransmitter release. 3. Ross and Cobb broiler chickens of either sex (approximately 7 to 8 weeks old) were used. Slices of hyperstriatal tissue were preincubated with [3H]noradrenaline, [3H]dopamine or [3H]5-hydroxytryptamine (5-HT), washed, perfused and electrically stimulated at three time points (S1, S2 and S3) which released [3H]noradrenaline, [3H]dopamine and [3H]5-HT, as determined by scintillation spectrometry. 4. When calcium was removed from, or TTX added to, the superfusion medium prior to and including the second period of electrical stimulation (S2) the evoked releases of [3H]noradrenaline, [3H]dopamine and [3H]5-HT at S2 were abolished. 5. In the presence of the selective alpha2-adrenoceptor agonist UK 14304 during the S2 period, the S2/S1 ratio was lower than the control ratio due to a reduction in the stimulated release of [3H]noradrenaline. The selective alpha2-adrenoceptor antagonist RX 821002 blocked the UK 14304-induced reduction of evoked release and the S2/S1 ratio was similar to the control ratio. 6. The D2-like receptor agonist quinpirole reduced the S2/S1 ratio for [3H]dopamine release, an effect blocked by the antagonist AJ 76. The 5-HT1B receptor agonist CP 94253 during S2 reduced the S2/S1 ratio due to a reduction in evoked [3H]5-HT. This effect was blocked by the 5-HT1B receptor antagonist GR 55562. 7. The results demonstrate, for the first time, the functional presence of presynaptic alpha2-adrenoceptors, presynaptic 5-HT1B autoreceptors and presynaptic D2-like autoreceptors in broiler chicken hyperstriatal neurones in vitro.

In vitro and in vivo effect of BU99006 (5-isothiocyanato-2-benzofuranyl-2-imidazoline) on I2 binding in relation to MAO: Evidence for two distinct I2 binding sites

BU99006 is an irreversible I(2) ligand which selectively inactivates I(2) binding sites, making it an ideal tool with which to study I(2) site mechanism. We sought to determine the effects of BU99006 on I(2) binding in relation to monoamine oxidase (MAO), and the time course of these effects. In vitro, rat brain membranes that were pre-treated with 10 microM BU99006 showed no change in MAO activity, despite suffering a significant reduction in [(3)H]2BFI binding (52.5+/-19.6 to 8.5+/-3.8 fmol mg(-1), 84%). Furthermore, reversible I(2) ligands 2BFI and BU224 were able to inhibit MAO, whether treated with BU99006 or not. In vivo, a 5 mg kg(-1) i.v. dose of BU99006 in rats rapidly reduced [(3)H]2BFI binding with similar magnitude (85%, maximal reduction after 20 min), without effect on either MAO activity or the specific binding of selective MAO-A and MAO-B radioligands. Moreover, following this irreversible treatment, recovery of central [(3)H]2BFI binding occurred with a rapid half-life of 4.3 h in rat brain (2.0 h in mouse), which is not consistent with a site on MAO. These data indicate that the high affinity site which is occupied by [(3)H]2BFI and irreversibly binds BU99006, is not the same as that which causes inhibition of MAO, and may point to the existence of another I(2) binding site.

2-(4,5-Dihydroimidazol-2-yl)benzimidazoles as highly selective imidazoline I2/adrenergic α2 receptor ligands

2-(4,5-Dihydroimidazol-2-yl)benzimidazoles have been identified as selective imidazoline I2/alpha2-adrenoceptor ligands. 4-Methyl (2) and 4-chloro (4) derivatives display I2 affinity at nanomolar concentration (Ki=4.4 and 17.7 nM, respectively) and high I2/alpha2 selectivity ratio=4226 and 5649, respectively. An evidence has been obtained that pKa value influences considerably the I2/alpha2-selectivity ratio of this class of imidazoline I2 receptor ligands.

Autoradiographical distribution of imidazoline binding sites in monoamine oxidase A deficient mice

This study has used receptor autoradiography to characterize imidazoline binding sites (I-BS) in monoamine oxidase (MAO) A knockout and wild-type mice. A comparison between MAO-A and MAO-B, binding of the endogenous beta-carboline [(3)H]harmane, and I-BS, has been made using sections from brain and kidney. The loss of binding to MAO-A in the knockout animals was confirmed using the selective radioligand [(3)H]Ro41-1049, with labelling reduced to background levels. The binding of [(3)H]Ro19-6327 to MAO-B was unaffected, indicating no change in this isoform in response to the loss of MAO-A. A reduction in binding to the I(2)-BS, as labelled by both [(3)H]idazoxan and [(3)H]2-BFI (2-(2-benzofuranyl)-2-imidazoline), was seen in the MAO-A knockout animals in both brain and kidney sections, whereas binding to the I(1)-BS in kidney sections remained unchanged. The loss of I(2) binding was found to be regionally dependent and was positively correlated with the relative expression of MAO-A in specific regions in the wild-type animals. Using the MAO-A knockout mice it was also possible to demonstrate a non-MAO-A population of binding sites labelled by the putative I-BS endogenous ligand, harmane.

Preparation, structure and affinity for imidazoline I2 receptors and alpha2-adrenoceptors of 1-[(4,5-dihydroimidazolidin-2-yl)imino]indan-2-ols

Two enantiomers IR, 2S-(+)-cis (3a) and IS, 2R-(-)-cis (3b) of 1-[(4,5-dihydroimidazolidin-2-yl)imino]indan-2-ol were prepared by reacting 2-chloro-4,5-dihydroimidazole (1) with corresponding 1-amino-indan-2-ols (2a-b). The compounds obtained are structural analogues of PMS 952 agent containing imino bridge in place of methylene group. Compound 3a exhibited moderate almost equal activity at both imidazoline I2 receptors and alpha2-adrenoceptors, while enantiomer 3b was found to be selective for alpha2-adrenoceptors (alpha2/I2 selectivity ratio = 10.4).

In vitro and ex vivo distribution of [3H]harmane, an endogenous beta-carboline, in rat brain

The endogenous beta-carboline, harmane, has been shown to bind to monoamine oxidase A (MAO-A) and a separate, high affinity, non-MAO site. Research in our laboratory has shown that harmane is an active component of clonidine-displacing substance (CDS), the proposed endogenous ligand for imidazoline binding sites (IBS). In the present study we have investigated the distribution of [3H]harmane in rat brain, and related the binding profile to the distribution of the MAO-A selective ligand [3H]Ro41-1049 and the I2BS ligand [3H]2-BFI. The in vivo distribution of [3H]harmane following intravenous administration was also investigated. Receptor autoradiography revealed a highly significant correlation for the distribution of [3H]harmane and [3H]Ro41-1049, and a significant correlation for [3H]harmane and the I2BS ligand [3H]2-BFI. The in vivo distribution of [3H]harmane suggests that the ligand accumulates in the adrenal gland and throughout the brain with the primary route of excretion occurring via the duodenum. In conclusion, these studies have shown that [3H]harmane labels a population of binding sites that reflect the distribution of MAO-A. Further evidence for a non-MAO, IBS [3H]harmane population has not been shown but the high level of expression of the MAO-A site is likely to have masked the much smaller population of I2BS.

Characterisation of imidazoline I2 binding sites in pig brain

The imidazoline I2 binding sites in the central nervous system have previously been described in several different species including rat, mouse, rabbit and frog. The present study has investigated the imidazoline I2 binding site, and its relationship to the monoamine oxidase isoforms, in pig whole brain and compared the results obtained with data from other species. Results from saturation binding studies revealed that the imidazoline I2-selective ligand, [3H]2BFI (2-(2-benzofuranyl)-2-imidazoline) labelled a single saturable population of sites with a KD=6.6 nM and Bmax=771.7 fmol/mg protein. The pharmacological characterisation of the sites was similar to that previously reported with a rank order of potency for the imidazoline I2 ligands of 2BFI>BU224>Idazoxan>BU226. Displacement by the imidazoline I1 ligands was low affinity and the monoamine oxidase inhibitors displaced with micromolar affinity. The majority of compounds displaced the binding in a monophasic manner, however, displacement by the putative endogenous ligand, harmane was biphasic. The relative populations of the two monoamine oxidase isoforms revealed a 10 fold greater expression of monoamine oxidase B relative to monoamine oxidase A. These data confirm the presence of imidazoline I2 binding sites in pig brain and show that their pharmacology is characteristic of that seen in other species. The proportion of monoamine oxidase A and B expressed in the pig brain is similar to that seen in the human brain therefore, given the association between imidazoline I2 binding sites and monoamine oxidase, the pig may provide a more useful model for human imidazoline I2 binding sites than other species such as the rat.

Comparison of alterations in c-fos and Egr-1 (zif268) expression throughout the rat brain following acute administration of different classes of antidepressant compounds

The majority of immediate-early gene (IEG) studies focus on a few key brain regions associated with the class of psychoactive compound being studied. Recently, using a meta-analysis of the c-fos literature, we demonstrated the utility of c-fos profiling to classify such compounds. The present study examined acute delivery of a range of antidepressant classes; fluoxetine, imipramine, LiCl, and mirtazapine. The dual aims were to study the IEG profiles of these varying classes of antidepressants throughout the rat brain and to compare the utility of c-fos or Egr-1 as IEGs to classify clinically efficacious antidepressants. All antidepressants increased c-fos mRNA in the central amygdala, as previously shown, while c-fos was also increased in the anterior insular cortex and significantly decreased within the septum. Although acute antidepressant administration altered c-fos expression in a number of brain regions, Egr-1 expression was only significantly altered in the central amygdala, suggesting that Egr-1 may not be as useful a marker to investigate acute antidepressant treatment. The fact that these drugs, including the previously unclassified antidepressant mirtazapine, share a number of common loci of activation, which are implicated by human and animal studies in depression, adds further support to the use of IEG mapping to classify psychoactive compounds.

The uptake of a fluorescently labelled antisense oligonucleotide in vitro and in vivo

Antisense oligonucleotides have been used to target a range of different gene products in the CNS including neurotransmitter receptors. Previous studies using antisense oligonucleotides to target the rat alpha(2A/D)-adrenoceptor revealed changes in receptor expression in specific brain areas following i.c.v. administration but no reduction was observed following antisense treatment in primary cortical neurones. In order to resolve these discrepant results, the uptake and distribution of the antisense sequence has been determined. In vivo, the fluorescent signal was detected close to the site of injection (2-3 mm) and on the same side of the brain as the injection. Although the oligonucleotides (ODN) were distributed throughout the CSF, the ODN was not widely distributed within the mid or hindbrain parenchyma. In vitro uptake studies revealed the antisense was poorly taken up into primary cortical neurones but a higher level of fluorescence was detected in a small sub-population of cells. These studies demonstrate that antisense is rapidly taken up into cells in vivo but poorly taken up into primary cortical neurones in culture. These data provide further evidence for the uptake and distribution of antisense oligonucleotides in neuronal tissue in vivo.

Harmane and harmalan are bioactive components of classical clonidine-displacing substance

Elucidation of the structure of the endogenous ligand(s) for imidazoline binding sites, clonidine-displacing substance (CDS), has been a major goal for many years. Crude CDS from bovine lung was purified by reverse-phase high-pressure liquid chromatography. Electrospray mass spectrometry (ESMS) and nuclear magnetic resonance ((1)H NMR) analysis revealed the presence of L-tryptophan and 1-carboxy-1-methyltetrahydro-beta-carboline in the active CDS extract. Competition radioligand binding studies, however, failed to show displacement of specific [(3)H]clonidine binding to rat brain membranes for either compound. Further purification of the bovine lung extract allowed the isolation of the beta-carbolines harmane and harmalan as confirmed by ESMS, (1)H NMR, and comparison with synthetic standards. Both compounds exhibited a high (nanomolar) affinity for both type 1 and type 2 imidazoline binding sites, and the synthetic standards were shown to coelute with the active classical CDS extracts. We therefore propose that the beta-carbolines harmane and harmalan represent active components of classical CDS. The identification of these compounds will allow us to establish clear physiological roles for CDS.

Synthesis of 2,3,5,6-tetrahydro-3H-imidazo[2,1-b] [1,3,5]benzotriazepines and their oxidative ring contraction into 1-(4,5-dihydro-1H-imidazol-2-yl)-1H-benzimidazoles

Syntheses of novel 5-aryl-2,3,5,6-tetrahydro-3H-imidazo[2,1-b] [1,3,5]benzotriazepine derivatives 3a-g were performed by reacting 2-(2-aminoarylimino)imidazolidines 1a-b with corresponding aryl aldehydes. The compounds 3 incorporating aminal group upon treatment with 2,3-dichloro-5,6-dicyano-1,2-benzoqinone (DDQ) underwent the oxidative ring contraction to give 1-(4,5-dihydro-1H-imidazol-2-yl)-2-aryl-benzimidazoles 4a-g. Reactions of the compounds 1a-c with carbonyldiimidazole (CDI) afforded novel 2,3,5,6-tetrahydro-1H-imidazo[2,1-b] [1,3,5]benzotriazepin-5-ones 5a-c which when heated in boiling methanol gave the corresponding 1-(4,5-dihydro-1H-imidazol-2-yl)-1,3-dihydro-2H-benzimidazol-2-ones 6a-c. Radioligand binding studies using rat central imidazoline I2 receptors and alpha2-adrenoceptors demonstrated that benzimidazoles 4a-g display a low affinity (microM) for these receptors while benzimidazol-2-ones 6a-b elicited a moderate affinity for I2 receptor with Ki values of 490 and 220 nM, respectively.

Binding of beta-carbolines at imidazoline I2 receptors: a structure-affinity investigation

A series of ring-substituted (i.e., methoxy and bromo) 3,4-dihydro- and 1,2,3,4-tetrahydro-beta-carbolines was examined at I(2) imidazoline receptors, as was the effect of ring-opening, ring-expansion, and translocation of the piperidinyl nitrogen atom. Several analogues were identified that bind with K(i) <20 nM at I(2) sites and with reduced affinity at alpha(2)-adrenergic receptors, and 1,2,3,4-tetrahydro-gamma-carbolines were identified as a novel class of I(2) imidazoline receptor ligand.

Invited review: the evolution of antidepressant mechanisms

Present antidepressants are all descendents of the serendipitous findings in the 1950s that the monoamine oxidase inhibitor iproniazid and the tricyclic antidepressant imipramine were effective antidepressants. The identification of their mechanism of action, and those of reserpine and amphetamine, in the 1960s, led to the monoamine theories of depression being postulated; first, with noradrenaline then 5-hydroxytryptamine being considered the more important amine. These monoamine theories of depression predominated both industrial and academic research for four decades. Recently, in attempts to design new drugs with faster onsets of action and more universal therapeutic action, downstream alterations common to current antidepressants are being examined as potential antidepressants. Additionally, the use of animal models has identified a number of novel targets some of which have been subjected to clinical trials in humans. However, monoamine antidepressants remain the best current medications and it may be some time before they are dislodged as the market leaders.

Effects of the beta-carbolines, harmane and pinoline, on insulin secretion from isolated human islets of Langerhans

It is well known that certain imidazoline compounds can stimulate insulin secretion and this has been attributed to the activation of imidazoline I(3) binding sites in the pancreatic beta-cell. Recently, it has been proposed that beta-carbolines may be endogenous ligands having activity at imidazoline sites and we have, therefore, studied the effects of beta-carbolines on insulin secretion. The beta-carbolines harmane, norharmane and pinoline increased insulin secretion two- to threefold from isolated human islets of Langerhans. The effects of harmane and pinoline were dose-dependent (EC(50): 5 and 25 microM, respectively) and these agents also blocked the inhibitory effects of the potassium channel agonist, diazoxide, on glucose-induced insulin release. Stimulation of insulin secretion by harmane was glucose-dependent but, unlike the imidazoline I(3) receptor agonist efaroxan, it increased the rate of insulin release beyond that elicited by 20 mM glucose (20 mM glucose alone: 253+/-34% vs. basal; 20 mM glucose plus 100 microM harmane: 327+/-15%; P<0.01). Stimulation of insulin secretion by harmane was attenuated by the imidazoline I(3) receptor antagonist KU14R (2 (2-ethyl 2,3-dihydro-2-benzofuranyl)-2-imidazole) and was reduced when islets were treated with efaroxan for 18 h, prior to the addition of harmane. The results reveal that beta-carbolines can potentiate the rate of insulin secretion from human islets and suggest that these agents may be useful prototypes for the development of novel insulin secretagogues.

Pharmacological characterisation of novel α2-adrenoceptor antagonists as potential brain imaging agents

Development of suitable imaging ligands to facilitate in vivo characterisation of alpha(2)-adrenoceptors has been limited in its success. In the present study, a series of iodinated derivatives and a fluorinated derivative of the classical alpha(2)-adrenoceptor antagonist, idazoxan, have been evaluated as potential imaging ligands. These compounds are based on the structure of idazoxan but more closely resemble the selective alpha(2)-adrenoceptor antagonists 2-methoxy-idazoxan (RX821002) and 2-ethoxy-idazoxan (RX811059). Preliminary studies, investigating their affinities at alpha(2)-adrenoceptors, using brain membranes prepared from a variety of species, and their ability to antagonise UK14, 304-induced inhibition of twitch in mouse vas deferens highlighted 2-iodopropoxy-idazoxan and 2-fluoroethoxy-idazoxan as the most promising candidates. Further characterisation of these two compounds showed they had a good selectivity for alpha(2)-adrenoceptors compared with imidazoline(2)-binding sites and beta-adrenoceptors. Additional functional studies also showed a lack of intrinsic activity at alpha(2)-adrenoceptors. Following intravenous injection, both compounds were able to cross the blood brain barrier when tested using an ex vivo binding assay. These data show that both 2-iodopropoxy-idazoxan and 2-fluoroethoxy-idazoxan have binding and functional properties suitable for imaging ligands. Further studies using radiolabelled forms of these ligands and a more extensive characterisation of their binding profiles are necessary but these initial evaluations demonstrate their potential.

Imidazoline2 (I2) receptor- and alpha2-adrenoceptor-mediated modulation of hypothalamic-pituitary-adrenal axis activity in control and acute restraint stressed rats

Central noradrenaline regulates the activity of the hypothalamic-pituitary-adrenal (HPA) axis and the neuroendocrine response to stress. alpha2-adrenoceptors and imidazoline2 (I2) receptors modulate the activity of the central noradrenergic system. The present set of experiments investigated the role of alpha2-adrenoceptors and I2 receptors in the regulation of HPA axis activity under basal conditions and during exposure to the acute psychological stress of restraint. Three separate experiments were carried out in which rats were given an i.p. injection of either saline vehicle, the combined alpha2-adrenoceptor antagonist and I2 receptor ligand idazoxan (10 mg/kg), the selective I2 receptor ligand BU224 (2.5 or 10 mg/kg) or the selective alpha2-adrenoceptor antagonist RX821002 (2.5 mg/kg) with or without restraint stress. Drugs were administered immediately prior to restraint of 60 min duration. Blood was sampled pre-injection, 30, 60 and 240 min post-injection and plasma corticosterone was measured by radioimmunoassay. In experiment 1, idazoxan increased plasma corticosterone levels in naive animals and potentiated the corticosterone response to acute restraint stress. In experiment 2, BU224 administration increased plasma corticosterone levels in a dose-related manner in naive rats. The results of experiment 3 indicated that RX821002 also elevated plasma corticosterone levels in naive rats, however, only BU224 potentiated the corticosterone response to restraint stress. These studies suggest that both alpha2-adrenoceptors and I2 receptors play a role in modulating basal HPA axis activity and that I2 receptors may play a more important role than alpha2-adrenoceptors in modulating the HPA axis response to the acute psychological stress of restraint.

Pyrazino[1,2- a ]indoles as novel high-affinity and selective imidazoline I 2 receptor ligands

1,2,3,4-Tetrahydropyrazino[1,2-a]indoles are described as a novel class of I(2) imidazoline receptor ligands. In particular, 8-methoxy-1,2,3,4-tetrahydropyrazino[1,2-a]indole (8-OMe THPI; 3c) binds with high affinity at I(2) imidazoline receptors (K(i)=6.2 nM) and with exceptional (> or =1000-fold) selectivity relative to its affinity for I(1) imidazoline receptors, alpha(2)adrenergic receptors, and 5-HT(2A) and 5-HT(2C) serotonin receptors.

Binding of an imidazopyridoindole at imidazoline I2 receptors

3,5,6,11-Tetrahydro-2H-imidazo[1',2':1,2]pyrido[3,4-b]indole (10) might be viewed as a fusion structure of two classes of I(2) imidazoline receptor ligands: 2-(2-benzofuranyl)-2-imidazolines and beta-carbolines. Its high affinity (K(i)=7.3 nM) provides insight to how the two classes of agents might bind relative to one another at I(2) receptors.

Estimation of endogenous noradrenaline release in rat brain in vivo using [3H]RX 821002

Noradrenaline plays an important role in many normal brain functions, e.g., attention, memory, and emotion. Dysfunction in the noradrenergic system is thought to lead to a number of abnormal brain conditions. The lack of suitable in vivo tracers to monitor noradrenaline release, levels, and regulation has hampered our fully understanding the roles that it plays in the brain. Presented here are data showing that the in vivo binding of the alpha2-adrenoceptor antagonist [3H]RX 821002 is sensitive to endogenous noradrenaline. Elevation of extracellular noradrenaline, using three different pharmacological challenges in rat, led to a reduction in the binding potential (BP) of [3H]RX 821002 when compared with vehicle controls. The challenges used were i.p. administration of D-amphetamine, the imidazoline2 binding site-selective ligand BU224, and L-deprenyl. Of the cortical regions measured, the reduction in BP reached significance in the anterior cingulate cortex for all of these pharmacological challenges. These initial observations in rat indicate that labelling of the alpha2-adrenoceptors with RX 821002 can be used to estimate changes in extracellular noradrenaline concentration in the cortex. This has the potential to enable the investigation of the role that noradrenaline plays both in the normal and abnormal brain and, if the ligand can be radiolabelled with a suitable positron-emitting isotope at high specific radioactivity, it could be an invaluable PET tracer.

Novel Ligands for the Investigation of Imidazoline Receptors and Their Binding Proteins

New ligands for imidazoline receptors are described so that these receptors can be more fully explored and understood. BU224, (2-(4,5-dihydroimidaz-2-yl)-quinoline, shows high affinity and is selective for the imidazoline-2 (I(2)) class of receptors. BU224 was tested in the rat Porsolt forced swim paradigm where it was found to decrease time spent immobile and increase the time spent swimming, consistent with an antidepressant profile. BU224 was tritiated and, in radioligand binding studies, was found to label a single population of saturable sites with high affinity. In vitro brain autoradiography with [(3)H]BU224 also showed a pattern of distribution similar to the known labeling of I(2) receptors. A new series of four 2BFI (2-(benzofuranyl)-2-imidazoline) derivatives were investigated as potential ligands for imaging brain I(2) receptors using positron emission tomography (PET). At least two, BU20012 and BU20013, retained high affinity and moderate selectivity and penetrated the brain when administered peripherally in the mouse. 2BFI has undergone the Mannich reaction to immobilized diaminodipropyl amine to fabricate an affinity column, which was used to isolate a protein from rabbit brain; this protein was sequenced and identified as the enzyme creatine kinase.

In Vivo Estimation of Imidazoline2 Binding Site Turnover

Turnover of imidazoline(2) (I(2)) binding sites in the mouse and rat brain has been measured following an acute intravenous dose of BU99006. This ligand selectively and irreversibly knocks out I(2) sites, as defined by [(3)H]2BFI binding. Recovery was measured using radioligand binding and autoradiography to determine global and regional changes in I(2) density. The density of I(2) sites in brain recovered from BU99006 treatment with a half-life of 2.1 hours in mice and 4.3 hours in rats. Monoamine oxidase (MAO) activity and MAO binding density were unaltered in the brains of BU99006-treated animals. These data suggest that the I(2) site that reacts with BU99006 recovers rapidly and is independent of MAO.

Relationship Between Imidazoline2 Sites and Monoamine Oxidase

I(2) site-selective compounds are known to interact with and inhibit monoamine oxidase (MAO), but it remains unclear as to whether this interaction occurs through an allosteric or competitive interaction. This study used the new selective, irreversible I(2) ligand BU99006, to clarify the relationship between MAO and the I(2) binding sites (I(2)-BS). Results demonstrate that irreversible binding of BU99006 to rat brain membranes does not inhibit the enzyme or interfere with its interaction with other imidazoline enzyme inhibitors. This finding suggests that the I(2) sites that react with BU99006 are not those implicated in MAO inhibition and points to the existence of at least two distinct I(2) binding proteins.

Comparative Effects of Efaroxan and b-Carbolines on the Secretory Activity of Rodent and Human b Cells

The pancreatic beta-cell expresses an imidazoline-binding site that is involved in the regulation of insulin secretion. This site is pharmacologically atypical in comparison with the I(1) and I(2) sites described in other tissues, and it has been classified as I(3). The structural requirements for binding of ligands to the I(3) site have not been fully defined, although a range of synthetic I(3) ligands have been characterized in functional terms. Evidence has been presented that an endogenous I(3) ligand may exist, because extracts of brain contain an active principle that stimulates insulin secretion in a manner consistent with the involvement of I(3) sites. The active component has not been identified but has been equated with the long-sought clonidine displacing substance (CDS) that is proposed as the endogenous ligand for imidazoline-binding sites. Recent evidence has indicated that one active component of CDS may be a beta-carboline, but it is not known whether beta-carbolines can stimulate insulin secretion. Thus, we have studied the effects of beta-carbolines on insulin secretion and cytosolic Ca(2+) levels in rodent and human islet cells. The results reveal that harmane, pinoline, and norharmane cause a dose- and glucose-dependent increase in insulin secretion but show that this response differs in a number of ways from that elicited by the well-characterized I(3)-agonist, efaroxan. Thus, beta-carbolines represent a new class of insulin secretagogues, although it remains unclear whether their action is mediated solely by I(3) sites in the beta cell.

Investigation of the Affinities of Two New b-Carbolines for Rat Brain Imidazoline2 Receptors

The beta-carbolines are possible endogenous ligands and modulators of the imidazoline binding sites (I-BSs). Relatively little is known about this class of compound and its interaction with the I-BS. Presented here are the binding data for two aryl ring substituted dihydro-beta-carbolines at the imidazoline(2) binding site (I(2)-BS) and alpha(2)-adrenoceptor: BG-326 (5-bromo-4,9-dihydro-3H-b-carboline) and BG-350 (5-methoxy-4,9-dihydro-3H-b-carboline). Both compounds show good affinity and selectivity for the I(2)-BS.

Endogenous -Carbolines as Clonidine-Displacing Substances

Endogenous beta-carbolines, such as harmane, are known to occur in mammalian species including humans. Radioligand binding studies have revealed that certain beta-carbolines display high affinity for both I(1) and I(2) imidazoline-binding sites (IBS). Functional studies have shown that the beta-carboline harmane elicits many characteristics expected of an endogenous ligand IBS. This article discusses the evidence relating to beta-carbolines as endogenous ligands and presents a case for harmane and related compounds as endogenous ligands for IBS.

Identification of an I2 Binding Protein From Rabbit Brain

Imidazoline-2 binding proteins exist as a heterogeneous population. The aim of this study was to isolate and identify I(2) binding proteins from rabbit brain using an affinity column synthesized with a highly selective I(2) ligand, 2-(2-benzofuranyl)2-imidazoline (2BFI). The results revealed an approximately 45-kD protein to be brain creatine kinase (EC 2.7.3.2). [(3)H]-2BFI (5nM) was able to bind specifically to the purified enzyme. This study has identified brain creatine kinase as a novel I(2) binding protein.

Initial Evaluation of Novel Selective Ligands for Imidazoline2 Receptors in Rat Whole Brain

Indazim, the indazole analogue of 2BFI, and four methyl-substituted analogues were tested for their affinity at the imidazoline(2) binding site (I(2)-BS), and this affinity was compared with their affinity at the alpha(2)-adrenoceptor to determine their structure, affinity relationship, and selectivity at the I(2)-BS. These studies showed that these ligands were highly selective for the I(2)-BS compared with 2BFI and that substitution at the 4 and 7 positions increased affinity without affecting selectivity.