Effects of the CCKB antagonist L-365, 260 on benzodiazepine withdrawal-induced hypophagia in rats

The effect of the selective CCK_B antagonist L-365, 260 on chlordiazepoxide (CDP) withdrawal-induced hypophagia was assessed in two related studies in rats pretreated for 21 days with CDP at doses escalated from 10 to 30 mg/kg per day (b.i.d.). L-365, 260 was studied at doses from 0.001 to 10 mg/kg (b.i.d.). There was no evidence that L-365, 260 at any dose alleviated CDP withdrawal-induced hypophagia. These data contrast with reports that CCK_B antagonists alleviate behavioural benzodiazepine (BZ) withdrawal symptoms considered to be indicative of anxiogenesis. Presumably, such positive effects of CCK_B antagonists are due to functional antagonism, with enhanced anxiety during BZ withdrawal being attenuated by anxiolytic actions of CCK_B antagonists. Collectively, studies with CCK_B antagonists and other agents involving a number of different BZ withdrawal signs suggest that BZ withdrawal is a heterogeneous syndrome, with various different underlying mechanisms. CCK_B antagonists appear to alleviate only a subset of possible BZ withdrawal signs.     

Differential profile of the CCKB receptor antagonist CI-988 and diazepam in the four-plate test

The cholecystokinin_B receptor antagonist CI-988 ([R-(R*,R*)]-4-[[2-[[3-(1H-indol-3-yl)-2-methyl-1-oxo-2-[[(tricyclo[3.3.1. 1^3,7]dec-2-yloxy)carbonyl]amino]-propyl]amino]-1-phenylethyl]amino]-4-oxobbutanoic acid compound with 1-deoxy-1-(methylamino)-D-glucitol (1:1)) and the benzodiazepine receptor agonist diazepam were tested for potential anxiolytic effects on punished exploratory behavior in the four-plate test using mice. Diazepam (0.31–5 mg/kg PO) increased the number of shocks taken in a dose-dependent manner, an effect blocked by the benzodiazepine receptor antagonist flumazenil. CI-988 (0.00001–1 mg/kg PO) tended to increase the number of delivered shocks over the chosen dose range; this effect was, however, not dose-related or as large as that produced by diazepam. A limited testing of the 5-hydroxytryptamine₃ receptor antagonist ondansetron (0.1 and 1 mg/kg PO) suggested an effect similar to CI-988. These results indicate that distinct and contrasting dose-response profiles exist for these classical and atypical drugs in an animal model of anxiety based on electric shock.     

Opposite effects of CCKB agonists in grooming behaviour in rats: further evidence for two CCKB subsites

1. The hypothesis of the existence of two CCK_B receptor subsites, CCK_B1 and CCK_B2 corresponding probably to different coupling states of CCK_B receptors, was studied by measuring grooming behaviour in rats.
2. The B1 receptor agonist, BC197 (300 μg kg⁻¹, i.p.) produced a 45–50% decrease in grooming activity, which was prevented by both the CCK_B receptor antagonists CI-988 (20 μg kg⁻¹ i.p.) and L-365,260 (200 μg kg⁻¹, i.p.).
3. In contrast, 3, 10 and 30 μg kg⁻¹, i.p., of the potent B2 receptor agonist, BC264, enhanced grooming (150–190%). This effect was prevented by previous injection of 75 μg kg⁻¹ of L-365,260 while higher doses (200 μg kg⁻¹, i.p.) produced only a partial antagonism. Moreover, CI-988 (20 μg kg⁻¹, i.p.), showed an opposite effect in potentiating the responses induced by BC264. However, 200 μg kg⁻¹ of CI-988 tended to suppress the increase of grooming induced by BC264.
4. The effects of BC264 were prevented by the D₁ receptor (SCH 23390) and D₂ receptor (sulpiride) antagonists, while those of BC197 were only antagonized by sulpiride, emphasizing the existence of a link between peptidergic (CCK) and dopaminergic systems.
5. This study brings additional evidence for the existence of the two CCK_B receptor subsites and suggests that particular attention should be focused on the selectivity of CCK_B receptor agonists, notably to explain the fact that some compounds such as Boc-CCK4 induce anxiogenic-like effects while others, including BC264, are devoid of these effects.

     

Evidence that 5-HT2C receptor antagonists are anxiolytic in the rat Geller-Seifter model of anxiety

Four non-selective 5-HT_2C/5-HT_2A receptor antagonists, mianserin (2–8 mg/kg), 1-naphthyl piperazine (1-NP) (0.5–1 mg/kg), ICI 169,369 (20 mg/kg) and LY 53857 (5 mg/kg), increased punished responding for a food reward in the rat Geller-Seifter test 30 min after subcutaneous (SC) administration. This property was shared by the benzodiazepine anxiolytic chlordiazepoxide (5 mg/kg SC). However, the selective 5-HT_2A receptor antagonists ketanserin (0.2–1 mg/kg SC) and altanserin (0.5, 1 mg/kg SC) had little effect. The 5-HT_1A, 5-HT_1B and-adrenergic receptor antagonists pindolol and cyanopindolol (6 mg/kg SC) did not affect punished responding either, nor did the 5-HT_1D receptor partial agonist and ₂ adrenergic receptor antagonist yohimbine (2.5 mg/kg SC) or the histamine H₁ receptor antagonist mepyramine (1 mg/kg SC). Unpunished responding was also modestly increased after some doses of the 5-HT_2C/5-HT_2A receptor antagonists. However, this effect was inconsistent and was also seen after chlordiazepoxide. Furthermore, it was not associated with the increase in punished responding observed in rats orally treated with mianserin (10, 20 mg/kg), 1-NP (10, 20 mg/kg) or ICI 169,369 (50 mg/kg). The action of the 5-HT_2C/5-HT_2A receptor antagonists tested is therefore consistent with anxiolysis. The results also strongly suggest that this effect is mediated by blockade of the 5-HT_2C receptor, although the possibility of 5-HT_2B receptor mediation is discussed.     

Pharmacological evaluation of IQM-95,333, a highly selective CCKA receptor antagonist with anxiolytic-like activity in animal models

1. The pyridopyrimidine derivative IQM-95,333 ((4aS,5R)-2-benzyl-5-[N^α-tert-butoxicarbonyl)L-tryptophyl]amino-1,3dioxoperhydropyrido[1,2-c]pyrimidine), a new non-peptide antagonist of cholecystokinin type A (CCK_A) receptors, has been evaluated in vitro and in vivo in comparison with typical CCK_A and CCK_B receptor antagonists, such as devazepide, lorglumide, L-365,260 and PD-135,158.
2. IQM-95,333 displaced [³H]-CCK-8S binding to CCK_A receptors from rat pancreas with a high potency in the nanomolar range. Conversely, the affinity of this new compound at brain CCK_B receptors was negligible (IC₅₀>10 μM). IQM-95,333 was a more selective CCK_A receptor ligand than devazepide and other CCK_A receptor antagonists.
3. Like devazepide, IQM-95,333 was a more potent antagonist of CCK-8S- than of CCK-4-induced contraction of the longitudinal muscle from guinea-pig ileum, suggesting selective antagonism at CCK_A receptors.
4. IQM-95,333 and devazepide were also potent inhibitors of CCK-8S-stimulated amylase release from isolated pancreatic acini, a CCK_A receptor-mediated effect. The drug concentrations required (IC₅₀s around 20 nM) were higher than in binding studies to pancreas homogenates.
5. Low doses (50–100 μg kg⁻¹, i.p.) of IQM-95,333 and devazepide, without any intrinsic effect on food intake or locomotion, blocked the hypophagia and the hypolocomotion induced by systemic administration of CCK-8S, two effects associated with stimulation of peripheral CCK_A receptors.
6. IQM-95,333 showed an anxiolytic-like profile in the light/dark exploration test in mice over a wide dose range (10–5,000 μg kg⁻¹). Typical CCK_A and CCK_B antagonists, devazepide and L-365,260 respectively, were only effective within a more limited dose range.
7. In a classical conflict paradigm for the study of anxiolytic drugs, the punished-drinking test, IQM-95,333, devazepide and L-365,260 were effective within a narrow dose range. The dose-response curve for the three drugs was biphasic, suggesting that other mechanisms are operative at higher doses.
8. In conclusion, IQM-95,333 is a potent and selective CCK_A receptor antagonist both in vitro and in vivo with an anxiolytic-like activity in two different animal models, which can only be attributed to blockade of this CCK receptor subtype.

     

Effects of H1-receptor antagonists on responding punished by histamine injection or electric shock presentation in squirrel monkeys

Squirrel monkeys were trained to press a key under a two-component schedule of food presentation. In the presence of either green or red stimulus lights, the 30th response produced a food pellet (fixed-ratio schedule). During the red stimulus lights (punishment component), the first response of each fixed ratio produced either an IV injection of histamine (100.0 g/kg/inj) or a brief electric shock (3.0 mA). Responding was selectively suppressed in either punishment component. Presession IM administration of chlorpheniramine (0.1 and 0.3 mg/kg), diphenhydramine (1.0 and 3.0 mg/kg), or pyrilamine (0.1 and 0.3 mg/kg) increased rates of responding punished by histamine but not those punished by electric shock. Presession administration of promethazine (0.1–3.0 mg/kg) or tripelennamine (0.1 and 0.3 mg/kg) also increased rates of responding punished by histamine in all subjects and response rates punished by electric shock in one of three subjects. Chlordiazepoxide (3.0–56.0 mg/kg) increased rates of responding punished by either histamine or electric shock. These results suggest that the punishing effects of histamine injection are mediated by H₁ receptors and that H₁-receptor antagonists increase rates of responding suppressed by punishment only under limited conditions including those in which histamine is the punishing stimulus.     

Cholecystokinin-8 regulation of NGF concentrations in adult mouse brain through a mechanism involving CCKA and CCKB receptors

1. Nerve growth factor (NGF), a powerful agent for the growth, differentiation and regeneration of lesioned cells of the central and peripheral nervous systems, has in recent years been indicated as a potential therapeutic agent capable of reversing the processes of cell damage in neurodegenerative events in man. Since NGF does not cross the blood-brain barrier and central NGF administration requires invasive surgical procedures, the discovery of substances modulating in vivo NGF synthesis in the brain will be extremely useful for a possible clinical use of NGF.
2. The aim of the present study to analyse if the content of NGF in the brain of adult mice can be affected by peripheral administration of cholecystokinin-8 (CCK-8), a well known neuropeptide which has stimulant actions on neurons in the brain and promotes a variety of neurobehavioural effects both in man and rodents.
3. The dose-response and time course effects of an i.p. injection of CCK-8 on the NGF concentrations in the hippocampus, cortex, hypothalamus and pituitary of adult male mice were analysed by use of a sensitive immunoenzymatic assay for NGF. The effects of pretreatment with selective CCK_A and CCK_B receptor antagonists and atropine on the NGF response to CCK injection were also studied.
4. The effects of CCK-8 were dose- and time-dependent and the injection of 8 nmol kg^?1 resulted in a 3 fold increase of NGF levels in the hypothalamus and pituitary, and about a 60% increase in the hippocampus. No effects were observed in the cortex. Pretreatment with a selective CCK_A receptor antagonist blocked the CCK-induced NGF increase in the hypothalamus and pituitary. In the hippocampus the same effect was obtained with a CCK_B receptor antagonist. Pretreatment with atropine suppressed the CCK-induced effects on NGF levels in all the brain regions examined.
5. Our results showing that i.p. injection with CCK-8 can modulate NGF levels in the brain through a mechanism which seems, in part, to be mediated via the vagal afferents, indicate that this neuropeptide may represent a useful pharmacological approach to enhance endogenous NGF levels in neuropathologies associated with a neurotrophin deficit.

     

Therapeutic potential for novel drugs targeting the type 1 cholecystokinin receptor

Cholecystokinin (CCK) is a physiologically important gastrointestinal and neuronal peptide hormone, with roles in stimulating gallbladder contraction, pancreatic secretion, gastrointestinal motility and satiety. CCK exerts its effects via interactions with two structurally related class I guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs), the CCK₁ receptor and the CCK₂ receptor. Here, we focus on the CCK₁ receptor, with particular relevance to the broad spectrum of signalling initiated by activation with the natural full agonist peptide ligand, CCK. Distinct ligand-binding pockets have been defined for the natural peptide ligand and for some non-peptidyl small molecule ligands. While many CCK₁ receptor ligands have been developed and have had their pharmacology well described, their clinical potential has not yet been fully explored. The case is built for the potential importance of developing more selective partial agonists and allosteric modulators of this receptor that could have important roles in the treatment of common clinical syndromes.This article is part of a themed section on Molecular Pharmacology of GPCR. To view the editorial for this themed section visit http://dx.doi.org/10.1111/j.1476-5381.2010.00695.x     

Cholecystokinin peptides and receptors in the rat brain during stress

Cholecystokinin (CCK) has been implicated in stress and anxiety disorders. We have studied the levels of different molecular forms of CCK and CCK receptor characteristics in rats kept for 1 h in individual cages and exposed to decapitation of conspecifics, and a control group which was decapitated immediately. Total CCK concentration was found to be increased in the hippocampus of stressed animals in the first experiment: this finding was not confirmed in further studies. No effect of stress was found on total CCK levels in the frontal cortex, hypothalamus, striatum, and septum. CCK-8-sulphated, CCK-8-nonsulphated, CCK-5, and CCK-4 were separated by HPLC and measured with two antibodies with different selectivity: no effect of stress was found on the levels of any of these molecular forms of CCK. Injection procedure and diazepam (5 mg/kg) administration had no effect on total CCK levels. Exposition of rats to the decapitation procedure increased [³H]-CCK-8 binding in the frontal and cerebral (whole - frontal) cortex. This effect could not be blocked by diazepam pretreatment. Injection procedure itself increased CCK receptor binding in the cerebral cortex, but the effect of this type of stress was smaller in magnitude. The upregulation of CCK receptors in stressed animals was due to the increased binding of radioligand on CCK_B receptor subtype.     

The CCKB antagonist PD-134,308 facilitates rewarding effects of endogenous enkephalins but does not induce place preference in rats

The interaction between cholecystokinin and endogenous opioid systems on rewarding responses was examined. Motivational effects induced by peripheral administration of a complete inhibitor of enkephalin catabolism, RB 101 or the CCK_B antagonist PD-134,308, and by both compounds in combination were evaluated in the conditioned place preference test in rats. RB 101 (5, 10, 20, 40 and 80 mg/kg, IP, and 20 mg/kg, IV) given alone produced a bell-shaped dose-effect function. A significant increase of the preference for the drug-associated compartment was only observed at doses of 10 and 20 mg/kg (IP). The effect observed with morphine was stronger, and all the doses used of this compound (1.25, 2.5 and 5 mg/kg, SC) were found to be active. These results suggest that the inhibitor of enkephalin catabolism has weak rewarding properties. Pretreatment with the CCK_B antagonist PD-134,308 (0.1, 0.3, 1 and 3 mg/kg, IP) alone failed to produce a reliable aversion or preference on the paradigm studied. When PD-134,308 (0.3 mg/kg, IP) was coadministered with a subthreshold dose of morphine (0.6 mg/kg, SC) or RB 101 (5 mg/kg, IP), a conditioned place preference was observed, indicating that the CCK_B antagonist facilitated the motivational responses induced by endogenous enkephalins as compared to morphine. This suggests that endogenous cholecystokinin, acting through CCK_B receptors, modulates the rewarding effects of endogenous enkephalins.     

Lack of efficacy of melanin-concentrating hormone-1 receptor antagonists in models of depression and anxiety

The aim of this study was to validate melanin-concentrating hormone (MCH)-1 receptor antagonism as a potential treatment of mood disorders. We attempted to replicate the effects previously reported with SNAP-7941 and expanded the investigation to three other orally bioavailable MCH-1 receptor antagonists with good brain penetration. SNAP-7941 (3–30 mg/kg, i.p.) and T-226296 (5–60 mg/kg, p.o.) (± racemate), were evaluated in the rat forced swim and mouse tail suspension tests. (+)SNAP-7941 (3–10 mg/kg, p.o.) was also tested in a modified 5-min rat forced swim protocol as previously reported. A-665798 (3–30 mg/kg, p.o.) and A-777903 (3–30 mg/kg, p.o.) were tested in mouse tail suspension and rat Vogel tests. None of the compounds showed meaningful efficacy in the paradigms tested. The lack of efficacy with four structurally different MCH-1 receptor antagonists does not support a role for therapeutic treatment of depression/anxiety via this mechanism of action.     

Antidepressant and anxiolytic profiles of newly synthesized arginine vasopressin V1B receptor antagonists: TASP0233278 and TASP0390325

BACKGROUND AND PURPOSE

Vasopressin V_1B receptor antagonists may be effective for the treatment of depression and anxiety and the objective of this study was to characterize the pharmacological profiles of two newly synthesized arginine vasopressin receptor 1B (V_1B receptor) antagonists, TASP0233278 and TASP0390325.

EXPERIMENTAL APPROACH

We investigated the in vitro profiles of TASP0233278 and TASP0390325. In addition, the effect of TASP0390325 on the increase in plasma adrenocorticotropic hormone (ACTH) levels induced by corticotropin-releasing factor (CRF)/desmopressin (dDAVP) was investigated. We also investigated the antidepressant and anxiolytic profiles of TASP0233278 and TASP0390325 in animal models.

KEY RESULTS

Both TASP0233278 and TASP0390325 showed a high affinity and potent antagonist activity for V_1B receptors. Oral administration of TASP0390325 antagonized the increase in plasma ACTH levels induced by CRF/dDAVP in rats, indicating that TASP0390325 blocks the anterior pituitary V_1B receptor in vivo. Oral administration of TASP0233278 or TASP0390325 also exerted antidepressant effects in two models of depression (a forced swimming test and an olfactory bulbectomy model). Moreover, TASP0233278 improved depressive-like behaviour induced by repeated treatment with corticosterone, a model that has been shown to be resistant to treatment with currently prescribed antidepressants. In addition to depression models, TASP0233278 or TASP0390325 exerted anxiolytic effects in several anxiety models (social interaction, elevated plus-maze, stress-induced hyperthermia, separation-induced ultrasonic vocalization and sodium lactate-induced panic-like responses in panic-prone rats).

CONCLUSION

TASP0233278 and TASP0390325 are potent and orally active V_1B receptor antagonists with antidepressant and anxiolytic activities in rodents.     

Effects of scopolamine, amphetamine and benzodiazepines on conditioned suppression

Conditioned suppression of operant behavior was produced by preshock stimuli (i.e., stimuli that precede the noncontigent presentation of electric shock), or prereward stimuli (i.e., stimuli that precede the noncontingent presentation of food) in rats and squirrel monkeys responding on a variable interval schedule of food reinforcement. Benzodiazepine derivatives and amphetamine differentially affect conditioned reactions which are elicited by preshock and prereward stimuli. Conditioned suppression to prereward stimuli were unaffected by chlordiazepoxide, diazepam, scopolamine hydrobromide and scopolamine methyl nitrate but clearly reduced by amphetamine. On the other hand, chlordiazepoxide attenuated the conditioned suppression to preshock stimuli whereas amphetamine, scopolamine hydrobromide and scopolamine methyl nitrate had no significant effects in this paradigm. The results suggest that the effects of drugs on conditioned suppression cannot be interpreted, a priori, in terms of selective effects on mechanisms related to emotional behavior or inhibition.     

Effects of GABA B receptor antagonists CGP63360, CGP76290A and CGP76291A on learning and memory processes in rodents

Data in literature that use methods for studying the learning and memory processes suggest that GABA and especially GABA _B receptor antagonists may be active against amnesia. The aim of our study was to examine the effects of three new GABA _B -antagonists on learning and memory processes. Active and passive avoidance tests with negative reinforcement in rats were used. The rats treated with different GABA _B receptor antagonists showed improving effects in both tests (active and passive avoidances)on learning as well as on memory retention. There are some differences in their activities, probably due to its chemical structures. The phosphinic analogue CGP63360A is potent to the point that the benzoic one CGP76290A and the left isomer of the benzoic analogue CGP76291A has no effect. It may be concluded that the obtained results on the GABA _B receptor antagonists could contribute to their pharmacological characteristics and might be of interest for potential clinical implication.     

Discovery and therapeutic potential of kinin receptor antagonists

Introduction: Kinins are bioactive peptide hormones that exert biological effects by activating two types of G protein-coupled receptors namely, B₁ (B₁R) and B₂ (B₂R). These modulate normal physiological cellular functions, inflammatory disorders and carcinogenesis. New and novel kinin receptor antagonists have been synthesized and their efficacy evaluated.

Areas covered: The authors provide a comprehensive review on the cellular and molecular biology of kinins and their receptors is delineated along with evolution and discovery of selective peptide and non-peptide antagonists. The authors describe the in vitro and in vivo methods used to understand the relative functional roles of B₁R and B₂R in physiology and pathohysiology. Furthermore, the authors translate the evaluation of kinin antagonists in selected preclinical models and associated clinical indications. Literature was surveyed from original publications, standard sources, SciFinder, patent applications and clinical trials.

Expert opinion: The authors suggest that several key areas of functional biology need consideration, namely: re-evaluation, particularly in vivo, of the mechanism of action and relative functional roles of the B₁R and B₂R in physiology and acute and chronic disease in animals and man; need for improved animal models with increased use of humanized and human systems; development of fluorescent probes for use in vivo in animals and man using advanced imaging techniques; combination of kinin receptor antagonists and traditional chemotherapy for various cancers.     

Effect of intracerebroventricular and systemic injections of caerulein,a CCK analogue,on electrical self-stimulation and its interaction with the CCKA receptor antagonist,L-364,718 (MK-329)

Systemic administration of caerulein (10–100 µg/kg SC), a potent analogue of cholecystokinin, caused a profound dose-related depression of variable-interval self-stimulation, followed by progressive recovery within 60 min. Intracerebroventricular injection of caerulein (3–1000 ng) was not more effective than systemic injection, while injections into the nucleus accumbens (3–100 ng bilaterally) were without detectable effect. Systemic injections of L-364,718 (70–700 µg/kg IP), a specific competitive antagonist of CCK_A (peripheral-type) receptors, had no effect on self-stimulation when given alone. When given in combination with caerulein, L-364,718 (200 µg/kg IP) significantly reduced the inhibitory effect of caerulein (30 µg/kg SC); however, this dose, and higher doses of L-364,718, failed to confer complete protection. It is concluded that self-stimulation performance may be subject to modulation by CCK receptors distributed predominantly in the peripheral nervous system and that some but not all of these receptors are CCK_A receptors.     

Lack of effects of 5HT3 receptor antagonists in the social interaction and elevated plus-maze tests of anxiety in the rat

The effects of three 5HT₃ receptor antagonists: BRL 43964 (0.1 and 1 mg/kg, oral), GR 38032F (0.1 and 1 mg/kg, oral), and zacopride (0.01, 0.1 and 1 mg/kg, IP) were examined in low light test conditions of the social interaction test. None of the three 5HT₃ receptor antagonists had a significant effect on social interaction. In contrast, in two experiments chlordiazepoxide (7.5 mg/kg) significantly increased social interaction and this effect was greatest in the unfamiliar test condition. In a third experiment, the effects of GR 38032F (0.1 and 1 mg/kg, oral) and zacopride (0.01, 0.1 and 1 mg/kg, oral) were investigated in the high light test conditions of the social interaction test; neither compound had a significant effect. In the elevated plus-maze, chlordiazepoxide (7.5 mg/kg oral or IP) significantly increased both the per cent number of entries made onto open arms and the per cent of time spent on the open arms, indicating an anxiolytic action. Zacopride (0.01, 0.1 and 1 mg/kg, oral or IP) had no significant effect in this test. The effect of the baseline rate of responding in the social interaction test on the effects of 5-HT₃ antagonists is discussed. The results from the present experiment and those from other animal tests of anxiety caution against the conclusion that 5HT₃ receptor antagonists are anxiolytic.     

Characterization of the receptor and the mechanisms underlying the inflammatory response induced by des-Arg9-BK in mouse pleurisy

1. The characterization of the B₁ kinin receptor, and some mediators involved in the inflammatory response elicited by intrathoracic (i.t.) administration of des-Arg⁹-bradykinin (BK) in the mouse model of pleurisy, was investigated.
2. An i.t. injection of des-Arg⁹-BK (10–100 nmol per site), a selective B₁ agonist, caused a significant and dose-related increase in the vascular permeability observed after 5 min, which peaked at 1 h, associated with an increase in cell influx, mainly neutrophils, and, to a lesser extent, mononuclear cell influx, peaking at 4 h and lasting for up to 48 h. The increase in fluid leakage caused by des-Arg⁹-BK was completely resolved 4 h after peptide injection. I.t. injection of Lys-des-Arg⁹-BK (30 nmol per site) caused a similar inflammatory response.
3. Both the exudation and the neutrophil influx elicited by i.t. injection of des-Arg⁹-BK were significantly antagonized (P<0.01) by an i.t. injection of the selective B₁ antagonists des-Arg⁹-[Leu⁸]-BK (60 and 100 nmol per site) or des-Arg⁹-NPC 17731 (5 nmol per site), administered in association with des-Arg⁹-BK (P<0.01), or 30 and 60 min before the cellular peak, respectively. In contrast, an i.t. injection of the B₂ bradykinin selective receptor antagonist Hoe 140 (30 nmol per site), at a dose which consistently antagonized bradykinin (10 nmol per site)-induced pleurisy, had no significant effect on des-Arg⁹-BK-induced pleurisy.
4. An i.t. injection of the selective tachykinin receptor antagonists (NK₁) FK 888 (1 nmol per site), (NK₂) SR 48968 (20 nmol per site) or (NK₃) SR 142801 (10 nmol per site), administered 5 min before pleurisy induction, significantly antagonized neutrophil migration caused by i.t. injection of des-Arg⁹-BK. In addition, FK 888 and SR 142801, but not SR 48968, also prevented the influx of mononuclear cells in response to i.t. injection of des-Arg⁹-BK (P<0.01). However, the NK₃ receptor antagonist SR 142801 (10 nmol per site) also significantly inhibited des-Arg⁹-BK-induced plasma extravasation. An i.t. injection of the calcitonin gene-related peptide (CGRP) receptor antagonist CGRP_8–37 (1 nmol per site), administered 5 min before pleurisy induction, inhibited des-Arg⁹-BK-induced plasma extravasation (P<0.01), without significantly affecting the total and differential cell migration.
5. The nitric oxide synthase inhibitors L-NOARG and L-NAME (1 pmol per site), administered 30 min beforehand, almost completely prevented des-Arg⁹-BK (i.t.)-induced neutrophil cell migration (P<0.01), and, to a lesser extent, mononuclear cell migration (P<0.01). The D-enantiomer D-NAME had no effect on des-Arg⁹-BK-induced pleurisy. At the same dose range, L-NOARG and L-NAME inhibited the total cell migration (P<0.01). L-NAME, but not L-NOARG caused significant inhibition of des-Arg⁹-BK-induced fluid leakage. Indomethacin (1 mg kg⁻¹, i.p.), administered 1 h before des-Arg⁹-BK (30 nmol per site), inhibited the mononuclear cell migration (P<0.05), but, surprisingly, increased the neutrophil migration at 4 h without interfering with plasma extravasation. The administration of terfenadine (50 mg kg⁻¹, i.p.), 30 min before des-Arg⁹-BK (30 nmol per site), did not interfere significantly with the total cell migration or with the plasma extravasation in the mouse pleurisy caused by i.t. injection of des-Arg⁹-BK.
6. Pretreatment of animals with the lipopolysaccharide of E. coli (LPS; 10 μg per animal, i.v.) for 24 h did not result in any significant change of the inflammatory response induced by i.t. injection of des-Arg⁹-BK compared with the saline treated group. However, the identical treatment of mice with LPS resulted in a marked enhancement of des-Arg⁹-BK induced paw oedema (P<0.01).
7. In conclusion, we have demonstrated that the inflammatory response induced by i.t. injection of des-Arg⁹-BK, in a murine model of pleurisy, is mediated by stimulation of constitutive B₁ receptors. These responses are largely mediated by release of neuropeptides such as substance P or CGRP and also by NO, but products derived from cyclo-oxygenase pathway and histamine seem not to be involved. Therefore, these results further support the notion that the B₁ kinin receptor has an important role in modulating inflammatory responses, and it is suggested that selective B₁ antagonists may provide therapeutic benefit in the treatment of inflammatory and allergic conditions.

     

Latest advances in cannabinoid receptor antagonists and inverse agonists

This review covers the progress made in the field of CB₁ and CB₂ cannabinoid receptor antagonists and inverse agonists since 2004. The high therapeutic potential of these compounds is reflected by the great number of patents filed during the last 3 years. Although the vast majority of the patents are related to CB₁ due to the known therapeutic potential of CB₁ antagonists, several compounds acting at CB₂ have also been disclosed. Obesity, metabolic syndrome and smoking cessation are CB₁ antagonists indications supported by the recent clinical trials results.     

Effects of the selective angiotensin II receptor antagonists losartan and PD123177 in animal models of anxiety and memory

There is increasing interest in the potential functional role of the octapeptide angiotensin II (AII) in psychiatric and cognitive disorders. The novel angiotensin II (AII) receptor antagonists, losartan and PD123177, selective for the AT₁ and AT₂ receptor subtypes respectively, constitute important pharmacological tools for the assessment of the behavioural consequences of modulation of AII function. The present series of studies investigated the effects of each compound in two animal models of anxiety, the rat elevated zero-maze and mouse light/dark box, and two models of working memory in the rat, the operant delayed matching to position (DMTP) task and the spatial reinforced alternation test in the T-maze. Our data indicate that both compounds (0.01–10 mg/kg SC) were without significant effect in any of the behavioural assays. Using the present methods and strains of laboratory rodents, these findings provide no support for the involvement of AII receptor function in the mediation of anxiety or working memory.