Mechanisms mediating the ability of caffeine to influence MDMA (��Ecstasy��)-induced hyperthermia in rats

Background and purpose:

Caffeine exacerbates the hyperthermia associated with an acute exposure to 3,4 methylenedioxymethamphetamine (MDMA, ‘Ecstasy’) in rats. The present study investigated the mechanisms mediating this interaction.

Experimental approach:

Adult male Sprague-Dawley rats were treated with caffeine (10 mg·kg⁻¹; i.p.) and MDMA (15 mg·kg⁻¹; i.p.) alone and in combination. Core body temperatures were monitored before and after drug administration.

Key results:

Central catecholamine depletion blocked MDMA-induced hyperthermia and its exacerbation by caffeine. Caffeine provoked a hyperthermic response when the catecholamine releaser d-amphetamine (1 mg·kg⁻¹) was combined with the 5-HT releaser d-fenfluramine (5 mg·kg⁻¹) or the non-selective dopamine receptor agonist apomorphine (1 mg·kg⁻¹) was combined with the 5-HT₂ receptor agonist DOI (2 mg·kg⁻¹) but not following either agents alone. Pretreatment with the dopamine D₁ receptor antagonist Schering (SCH) 23390 (1 mg·kg⁻¹), the 5-HT₂ receptor antagonist ketanserin (5 mg·kg⁻¹) or α₁-adreno- receptor antagonist prazosin (0.2 mg·kg⁻¹) blocked MDMA-induced hyperthermia and its exacerbation by caffeine. Co-administration of a combination of MDMA with the PDE-4 inhibitor rolipram (0.025 mg·kg⁻¹) and the adenosine A_1/2 receptor antagonist 9-chloro-2-(2-furanyl)-[1,2,4]triazolo[1,5-C]quinazolin-5-amine 15943 (10 mg·kg⁻¹) or the A_2A receptor antagonist SCH 58261 (2 mg·kg⁻¹) but not the A₁ receptor antagonist DPCPX (10 mg·kg⁻¹) exacerbated MDMA-induced hyperthermia.

Conclusions and implications:

A mechanism comprising 5-HT and catecholamines is proposed to mediate MDMA-induced hyperthermia. A combination of adenosine A_2A receptor antagonism and PDE inhibition can account for the exacerbation of MDMA-induced hyperthermia by caffeine.     

A study of the neurotoxic effect of MDMA (‘ecstasy') on 5-HT neurones in the brains of mothers and neonates following administration of the drug during pregnancy

1. It is well established that 3,4-methylenedioxymethamphetamine (MDMA or ‘ecstasy'') is neurotoxic and produces long term degeneration of cerebral 5-hydroxytryptamine (5-HT) nerve terminals in many species. Since MDMA is used extensively as a recreational drug by young people, it is being ingested by many women of child bearing age. We have therefore examined the effect of administering high doses of MDMA to rats during pregnancy on the cerebral content of both the dams and the neonates.
2. MDMA (20 mg kg⁻¹, s.c.) was injected twice daily on days 14–17 of the gestation period. The initial dose produced a marked hyperthermic response in the dam which was progressively attenuated in both peak height and area under the curve following further doses of the drug. The body weight of the dams decreased during the period of treatment.
3. There was a modest decrease in litter size (−20%) of the MDMA-treated dams.
4. The concentration of 5-HT and its metabolite 5-HIAA was decreased by over 65% in the hippocampus and striatum and 40% in the cortex of the dams 1 week after parturition. In contrast, the content of 5-HT and 5-HIAA in the dorsal telencephalon of the pups of the MDMA-treated dams was the same as that seen in tissue from pups born to control animals.
5. Administration of MDMA (40 mg kg⁻¹, s.c.) to adult rats increased thiobarbituric acid reacting substances (TBARS) in cortical tissue 3 h and 6 h later, indicating increased lipid peroxidation. No increase in TBARS was seen in the cortical tissue of 7–10 day neonates injected with this dose of MDMA 3 h or 6 h earlier.
6. The data suggest that exposure to MDMA in utero during the maturation phase does not produce damage to 5-HT nerve terminals in the foetal rat brain, in contrast to the damage seen in the brains of the mothers. This may be due to MDMA being metabolized to free radical producing entities in the adult brain but not in the immature brain or, alternatively, to more effective or more active free radical scavenging mechanisms being present in the immature brain.

     

Visuospatial memory impairments in users of MDMA (‘ecstasy’)

Rationale Previous studies have presented conflicting findings regarding visuospatial span deficits in MDMA (ecstasy) users, possibly attributable to a lack of distinction between simple visuospatial span and visuospatial working memory span. Both draw upon central executive processing, while the latter also involves concurrent goal-orientated visuospatial processing.Objectives This study compared visuospatial working memory span for MDMA users and controls. An additional concurrent task also loading on the central executive tested for inter-group differences related to central executive workload.Method MDMA user group (25 current users, 10 previous users and 18 non-users) was between-participants, and dual task condition (concurrent alphabetic generation, random letter generation, and no dual task) was within-participants. The visuospatial working memory task required participants to serially recall a spatial sequence while simultaneously completing a visual judgement task, and was completed on its own and under dual task conditions.Results Overall, non-users performed significantly better than both MDMA user groups. However, contrary to expectation, the performance decrement among users was no worse with concurrent random generation than under control conditions. Analyses controlling for background variables and the use of other drugs in the previous 3 months showed that the main effect of MDMA remained significant following control for intelligence, alcohol, amphetamines and cocaine, among other potential confounds. Unclear results were found following control for cannabis use.Conclusions The MDMA users experienced deficits in visuospatial working memory span. The lack of interaction between dual task condition and user group may be due to inter-group differences in central executive utilisation under different task conditions.     

A comparison of sodium picosulphate (Laxoberal) with standardised senna (‘Senokot’) in geriatric patients

Summary

A comparison was made between the effectiveness of sodium picosulphate and that of standardised senna in a group of 50 long-stay geriatric patients. Both were found to be equally effective as laxatives, but there were wide variations in the responses of individual patients to these agents. Side-effects were uncommon. They may well have been reduced further if a small starting dose of sodium picosulphate had been used.     

Double-blind comparison of two similar lotion formulations,one without and the other with hydrocortisone acetate (‘Actinac’) in the treatment of acne vulgaris

Summary

A double-blind, randomized trial was carried out in 44 patients with acne vulgaris to assess the effectiveness of two similar topical combination preparations, one containing hydrocortisone acetate (‘Actinac’) and the other without the steroid, when applied in lotion form. Patients used one or other of the two formulations twice daily for the first 4 days and then at night only for the remainder of the 3-month study period. The results showed that both treatments were effective but the full formulation-treated group showed a better response at the end of the first month's treatment in terms of percentage reduction in lesion count score, although this did not reach statistical significance. After 3 months, the average lesion count scores dropped from 82 to 11 in the full formulation and from 81 to 8 in the formulation minus hydrocortisone group.     

Stereoselective metabolism of (±)-praeruptorin A, a calcium channel blocker from Peucedani Radix, in pooled liver microsomes of rats and humans

(±)-Praeruptorin A (PA) is the major component of Peucedani Radix. The present study investigated stereoselectivity in PA metabolism in liver microsomes of rats (RLMs) and humans (HLMs), for the first time. PA was enantioseparated by semi-preparative chiral HPLC. Metabolic profiles of the dextrorotatory (dPA) and the levorotatory (lPA) forms in HLMs and RLMs were determined using LC-MS/MS. (-)-cis-Khellactone (D1) prepared from basic hydrolysis of dPA, and (3'R, 4'R)-4'-angeloyl-khellactone (L8) and (3'R, 4'R)-3'-angeloyl-khellactone (L9) isolated from a scale-up incubation of lPA with rat plasma were unambiguously identified by LC-MS/MS and NMR analysis. Other metabolites were tentatively identified using LC-MS/MS. In the absence of NADPH-regenerating system, dPA remained intact, however, lPA yielded L8 and L9 via a carboxylesterase(s)-mediated process. In the presence of NADPH-regenerating system, lPA produced 9 (L1-9) metabolites in both species, while dPA generated 12 (D1-12) and 6 (D1-3, 6, 9 and 10) metabolites in RLMs and HLMs, respectively. Hydrolysis, oxidation and acyl migration were demonstrated to be the predominant pathways for both enantiomers. Both enantiomers were eliminated faster in RLMs than in HLMs, while lPA showed greater species difference. PA enantiomers exhibited stereoselective metabolism in RLMs and HLMs, implying chiral discrimination in their actions.     

The influence of polymer architecture on the protective effect of novel comb shaped amphiphilic poly(allylamine) against in vitro enzymatic degradation of insulin—Towards oral insulin delivery

Nanocomplexes formed between amphiphilic poly(allylamine) (PAA) and insulin were prepared, characterised and the impact of polymer architecture on the protection of insulin against three enzymes was investigated. PAA previously modified with either cetyl or cholesteryl pendant groups at two levels of hydrophobic grafting and its quaternised derivatives were used to produce polymer–insulin nanocomplexes. Transmittance study, differential scanning calorimetry, hydrodynamic size and zeta potential measurement were conducted and the morphology of the complexes were visualised using transmission electron microscopy. All polymers were found to have an optimal polymer to insulin ratio of 0.4:1 mg mL^?1 with particle size ranging from 88 to 154 nm. Polymer architecture has an impact on the morphology of the complexes produced but has little influence on the complexation efficiency (CE). Almost all polymers were unable to produce complexes with a CE of above 50%. Most polymers demonstrated an ability to reduce insulin degradation by trypsin while the polymer architecture plays a pivotal role against α-chymotrypsin and pepsin degradation. Quaternised cholesteryl polymers were able to significantly limit insulin degradation by α-chymotrypsin while cetyl polymers were particularly effective against pepsin degradation. These results indicated that a combination of polymers might be required to enhance protection against all three proteolytic enzymes for efficacious oral delivery of insulin.     

A double blind crossover comparison of Diazepam (Valium,Ro 5–2807) with chlordiazepoxide (Librium) in the treatment of neurotic anxiety

Résumé Soixante quinze neurotiques malades (névrosés) se plaignant d'angoisse ont chacun été traités avec du chlordiazepoxide (Librium) et diazepam (Valium). Chaque malade a reçu deux semaines de traitement avec dix mg. d'un produit trois fois par jour, suivi immédiatement de deux semaines de traitement avec le même dosage de l'autre produit. Diazepam s'est révélé plus efficace a calmer l'angoisse chez ces malades, mais a provoqué plus d'effets soporifiques.     

Estimating the relative reinforcing strength of (±)-3,4-methylenedioxymethamphetamine (MDMA) and its isomers in rhesus monkeys: comparison to (+)-methamphetamine

Rationale (±)3,4-Methylenedioxymethamphetamine (MDMA) is an analog of methamphetamine (MA) and a drug of abuse. MA, MDMA, and its isomers release monoamine neurotransmitters with varying selectivities and would, therefore, be predicted to vary in their relative strength as reinforcers.Objectives This study compared self-administration of MA, MDMA, and its isomers using a progressive-ratio schedule in rhesus monkeys.Methods Rhesus monkeys [n = 6, MA and MDMA; n = 5, (+)-MDMA and (−)-MDMA] were prepared with chronic i.v. catheters and allowed to self-administer cocaine or saline in daily baseline sessions. When responding was stable, MA (0.006–0.1 mg/kg per injection), MDMA (0.025–0.8 mg/kg injection), (+)-MDMA (0.025–0.8 mg/kg per injection), or (−)-MDMA (0.05–0.8 mg/kg per injection) was made available in test sessions.Results MA, MDMA, and (+)-MDMA functioned as positive reinforcers in all monkeys with a potency relationship of MA > (+)-MDMA > (±)-MDMA. Two of five monkeys took (−)-MDMA above saline levels. Dose–response relationships were biphasic for MA and (±)-MDMA, and asymptotic for (+)-MDMA. In terms of maximum number of injection per session, a measure of relative reinforcing strength, the order was MA > (+)-MDMA = (±)-MDMA > (−)-MDMA.Conclusions MDMA and (+)-MDMA were consistent positive reinforcers, but weaker than MA, whereas (−)-MDMA was, at best, a weak reinforcer in some monkeys. The reinforcing strength of MDMA appears to derive primarily from (+)-MDMA. Because MDMA and its isomers have been shown to have relatively higher serotonin to dopamine releasing potency, these data support the hypothesis that increasing 5-HT releasing potency relative to DA is associated with weaker reinforcing effects.     

Role of tumor necrosis factor and nitric oxide in the protection of N-methyl-N-(3,4-methylenedioxybenzoyl) methyl-acetamide against immunological liver injury in mice

研究了Ｎ－甲基－Ｎ－（３，４－亚甲二氧基苯甲酰）甲基－乙酰胺（ＳＹ－６４０）的保肝作用及其机理．给小鼠ｉｖ活卡介苗（ＢＣＧ）１２ｄ后再ｉｖ脂多糖（ＬＰＳ）诱导小鼠血浆一氧化氮（ＮＯ），肿瘤坏死因子（ＴＮＦ），谷丙转氨酶（ＧＰＴ），谷草转氨酶（ＧＯＴ）剧烈升高及严重的肝损伤．以ＳＹ－６４０给小鼠ｉｇ（每日一次，连续１０ｄ），显著降低ＢＣＧ＋ＬＰＳ诱导的肝损伤小鼠血浆ＧＰＴ，ＧＯＴ和ＴＮＦ水平的升高，血浆ＮＯ水平的升高更加显著，肝损伤减轻．以单甲基精氨酸抑制ＮＯ的生成，ＳＹ－６４０的上述作用被抵消．ＳＹ－６４０对正常小鼠血浆ＮＯ，ＧＰＴ，ＧＯＴ水平无影响．可见，ＳＹ－６４０的保肝作用与其升高血浆ＮＯ，降低血浆ＴＮＦ水平有关．     

The role of 5-HT in the impairment of thermoregulation observed in rats administered MDMA (‘ecstasy’) when housed at high ambient temperature

Rationale Administration to rats of a neurotoxic dose of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) produces an impairment in thermoregulation which is reflected in a prolonged hyperthermic response to a subsequent dose of MDMA given to rats housed at high ambient temperature.Objective We wished to examine whether the impaired thermoregulation was associated with decreased cerebral 5-HT content produced by the prior neurotoxic dose of MDMA.Methods Rats were injected with drugs decreasing 5-HT function [the tryptophan hydroxlase inhibitor p-chlorophenylalanine (PCPA), and 5-HT receptor antagonists] and rectal temperature was measured after administering MDMA to rats housed at 30°C.Results PCPA pretreatment decreased 5-HT and 5-HIAA concentrations in cortex, hippocampus and striatum by >80% and prolonged the hyperthermia induced in rats housed at 30°C by administering MDMA (5 mg/kg i.p.). A similar prolongation of the hyperthermic response to MDMA was seen when rats were pretreated with methysergide (10 mg/kg i.p.) or the 5-HT_1A antagonist WAY100635 (0.5 mg/kg s.c.).Conclusions Decreasing 5-HT function in diverse ways enhanced the hyperthermic response to MDMA given to rats housed at high ambient temperature. This suggests that loss of 5-HT acting on 5-HT_1A receptors leads to impaired thermoregulation in rats and suggests that the impairment seen in MDMA pretreated rats housed at high ambient temperature is due to a loss in 5-HT function. These data could have implications for recreational users of MDMA, who may have damaged serotoninergic neurons because of prior heavy or frequent use of the drug, when taking further doses of MDMA in hot environments such as dance clubs.     

A clinical trial of glycosaminoglycan-peptide complex (‘Rumalon’) in patients with osteoarthritis of the knee

Summary

A clinical trial was undertaken in 50 patients with osteoarthritis of the knee to assess the therapeutic value of glycosaminoglycan-peptide complex in treatment. The first year consisted of a randomized, double-blind, placebo-controlled, parallel-group trial (25 patients in each group), after which all patients received active treatment for a further 2 years. Treatment consisted of three 8-week courses in the first year and 2 such courses per year in subsequent years, each consisting of 2 ml intramuscular injections given 3 times per week. Patients were permitted to continue taking anti-inflammatory drugs and to receive physiotherapy during the trial period. At the end of the first year of the trial (double-blind phase), there were no significant differences between the two treatment groups. However, after the second year, those patients who had received glycosaminoglycan-peptide complex for 2 years had significantly greater improvements in night pain andrestpain than did those who had received active treatment for only 1 year. At the end of 3 years (when half the patients had received active treatment for 2 years and half for 3 years), there were significant overall improvements in relation to rest pain, pain on walking and morning stiffness, but not in respect to night pain, pain on standing or climbing stairs. At the same time, improvements were seen in radiological severity of disease (assessed double-blind) in 16% of patients, with ‘no change’ in 74% and deterioration in lo%, these figures being considerably better than might be expected with conventional therapy. Glycosaminoglycan-peptide complex was extremely well tolerated.     

Recent advances in the study of (–)clausenamide: chemistry,biological activities and mechanism of action

Clausenamide (clau) is one of seven novel compounds isolated from Clausena lansium (Lour) skeels. Clau is unusual in that it contains 4 chiral centers yielding 8 pairs of enantiomers. After identification of the configuration of these enantiomers, the synthesis of 16 enantiomers, including optically active clau and (+) and (–)clau was carried out. During this study, many stereochemical and synthetic difficulties were solved and the Baldwin principle was updated. Production scale is now sufficient to meet the needs of clinical practice. In a pharmacological study numerous models and indicators showed that (–)clau is the active enantiomer, while (+)clau is inactive and elicits greater toxicity than (–)clau. The principal pharmacological effects of (–)clau are to increase cognition, demonstrated in ten models of memory impairment, as well as to inhibit β-amyloid (Aβ) toxicity, blocking neurofibrillary tangle formation by inhibiting the phosphorylation of tau protein. This anti-dementia effect is characterized by increased synaptic plasticity both in efficacy and in structure and provides new support for the theory that synaptic loss is the main cause of dementia. (–)Clau is considered to be a promising drug candidate for treatment of Alzheimer׳s disease and other neurodegenerative disorders.KEY WORDS: (–)Clausenamide, Enantiomers, Cognition, Alzheimer׳s disease pathology, Tau, High phosphorylation, Synaptic plasticity     

Comparison of nystatin (‘Nystan’) and hydrargaphen (‘Penotrane’) in the treatment of vaginal candidosis in pregnancy

Summary

A double-blind comparison of nystatin (‘Nystan’) pessaries and hydrargaphen (‘Strong Penotrane’) pessaries for the treatment of vaginal candidosis showed that the former is more effective on clinical and mycological assessment. Relief from symptoms was obtained in 95.9% and 84.6% of the patients treated with nystatin and hydrargaphen respectively. On stopping treatment, yeasts could no longer be isolated from 75.0% of the cases receiving 'Nystan' and from 23.1% receiving 'Strong Penotrane'. There was no evidence of resistance to either drug before, during or after therapy.     

Rosiglitazone, a PPAR-γ agonist, protects against striatal dopaminergic neurodegeneration induced by 6-OHDA lesions in the substantia nigra of rats

Rosiglitazone is a commonly prescribed insulin-sensitizing drug with selective agonistic activity at the peroxisome proliferator-activated receptor-γ (PPARγ). Previously, rosiglitazone was shown to attenuate dopaminergic cell loss in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease (PD), an effect attributed to its anti-inflammatory properties. To elucidate the neuroprotective mechanisms of rosiglitazone, we investigated the effects of rosiglitazone on the expressions of striatal tyrosine hydroxylase (TH), cyclooxygenase-2 (COX-2) and glial fibrillary acidic protein (GFAP) in a 6-OHDA-lesioned rat PD model. Rosiglitazone (3mg/kg) was administered intraperitoneally at 24h and 30min prior to the creation of an intranigral 6-OHDA lesion. A reduction in TH protein expression began at 3days and a prominent decrease was observed at 7days post-lesion, and decreases of dopamine (DA) levels began at 1day post-lesion. In contrast, GFAP expression was significantly increased at 3days and preserved for up to7 days post-lesion and the patterns of GFAP expression was inversely correlated to changes in TH expression. Furthermore, COX-2 expression in the rostral striatum showed a significant increase at 6h post-lesion while that of the caudal striatum was increased at 12h. In the 6-OHDA-lesioned model, the activation of PPARγ by rosiglitazone significantly prevented TH protein expression reductions, and inhibited 6-OHDA-induced microglia activation in striatum. In addition, rosiglitazone attenuated in production of both COX-2 and TNF-α expression. In contrast, rosiglitazone pretreatment led to greater increases in striatal GFAP expression than 6-OHDA alone and changes in the expression of this protein preceded the changes that were seen with TH expression. These results suggest that the neuroprotection observed with rosiglitazone treatment may be partially due to the attenuation of COX-2 production and the strengthening of astrocyte function. Our results provide insight into the neuroprotective mechanisms of rosiglitazone against 6-OHDA-induced neuronal damages.     

Effect of ambient temperature and a prior neurotoxic dose of 3,4-methylenedioxymethamphetamine (MDMA) on the hyperthermic response of rats to a single or repeated (‘binge’ ingestion) low dose of MDMA

Rationale 3,4-Methylenedioxymethamphetamine (MDMA, ecstasy) administration to rats produces acute hyperthermia and long-term neurotoxic damage to 5-hydroxytryptamine (serotonin, 5-HT) neurones.Objective We wished to examine MDMA-induced hyperthermia in rats housed at normal (19°C) and high (30°C) room temperatures and investigate the effect of a prior neurotoxic lesion.Methods Rectal temperature was measured after administration of single or repeated doses of MDMA to rats housed at 19°C and 30°C.Results MDMA (5 mg/kg IP) produced a sustained hyperthermic response in rats housed at 30°C, but not in rats housed at 19°C. A prior (5 weeks earlier) neurotoxic dose of MDMA (12.5 mg/kg IP) resulted in MDMA (5 mg/kg) producing a greater hyperthermic response in rats housed at 30°C than in non-pre-treated animals. Repeated MDMA administration (binge dosing; 2, 4 or 6 mg/kg ×3) produced dose-dependent hyperthermia in rats housed at 19°C, with MDMA (2 mg/kg ×3) having little effect. However, this dose produced significant hyperthermia (2°C above control values)in rats housed at 30°C following the third dose. A prior neurotoxic dose of MDMA resulted in MDMA (2 mg/kg ×3) producing marked hyperthermia (>1°C) after the first dose and severe hyperthermia (2°C) after the third dose.Conclusions MDMA administration to rats housed at 30°C produces a more severe hyperthermic response than that seen in rats housed at 19°C. A prior neurotoxic dose enhances the response further in animals housed at 30°C. Binge dosing produces a higher final peak response than a similar non-divided dose. This effect is more marked in animals housed at high room temperature. These data may have implications for recreational users of MDMA in hot environments, particularly those who may have damaged serotoninergic neurones because of prior heavy or frequent use of the drug.     

A doubie-blind,between-patient comparison of alclofenac (‘Prinalgin’) and indomethacin in the treatment of low back pain and sciatica

Summary

A double-blind, between-patient comparison of alclofenac and indomethacin was carried out in 60 patients with low back pain and sciatica. Pain, functional disability and signs of dural irritation (Laségue's sign) were rated by the clinician before and at the end of each 7-day treatment period, and an overall assessment of treatment effectiveness was made by both clinician and patients.

Response to treatment in terms of patient improvement was considered satisfactory with both drugs, but more erratic in those patients with an acute condition. Analysis of pain scores showed a significant tendency for patients with acute or chronic low back pain to improve more with alclofenac than with indomethacin treatment. Overall assessments by the clinician and patients also indicated signiJcantly greater improvement with alclofenac.     

Effects of the novel BK (KCa1.1) channel opener GoSlo-SR-5-130 are dependent on the presence of BKβ subunits

Background and Purpose

GoSlo-SR compounds are efficacious BK (K_Ca1.1) channel openers, but little is known about their mechanism of action or effect on bladder contractility. We examined the effects of two closely related compounds on BK currents and bladder contractions.

Experimental Approach

A combination of electrophysiology, molecular biology and synthetic chemistry was used to examine the effects of two novel channel agonists on BK channels from bladder smooth muscle cells and in HEK cells expressing BKα alone or in combination with either β₁ or β₄ subunits.

Key Results

GoSlo-SR-5-6 shifted the voltage required for half maximal activation (V_1/2) of BK channels approximately −100 mV, irrespective of the presence of regulatory β subunits. The deaminated derivative, GoSlo-SR-5-130, also shifted the activation V_1/2 in smooth muscle cells by approximately −100 mV; however, this was reduced by ∼80% in HEK cells expressing only BKα subunits. When β₁ or β₄ subunits were co-expressed with BKα, efficacy was restored. GoSlo-SR-5-130 caused a concentration-dependent reduction in spontaneous bladder contraction amplitude and this was abolished by iberiotoxin, consistent with an effect on BK channels.

Conclusions and Implications

GoSlo-SR-5-130 required β₁ or β₄ subunits to mediate its full effects, whereas GoSlo-SR-5-6 worked equally well in the absence or presence of β subunits. GoSlo-SR-5-130 inhibited spontaneous bladder contractions by activating BK channels. The novel BK channel opener, GoSlo-SR-5-130, is approximately fivefold more efficacious on BK channels with regulatory β subunits and may be a useful scaffold in the development of drugs to treat diseases such as overactive bladder.     

Involvement of K+ channel permeability changes in the L-NAME and indomethacin resistant part of adenosine-5′-O-(2-thiodiphosphate)-induced relaxation of pancreatic vascular bed

1. We have previously demonstrated that adenosine-5′-O-(2-thiodiphosphate) (ADPβS), a potent P2Y-purinoceptor agonist, relaxed pancreatic vasculature not only through prostacyclin (PGI₂) and nitric oxide (NO) release from the endothelium but also through other mechanism(s). In this study, we investigated the effects of an inhibitor of the Na⁺/K⁺ pump, of ATP-sensitive K⁺ (K_ATP) channels and of small (SK_Ca) or large (BK_Ca) conductance Ca²⁺-activated K⁺ channels. Experiments were performed at basal tone and during the inhibition of NO synthase and cyclo-oxygenase.
2. In control conditions, ADPβS (15 μM) induced an initial transient vasoconstriction followed by a progressive and sustained vasodilatation. In the presence of N^ω-nitro-L-arginine methyl ester (L-NAME, 200 μM) the transient vasoconstriction was reversed into a one minute vasodilator effect, which was then followed by a progressive and sustained vasodilatation similar to that observed with ADPβS alone. The addition of indomethacin (10 μM) did not significantly modify the profile of ADPβS-induced vasodilatation.
3. Ouabain (100 μM) decreased basal pancreatic flow rate and did not modify ADPβS-induced relaxation. This inhibitor of the Na⁺/K⁺ pump increased the pancreatic vasoconstriction induced by L-NAME or by the co-administration of L-NAME and indomethacin. Ouabain did not modify either the L-NAME or the L-NAME/indomethacin resistant part of the ADPβS vasodilatation.
4. The K_ATP inhibitor tolbutamide (185 μM) did not significantly modify basal pancreatic flow rate and ADPβS-induced relaxation. This inhibitor which did not change L-NAME-induced vasoconstriction, significantly diminished the L-NAME resistant part of ADPβS-induced vasodilatation. Tolbutamide intensified the vasoconstriction induced by the co-administration of L-NAME and indomethacin. In contrast, the L-NAME/indomethacin resistant part of ADPβS vasodilatation was not changed by the closure of K_ATP.
5. The SK_Ca inhibitor apamin (0.1 μM) did not significantly change pancreatic vascular resistance whatever the experimental conditions (in the absence or in presence of L-NAME or L-NAME/indomethacin). In the presence of L-NAME, the closure of SK_Ca channels changed the one minute vasodilator effect of ADPβS into a potent vasoconstriction and thereafter modified only the beginning of the second part of the L-NAME-resistant part of the ADPβS-induced vasodilatation. In contrast, the L-NAME/indomethacin resistant part of ADPβS-induced relaxation remained unchanged in the presence of apamin.
6. Charybdotoxin (0.2 μM), an inhibitor of BK_Ca, increased pancreatic vascular resistance in the presence of L-NAME/indomethacin. In the presence of L-NAME, the closure of BK_Ca channels reversed the one minute vasodilator effect of ADβPS into a potent vasoconstriction and drastically diminished the sustained vasodilatation. In contrast the L-NAME/indomethacin resistant part of ADPβS-induced relaxation was not modified by the presence of charybdotoxin. Under L-NAME/indomethacin/charybdotoxin/apamin infusions, ADPβS evoked a drastic and transient vasoconstriction reaching a maximum at the second minute, which was followed by a sustained increase in the flow rate throughout the ADPβS infusion. The maximal vasodilator effect of ADPβS observed was not modified by the addition of apamin.
7. The results suggest that the L-NAME-resistant relaxation induced by ADPβS in the pancreatic vascular bed involves activation of BK_Ca, K_ATP and to a lesser extent of SK_Ca channels, but the L-NAME/indomethacin resistant part of ADPβS-induced relaxation is insensitive to the closure of K_ATP, SK_Ca and BK_Ca channels.