Role of cannabinoid receptors in the regulation of cardiac contractility during ischemia/reperfusion

We studied the effect of selective ligands of cannabinoid (CB) receptors on contractility of isolated Langendorff-perfused rat heart under conditions of 45-min total ischemia and 30-min reperfusion. Perfusion with a solution containing selective CB receptor agonist HU-210 for 10 min before ischemia increased the severity of reperfusion contractile dysfunction. This drug decreased left ventricular developed pressure and maximum rates of contraction and relaxation, but had no effect on heart rate and end-diastolic pressure. The negative inotropic effect of the drug was transitory and disappeared after 5-min reperfusion. Pretreatment with selective CB1 receptor antagonist SR141716A and selective CB2 receptor antagonist SR144528 had no effect on heart rate and myocardial contractility during reperfusion. Our results indicate that stimulation of CB receptors can increase the degree of reperfusion-induced cardiac contractile dysfunction. However, endogenous cannabinoids are not involved in the development of myocardial contractile dysfunction during ischemia/reperfusion of the isolated heart. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 142, No. 11, pp. 500–504, November, 2006     

Cannabinoid Receptor Antagonists SR141716 and SR144528 Exhibit Properties of Partial Agonists in Experiments on Isolated Perfused Rat Heart

We studied the effect of selective cannabinoid receptor ligands on contractility of isolated Langendorff-perfused rat heart. It was found that 10-min perfusion of rat heart with a solution containing selective agonist of CB1 and CB2 receptors HU-210 (10 nM) decreased left ventricular developed pressure and maximum rates of contraction and relaxation. However, HU-210 had no effect on heart rate and end-diastolic pressure. Treatment with selective CB1 receptor antagonist SR141716 (1 µM) and selective CB2 receptor antagonist SR144528 (1 µM) decreased left ventricular developed pressure and maximum rates of contraction and relaxation, but had no effect on heart rate and end-diastolic pressure. Ten-minute perfusion of rat heart with a solution containing selective agonist of CB1 and CB2 receptors HU-210 (10 nM) decreased cAMP concentration in the heart. CB receptor antagonists had little effect on cAMP concentration in the heart. The negative inotropic effect of HU-210 and CB receptor antagonists is probably mediated by activation of CB1 receptors. It can be hypothesized that the decrease in heart cAMP concentration is related to stimulation of CB2 receptors. Our results suggest that selective CB receptor antagonists SR141716 and SR144528 in a final concentration of 1 µM exhibit properties of partial CB receptor agonists.__________Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 139, No. 5, pp. 512–516, May, 2005     

Involvement of central and peripheral cannabionoid receptors in the regulation of heart resistance to arrhythmogenic effects of epinephrine

Intravenous injection of the selective cannabinoid receptor agonist HU-210 in doses of 0.05 and 0.25 mg/kg increased heart resistance to arrhythmogenic effects of epinephrine, while intracerebroventricular infusion of this substance had no effect on the incidence of epinephrine-induced arrhythmia. The selective antagonist of type I cannabinoid receptors SR141716A in a dose of 3 mg/kg and ganglion blocker hexamethonium in a dose of 10 mg/kg did not modify the antiarrhythmic effect of HU-210. This effect of HU-210 is probably related to activation of type II peripheral cannabinoid receptors. Translated fromByulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 130, No. 11, pp. 552–554, November, 2000     

Activation of type II cannabinoid receptors improves myocardial tolerance to arrhythmogenic effects of coronary occlusion and reperfusion

Preliminary intravenous injection of cannabinoid receptor agonist HU-210 (0.05 mg/kg) reduced the incidence of ventricular arrhythmias during 10-min coronary occlusion and 10-min reperfusion in chloralose-anesthetized rats. Preliminary injection of type I cannabinoid receptor antagonist SR 141716A (3 mg/kg) had no effect on the antiarrhythmic effect of HU-210, while type II cannabinoid receptor antagonist SR 144528 (1 mg/kg) completely abolished the effect of HU-210. Preconditioning with glibenclamide (0.3 mg/kg), an inhibitor of ATP-dependent K⁺-channels, did not affect the antiarrhythmic activity of HU-210. These findings suggest that antiarrhythmic effect of HU-210 is mediated through activation of type II cannabinoid receptors rather than activation of K⁺-channels.     

Selective cannabinoid receptor agonist HU-210 decreases pump function of isolated perfused heart: Role of cAMP and cGMP

The rate and strength of heart contractions decreased after 10-min perfusion of rat myocardium with Krebs—Henseleit solution containing a selective cannabinoid receptor agonist HU-210 in a final concentration of 10 nM. HU-210 completely blocked the positive inotropic and chronotropic effect of -adrenoceptor agonist isoproterenol, decreased the basal level of cAMP, and abolished the isoproterenol-induced increase in myocardial cAMP concentration. cGMP concentration remained unchanged under these conditions. The decrease in myocardial cAMP concentration after activation of cannabinoid receptors did not correlate with changes in the strength and rate of heart contractions. Our results suggest that the negative inotropic and chronotropic effects of HU-210 are not associated with decreased cAMP concentration in the myocardium.Translated from Byulleten Eksperimentalnoi Biologii i Meditsiny, Vol. 138, No. 12, pp. 622–625, December, 2004This revised version was published online in April 2005 with a corrected cover date.     

Overexpressed protein disulfide isomerase in brains of patients with sporadic Creutzfeldt-Jakob disease

Cannabinoids produce antinociception via specific cannabinoid receptor activation, but there are also non-receptor mediated effects like for example the activation of the arachidonic acid cascade. Here we investigate the influence of cannabinoids (CB) on sleep duration after isoflurane anesthesia. We found that the CB receptor agonists R(-)-7-hydroxy-delta-6-tetra-hydrocannabinol-dimethylheptyl (HU-210) (0.1 mg/kg), 2-O-arachidonoylglycerylether (30 mg/kg) and arachidonyl-2-chloroethylamide (3 mg/kg) significantly prolong the duration of isoflurane induced sleep in mice (P<0.05). This effect was absent when co-injecting the selective CB(1) antagonist N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (1 mg/kg). Furthermore, HU-210 was ineffective in CB(1) receptor knockout mice (CB(1)-/-). Our behavioral tests (tail flick, rotarod) indicate that the sleep latency can be prolonged even at low drug dosages which do not influence thermal nociception. In the chosen dosages thimerosal (20 mg/kg), 2-AG (10 mg/kg), R(1)-methanandamide (R(1)-MAEA) (10 mg/kg) and flurbiprofen (27 mg/kg) were ineffective to increase sleep duration.     

Involvement of central and peripheral cannabionoid receptors in the regulation of heart resistance to arrhythmogenic effects of epinephrine

Intravenous injection of the selective cannabinoid receptor agonist HU-210 in doses of 0.05 and 0.25 mg/kg increased heart resistance to arrhythmogenic effects of epinephrine, while intracerebroventricular infusion of this substance had no effect on the incidence of epinephrine-induced arrhythmia. The selective antagonist of type I cannabinoid receptors SR141716A in a dose of 3 mg/kg and ganglion blocker hexamethonium in a dose of 10 mg/kg did not modify the antiarrhythmic effect of HU-210. This effect of HU-210 is probably related to activation of type II peripheral cannabinoid receptors.     

The cannabinoid receptor agonist, WIN 55,212-2, inhibits cool-specific lamina I medullary dorsal horn neurons

Cannabinoid receptor agonists have been demonstrated to inhibit medullary and spinal cord dorsal horn nociceptive neurons. The effect of cannabinoids on thermoreceptive specific neurons in the spinal or medullary dorsal horn remains unknown. In the present study, single-unit recordings from the rat medullary dorsal horn were performed to examine the effect of a cannabinoid receptor agonists on cold-specific lamina I spinothalamic tract neurons. The cannabinoid CB1/CB2 receptor agonist, WIN 55,212-2 (WIN-2), was locally applied to the medullary dorsal horn and the neuronal activity evoked by cooling the receptive field was recorded. WIN-2 (1 microg/microl and 2 microg/microl) significantly attenuated cold-evoked activity. Co-administration of the CB1 receptor antagonist SR 141716 with WIN-2 did not affect cold-evoked activity. These results demonstrate a potential mechanism by which cannabinoids produce hypothermia, and also suggest that cannabinoids may affect non-noxious thermal discrimination.     

Chronotropic effect of D-Ala<Superscript>2</Superscript>,Leu<Superscript>5</Superscript>,Arg<Superscript>6</Superscript>-enkephalin (dalargin) is associated with activation of peripheral κ-opioid receptors

Intravenous infusion of D-Ala²,Leu⁵,Arg⁶-enkephalin (dalargin) caused bradycardia in narcotized rats. This effect was not observed during opioid receptor blockade with naloxone, naloxone methiodide, and norbinaltorphimine. Dalargin and (-)-U-50,488 added to Krebs—Henseleit perfusion solution for isolated rat heart decreased heart rate. Ganglionic blocker hexamethonium potentiated the negative chronotropic effect of dalargin. The negative chronotropic effect of dalargin is probably associated with activation of cardiac κ-opioid receptors. It should be noted that dalargin caused tachycardia in some animals. This reaction was not observed after treatment with hexamethonium. The positive chronotropic effect of dalargin is probably related to modulation of the parasympathetic autonomic nervous system. Agonists and antagonists of δ-opioid receptors caused persistent bradycardia. We hypothesized that selective δ-opioid antagonists exhibit properties of partial δ-receptor agonists. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 140, No. 12, pp. 633–638, December, 2005     

CB1 cannabinoid receptor inhibits synaptic release of glutamate in rat dorsolateral striatum

CB1 cannabinoid receptors in the neostriatum mediate profound motor deficits induced when cannabinoid drugs are administered to rodents. Because the CB1 receptor has been shown to inhibit neurotransmitter release in various brain areas, we investigated the effects of CB1 activation on glutamatergic synaptic transmission in the dorsolateral striatum of the rat where the CB1 receptor is highly expressed. We performed whole cell voltage-clamp experiments in striatal brain slices and applied the CB1 agonists HU-210 or WIN 55,212-2 during measurement of synaptic transmission. Excitatory postsynaptic currents (EPSCs), evoked by electrical stimulation of afferent fibers, were significantly reduced in a dose-dependent manner by CB1 agonist application. EPSC inhibition was accompanied by an increase in two separate indices of presynaptic release, the paired-pulse response ratio and the coefficient of variation, suggesting a decrease in neurotransmitter release. These effects were prevented by application of the CB1 antagonist SR141716A. When Sr(2+) was substituted for Ca(2+) in the extracellular solution, application of HU-210 (1 microM) significantly reduced the frequency, but not amplitude, of evoked, asynchronous quantal release events. Spontaneous release events were similarly decreased in frequency with no change in amplitude. These findings further support the interpretation that CB1 activation leads to a decrease of glutamate release from afferent terminals in the striatum. These results reveal a novel potential role for cannabinoids in regulating striatal function and thus basal ganglia output and may suggest CB1-targeted drugs as potential therapeutic agents in the treatment of Parkinson's disease and other basal ganglia disorders.     

Negative inotropic and chronotropic effects of δ-opioid receptor antagonists are mediated via non-opioid receptors

Ten-minute perfusion of intact isolated rat heart with Krebs-Henseleit solution containing δ-opioid receptor agonists (DPDPE, (−)-TAN-67) or δ-opioid receptor antagonists (naltrindole, TIPP[Ψ], ICI 174,864) at a final concentration of 0.1 mg/liter decreased HR, blood pressure in the left ventricle, and the rates of myocardial contraction and relaxation. Intravenous injection of δ-agonists (DPDPE, (−)-TAN-67, deltorphin II) or δ-antagonists (naltrindole, TIPP[Ψ], ICI 174,864) decreased HR in narcotized rats. Naloxone and naltrexone produced no effect on contractility and HR both in vivo and in vitro. Preliminary injection of naloxone and naltrexone did not prevent the negative chronotropic effect of ICI 174,864 in vitro. The negative inotropic and chronotropic effects of δ-opioid receptor antagonists are mediated by unknown non-opioid receptors in the heart. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 141, No. 4, pp. 404–407, April, 2006     

Activation of CB1 cannabinoid receptors impairs memory consolidation and hippocampal polysialylated neural cell adhesion molecule expression in contextual fear conditioning

We investigated the role of CB1 receptors in hippocampal-dependent memory consolidation mediated by polysialylated neural cell adhesion molecule (PSA-NCAM) during contextual fear conditioning (CFC). The CB1 receptor agonist 3-(1,1-dimethylheptyl)-(-)-11-hydroxy-Δ⁸-tetrahydrocannabinol (HU-210) (0.1 mg/kg) was given immediately after training during the memory consolidation phase, and freezing behavior was measured 24 h after conditioning. Administration of HU-210 attenuated freezing behavior measured in CFC. Western blot analysis showed that CFC induced a decrease in the expression of NCAM-180, but did not change the level of NCAM-140 and increased PSA-NCAM expression measured 24 h after training in the rat hippocampus. HU-210 (0.1 mg/kg) injection did not affect the reduction in NCAM-180 levels induced by CFC, but it blocked the increase in PSA-NCAM expression. Since the dentate gyrus (DG) of the hippocampus is known to be involved in memory consolidation and expresses a high level of PSA-NCAM protein, we measured the effects of CFC and HU-210 administration on PSA-NCAM-immunoreactive (IR) cells in the DG. CFC caused an increase in the number of PSA-NCAM-IR cells in the DG, but not K_i-67- or doublecortin (DCX)-IR cells. This increase in PSA-NCAM-IR cells was abolished by HU-210 injection. Administration of the CB1 receptor antagonist N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM-251) (3 mg/kg immediately before HU-210) inhibited the effects of HU-210 on freezing behavior and PSA-NCAM expression in the DG. These results indicate that activation of CB1 receptors disturbs consolidation of fear memory in CFC, likely by affecting PSA-NCAM expression in the DG, which plays an important role in synaptic rearrangement during the formation of memory traces.     

Role of P2X receptors in positive inotropic effect of rat myocardium during ontogeny

Experiments with selective agonists and antagonists of purinoceptors allowed us to evaluate the subtype of P2X receptors. We showed that the myocardium of 14–100-day-old rats contains functionally active P2X₁ receptors. These receptors are involved in the realization of the positive inotropic effect of the atria and ventricles. Selective P2X₁ receptor agonist β,γ-methylene-ATP induced a dose-dependent increase in the strength of atrial and ventricular contractions. P2X₁ receptor antagonist TNP-ATP abolished the effect of the agonist in rats of all age groups. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 145, No. 2, pp. 133–135, February, 2008     

Activation of k<Subscript>1</Subscript>-opioid receptor as a method for prevention of ischemic and reperfusion arrhythmias: Role of protein kinase C and K<Subscript>ATP</Subscript> channels

Intravenous pretreatment with κ-opioid receptor antagonist (−)-U-50,488 (1 mg/kg) improved heart resistance to the arrhythmogenic effect of coronary occlusion and reperfusion. Selective κ₁-opioid receptor antagonist norbinaltorphimine and nonselective blocker of peripheral opioid receptors methylnaloxone abolished this antiarrhythmic effect. Preliminary blockade of protein kinase C with chelerythrine or inhibition of ATP-dependent K⁺ channels (K_ATP channels) with glybenclamide abolished the antiarrhythmic effect of κ-opioid receptor activation. Selective inhibitor of sarcolemmal K_ATP channels did not modulate the κ-opioid receptor-mediated increase in cardiac electrical stability. Our results suggest that protein kinase C and mitochondrial K_ATP channels play an important role in the antiarrhythmic effect associated with activation of peripheral κ-opioid receptors. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 143, No. 2, pp. 145–148, February, 2007     

Anandamide enhances extracellular levels of adenosine and induces sleep: an in vivo microdialysis study

STUDY OBJECTIVES: The principal component of marijuana, delta-9-tetrahydrocannabinol increases sleep in humans. Endogenous cannabinoids, such as N-arachidonoylethanolamine (anandamide), also increase sleep. However, the mechanism by which these molecules promote sleep is not known but might involve a sleep-inducing molecule such as adenosine. Microdialysis samples were collected from the basal forebrain in order to detect levels of adenosine before and after injection of anandamide. DESIGN: Rats were implanted for sleep studies, and a cannula was placed in the basal forebrain to collect microdialysis samples. Samples were analyzed using high-performance liquid chromatography. SETTINGS: Basic neuroscience research laboratory. PARTICIPANTS AND INTERVENTIONS: Three-month-old male F344 rats. At the start of the lights-on period, animals received systemic injections of dimethyl sulfoxide (vehicle), anandamide, SR141716A (cannabinoid receptor 1 [CB1] antagonist), or SR141716A and anandamide. One hour after injections, microdialysis samples were collected (5 microL) from the basal forebrain every hour over a 20-minute period for 5 hours. The samples were immediately analyzed via high-performance liquid chromatography for adenosine levels. Sleep was also recorded continuously over the same period. MEASUREMENTS AND RESULTS: Anandamide increased adenosine levels compared to vehicle controls with the peak levels being reached during the third hour after drug injection. There was a significant increase in slow-wave sleep during the third hour. The induction in sleep and the rise in adenosine were blocked by the CB1-receptor antagonist, SR141716A. CONCLUSIONS: Anandamide increased adenosine levels in the basal forebrain and also increased sleep. The soporific effects of anandamide were mediated by the CB1 receptor, since the effects were blocked by the CB1-receptor antagonist. These findings identify a potential therapeutic use of endocannabinoids to induce sleep in conditions where sleep may be severely attenuated.     

Modulation of electrically evoked acetylcholine release through cannabinoid CB1 receptors: evidence for an endocannabinoid tone in the human neocortex

Cannabinoids are known to inhibit neurotransmitter release in the CNS through CB1 receptors. The present study compares the effects of synthetic cannabinoids on acetylcholine (ACh) release in human and mice neocortex. We further investigated a possible endocannabinoid tone on CB1 receptors in human neocortex caused by endogenous agonists like anandamide or 2-arachidonylglycerol. Brain slices, incubated with [3H]-choline, were superfused and stimulated electrically under autoinhibition-free conditions to evoke tritium overflow assumed to represent ACh release. The first series of experiments was performed with 26 pulses, 60 mA, at 0.1 Hz. In mice neocortical slices, the cannabinoid receptor agonist WIN55212-2 decreased ACh release (pIC50=6.68, I(max)=67%). In the human neocortex the concentration-response curve of WIN55212-2 was bell-shaped and flat (I(max observed) approximately 30%). The estimated maximum possible inhibition, however, was much larger: I(max derived)=79%. Lec, the negative logarithm (lg) of the biophase concentration of endocannabinoids in 'WIN55212-2 units,' was -6.52, the pKd of WIN55212-2 was 7.47. The CB1 receptor antagonist/inverse agonist SR141716 enhanced ACh release in the human neocortex (by 38%) and prevented the inhibitory effect of WIN55212-2. The concentration-response curve of WIN55212-2 was changed in its shape including a shift to the right due to the presence of SR141716. A pA2 of this antagonist between 11.60 and 11.18 was obtained. SR141716 alone had no effect in mice neocortical slices. A partial agonist without inverse agonistic activity, O-1184, enhanced ACh release in the human neocortex. The endocannabinoid uptake-inhibitor AM404 decreased ACh release in human, but not in mice, neocortical slices. Change of the stimulation parameters (eight trains of pseudo-one-pulse bursts (4 pulses, 76 mA, 100 Hz), spaced by 45 s intervals) led to a stronger inhibitory effect of WIN55212-2, and abolished the disinhibitory effect of SR141716 and O-1184. The results show that activation of CB1 cannabinoid receptors leads to inhibition of ACh release in the human and mouse neocortex. The endocannabinoid tone is high in the human, but not in the mouse neocortex and is dependent on neuronal activity. SR141716 acts as a competitive CB1 receptor antagonist.     

Cannabinoids attenuate depolarization-dependent Ca2+ influx in intermediate-size primary afferent neurons of adult rats

CB1 receptors have been localized to primary afferent neurons, but little is known about the direct effect of cannabinoids on these neurons. The depolarization-evoked increase in the concentration of free intracellular calcium ([Ca(2+)](i)), measured by microfluorimetry, was used as a bioassay for the effect of cannabinoids on isolated, adult rat primary afferent neurons 20-28 h after dissociation of dorsal root ganglia. Cannabinoid agonists CP 55,940 (100 nM) and WIN 55,212-2 (1 microM) had no effect on the mean K(+)-evoked increase in [Ca(2+)](i) in neurons with a somal area<800 microm(2), but the ligands attenuated the evoked increase in [Ca(2+)](i) by 35% in neurons defined as intermediate in size (800-1500 microm(2)). The effects of CP 55,940 and WIN 55,212-2 were mediated by the CB1 receptor on the basis of relative effective concentrations, blockade by the CB1 receptor antagonist SR141716A and lack of effect of WIN 55,212-3. Intermediate-size neurons rarely responded to capsaicin (100 nM). Although cannabinoid agonists generally did not inhibit depolarization-evoked increases in [Ca(2+)](i) in small neurons, immunocytochemical studies indicated that CB1 receptor-immunoreactivity occurred in this population. CB1 receptor-immunoreactive neurons ranged in size from 227 to 2995 microm(2) (mean somal area of 1044 microm(2)). In double labeling studies, CB1 receptor-immunoreactivity co-localized with labeling for calcitonin gene-related peptide and RT97, a marker for myelination, in some primary afferent neurons.The decrease in evoked Ca(2+) influx indicates that cannabinoids decrease conductance through voltage-dependent calcium channels in a subpopulation of primary afferent neurons. Modulation of calcium channels is one mechanism by which cannabinoids may decrease transmitter release from primary afferent neurons. An effect on voltage-dependent calcium channels, however, represents only one possible effect of cannabinoids on primary afferent neurons. Identifying the mechanisms by which cannabinoids modulate nociceptive neurons will increase our understanding of how cannabinoids produce anti-nociception in normal animals and animals with tissue injury.     

Chronotropic and dromotropic components of cardiac reflexes in the cat

The relationship between dromotropic and chronotropic components of various cardiac reflexes was studied in cats. Intravenous infusion of blood was mainly accompanied by unidirectional negative chronotropic and dromotropic effects, but the dynamics of these effects was different. Clumping of the carotid arteries in most animals induced unidirectional negative chronotropic and dromotropic effects. Their dynamics was also different and differed from that observed during intravenous blood infusion. Pulsatile increase in blood pressure in the carotid artery was accompanied by a unidirectional negative effect in the majority of animals. The opposite chronotropic and dromotropic effects with similar temporal dynamics were revealed in 1/3 animals. The ratio of positive and negative effects was similar during clumping of the abdominal aorta (1/3 unidirectional, 1/3 opposite, and 1/3 isolated chronotropic and dromotropic effects). Aschner test was characterized by the prevalence of isolated chronotropic effect (negative effect in the majority of animals; positive effect in 1/3 animals). Hence, different cardiac reflexes are characterized by different ratio between chronotropic and dromotropic components. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 145, No. 2, pp. 127–132, February, 2008     

Precipitated withdrawal counters the adverse effects of subchronic cannabinoid administration on male rat sexual behavior

In the present study, sexual behavior of male rats was assessed following prolonged treatment with the CB₁ receptor agonist, HU-210 (0.1 mg/mg/day for 10 days) under conditions of drug maintenance, spontaneous withdrawal and precipitated withdrawal (induced via administration of the CB₁ receptor antagonist AM251; 1 mg/kg). Following subchronic cannabinoid treatment, sexual activity in male rats was impaired under both the drug maintenance and spontaneous withdrawal conditions, as revealed by a reduction in frequency of both intromissions and ejaculations. Notably, the induction of precipitated drug withdrawal reversed the negative effects of subchronic HU-210 treatment on sexual activity as seen by a reversal of the suppression of ejaculations. These data illustrate that, contrary to expectations, the impairments in male sexual activity following protracted cannabinoid administration are not due to drug withdrawal, per se, but are likely mediated by neuroadaptive changes provoked by repeated drug exposure.     

Endogenous cannabinoid receptor agonists inhibit neurogenic inflammations in guinea pig airways

BACKGROUND: Although neurogenic inflammation via the activation of C fibers in the airway must have an important role in the pathogenesis of asthma, their regulatory mechanism remains uncertain. OBJECTIVE: The pharmacological profiles of endogenous cannabinoid receptor agonists on the activation of C fibers in airway tissues were investigated and the mechanisms how cannabinoids regulate airway inflammatory reactions were clarified. METHODS: The effects of endogenous cannabinoid receptor agonists on electrical field stimulation-induced bronchial smooth muscle contraction, capsaicin-induced bronchoconstriction and capsaicin-induced substance P release in guinea pig airway tissues were investigated. The influences of cannabinoid receptor antagonists and K+ channel blockers to the effects of cannabinoid receptor agonists on these respiratory reactions were examined. RESULTS: Both endogenous cannabinoid receptor agonists, anandamide and palmitoylethanolamide, inhibited electrical field stimulation-induced guinea pig bronchial smooth muscle contraction, but not neurokinin A-induced contraction. A cannabinoid CB2 antagonist, SR 144528, reduced the inhibitory effect of endogenous agonists, but not a cannabinoid CB1 antagonist, SR 141716A. Inhibitory effects of agonists were also reduced by the pretreatment of large conductance Ca2+ -activated K+ channel (maxi-K+ channel) blockers, iberiotoxin and charybdotoxin, but not by other K+ channel blockers, dendrotoxin or glibenclamide. Anandamide and palmitoylethanolamide blocked the capsaicin-induced release of substance P-like immunoreactivity from guinea pig airway tissues. Additionally, intravenous injection of palmitoylethanolamide dose-dependently inhibited capsaicin-induced guinea pig bronchoconstriction, but not neurokinin A-induced reaction. However, anandamide did not reduce capsaicin-induced guinea pig bronchoconstriction. CONCLUSIONS: These findings suggest that endogenous cannabinoid receptor agonists inhibit the activation of C fibers via cannabinoid CB2 receptors and maxi-K+ channels in guinea pig airways.