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.
Yoshihara
Shigemi
S
Department of Pediatrics, Dokkyo University School of Medicine, 880 Kitakobayashi, Mibu-machi, Shimotsuga-gun, Tochigi 321-0293, Japan. shigemi@dokkyomed.ac.jp
Morimoto
Hiroshi
H
Ohori
Makoto
M
Yamada
Yumi
Y
Abe
Toshio
T
Arisaka
Osamu
O
D000577:Amides; D000818:Animals; D001095:Arachidonic Acids / Q000494:pharmacology; D001980:Bronchi / Q000187:drug effects* / Q000294:innervation; D016084:Bronchoconstriction / Q000187:drug effects; D002121:Calcium Channel Blockers / Q000494:pharmacology; D001892:Camphanes / Q000494:pharmacology; D063386:Cannabinoid Receptor Agonists; D002211:Capsaicin / Q000633:toxicity; D004558:Electric Stimulation; D063388:Endocannabinoids; D004983:Ethanolamines; D006168:Guinea Pigs; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects; D036421:Nerve Fibers, Unmyelinated / Q000187:drug effects*; D020078:Neurogenic Inflammation / Q000209:etiology / Q000517:prevention & control*; D009924:Organ Culture Techniques; D010169:Palmitic Acids / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D053284:Polyunsaturated Alkamides; D026902:Potassium Channel Blockers / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D043882:Receptors, Cannabinoid / Q000187:drug effects*; D000077285:Rimonabant; D013373:Substance P / Q000096:biosynthesis / Q000187:drug effects
D000577:Amides; D001095:Arachidonic Acids; D002121:Calcium Channel Blockers; D001892:Camphanes; D063386:Cannabinoid Receptor Agonists; D063388:Endocannabinoids; D004983:Ethanolamines; D010169:Palmitic Acids; D010880:Piperidines; D053284:Polyunsaturated Alkamides; D026902:Potassium Channel Blockers; D011720:Pyrazoles; D043882:Receptors, Cannabinoid; C110630:SR 144528; D013373:Substance P; C005958:palmidrol; D000077285:Rimonabant; D002211:Capsaicin; C078814:anandamide