Ghrelin inhibits inflammatory pain in rats: involvement of the opioid system.
This study examined the effects of intracerebroventricular (i.c.v.), intraperitoneal (i.p.) or intraplantar (i.pl.) administration of ghrelin, the endogenous ligand of the growth hormone secretagogue receptor, in the development of hyperalgesia and edema induced by intraplantar injection of carrageenan in rats. Central ghrelin (4 ng to 4 microg/rat) given 5 min before carrageenan produced a dose-related reversal of carrageenan-induced mechanical hyperalgesia measured by Randall-Selitto test with an ED50 of 81.7 ng/rat. Ghrelin at the dose of 4 microg/rat i.c.v. was also effective in inhibiting edema. When ghrelin (4 microg/rat i.c.v.) was administered 150 min after carrageenan, it failed to modify either hyperalgesia or the paw volume. Given i.p., 30 min before carrageenan, ghrelin (20-160 microg/kg) induced a significant dose-dependent inhibition of hyperalgesia with an ED50 of 77 microg/kg and a slight reduction of edema. Intraplantar ghrelin (40 ng to 12 microg/rat) did not significantly modify both the hyperalgesic and edematous activities of carrageenan. The anti-hyperalgesic and anti-edematous effects of ghrelin (4 microg/rat i.c.v.) were reversed by naloxone (10 microg/rat i.c.v.). Systemic administration of the peripheral selective opioid antagonist, naloxone methiodide (3 mg/kg s.c.), did not antagonize antinociception elicited by i.p. ghrelin. Overall these data indicate that ghrelin exerts an inhibitory role on inflammatory pain through an interaction with the central opioid system.
Sibilia
Valeria
V
Department of Pharmacology, Chemotherapy and Medical Toxicology, University of Milano, Via Vanvitelli, 32, 20129 Milan, Italy. valeria.sibilia@unimi.it
Lattuada
Norma
N
Rapetti
Daniela
D
Pagani
Francesca
F
Vincenza
DeLuca
D
Bulgarelli
Ilaria
I
Locatelli
Vittorio
V
Guidobono
Francesca
F
Netti
Carmela
C
D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D002351:Carrageenan; D016207:Cytokines / Q000097:blood; D004305:Dose-Response Relationship, Drug; D004333:Drug Administration Routes; D004347:Drug Interactions; D004487:Edema / Q000139:chemically induced / Q000517:prevention & control; D005786:Gene Expression Regulation / Q000187:drug effects; D054439:Ghrelin; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D010146:Pain / Q000139:chemically induced / Q000517:prevention & control*; D010147:Pain Measurement / Q000379:methods; D017288:Pain Threshold / Q000187:drug effects*; D036361:Peptide Hormones / Q000008:administration & dosage*; D011333:Pro-Opiomelanocortin / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D013997:Time Factors
D016207:Cytokines; D054439:Ghrelin; D009292:Narcotic Antagonists; D036361:Peptide Hormones; D012333:RNA, Messenger; D009270:Naloxone; D011333:Pro-Opiomelanocortin; D002351:Carrageenan