Mechanisms involved in the antinociception caused by agmatine in mice.
The present study examined the antinociceptive effects of agmatine in chemical behavioural models of pain. Agmatine (1-30 mg/kg), given by i.p. route, 30 min earlier, produced dose-dependent inhibition of acetic acid-induced visceral pain, with mean ID50 value of 5.6 mg/kg. Given orally, 60 min earlier, agmatine (10-300 mg/kg) also produced dose-related inhibition of the visceral pain caused by acetic acid, with mean ID50 value of 147.3 mg/kg. Agmatine (3-100 mg/kg, i.p.) also caused significant and dose-dependent inhibition of capsaicin- and glutamate-induced pain, with mean ID50 values of 43.7 and 19.5 mg/kg, respectively. Moreover, agmatine (1-100 mg/kg, i.p.) caused marked inhibition of both phases of formalin-induced pain, with mean ID50 values for the neurogenic and the inflammatory phases of 13.7 and 5.6 mg/kg, respectively. The antinociception caused by agmatine in the acetic acid test was significantly attenuated by i.p. treatment of mice with L-arginine (precursor of nitric oxide, 600 mg/kg), naloxone (opioid receptor antagonist, 1 mg/kg), p-chlorophenylalanine methyl ester (PCPA, an inhibitor of serotonin synthesis, 100 mg/kg once a day for 4 consecutive days), ketanserin (a 5-HT2A receptor antagonist, 0.3 mg/kg), ondansetron (a 5-HT3 receptor antagonist, 0.5 mg/kg), yohimbine (an alpha2-adrenoceptor antagonist, 0.15 mg/kg) or by efaroxan (an I1 imidazoline/alpha2-adrenoceptor antagonist, 1 mg/kg). In contrast, agmatine antinociception was not affected by i.p. treatment of animals with pindolol (a 5-HT1A/1B receptor antagonist, 1 mg/kg) or idazoxan (an I2 imidazoline/alpha2-adrenoceptor antagonist, 3 mg/kg). Likewise, the antinociception caused by agmatine was not affected by neonatal pre-treatment with capsaicin. Together, these results indicate that agmatine produces dose-related antinociception in several models of chemical pain through mechanisms that involve an interaction with opioid, serotonergic (i.e., through 5-HT2A and 5-HT3 receptors) and nitrergic systems, as well as via an interaction with alpha2-adrenoceptors and imidazoline I1 receptors.
Santos
Adair R S
AR
Departamento de Ciências Fisiológicas, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina, Campus Universitário, Trindade, Florianópolis, Santa Catarina 88040-900, Brazil. arssantos@ccb.ufsc.br
Gadotti
Vinicius M
VM
Oliveira
Gerson L
GL
Tibola
Daiane
D
Paszcuk
Ana Flavia
AF
Neto
Amaro
A
Spindola
Humberto M
HM
Souza
Márcia M
MM
Rodrigues
Ana Lucia S
AL
Calixto
João B
JB
D000376:Agmatine / Q000494:pharmacology*; D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D005260:Female; D008297:Male; D051379:Mice; D010147:Pain Measurement / Q000187:drug effects* / Q000379:methods*
D000700:Analgesics; D000376:Agmatine