Abstract
The characteristic of the antinociceptive effect of a tetrapeptide, Asn-Ala-Gly-Ala (NAGA), was examined. Intracisternal (i. cist.) administration of NAGA to mice produced does-dependent and long-lasting antinociceptive effect as evaluated by the hot plate and tail flick methods. NAGA-induced antinociception was reversed by naloxone (2 mg/kg), reserpine (2 mg/kg×2 d) and α-methyl-p-tyrosine (100 mg/kg). NAGA (10 μM) did not significantly affect the actions of opioid peptides on the electrically evoked twitches of the myenteric plexus-longitudinal muscle strips from the guinea-pig esophagus and strips of the mouse vas deferens. NAGA-induced antinociception was scarcely affected by p-chloro-phenylalanine (PCPA, 300 mg/kg×2 d) and methysergide (2 mg/kg). From the above results, it was suggested that the antinociceptive effect of NAGA may involve the participation of endogenous opioid peptides and endogenous catecholamines.
