Sulpiride attenuates ranatensin-M-induced antinociception.
Intracerebroventricular (icv) administration of ranatensin-M (RM), a bombesin-like peptide isolated from the skin of Chinese frog Rana margaratae, produced a dose-dependent prolongation in the hot-plate latency in mice. Naloxone 1, 2, or 10 mg.kg-1 ip failed to antagonize the effects of RM. However, RM-induced antinociception was attenuated by pretreatment with sulpiride (Sul, 100 mg.kg-1, ip), a selective DA2 receptor blocker. Sul (100 mg.kg-1, ip) did not affect hot-plate latencies when administered alone. Sch 23390 (0.2 mg.kg-1, ip), a selective DA1 receptor blocker, did not significantly affect RM-induced antinociception. The results suggest that RM-induced antinociception may be mediated by dopamine neurotransmission within the CNS and that it is mainly the D2 receptor which was involved in this effects.