Caerulein changes morphine-induced antinociception depending on pretreatment times

1. In the present study, the effect of caerulein (CLN) on morphine analgesia has been tested. 2. Different doses of morphine produced antinociception in a dose dependent manner. When animals were pretreated with CLN 5 min before morphine administration, the morphine response was decreased. However, when CLN was injected 30 or 60 min prior to morphine, the drug effect was increased. 3. Naloxone, sulpiride, metergoline or proglumide decreased the potentiation of morphine response caused by CLN. CLN, proglumide, sulpiride, metergoline and naloxone alone did not exert any effect on tail-flick latency. 4. It is concluded that, depending on pretreatment times of CLN administration the response of morphine was decreased or increased and D-2 dopamine, serotonin and/or CCK receptors may be involved in the potentiation of morphine response induced by CLN.