L-365,260 reversed effect of sincalide against morphine on electrical and mechanical activities of rat duodenum in vitro

AIM: To study the antagonism of sincalide (CCK-8) to the effect of morphine and
its mechanism.
METHODS: The electrical and mechanical activities of rat duodenum in vitro were
recorded simultaneously.
RESULTS: Acetylcholine (ACh, 300 nmol/L) increased the spike potential amplitude
(SPA) and the number (SPN) of rat duodenum in vitro, followed by an increase of
duodenal contraction amplitudes (CA). The SPA, SPN, and CA of duodenum in vitro
were not obviously affected by injection of morphine (330 nmol/L), but it could
selectively inhibit the potentiation of ACh. After administration of CCK-8 (0.7
nmol/L), the SPA, SPN, and CA of duodenal segment did not exhibit obvious
changes. But CCK-8 could selectively antagonize the effects of morphine, ie, the
SPA and SPN were increased again, followed by an increase of CA. CCK-B receptor
antagonist L-365,260 (30 nmol/L) reversed the antagonism of CCK-8 to the effect
of morphine.
CONCLUSION: CCK-8 could selectively antagonize the effect of morphine which
inhibited the potentiation of ACh on duodenal activities in vitro. The
antagonistic effect of CCK-8 on morphine was mainly mediated by CCK-B receptor.