Interactions of caerulein and morphine on gastrointestinal propulsion in the mouse

The effects of subcutaneously administered caerulein (ceruletide) and morphine hydrochloride on gastric emptying and gastrointestinal propulsion were studied in male mice. Drug effects were evaluated by the movement of Indian ink administered directly into the stomach after drug injection. Morphine inhibited both gastrointestinal propulsion ( ED50 = 2.1 mumol/kg) and gastric emptying (ED50 - 43 mumol/kg). Caerulein enhanced gastrointestinal propulsion (ED50 = 0.93 nmol/kg) but inhibited gastric emptying (ED50 = 17 nmol/kg). Inhibition of gastric emptying was further potentiated by the combined administration of caerulein and morphine. Naloxone reversed both effects of morphine but not those of caerulein. Morphine antagonized the propulsion-enhancing effect of caerulein.