Effects of ceruletide and cholecystokinin octapeptide on eating in mice. Interactions with naloxone and the enkephalin analogue, FK 33-824.

Subcutaneous (SC) injections of ceruletide (caerulein diethylammonium hydrate, CER) and the octapeptide of cholecystokinin (CCK-8) reduced the intake of liquid food in male NMRI mice starved for 18 h. The corresponding ED50 values were 2 micrograms/kg for CER and 24 micrograms/kg for CCK-8; hence, on a molar basis, CER was 14 times more potent than CCK-8. Naloxone (0.2 and 1 mg/kg, SC) inhibited eating. (D-Ala)2(MePhe)4-(Met(O)-ol)5-enkephalin (FK 33-824; 0.3 and 1 mg/kg) was only stimulatory. Naloxone enhanced the effect of CER, whereas FK 33-824 antagonized it. It is concluded that concerning the inhibition of food intake, opioid peptides can be antagonists of CCK-like peptides. This is consistent with the current view of the regulation of appetitive behaviour.