Intraperitoneal, but not subcutaneous, administration of the sulphated cholecystokinin octapeptide (CCK-8S) inhibits operant and nonoperant food intake in rats: implications for the CCK-satiety hypothesis.

The effects of administering CCK-8S by the subcutaneous (s.c.) and intraperitoneal (i.p.) routes were investigated on both operant and nonoperant food intake in rats that had been fasted for 22 h. Intraperitoneal administration of CCK-8S (5 micrograms/kg) significantly reduced both operant and nonoperant food intake. In contrast, CCK-8S (5-50 micrograms/kg) administered s.c. had no effects on food intake in both types of behavioral paradigms. The results show that the peripheral route of administration of CCK-8S is an important factor to be taken into consideration when investigating its effects on food intake. The results are discussed in terms of the hypothesis that CCK released from the small intestine during a meal acts in a paracrine fashion to produce satiety.