Effect of cholecystokinin octapeptide on food intake in pigs.

Considerable interest has been aroused by the suggestion that the gut hormone cholecystokinin (CCK) is released during feeding and then acts as a satiety signal (Gibbs et al. 1973). Many studies, in species ranging from the mouse to man, have shown that peripheral administration of CCK, or its octapeptide, will reduce food intake. However, inhibition of feeding could be produced via a satiety system specific to food or by a transient malaise affecting all motivated behaviours. In the rat, CCK induces behaviour resembling that seen during normal satiety (Antin et aZ. 1975) and does not affect drinking in thirsty animals (Gibbs e ta l . 1973). Using rats, some workers have been able to produce avoidance of a novel food whose presentation was paired with CCK administration (Deutsch & Hardy, 1977) and such ‘bait-shyness’ is indicative of illness. By contrast, others have been unable to demonstrate this effect either in rats (Gibbs et al. 1973) or rabbits (Houpt et al. 1978). In man, although slow intravenous infusion of CCK does not cause marked side-effects, the authors state that ‘some individuals may have experienced discomfort’ (Kissileff et al. 1981) and high doses cause nausea (Sturdevant & Goetz, 1976). It appears that, in some species, administration of CCK may cause transient malaise and that tests using non-food reinforcers may help to clarify the situation. Intravenously administered CCK reduces consummatory food intake in the 4-hour fasted pig (Anika et al. 1981) and the present study extends these observations using operant techniques developed in this laboratory for the pig. We have investigated the effect on operant feeding of intravenous injection of CCK octapeptide and have compared this with effects on operant drinking of water or sucrose solution and on operant responding for radiant heat.