Effects of food deprivation, strain, diet and age on feeding responses of fowls to intravenous injections of cholecystokinin

Abstract

This paper presents new information about inhibitory effects of intravenous injections of cholecystokinin-octapeptide (CCK-8) on feeding activity in birds, with particular reference to variation in motivational state. With increasing food deprivation (0, 1, 2 or 3 h) before injection, doses of 2 and 8 micrograms/kg CCK-8 became progressively less effective in suppressing feeding of domestic fowls. As with mammals, latency to feed was shorter, and subsequent feeding activity greater, with deprived than with undeprived birds. Fowls of broiler (meat-type) and layer strains, which have different absolute food requirements but similar relative (per kg body weight) requirements, did not differ in their feeding responses to injections of 1, 8 and 16 micrograms/kg CCK-8. Food intake of fowls fed on a diet diluted with 40% powdered cellulose was suppressed less by the same three doses of CCK-8 than that of birds fed on undiluted food. This may have been because birds with the more bulky diluted food had to spend a greater proportion of time feeding. Broiler chicks aged 2 and 6 weeks, which may have different blood-brain resistance to circulating CCK and which have different relative food requirements, did not differ in their feeding responses to injections of 2 and 8 micrograms/kg CCK-8. These results do not satisfy one of the criteria proposed for demonstrating the action of a satiety agent, that feeding should be suppressed in a consistent manner regardless of motivational state. An alternative explanation for the apparent satiating properties of CCK-8 is suggested, based on similarities in their time-course, and dependence on deprivation level, to abnormal gastrointestinal responses with similar doses of the peptide.