Effect of fasting interval on CCK-8 suppression of food intake in the baboon.

Baboons were infused intravenously for 5 min with the octapeptide of cholecystokinin (CCK-8) after either a 16.5- or 3.5-h fast. After a 3.5-h fast, food intake was significantly suppressed over the ensuing 30 min by 2 micrograms/kg of CCK-8 (-156 +/- 34 kcal compared with control days, P less than 0.02) and by 4 micrograms/kg of CCK-8 (-257 +/- 31 kcal, P less than 0.01). In contrast, CCK-8 had no reliable effect on food intake after the same baboons had been fasted for 16.5 h (2 micrograms/kg: -93 +/- 40 kcal, P greater than 0.05; 4 micrograms/kg: -30 +/- 82 kcal, P greater than 0.05). There was no reliable effect of 1 microgram/kg of CCK-8 on food intake at either deprivation interval. CCK-8 infusions resulted in a small increase of fasting plasma immunoreactive insulin (IRI); this effect was not related to either dose or deprivation length. Postprandial IRI and glucose concentrations were significantly suppressed by CCK-8 independently of its effect on food intake. Thus, after a 16.5-h fast, 4 micrograms/kg of CCK-8 decreased postprandial IRI from 145 +/- 65 to 29 +/- 4 microU/ml (P less than 0.01) and glucose from 101 +/- 5 to 80 +/- 3 mg/dl (P less than 0.02), despite no concomitant effect on food intake. Similar suppression of plasma IRI and glucose were observed after infusions of 1 and 2 micrograms/kg in 16.5-h-fasted animals. All doses of CCK-8 (1, 2, and 4 micrograms/kg) suppressed postprandial IRI and glucose after a 3.5-h fast.(ABSTRACT TRUNCATED AT 250 WORDS)