1. Intravenous infusions of the brain/gut hormone, cholecystokinin, have been shown to reduce food intake in a subsequent test meal. However, in previous studies the doses administered were large and likely to have produced plasma concentrations far in excess of the normal post-prandial range.

2. In this study cholecystokinin-8 was infused intravenously to six healthy subjects in doses that reproduced physiological post-prandial concentrations. Plasma concentrations of cholecystokinin were measured using a novel sensitive and specific radioimmunoassay. The effect of cholecystokinin-8 infusion on subsequent food intake in a standard test meal was compared with the effect of saline infusion in the same subjects.

3. Food intake (mean ± SEM) was significantly less during cholecystokinin (5092 ± 665 kJ) than during saline infusion (6418 ± 723 kJ, P = 0.03). During cholecystokinin infusion, plasma concentrations increased from 0.45 ± 0.06 pmol/l to 7.28 ± 2.43 pmol/l immediately before the meal. With saline infusion there was no premeal increase in plasma cholecystokinin concentration.

4. This paper describes a novel radioimmunoassay for measurement of plasma concentrations of cholecystokinin. Using this assay we have demonstrated that cholecystokinin is important in control of satiety in humans.

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