CCK, a hormone released when digested fats and proteins are present that reduces food intake, stimulates enzyme secretion in the pancreas.
The process eventually leads to inhibiting gastric emptying of the stomach's foods, thereby causing gastric distension. It has been suggested that increased gastric distension, induced by slowing of gastric emptying, may be the method by which CCK reduces food intake.
For the small study the research team led by Harry Kissileff, at Columbia university in New York, together with New York Obesity Research Center, looked at eight non-obese males and eight non-obese female volunteers in good health. All met the following criteria: weight within 15 per cent of the desirable weight for height; between the ages of 18 and 35, non-smokers with no active medical problems or taking any medications; had no allergies or history of weight problems; and were unrestrained eaters. Participants were also screened to eliminate candidates that did not like the test meal food.
Each subject reported to the laboratory six times after an overnight fast, given a standardised 300-kcal breakfast of one English muffin with butter and apple juice, which they consumed prior to leaving the lab. They were instructed not to eat or drink anything except water before returning to the laboratory 2.25 h later.
When the subject returned, the back of his/her throat was anesthetised and a thin latex balloon (attached to a double-lumen tube) was passed orally into the stomach.
A catheter connected to a dual-reservoir portable infusion pump was inserted into a vein, and saline was infused. Each of the two reservoir bags connected to the pump contained 40 ml of infusate. One reservoir always contained isotonic saline, and, depending on the peptide administration schedule, the other reservoir bag contained either CCK or saline as the test solution. The subject was given time to adjust to the infusion and balloon.
When the subject felt comfortable, the balloon was filled with warm water. The tube was then gently retracted until resistance was met at the cardia and then pushed back down to prevent obstruction of the gastroesophageal junction. The end of the tube exiting the mouth was anchored, securing the balloon's position in the stomach. The tube was connected to a water manometer to record stomach pressure during and after balloon filling. Immediately after the balloon was positioned and secured, it was emptied.
The subject was instructed to fill out the first questionnaire (baseline). After completing it, the balloon was filled to 100 ml at the rate of 100 ml/min. The subject was then instructed to fill out the second questionnaire. After filling it out, the balloon was filled to 200 ml and the subject completed the third survey. The balloon was then filled to 300 ml, and the subject filled out the fourth questionnaire.
Then, infusion of either CCK-8 or saline began and continued for 21 min. Two minutes before the IV infusion terminated, subjects completed a fifth questionnaire before being served a yoghurt shake and instructed to consume as much of it as they would during a normal meal. Five minutes after indicating they were finished, they filled out the sixth questionnaire. The balloon was then emptied and the participant filled out the seventh questionnaire, after which the balloon was removed. After removal of the balloon and IV, the subject answered the postmeal questionnaire.
The scientists reported the following observations. The combination of CCK and distension of 300 ml reduced food intake by a mean of 200 g compared with the saline nondistension condition. CCK reduced intake significantly when the stomach was distended. Without distension, CCK did not significantly reduce intake in men but did significantly reduce intake in women.
Distension alone had little effect. In contrast, during CCK infusion, intake was significantly lower after distension compared with nondistension in men but was not significantly lower in women. This is the one contrast in which men and women differed, although the difference between them was not significant.
Because CCK combined with (but not without) distension significantly reduced intake, CCK enhanced the distension effect by an average (both sexes combined) of 73 g. Put another way, the CCK effect was 73 g greater with than without distension. However, this interaction effect was not significant in either sex alone or in the two sexes together, report the authors.
Meal duration was reduced significantly by CCK combined with 300 ml of distension in both sexes. CCK reduced meal duration significantly when the stomach was distended but the reduction was not significant in either sex alone, unlike intake. Distension alone reduced meal duration in men (unlike intake) but not in women and not in both sexes together (similar to intake).
The scientists concluded that the main results for the genders together showed a significant reduction in intake after a combination of CCK and distension, supporting the notion that gastric distension, rather than nutrient content, is likely to be the major determinant of the enhanced food intake-reducing effect of CCK.
Taken together, concluded the US scientists, all the findings suggest that the combination of a gastric distension with stimulation of CCK receptors could lead to the development of an effective appetite-suppressing agent that relies on natural satiety-inducing processes.
Full findings are published in the November 2003 edition of the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology.