Cholecystokinin used to be known as pancreozymin due to its actions on the pancreas but now it is commonly abbreviated to CCK; CCK-PZ
Cholecystokinin is produced by I-cells in the lining of the duodenum and is also released by some neurons in the brain. It acts on two types of receptors found throughout the gut and central nervous system.
The most recognised functions of this hormone are in digestion and appetite. It improves digestion by slowing down the emptying of food from the stomach and stimulating the production of bile in the liver as well as its release from the gall bladder. Bile acts like a detergent making the fat droplets smaller so that enzymes can break it down more easily. Cholecystokinin also increases the release of fluid and enzymes from the pancreas to break down fats, proteins and carbohydrates.
Cholecystokinin seems to be involved with appetite by increasing the sensation of fullness in the short-term, that is, during a meal rather than between meals. It may do this by affecting appetite centres in the brain as well as delaying emptying of the stomach. However, more research is needed to confirm this finding.
There is also evidence to suggest that cholecystokinin may have a role in anxiety and panic disorders. This is an effect of cholecystokinin released in the brain, not an effect of secretion from other parts of the body.
Fat and protein in the stomach cause the release of cholecystokinin. Increased blood levels of cholecystokinin can be found 15 minutes after a meal has begun and levels remain raised for three hours afterwards. The release of cholecystokinin is blocked by the hormone somatostatin and by bile acids in the small intestine.
There are no known cases of too much cholecystokinin. However, weight loss drugs are currently under development that copy the appetite-reducing actions of cholecystokinin.
Some research has been carried out to examine blood levels of cholecystokinin when people are fasting or just after they have eaten. There appears to be evidence of less than average cholecystokinin in very obese people, unlike the levels in obese and slim people. This low level of cholecystokinin may contribute to reduced feelings of fullness and difficulty in losing weight in very obese people. However, more research is needed to confirm this finding. Variations in the cholecystokinin gene itself have been associated with obesity, with an increased risk of 60% if people carry the slightly different form (variant) called cholecystokinin H3. How this happens is currently unclear.
Last reviewed: Mar 2018