Cholecystokinin (CCK) is one of the classical gut hormones. It is believed to be a major regulator of gall bladder contraction and pancreatic enzyme secretion.
CCK occurs in many different molecular forms.
EURIA CCK radioimmunoassay is based on an antiserum with very low cross-reactivity to gastrin-17 and it has been optimized to a very high sensitivity of 0,3 pmol/L.
The CCK EURIA is a highly sensitive and specific radioimmunoassay for the determination of of CCK in plasma.
Intended use
The intended use of these reagents is for assay of CCK in plasma. CCK is extracted from plasma by an ethanol extraction method.
This product is also available as research use only. Product code: RB 302 RUO
For complete product description, claims and use, please refer to the Instructions For Use. Contact your local representative for availability in your country.
Background
Cholecystokinin (CCK) is one of the classical gut hormones. It is believed to be a major regulator of gall bladder contraction and pancreatic enzyme secretion.
CCK occurs in many different molecular forms. In 1971, Mutt and Jorpes isolated a 33-amino-acid polypeptide which exhibited the properties ascribed to CCK. Later a CCK-39 with a further 6 amino acid residues linked to the NH2 terminus of the triacontatriapeptide was described. An identical sequence of the c-terminal octapeptide (CCK-8) has been found in mammals except for the guinea pig and the chinchilla, where valine substitutes methionine at position 6 from the C-terminus. The structures of CCK in the small intestine have been determined for peptides of 58 amino acids from the dog, 25 and 18 amino acids from the dog, 22 and 8 amino acids from the rat and guinea pig and 7 and 5 amino acids from the dog.
The structure of a preproCCK has been determined. It consists of 115 amino acids in man. The C-terminal sulphation (Tyr 27 in CCK-33) and the C-terminal amidation are important for the biological activity. CCK shares an identical sequence with gastrin in the 5 C-terminal amino acids. Definite physiological actions of CCK that occur during the intravenous infusion of CCK are:
1/ Stimulation of gall bladder contraction
2/ stimulation of pancreatic enzyme secretion
3/ enhancement of secretin-induced water and bicarbonate secretion from the exocrine pancreas
4/ inhibition of gastric emptying
There are three main problems in the development of specific radioimmunoassays for CCK,
First, the homology of the antigenic C-terminal penta-peptide with gastrin requires an antiserum with very low cross-reactivity towards gastrin. CCK in plasma and in intestinal tissue is heterogeneous. Thus, the antiserum used should ideally bind all biological active forms with equimolar potency.
Second, the radioiodination of CCK requires special, mild labelling since oxidation of the methionine residues occurs in oxidative labelling methods.
Third, plasma concentrations of CCK are very low which makes it necessary to have a very highly sensitive assay system. The Euro-Diagnostica CCK radioimmunoassay is based on an antiserum with very low cross-reactivity to gastrin-17, sulphated gastrin. The assay system has been optimized to a very high sensitivity: 0,3 pmol/L.
Clinical considerations
Decreased CCK secretion has been found for patients with celiac disease. Those patients had an impaired gallbladder contraction after meal. CCK secretion and gallbladder contraction returns to normal in patients on a gluten-free diet with a normal jejunal mucosa. Increased plasma CCK concentrations in patients with chronic pancreatitis have been reported. Recent investigations with specific and sensitive CCK assays have shown normal fasting levels in patients with chronic pancreatitis.
Elevated CCK concentrations have been reported in patients with hepatic cirrhosis. In a later study no difference was observed between cirrhotics and controls. Increased postprandiol CCK response has been observed in non-insulin-dependent diabetes.
High amounts of CCK have been found in pituitary adenomas of patients with Nelson´s syndrome and some patients with Cushing´s disease. Increased basal concentration of sulphated CCK was found in plasma of one unoperated patient with Nelsons´s syndrome.
Normal fasting level of CCK: <1.12 pmol/L.
Technical information
CCK in extracts is assayed by a competitive radioimmunoassay using an antiserum raised against CCK-8 sulphate N-terminally conjugated to bovine albumin. CCK in standards and samples compete with 125I-CCK8 sulphate in binding to the antibodies. 125I-CCK-8 sulphate binds in a reverse proportion to the concentration of CCK in standards and samples. The assay is standardized against CCK-8 sulphate. Antibody-bound 125I-CCK-8 sulphate is separated from the unbound fraction using double antibody solid phase. The radioactivity of the bound fraction is measured in a gamma counter. For professional use within a laboratory.
