Measurement of cholecystokinin in biological fluids

The wide expression of the CCK gene in various cell types combined with cell-specific expression cascades into different peptides has made CCK a complex multifunctional messenger system. CCK is not only a gut hormone and satiation signal traveling in blood; it is also a major transmitter in the central and peripheral nervous systems; a local paracrine regulator in the digestive tract; a growth factor for the pancreas; a cytokine in the immune system; and putatively a spermatogenic fertility factor. A premise for examination of the multiple roles in health and disease is accurate measurements in plasma, cerebrospinal fluid, and tissue extracts. The present chapter will first describe the principles of methods for THE measurement of CCK (bioassays, immunoassays, and mass-spectrometry). Particular focus, however, will then be given to the radioimmunoassay (RIA) technology, which is still the methodology of choice because of its broad applicability and potential for obtaining both precise epitope specificity as well as high sensitivity. An additional reason for RIA-focusing is that the establishment of specific CCK assays having the necessary sensitivity for plasma measurement has been unusually challenging.