CCK-58 is the only detectable endocrine form of cholecystokinin in rat

Abstract

CCK-58 differs from CCK-8 in patterns of expression of pancreatic secretion of fluid and amylase and gallbladder contraction. These differences have physiological relevance only if CCK-58 release is stimulated by nutrients entering the intestine and if CCK-58 circulates in sizeable amounts. In this study, we report that when radiolabeled CCK-58 is added to rat blood and plasma is formed, there is extensive loss and degradation of the radioactive peptide. Therefore, a new method was developed to minimize loss and degradation of this label. This method recovered >85% of the label with no detectable degradation. Furthermore, the optimized method recovered all unlabeled exogenous cholecystokinin molecular forms in >80% yields. Blood from fasted rats and rats in which cholecystokinin release was stimulated by the trypsin inhibitor camostat contained only CCK-58 (3.5 ± 0.5 and 17 ± 1.5 fmol/ml, respectively). Because CCK-58 predominates in the blood, this molecular form should be used in studies on the physiology and pathophysiology of cholecystokinin.

CCK-8 and CCK-58 differ in their effects on nocturnal solid meal pattern in undisturbed rats

“…Most of these studies were performed using CCK-8 because of its availability, and the concept that all forms of CCK that contain a sulfated tyrosine would have the same biological activity (26). However, as described above, we have reported that with proper blood processing, CCK-58 is the only detectable circulating form of rat CCK (42). Similar to the observations with the pancreas, CCK-8 and CCK-58 exert differential effects on food intake, although this has not been characterized in detail.…”

“…At equimolar doses CCK-8 significantly reduces IMI while CCK-58 does not. This suggests that meal size and IMI are regulated at different sites or they have different actions at the same site, and the common idea that all molecular forms of CCK have the same physiological actions needs reconsideration, highlighting the importance of studying the actual endogenous molecular form of peptides, especially considering the finding that CCK-58 is the only circulating form of cholecystokinin (9,13,42).…”

“…If rat blood is processed in a manner that prevents degradation of 125 I-labeled CCK-58, the only endocrine form detected is CCK-58 (42). Thus, endogenous endocrine CCK-8 detected by others (23,35) is most likely a product of peptide degradation during plasma formation.…”

“…In rats, endocrine forms suggested from chromatography of plasma samples and assay of fractions collected have varied from laboratory to laboratory. The major forms reported were CCK-8 (28), CCK-22 (16,34), CCK-33/39 (35,47), and CCK-58 (42,46). An important observation is that endocrine forms smaller than CCK-58 can be produced ex vivo during the processing of plasma samples.…”

“…Thus, endogenous endocrine CCK-8 detected by others (23,35) is most likely a product of peptide degradation during plasma formation. Importantly, CCK-58 is the major intestinal and endocrine form in dogs (8,13), rats (42), and humans (8,9,14), suggesting its biological action should be evaluated and the influence of CCK-58 on feeding patterns should be studied. The importance of this suggestion is indicated by the fact that CCK-8 and CCK-58 show different actions on various physiological processes.…”