Effect of synthetic human cholecystokinin-33 on exocrine pancreas

Cholecystokinin-33 is more effective than cholecystokinin-8 in inhibiting food intake and in stimulating the myenteric plexus and dorsal vagal complex

We compared the abilities of cholecystokinin-33 (CCK-33) and CCK-8 to reduce food intake and to activate feeding-related areas of the nervous system. (1) Overnight food-deprived rats were presented with a 10% sucrose solution, and intake was measured at 5-min intervals throughout a 90-min test beginning immediately after intraperitoneal injections of 1, 3, or 5 nMol/kg of CCK-33, CCK-8, or the vehicle control. In the initial 20 min (first meal), both peptides were equally effective, producing large reductions of food intake. Thereafter, however, CCK-33 was more effective than CCK-8, producing much more sustained reductions. Overall, both peptides reduced total food intake, but CCK-33 was more effective than CCK-8. (2) Possible roles for the myenteric plexus of the duodenum and the dorsal vagal complex (DVC) of the brainstem in the differential satiety effects of CCK-33 and CCK-8 were examined by quantifying CCK-33- and CCK-8-stimulated Fos-like immunoreactivity (Fos-LI) in each site. Consistent with the greater ability of CCK-33 to produce sustained inhibitions of food intake, CCK-33 produced more Fos-LI than CCK-8 in nearly every section of the sampled sites. The results demonstrate: (1) Different forms of CCK have different efficacies in reducing food intake; (2) CCK-33 produces a much more prolonged satiety action than CCK-8; and (3) the myenteric plexus and DVC may play roles in these differential satiety actions.

Comparison of the satiating potencies of cholecystokinin-33 and cholecystokinin-8

We investigated the satiating potency of CCK-33 and of CCK-8 administered IP to rats prior to a 30-min food intake test using a high-carbohydrate liquid diet. CCK-33 and CCK-8 produced dose-related inhibitions of intake. The ID50S and the slopes of the dose-response functions of the two peptides were not significantly different. We conclude that CCK-33 is as potent as CCK-8 for inhibiting food intake in the rat.

Receptor binding of cholecystokinin analogues in isolated rat pancreatic acini

The receptor binding of CCK analogues was determined in terms of the inhibition of [125I]CCK binding in isolated rat pancreatic acini. The inhibition curve produced by CCK-8 showed the same feature as that produced by synthetic human CCK-33. The relative potency values of CCK analogues to half-maximally inhibit specific CCK binding were calculated; CCK-8 was equal to human CCK-33, 3-fold stronger than natural porcine CCK-33 and 39, and 700-fold stronger than the unsulphated form of synthetic human CCK-33. Our data suggest that CCK-33, one of the longer molecular forms of CCK, is as important as CCK-8 in the mechanism of physiological actions of CCK.

Role of sulphated tyrosine residue in influencing the biologic activity of human cholecystokinin-33

To evaluate the role of the sulphated tyrosine residue in position 27 in human cholecystokinin-33, parallel bioassay of the sulphated form of human cholecystokinin-33 and the unsulphated form of human cholecystokinin-33 was performed on the pancreatic protein secretion. Both peptides increased the protein output in a dose-related manner. However, the sulphated form possessed a considerably higher activity than the sulphated form. The relative potency of the unsulphated human cholecystokinin-33 compared to that of the sulphated human cholecystokinin-33 (taken as 1.0) was 0.08. From the results, it was suggested that the sulphated tyrosine may play an important role in controlling the activity of the longer molecular forms as well as that of the smaller forms of cholecystokinin.