Effects of C-terminal fragments of cholecystokinin on plasma insulin and glucagon concentrations in sheep.

The effects of three C-terminal fragments of cholecystokinin (CCK) (CCK-8-sulphated form [SF], CCK-8-non-sulphated form [NSF] and CCK-4) on insulin and glucagon secretion were examined in sheep in vivo. Each CCK fragment was injected intravenously at a wide range of doses (1 pmol to 3 x 10(5) pmol kg-1). CCK-8(SF) had the lowest threshold dose (10 pmol kg-1) and a maximal response dose of 10(3) pmol kg-1 for increasing plasma insulin concentration; the respective threshold doses of CCK-8(NSF) and CCK-8 for increasing plasma insulin were 30 and 100 times greater than that of CCK-8(SF). A maximal insulin response was not obtained at the highest doses of CCK-8(NSF) or CCK-4 tested (3 x 10(3) and 3 x 10(5) pmol kg-1, respectively). These results indicate that CCK-A type receptors rather than CCK-B receptors may be involved in CCK-induced insulin secretion in sheep. None of the CCK fragments affected plasma glucagon concentration. The lack of a glucagon response to exogenous CCK-fragments may be one of the characteristics of the endocrine pancreatic responses of ruminant species.