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) (CC K-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 CC K 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 (1 0 pmol kg(-1)) and a maximal response dose of 10(3) pmol kg(-1) for in creasing plasma insulin concentration; the respective threshold doses of CCK-8(NSF) and CCK-4 for increasing plasma insulin were 30 and 100 times greater than that of CCK-8(SF). A maximal insulin response was n ot 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 t hat CCK-A type receptors rather than CCK-B receptors may be involved i n CCK-induced insulin secretion in sheep. None of the CCK fragments af fected plasma glucagon concentration. The lack of a glucagon response to exogenous CCK fragments may be one of the characteristics of the en docrine pancreatic responses of ruminant species.