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

Abstract 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 × 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-4 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 × 10 3 and 3 × 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.