CA2-PIG ILEUM( ANTAGONISTS REVEAL A NOVEL INHIBITORY EFFECT OF CERULEIN ON GUINEA)

The peptide caerulein (CK) is a potent muscle stimulant of guinea pig ileum and its effect is Ca2+-dependent. Ca2+ antagonist drugs administ ered to the organ perfusion solution diminished the twitches of the el ectrically stimulated ileum. Subsequent administration of caerulein re inforced this inhibition of contraction and acetylcholine (ACh) releas e by the ileum. This effect was antagonized by cholecystokinin antagon ists (i.e., proglumide and loxiglumide) and by dibutyryl-cyclic-guanos ine monophosphate, which overcame the stimulant effect of the peptide. These findings indicate that in the guinea pig ileum, caerulein exert s two opposite effects, both of which are mediated by the same recepto r: a stimulation effect, with an increase in acetylcholine release whe n the organ is incubated in normal saline, and a relaxation effect, wi th a reduction in acetylcholine release when the ileum is bathed with calcium antagonist drugs.