MECHANISMS MEDIATING THE EFFECTS OF CHOLECYSTOKININ ON AVIAN SMALL-INTESTINE LONGITUDINAL SMOOTH-MUSCLE

The aims of this study were (1) to define the effects of CCK-8s and re lated peptides on chicken ileum longitudinal smooth muscle and (2) to explore the mechanisms by which such effects occur. The effects of CCK -8s were assayed in vitro on chicken longitudinal ileal strips. CCK-8s produced contraction of ileal strips (EC50 8.8.10(-9) M). CCK-8ns and CCK-4 did not have remarkable contractile effects even when added at concentrations 200-times higher than the EC50 for CCK-8s. L365,260 sli ghtly inhibited the effects of CCK-8s whereas L364,718 was ineffective . Tetrodotoxin (10(-6) M) markedly decreased the effects of CCK-8s. At ropine(10(-6) M) did not modify the neurally mediated effects of CCK-8 s, whereas ketanserin (10(-5) M) decreased the response to CCK-8s. Sub stance P-desensitized preparations exhibited reduced responses to CCK- 8s. Our results indicate that CCK receptors present in chicken ileum b ehave similarly but not identically to the CCK-A receptor described in mammals. Most of these CCK receptors are neurally located but a minor proportion is also present on smooth muscle. The neurally mediated re sponse to CCK-8s does not involve cholinergic mechanisms, but serotoni n and substance P releasing neurons.