Contractile responses of canine gastric muscle to peptides of the cholecystokinin group

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Abstract
Mechanical activity was recorded in isolated muscle preparations from the circular and longitudinal layers of different regions of canine stomach (16 dogs). At least eight muscle strips were excised from each stomach: longitudinal (lo) and circular (ci) strips from fundus (Fu), corpus (Co) and antrum (An), and circular strips from the inner and outer portion of the pyloric ring. Cholecystokinin 33 (CCK 33), cholecystokinin octapeptide (CCK 8), caerulein and pentagastrin produced the same pattern of responses, with differences in their potencies: caerulein was 10 times more potent than CCK 8, and CCK eight to ten times more potent than CCK 33 and pentagastrin. The most characteristic effect of the CCK peptides was an increase in frequency of the phasic activity of Fu-ci, Co and An preparations (threshold 10-10 mol/l for CCK 8), usually combined with weak or moderate increases of amplitude. Slight tonic activations were observed in Fu-lo, Co-lo and An-lo (around 10% of the ACH maximum), and stronger tonic activations in Fu-ci and Co-ci (around 50% of the ACH maximum). No responses to CCK were seen in pyrolic preparations. Experiments with receptor antagonists (adrenoceptors, muscarinic and histamine receptors), and with tetrodotoxin indicate that the peptides act by a direct effect on smooth muscle.

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