Responses of guinea-pig gastric, ileal and gall bladder smooth muscle to desamino-cholecystokinin-octapeptide (CCK 7)

Cholecystokinin 7 (CCK 7), a synthetic analogue of cholecystokinin/pancreozymin (CCK 33), increased in a dose-dependent manner the tone of the guinea-pig ileal, gastric and gall bladder smooth muscle preparations. In all these preparations CCK 7 was more potent than CCK 8 and CCK 33 and all three cholecystokinins were more potent than acetylcholine (ACH). Atropine and tetrodotoxin (TTX) did not influence the CCK 7 action in fundus and gall bladder muscle strips but reduced non-competitively its effect in ileal muscle strips. Neither GE 410 nor dbcGMP affected the ACH and histamine (His) response of the muscle strips but both antagonists shifted the dose-response curve of CCK 7 to the right, GE 410 (cholecystokinin antagonist) being a much more potent antagonist of CCK 7 as compared to dbcGMP. In all muscle strips a competitive action on the CCK 7 responses was found for GE 410. In gastric muscle strips a competitive influence on the CCK 7 responses was found for dbcGMP at low concentration (1 x 10(-5)M) and a non-competitive influence at high concentration (5 x 10(-4)M). The results suggest that the contractile effects of CCK 7 in the isolated ileal smooth muscle are realized by cholinergic and direct myogenic mechanisms, whereas in the isolated gall bladder and gastric smooth muscles, by a direct myogenic mechanism only.