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Evidence for two cholecystokinin receptors mediating the contraction of the guinea pig isolated ileum longitudinal muscle myenteric plexus

G Dal Forno, C Pietra, M Urciuoli, FT van Amsterdam, G Toson, G Gaviraghi and D Trist

Glaxo Research Laboratories, Verona, Italy.

In guinea pig isolated ileum longitudinal muscle myenteric plexus, cholecystokinin octapeptide (CCK-8S) produced a rapid (phasic) contraction followed by a slower tonic phase. The tetrapeptide derivative CCK-4 and pentagastrin elicited only the phasic response up to 10(-6) M, whereas the tonic phase was also apparent at higher concentrations. The rank order of potency for the effect of agonists on the tonic and phasic responses were CCK-8S much greater than gastrin greater than CCK-8US congruent to pentagastrin greater than CCK-4 and CCK-8S greater than gastrin congruent to pentagastrin greater than CCK- 4 greater than CCK-8US, respectively. Phasic responses of CCK-8S and CCK-4 were sensitive to atropine, whereas the tonic response could be completely abolished with the neurokinin-1 antagonist GR82334. The CCK- A receptor antagonist L-364,718 up to 10(-7) M had little effect on the phasic contracture of CCK-4. The CCK-B/gastrin receptor antagonist L- 365,260 had no effect on the CCK-8S phasic response up to 10(-7) M, but antagonized the phasic response induced by low concentrations of CCK-4 in a competitive manner with an estimated pKB of 8.51. This value is close to that of 8.53 found in a guinea pig cortical binding assay. Both the second phase of the CCK-4 phasic concentration response curve (CRC) and the tonic contraction were insensitive to L-365,260.(ABSTRACT TRUNCATED AT 250 WORDS)

Volume 261, Issue 3, pp. 1056-1063, 06/01/1992
Copyright © 1992 by American Society for Pharmacology and Experimental Therapeutics




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Copyright © 1992 by the American Society for Pharmacology and Experimental Therapeutics.