Nα-Carboxyacyl analogues of CCK with a substituted Gly: Interaction with pancreatic and gallbladder CCK receptors

Abstract

It has been reported that certain N α -carboxyacyl analogues of CCK-8 and of CCK-7 with a substituted Gly in position 3 or 4 of the peptide possess higher potencies at stimulating pancreatic enzyme secretion than at stimulating gallbladder contraction, suggesting that these analogues are able to differentiate subtypes of CCK A receptors. However, no studies examined directly the interaction of these peptides with the CCK receptors in both tissues. In the present study, CCK-8 and various N α -carboxyacyl analogues of CCK-7 and of CCK-8 were prepared by solid phase synthesis using Fmoc chemistry and were purified by HPLC; molecular weight and sufficient sulfation were determined by mass spectrometry. [ 125I]Bolton-Hunter(BH)-CCK-8 binding to sections of the guinea pig pancreas and gallbladder was determined under identical conditions; amylase release from pancreatic acini and contraction of gallbladder muscle strips were measured in vitro. Each peptide stimulated amylase release (EC 50): CCK-8 (0.09 nM ) > Suc[Sar 3]CCK-7 (0.23 n M ) > des(SO 3)CCK-8 (28 n M ) > Suc[ d-Trp 4]CCK-8 (32 n M ) > Suc[ d-Trp 3]CCK-7 (53 n M ) > Pht[ d-Trp 3]CCK-7 (180 n M ) > Glt[ d-Trp 3]CCK-7 (220 n M ). The same relative potencies were found for stimulation of gallbladder contraction, and for the inhibition of [ 125I]BH-CCK-8 binding to pancreas and gallbladder sections. These data demonstrate that the CCK A receptors in the pancreas and on gallbladder smooth muscle possess similar affinities for the various N α -carboxyacyl analogues of CCK-7 and CCK-8 with a substituted Gly and provide further evidence that the CCK A receptors in gallbladder and pancreas cannot be distinguished pharmacologically.