The third intracellular loop of the rat and mouse cholecystokinin-A receptors is responsible for different patterns of gene activation.

It has previously been reported that the cholecystokinin analog JMV-180 behaves differently on the rat and the mouse cholecystokinin-A receptor (CCK-AR). In mice this analog acts as an agonist on low- and high-affinity sites of the CCK-AR, whereas in rats this compound acts as an agonist on high-affinity sites and as an antagonist on low-affinity sites. In an attempt to understand why the same compound behaves differently on these two CCK-A receptors, we cloned the cDNA encoding the mouse CCK-AR. We then investigated a cellular model able to mimic the effect that was observed in rats and mice. HeLa cells were transiently cotransfected with plasmids leading to expression of the rat or mouse CCK-AR in the presence of pFos-Luc as reporter plasmid; such a plasmid placed the regulatory part of the human c-Fos gene upstream from the firefly luciferase structural gene (Luc). We then observed that the two CCK-A receptors behaved differently, not only in the presence of compound JMV-180 but also in the presence of cholecystokinin or even in absence of ligand; the rat CCK-AR was 2 to 3 times more potent than the mouse CCK-AR in inducing the reporter protein, whatever the ligand studied. This result was confirmed using the same kind of experiment with the reporter plasmid p(TRE)(3)-tk-Luc. Using various mutated receptors, we investigated the role of the putative third intracellular loop. We concluded that both the primary structure of the receptor and the cellular context are in part responsible for the differential behavior of these CCK-A receptors.

A synthetic glycine-extended bombesin analogue interacts with the GRP/bombesin receptor.

alpha-amidation of a peptide (which takes place from a glycine-extended precursor) is required to produce biologically active amidated hormones, such as gastrin-releasing peptide (GRP)/Pyr-Gln-Arg-Leu-Gly-Asn-Gln-Trp-Ala-Val-Gly-His-Leu-Met-NH(2) (bombesin). It was shown that glycine-extended gastrin mediates mitogenic effects on various cell lines by interacting with a specific receptor, different from the classical CCK(1) or CCK(2) receptors. On the basis of this observation, we have extended the concept of obtaining active glycine-extended forms of others amidated peptides to produce new active analogues. In this study, we have tested the biological behaviour of a synthetic analogue of the glycine-extended bombesin (para-hydroxy-phenyl-propionyl-Gln-Trp-Ala-Val-Gly-His-Leu-Met-Gly-OH or JMV-1458) on various in vitro models. We showed that compound JMV-1458 was able to inhibit specific (3-[125I]iodotyrosyl(15)) GRP ([125I]GRP) binding in rat pancreatic acini and in Swiss 3T3 cells with K(i) values of approximately 10(-8) M. In isolated rat pancreatic acini, we found that JMV-1458 induced inositol phosphates production and amylase secretion in a dose-dependent manner. In Swiss 3T3 cells, the glycine-extended bombesin analogue dose-dependently produced [3H]thymidine incorporation. By using potent GRP/bombesin receptor antagonists, we showed that this synthetic glycine-extended bombesin analogue induces its biological activities via the classical GRP/bombesin receptor.

Synthesis and biological evaluation of bombesin constrained analogues.

Analogues of bombesin which incorporate dipeptide or turn mimetics have been synthesized. One of them (compound 11) containing a seven-membered lactam ring revealed a good affinity for GRP/BN receptors on rat pancreatic acini (K(i) value of 1.7 +/- 0.4 nM) and on Swiss 3T3 cells (K(i) value of 1.0 +/- 0.2 nM). On the basis of this observation, antagonists containing the same dipeptide mimic were obtained by modification of the C-terminal part of the bombesin analogues. The most potent constrained compounds (15 and 17) were able to antagonize 1 nM bombesin-stimulated amylase secretion from rat pancreatic acini with high potency (K(i) = 21 +/- 3 and 3.3 +/- 1.0 nM, respectively) and 10(-7) M bombesin-stimulated ¿(3)Hthymidine incorporation into Swiss 3T3 cells (K(i) = 7.8 +/- 2. 0 and 0.5 +/- 0.1 nM, respectively).

The design and synthesis of the high efficacy, non-peptide CCK1 receptor agonist PD170292.

The design, synthesis and biological actions of a novel, non-peptide CCK1 receptor agonist (PD 170292) which exhibits a similar pharmacological profile to the CCK analogue JMV180 is reported. PD 170292 was designed based on a consideration of the structures of a peptide based CCK1 receptor selective agonist and a peptoid CCK2 receptor selective antagonist.

Oxyntomodulin inhibits pancreatic secretion through the nervous system in rats.

Glicentin (GLIC), oxyntomodulin (OXM), and peptide YY (PYY) released in blood by ileocolonic L-cells after meals may inhibit pancreatic secretion. Whereas OXM interacts with glucagon and tGLP-1 receptors, OXM 19-37, a biologically active fragment, does not. The purpose of this study was to measure the effect of OXM, OXM 19-37, GLIC, tGLP-1, and PYY on pancreatic secretion stimulated by 2 deoxyglucose (2DG), electrical stimulation of the vagus nerves (VES), acetylcholine and cholecystokinin octapeptide (CCK8) in anesthetized rats. The effect of OXM was also studied in dispersed pancreatic acini. Plasma oxyntomodulin-like immunoreactivity (OLI) was measured by radioimmunoassay after the exogenous infusion of OXM and after an intraduodenal meal. OXM 19-37, infused at doses mimicking postprandial plasma levels of OLI, decreased pancreatic secretion stimulated by 2DG, VES, or CCK8. Similar effects were found with OXM and GLIC. OXM 19-37 did not change the pancreatic stimulation induced by acetylcholine in vivo, or CCK-induced amylase release in isolated acini. Vagotomy completely suppressed the inhibitory effect of OXM 19-37 on CCK8-stimulated pancreatic secretion. PYY inhibited the effect of 2DG, but not that of CCK8, whereas tGLP-1, even in pharmacologic doses, had no effect on stimulated pancreatic secretion. OXM, OXM 19-37, but not tGLP-1, inhibit pancreatic secretion at physiologic doses, through a vagal neural indirect mechanism, different from that used by PYY, and probably through a GLIC-related peptide-specific receptor.

Syntheses and biological activities of potent bombesin receptor antagonists.

Bombesin receptor antagonists are potential therapeutic agents due to their ability to act as inhibitors of cellular proliferation. On the basis of our hypothesis concerning the mechanism of action of gastrin associating an activating enzyme to the receptor and on the results reported in the literature, we have synthesized bombesin analogs which have been modified in the C-terminal part. Potent bombesin receptor antagonists were obtained by replacement of Leu-13 with a statyl residue or with a residue bearing an hydroxyl group in place of the carbonyl function of Leu-13. Several inhibitors were able to recognize the bombesin receptor on rat pancreatic acini and antagonized bombesin stimulated amylase secretion in the nanomolar range. These compounds were also able to recognize the bombesin receptor and to inhibit [3H] thymidine incorporation in 3T3 cells with the same potency.

Synthesis and biological evaluation of C-terminal hydroxamide analogues of bombesin.

Bombesin pseudo-peptide analogues containing a hydroxamide function on the C-terminal part of the molecule, e.g. H-D-Phe-Gln-Trp-Ala-Val-Gly-His-Leu-NHOBzl 1 and H-D-Phe-Gln-Trp-Ala-Val-Gly-His-Leu-NHOH 2 were synthesized. These compounds were tested for their ability to recognize the bombesin receptor on rat pancreatic acini and on 3T3 cells, to stimulate (i) amylase secretion from rat pancreatic acini and (ii) accumulation of tritiated thymidine in 3T3 cells. Compounds 1 and 2 were able to recognize bombesin receptors on both models with high affinity (Ki = 7 +/- 2 and 5.8 +/- 0.9 nM on rat pancreatic acini, and Ki = 4.1 +/- 1.2 and 7.7 +/- 1.9 nM on 3T3 cells, respectively). Interestingly, compound 1 behaved as a potent agonist in stimulating amylase secretion from rat pancreatic acini and is able to stimulate thymidine accumulation in 3T3 cells, while compound 2 was able to potently antagonize bombesin-stimulated amylase secretion (Ki = 22 +/- 5 nM) in rat pancreatic acini and had no proper effect on 3T3 cells; however, it was able to inhibit bombesin-stimulated thymidine accumulation in 3T3 cells with high potency (Ki = 1.6 +/- 0.6 nM).

Comparative study of in vitro and in vivo activities of bombesin pseudopeptide analogs modified on the C-terminal dipeptide fragment.

Analogs of bombesin in which the peptide bond between the two last amino acid residues were replaced by a pseudopeptide bond mimicking the transition state analog were evaluated. These compounds were able to recognize the bombesin receptor on isolated rat pancreatic acini with high potency (Ki from 0.60 +/- 0.27 nM to 4.3 +/- 2.3 nM). Although they were devoid of agonist activity, they were able to antagonize bombesin-induced amylase secretion in this model, with potencies in accordance with their affinities (IC50 from 1.6 +/- 0.3 nM to 10.0 +/- 1.7 nM). When tested in vivo in the anesthetized rat, these bombesin receptor antagonists exhibited high potency in inhibiting bombesin-induced pancreatic secretion (H-DPhe-Gln-Trp-Ala-Val-Gly-His-NH-CH[CH2-CH(CH3)2]-CHOH-(CH 2)3-CH3, JMV845, was among the most potent compounds with ED50 of 7.82 +/- 2.89 nM in inhibiting bombesin-induced protein secretion). The results of this study showed that replacing the peptide bond between the two last amino acid residues in bombesin by mimicking the transition state analog resulted in in vitro and in vivo potent bombesin receptor antagonists.

CholecystokininB receptor from human Jurkat lymphoblastic T cells is involved in activator protein-1-responsive gene activation.

The aim of this study was to analyze the role of cholecystokinin (CCK(B)) receptor in human lymphoblastic Jurkat T cells. We investigated the trophic effect resulting from activation of such a receptor by using the reporter gene strategy. For this purpose, we transiently transfected Jurkat T cells with the reporter plasmid p[(TRE)3-tk-Luc] and found that CCK-8 was able to dose-dependently induce luciferase expression related to activator protein-1 (AP-1) activation with a maximal response identical to that obtained with compounds known to activate AP-1 complex (quantitatively, the same level of induction was obtained with 1 nM 12-O-tetradecanoylphorbol-13-acetate, 100 microM diacylglycerol, or 4 nM epidermal growth factor). The involvement of the CCK(B) receptor in such a stimulation was demonstrated by the inhibiting effect of the selective CCK(B) receptor antagonist PD-135,158. This effect was confirmed in COS-7 cells transfected with the cDNA of CCK(B) receptor cloned from Jurkat T cells. To better understand the AP-1-dependent luciferase expression in Jurkat T cells, we tested two specific inhibitors of serine/threonine phosphatases-1 and -2A: okadaic acid and calyculin A. These compounds strongly increased the phorbol-12-myristate-13-acetate response, whereas we have not observed a contribution of phosphatase inhibitors on a CCK-8-induced luciferase activity. To confirm that CCK(B) receptors are involved in AP-1 response, we investigated the CCK-8 effect on interleukin-2 expression, a natural endogenous gene regulated by several factors, including AP-1. In Jurkat T cells activated by phorbol-12-myristate-13-acetate and phytohemagglutinin, CCK-8 induced IL-2 expression. This induction was abolished by PD-135,158. Our results indicate that CCK-8 exerts a trophic effect in Jurkat T cells through stimulation of CCK(B) receptors by modulation of expression of AP-1-regulated genes.

A new biological contribution of cyclo(His-Pro) to the peripheral inhibition of pancreatic secretion.

The tripeptide pyro-Glu-His-Pro-NH2[thyrotropin-releasing hormone (TRH)] was isolated from the hypothalamus as a thyrotropin-releasing factor. It has a broad spectrum of central nervous system-mediated actions, including the stimulation of exocrine pancreatic secretion. TRH is also synthesized in the endocrine pancreas and found in the systemic circulation. Enzymatic degradation of TRH in vivo produces other bioactive peptides such as cyclo(His-Pro). Because of the short half-life of TRH and the stability of cyclo(His-Pro) in vivo, we postulated that at least part of the peripheral TRH effects on the exocrine pancreatic secretion may be attributed to cyclo(His-Pro), which has been shown to have other biological activities. This study determines in parallel the peripheral effects of TRH and cyclo(His-Pro) as well as the putative contribution of other TRH-related peptides on exocrine pancreatic secretion in rats. TRH and its metabolite cyclo(His-Pro) dose dependently inhibited 2-deoxy-D-glucose (2-DG)-stimulated pancreatic secretion. TRH and all the related peptides tested had no effect on the basal and cholecystokinin-stimulated amylase release from pancreatic acinar cells in vitro. These data indicate that cyclo(His-Pro) mimics the peripheral inhibitory effect of TRH on 2-DG-stimulated exocrine pancreatic secretion. This effect is not detected on isolated pancreatic acini. Our findings provide a new biological contribution for cyclo(His-Pro) with potential experimental and clinical applications.

Conformationally readdressed CCK-B/delta-opioid peptide ligands.

The sequence of a cholecystokinin (CCK) related peptide was modified to obtain analogues, which interact selectively either with CCK-B, or with delta-opioid receptors. Two kinds of peptides were designed, namely, the cyclic peptides of the H-Tyr-cyclo (D-Pen-Gly-Trp-L/D-3-transmercaptoproline)-Asp-Phe-NH2 sequence (compounds 1a and 1b, respectively), and the linear peptides of the H-Tyr-D-Val-Gly-Trp-L/D-3-trans-methylmercaptoproline-Asp-Phe- NH2 sequence (compounds 2a and 2b, respectively). The only difference between the chemical structures of the linear analogues compared to the cyclic ones is that one covalent bond has been eliminated and a sulfur atom is replaced by a methyl group. Molecular modeling showed that, among low-energy conformers of cyclic compounds 1, there are three-dimensional structures compatible to the model for delta-receptor-bound conformer, suggested earlier [G. V. Nikiforovich, V.J. Hruby, O. Prakash, and C.A. Gehrig (1991) Biopolymers, vol. 31, pp. 941-955]. Results of binding assays fully supported the rationale for the design of compounds 1 and 2. The cyclic analogue 1a has Ki values of 4.5 and > 5000 nM at delta- and mu-opioid receptors, respectively; and IC50 values of 1.6 and > 10,000 nM for CCK-A and CCK-B receptors, respectively. The results of this study demonstrate a possibility to redirect a peptide sequence that interacts with one type of receptors (CCK-B receptors) toward interaction with another type (delta-opioid receptors) belonging to a different physiological system. This redirection could be performed by changing the conformational properties of the peptide with very minimal changes in its chemical structure.

Synthesis and characterization of a new labeled gastrin ligand, 125-I-BH-[Leu15]-gastrin-(5-17), on binding to canine fundic mucosal cells and Jurkat cells.

In the course of our study concerning gastrin and cholecystokinin (CCK) receptors, we have synthesized and characterized a new labeled gastrin ligand, 125I-BH-[Leu15]-gastrin-(5-17) [(3-[125I]iodo-4-hydroxyphenyl)-propionyl-[Leu15]-gastrin-(5-17)]. Binding of 125I-BH-[Leu15]-gastrin-(5-17) to isolated canine fundic mucosal cells was specific, saturable and of high affinity. 125I-BH-[Leu15]-gastrin- (5-17) and 125I-BH-CCK-8[(3-[125I]iodo-4-hydroxyphenyl)-propionyl-CCK-8] interact with isolated canine fundic mucosal cells with small differences in maximal binding capacities and affinities, 3800 +/- 900 binding sites/cell (Kd = 0.52 +/- 0.23 nM) and 6200 +/- 1100 binding sites/cell (Kd = 0.31 +/- 0.18 nM), respectively. The relative order of potencies for gastrin and CCK analogs in displacing 125I-BH-[Leu15]-gastrin-(5-17) binding correlated well with those obtained using 125I-BH-CCK-8. Selective CCK/gastrin antagonists L-364,718 (MK-329) and L-365,260 also inhibited 125I-BH-[Leu15]-gastrin-(5-17) binding. These results indicate that 125I-BH-[Leu15]-gastrin-(5-17) binds to gastrin receptors in isolated canine fundic mucosal cells. We have also characterized 125I-BH-[Leu15]-gastrin-(5-17) binding to the human Jurkat lymphoblastic cell line (Jurkat cells) known to express the CCK-B/gastrin receptor. Saturation experiments have shown that both 125I-BH-[Leu15]-gastrin-(5-17) and 125I-BH-CCK-8 interact with a single class of high-affinity binding sites in the Jurkat cell line.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis and biological evaluation of cholecystokinin analogs in which the Asp-Phe-NH2 moiety has been replaced by a 3-amino-7-phenylheptanoic acid or a 3-amino-6-(phenyloxy)hexanoic acid.

Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-Asp-2-phenylethyl ester (JMV180), an analog of the C-terminal octapeptide of cholecystokinin (CCK-8), shows interesting biological activities behaving as an agonist at the high-affinity CCK binding sites and as an antagonist at the low-affinity CCK binding sites in rat pancreatic acini. Although we did not observe any major hydrolysis of the ester bond of Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-Asp-2-phenylethyl ester in our in vitro studies, we were aware of a possible and rapid cleavage of this ester bond during in vivo studies. To improve the stability of Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-Asp-2-phenylethyl ester, we decided to synthesize analogs in which the ester bond would be replaced by a carba (CH2-CH2) linkage. We synthesized the 3-amino-7-phenylheptanoic acid (beta-homo-Aph) with the R configuration in order to mimic the Asp-2-phenylethyl ester moiety and the 3-amino-6-(phenyloxy)hexanoic acid (H-beta-homo-App-OH), an analog of H-beta-homo-Aph-OH in which a methylene group has been replaced by an oxygen. (R)-beta-Homo-Aph and (R)-H-beta-homo-App-OH were introduced in the CCK-8 sequence to produce Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-(R)-beta-homo-Aph-OH and Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-(R)-beta-homo-App-OH. Both compounds were able to recognize the CCK receptor on rat pancreatic acini (IC50 = 12 +/- 8 nM and 13 +/- 5 nM, respectively), on brain membranes (IC50 = 32 +/- 2 nM and 57 +/- 5 nM, respectively), and on Jurkat T cells (IC50 = 75 +/- 15 nM and 65 +/- 21 nM, respectively). Like Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-Asp-2-phenylethyl ester, both compounds produced maximal stimulation of amylase secretion (EC50 = 6 +/- 2 nM and 4 +/- 2 nM, respectively) with no decrease of the secretion at high concentration indicating that these compounds probably act as agonists at the high-affinity peripheral CCK-receptor and as antagonists at the low-affinity CCK-receptor. Replacing the tryptophan by a D-tryptophan in such analogs produced full CCK-receptor antagonists. All these analogs might be more suitable for in vivo studies than Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-Asp-2-phenylethyl ester.

Cholecystokinin increases intracellular Ca2+ concentration in the Human JURKAT T Lymphocyte cell line.

We have recently demonstrated the presence of specific high-affinity cholecystokinin binding sites of the central type on the Human JURKAT T Lymphocyte Cell line. In this paper, changes in intracellular Ca2+ concentration ([Ca2+]i) in response to CCK (cholecystokinin) peptides were measured in the Human JURKAT T Lymphocyte Cell line by fura-2 fluorometry. CCK-8 (the C-terminal octapeptide of CCK), the potent CCK analog Boc-[Nle28,31]CCK-7, stimulated ([Ca2+]i) mobilization in a dose-dependent manner in cells preloaded with fura-2 AM with an EC50 of 2.4 +/- 1 nM and 8 +/- 2 nM, respectively. The selective CCKB receptor agonists, namely Boc-Trp-Nle-Asp-Phe-NH2 and the cyclic analog JMV320, [formula: see text], were also potent in stimulating mobilization of [Ca2+]i with an EC50 of 32 +/- 10 nM and 25 +/- 10 nM, respectively. Compound JMV180, Boc-Tyr(SO3H)-Nle-Trp-Nle-Asp-2-phenylethyl ester, did not stimulate [Ca2+]i but inhibited the mobilization of [Ca2+]i elicited by 10 nM CCK-8 in a dose-dependent manner with an IC50 of 10 +/- 2 nM. The selective non-peptide CCKB receptor antagonist L-365,260 was more potent than the selective CCKA receptor antagonist MK-329 in inhibiting the [Ca2+]i mobilization elicited by 10 nM CCK-8 with IC50 values of 20 +/- 8 nM and 400 +/- 100 nM, respectively. These data indicated that CCK-8 and potent CCK analogs induced [Ca2+]i mobilization in the Human JURKAT T cell line through the CCKB/gastrin receptor type.

Pharmacological characterization of new cholecystokinin analogues.

New analogues of cholecystokinin-7 (CCK-7) modified at amino acid residues 5 and 7 were assayed for their effect on gall bladder, pancreatic secretion, food intake (anorectic activity), amount of rearing (sedative activity) and analgesia, as well as their ability to inhibit 125I-CCK-8 binding to pancreatic cell membrane receptors and brain membrane receptors. The results were compared to the activities of standard compounds, CCK-8, cerulein, BOC-CCK-7 (BOC = tertbutyloxycarbonyl) and BOC-[Nle2,Nle5]CCK-7. All analogues exhibited agonistic effects. Their anorectic activity was significantly prolonged.

Pharmacological studies on CCKB receptors in guinea pig synaptoneurosomes.

Preliminary studies on CCK receptors in the central nervous system were carried out on guinea pig cerebral cortical synaptoneurosome preparations. In binding assays, the range of affinity of CCK-8, Boc-[Nle28,Nle31]CCK-7, a potent CCK analog, Boc-[Leu31]CCK-4 and of the two benzodiazepine CCK receptor antagonists L-365,260 and MK-329, is in agreement with the presence of CCKB receptors on this model. The effects of Boc-[Nle28,Nle31]CCK-7 on inositol phosphates, cAMP accumulation and 45Ca2+ efflux were investigated. Neither inositol phosphate nor cAMP accumulations could be observed. On the other hand, evidence of Boc-[Nle28,Nle31]CCK-7-, CCK-8- and Boc-[Leu31]CCK-4-induced 45Ca2+ efflux was found in a dose-dependent manner. The CCKB-selective receptor antagonist L-365,260 and, with a weaker efficiency, the CCKA-selective receptor antagonist MK-329, are able to block a maximal effect of Boc-[Nle28,Nle31]CCK-7-induced 45Ca2+ efflux, suggesting that CCKB receptors may regulate calcium ion mobilization.

Pharmacological characterization of type B cholecystokinin binding sites on the human JURKAT T lymphocyte cell line.

Recent studies have demonstrated the presence and the regulatory function of some neuropeptides in the immune system. In the present study, we have used labeled cholecystokinin (26-33) amide to characterize high affinity cholecystokinin (CCK) binding sites on a human JURKAT lymphoma cell line. Binding was temperature dependent, saturable, and specific. Analysis of the data demonstrated a single class of binding sites with high affinity for the ligand (Kd approximately 3.2 +/- 0.5 x 10(-11) M) and a binding capacity of 0.42 fmol/10(6) cells (approximately 300 sites/cell). These CCK binding sites displayed a typical CCK-B pharmacological profile, established by use of several agonists and antagonists selective for the CCK receptor types, namely compound L-364,718, the Merck CCK antagonist selective for the peripheral CCK receptor (CCK-A), and compound L-365,260, the Merck CCK antagonist selective for the central CCK receptor (CCK-B). The CCK cyclic analogue recently developed in our laboratory that is highly selective for the CCK-B receptor (i.e., JMV320) also showed high affinity for the CCK receptor on the JURKAT cell line. The presence of CCK-B-like binding sites on a lymphoid cell line could provide a useful model for pharmacological characterization of CCK-B binding sites and could contribute to a better understanding of their regulation.

[Structure-activity relationship of cystokinins: analogs exhibiting selective activity]. / Relations structure-activité de la cholécystokinine: analogues présentant des activités sélectives.

Structure-activity relationship on cholecystokinin is presented. C-terminal heptapeptide analogues of cholecystokinin exhibiting selective agonist or antagonist activities were synthesized and their biological and pharmacological properties studied. We showed that: 1) Suppression of the C-terminal phenylalanine residue leads to peripheral as well as central cholecystokinin receptor antagonists; 2) Suppression of the C-terminal amide function produces "partial agonists" exhibiting interesting biological and pharmacological activities; 3) Replacement of L-tryptophan residue by D-tryptophan in such "partial agonist analogues" resulted in potent CCK receptor antagonists; 4) The peptide bond between methionine28 and glycine29, as well as the glycine residue are quite significant for the central biological activity; 5) It is possible to obtain highly potent and selective CCK analogues for the central receptor (CCK-B) by cyclization including the C-terminal tetrapeptide. Synthesis and pharmacological studies with these analogues have allowed to precise the significance of some amino acid residues as well as of some peptide bonds. They are significant pharmacological tools for the study of CCK-A (peripheral) and CCK-B (central) receptors, their biological actions and their associated intracellular messengers.