Physiological role of cholecystokinin in meal-induced insulin secretion in conscious rats. Studies with L 364718, a specific inhibitor of CCK-receptor binding

It has been suggested that the gut hormone cholecystokinin (CCK), by modulating insulin output from pancreatic beta-cells, plays an important role in the enteroinsular axis. To investigate this hypothesis, eight rats were studied on two different occasions: after injection of L 364718, a specific antagonist of CCK binding to its membrane receptor, and after vehicle injection. In both studies a mixture of casein (11%) and glucose (9%) was infused through a chronic indwelling intraduodenal catheter to evoke CCK secretion. Plasma was analyzed for insulin, glucose, glucagon, and tyrosine many times during the procedure. Prior administration of the CCK antagonist significantly attenuated the increase in plasma insulin and glucagon after casein infusion. These results support the concept that cholecystokinin plays an important physiologic role in the in vivo regulation of postprandial plasma insulin and glucagon concentrations after protein ingestion.

Species differences in the localization of 'peripheral' type cholecystokinin receptors in rodent brain

A comparison of cholecystokinin (CCK) receptor binding to sections of rat, mouse and guinea pig brain has been performed using 125I-Bolton Hunter CCK and the selective peripheral CCK receptor antagonist L-365,031. In both rat and mouse, 125I-Bolton Hunter CCK binding in the region of the interpeduncular nucleus (IPN) was inhibited by L-365,031 indicating that these receptors resemble CCK receptors found in peripheral tissues. In the mouse especially, dense regions of peripheral CCK receptors were detected either side of the IPN. By contrast, in the guinea pig IPN no evidence of L-365,031-sensitive binding could be found. The present reports shows that in different species, regional variations in brain CCK receptor binding occur not only in the case of classical 'brain' receptors, but also for the more discretely localised 'peripheral' type CCK receptors.

Asperlicin: a unique nonpeptide cholecystokinin antagonist

The lack of a potent and specific cholecystokinin (CCK) receptor antagonist has greatly hampered studies of the role of CCK in controlling pancreatic growth, enzyme release, pancreatitis, and pancreatic carcinoma. Asperlicin, a newly described, CCK antagonist, has been shown to be a potent, competitive inhibitor of CCK-induced gallbladder and ileal muscle contraction. In this study, the effects of asperlicin on CCK- and carbachol-stimulated pancreatic enzyme release from dispersed guinea pig acini were investigated. Cholecystokinin caused a dose-dependent release of amylase and lipase. Half-maximal release of amylase (17.9% +/- 2.1%, mean +/- SEM, percent of total content) and lipase (27.3% +/- 2.1%) was seen with CCK 10(-11) mmol/L) both p less than 0.01). Asperlicin (10(-11) to 10(-4) mmol/L) caused a substantial inhibition (10(-11) mmol/L) of CCK-induced amylase release with a 50% maximal effective inhibitory dose of 10(-9) mmol/L (p less than 0.01) and maximum inhibition at 10(-6) mmol/L. Asperlicin was approximately 1000-fold more potent than proglumide (a previously described CCK receptor antagonist) which had a 50% effective inhibitory dose of 10(-6) mmol/L) and a maximal effect at 10(-4) mmol/L. Asperlicin (10(-10) to 10(-4) mmol/L) failed to alter carbachol-induced amylase release. Asperlicin is a new, potent CCK antagonist for pancreatic CCK receptors and should prove useful as an investigational tool. Such receptor antagonists may have therapeutic potential.

[Changes in the behavioral and biochemical effects of cerulein, an analog of cholecystokinin octapeptide, after prolonged administration of haloperidol]

In experiments on male mice and rats, long-term haloperidol administration (0.25 mg/kg twice a day during 15 days) significantly changed behavioural effects of caerulein, an agonist of CCK-8 receptors. As a rule, the effects of caerulein were reduced or inverted; only long-term antagonism with amphetamine motor excitation in rats increased after the cessation of haloperidol administration. The decrease or inversion of caerulein's effects was connected with reduction of high-affinity dopamine2- and low-affinity CCK-8 receptors' density, reflecting the inhibition of some interneurons' activity in subcortical forebrain structures after haloperidol treatment. A more pronounced inhibition of dopamine's release by caerulein was the reason for the increased antiamphetamine action after long-term haloperidol treatment. It seems possible that both above mechanisms are involved in the antipsychotic action of haloperidol.

Investigation of peripheral cholecystokinin receptor heterogeneity by cyclic and related linear analogues of CCK26-33: synthesis and biological properties

A possible heterogeneity of peripheral receptors for CCK26-33 [Asp-Tyr(SO3H)-Met-Gly-Trp-Met-Asp-Phe-NH2] (CCK8) was investigated by replacement of the flexible Gly29 residue, reported to be crucially involved in the CCK8 folding, by a D-Lys residue in Boc[Nle28,31]CCK27-33, a derivative as active as CCK8. The linear peptide Boc-Asp-Tyr(SO3H)-Nle-D-Lys-Trp-Nle-Asp-Phe-NH2 was cyclized through amide bond formation between the side chains of Asp26 and D-Lys29 to give the peptide Boc-Asp-Tyr(SO3H)-Nle-D-Lys-Trp-Nle-Asp-Phe-NH2. Analogues 1 and 2 were shown to stimulate secretion of amylase from rat pancreas with a potency that was respectively 40 and 80 times lower than that of CCK8. In contrast, both peptides acted as weak antagonists (EC50 approximately 10(-5) M) of the CCK8-induced contractions of guinea pig ileum. Peptides 3 and 4 obtained by removal of the phenylalanine from 1 and 2 were inactive in all bioassays despite amidification of their C-terminal Asp32 residue, a modification known to induce antagonist properties in CCK7. Cyclization between residues 28 and 31 in Boc[Asp28,Lys31]CCK27-33 gave compound Boc-Tyr(SO3H)-Asp-Gly-Trp-Lys-Asp-Phe-NH2, which was inactive in all bioassays. The pharmacological properties of these first described cyclic analogues of CCK8 were in agreement with their binding affinity to brain and pancreas receptors, suggesting the existence of a heterogeneity of peripheral receptors and emphasizing the usefulness of cyclic peptides in structure-activity studies.

Pharmacological characterisation of a new potent and specific nonpolypeptidic cholecystokinin antagonist

D,L-4-(3,4-Dichloro-benzoylamino)-5-(N-3-methoxypropyl- pentylamino)-5-oxo-pentanoic acid (CR 1505) belongs to a newly discovered class of agents with cholecystokinin (CCK) antagonistic activity. CR 1505 displaces CCK-8 from the central CCK receptors at concentrations of 9.1 mumol/l, and from the peripheral CCK receptors at concentrations of 0.33 mumol/l. CR 1505 antagonizes in vitro the contractant effects of CCK-8 on gall bladder strips of the guinea pig at 0.79 mumol/l and those on the small intestine at 1.6 mumol/l. These antagonistic effects are dose dependent and of competitive type. The antagonistic activities of CR 1505 against contractions of smooth muscles elicited by CCK-8 are at least 1000 times more potent than those against the contractions elicited by acetylcholine, BaCl2, histamine, serotonin, Substance P, bradykinin or dimethylphenylpiperazine. CR 1505 is also practically ineffective against the contractions of the small intestine of the guinea pig elicited by electrical field stimulations either as "cholinergic twich" (0.05 Hz), or as "cholinergic contractions" (trains of 10 min at 1 Hz), or as "non-cholinergic contractions" (200 impulses at 5 Hz in presence of atropine). CR 1505 is therefore a potent, specific, competitive and reversible CCK antagonist.

A synthetic peptide derivative that is a cholecystokinin receptor antagonist

So far, there are no known peptidic effective receptor antagonists of both peripheral and central effects of cholecystokinin (CCK). Here, we describe a synthetic peptide derivative of CCK, t-butyloxycarbonyl-Tyr(SO3-)-Met-Gly-D-Trp-Nle-Asp 2-phenylethyl ester 1 (where Nle is norleucine), which is a potent CCK receptor antagonist. In rat and guinea pig dispersed pancreatic acini, this peptide derivative did not alter amylase secretion, but was able to antagonize the stimulation caused by cholecystokinin-related agonists. It caused a parallel rightward shift in the dose-response curve for the stimulation of amylase secretion with half-maximal inhibition of CCK-8-stimulated amylase release at a concentration of about 0.1 microM. Compound 1 was able to inhibit the binding of labeled CCK-9 (the C-terminal nonapeptide of CCK) to rat and guinea pig pancreatic acini (IC50 = 5 X 10(-8) M) as well as to guinea pig cerebral cortical membranes (IC50 = 5 X 10(-7) M). These results indicate that Compound 1 is a potent competitive CCK receptor antagonist.

Characterization of [3H](+/-)L-364,718 binding to solubilized cholecystokinin (CCK) receptors of rat pancreas

The binding of [3H](+/-)L-364,718 (3S(-)-N-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4-benzodiazepine-3-yl )-1H-indole-2-carboxamide), an extremely potent nonpeptide cholecystokinin (CCK) receptor antagonist, to digitonin-solubilized CCK receptors from rat pancreas was characterized. [3H](+/-)L-364,718 binding to digitonin-solubilized receptors was assayed using polyethylene glycol precipitation followed by rapid filtration to separate free and bound [3H](+/-)L-364,718. Specific [3H](+/-)L-364,718 binding to solubilized receptors was dependent on the digitonin and receptor concentration and, under optimal conditions, represented greater than 90% of the total binding. Scatchard analysis indicated a single class of binding sites with a Kd of 0.53 nM and a Bmax of 3.1 pmol/mg protein. Specific [3H](+/-)L-364,718 binding to solubilized CCK receptors was inhibited by both CCK receptor agonists and antagonists in a stereospecific manner. After solubilization, the affinities of various antagonists to displace specific [3H](+/-)L-364,718 binding were similar to those obtained with membrane-bound receptors; however, the affinities of CCK agonists were reduced 10-100 times. Collectively, the data presented indicate that [3H](+/-)L-364,718 represents a new antagonist ligand which has apparent advantages over the agonist ligand [125I]CCK in assaying digitonin-solubilized receptors. Gel filtration of the digitonin-solubilized CCK receptors followed by [3H](+/-)L-364,718 binding determinations revealed an estimated molecular weight of 400,000 daltons.

Regulation of somatostatin-14 and gastrin I binding sites in rat gastrointestinal mucosa by ulcerogenic dose of cysteamine

A single duodenal ulcerogenic dose of cysteamine administered into rats induced time-dependent depletion of immunoreactive somatostatin in the gastric corporeal, antral, and duodenal mucosa with a parallel increase (up-regulation) of somatostatin binding sites. The concentration of somatostatin binding sites returned to the control level in the corporeal mucosa when measured at 24 hrs; however, in the duodenal mucosa there was only a partial return to the control level. Somatostatin binding sites in the antral mucosa did not return to control level even after 24 hrs. Except for the duodenum mucosal immunoreactive gastrin level was unaffected by cysteamine administration, but corporeal mucosal gastrin I binding sites were diminished (down-regulation) after 24 hrs.

Synthesis and biological activity of partially modified retro-inverso pseudopeptide derivatives of the C-terminal tetrapeptide of gastrin

The effects of partial retro-inverso modifications of selected peptide bonds of the N-terminal tetrapeptide of gastrin have been studied. In some of the synthesized compounds, the phenylalanyl residue has been replaced by the (R,S)-2-benzylmalonyl, 3-phenylpropionyl, benzylcarbamoyl, or benzyloxycarbonyl moieties. All pseudopeptides showed affinity for the gastrin receptor, in vitro, with potencies varying from IC50 = 10(-7) to IC50 = 10(-4) M. These compounds exhibited little or no activity on acid secretion in the anesthetized rat but were able to antagonize the action of gastrin. Among the most potent were Boc-Trp-Leu-gAsp-CO-CH2CH2C6H5 (20) (ED50 = 0.15 microM/kg), Boc-Trp-Leu-gAsp-m(R,S)Phe-NH2 (3) (ED50 = 0.15 microM/kg), and Boc-Trp-gLeu-D-Asp-m(R,S)Phe-NH2 (7) (ED50 = 0.3 microM/kg).

Dissociation of tolerance and dependence to morphine: a possible role for cholecystokinin

Since cholecystokinin (CCK) has been suggested to be an endogenous opiate antagonist, we tried to evaluate if this peptide could be involved in the development of tolerance to morphine. Naive rats were chronically administered morphine, either alone or concomitantly with proglumide or benzotript, two putative CCK receptor antagonists. Chronic treatments with both CCK antagonists alone were also established. Drugs were administered by the oral route, dissolved in the drinking water. At the end of the chronic treatments, the development of tolerance to morphine was assessed by an evaluation of the analgesic responses evoked by graded doses of acutely injected morphine in the tail-flick and hot plate tests. Proglumide and benzotript were able to inhibit the shift to the right of the dose-response curve for morphine, i.e. they prevented the development of tolerance to morphine-induced analgesia. Chronically given alone, the two CCK antagonists never modified the responses to the acute challenge with morphine. We also determined the development of physical dependence by looking at the withdrawal syndrome precipitated by graded doses of acutely injected naloxone. In these experiments the concomitant treatment with morphine and proglumide or benzotript did not modify the occurrence of dependence. These observations are consistent with the hypothesis of CCK being an endogenous opiate antagonist, involved in the development of tolerance to morphine-induced analgesia but not of dependence. Moreover, tolerance to and dependence on morphine can be pharmacologically dissociated.

Evaluation of a new and potent cholecystokinin antagonist on motor responses of the guinea-pig intestine

The potency and selectivity of D,L-4-(3,4-dichloro-benzoyl-amino)-5-(dipentyl-amino)-5-oxo-pen tan oic acid (CR 1409) as a cholecystokinin (CCK) antagonist was investigated on motor responses of the longitudinal and circular muscles of the guinea-pig isolated ileum. CR 1409 was further used to examine whether nerve-mediated motor responses to electrical field stimulation or distension of the gut wall may involve the release of CCK-like peptides. CR 1409 (0.06-2.1 microM) antagonized longitudinal muscle responses to ceruletide (caerulein, a CCK-related decapeptide) in a concentration dependent and competitive manner (pA2 7.77); responses to CCK-octapeptide (CCK-8) were antagonized with a similar potency. Contractions of the circular muscle evoked by ceruletide were also blocked by CR 1409 (0.2-0.4 microM). Longitudinal muscle contractions in response to dimethylphenylpiperazinium, bethanechol, histamine, substance P, or 5-hydroxytryptamine (5-HT), and circular muscle contractions evoked by acetylcholine, 5-HT, substance P, or substance K were not altered by CR 1409 (0.4 microM). Longitudinal muscle contractions induced by electrical field stimulation (with pulses delivered at 0.05 and 1 Hz in the absence, and at 5 Hz in the presence of atropine) were not or only slightly reduced by CR 1409 (0.4 microM). Longitudinal contractions due to activation of extrinsic nerves by capsaicin remained unaltered in the presence of CR 1409 (0.4 microM). Reflex contractions of the circular muscle, induced by balloon distension and recorded orally to the site of distension, and peristaltic activity elicited by intraluminal infusion of Tyrode solution remained unaffected by CR 1409 (0.4 microM). 5 These findings indicate that CR 1409 is a potent and selective antagonist of CCK-like peptides in the guinea-pig ileum. The results do not provide any evidence that CCK-like peptides, released from extrinsic or intrinsic neurones, are involved in nerve-mediated contractions of intestinal muscle and in the peristaltic reflex.

Pharmacologic characterization of excitatory and inhibitory cholecystokinin receptors of the cat gallbladder and sphincter of Oddi

The pharmacologic properties and specificity of cholecystokinin (CCK) receptors of the biliary tract were investigated by testing various sulfated and desulfated CCK fractions and by using specific CCK-gastrin antagonists. Sulfated CCK-7 (5-80 pmol/kg) caused gallbladder contraction and sphincter of Oddi relaxation. Denervation with tetrodotoxin decreased the gallbladder response by 50% and changed the sphincter of Oddi response from relaxation to contraction. Desulfated CCK-7 (80-400 pmol/kg) caused a weak gallbladder contraction that was unaffected by tetrodotoxin. The gallbladder did not respond to CCK-3 (10-80 nmol/kg) or to CCK-2 (10-160 nmol/kg) in doses that completely relaxed the sphincter of Oddi. These doses, however, were 5-2000 times higher than the maximal dose of sulfated CCK-7. After denervation with tetrodotoxin, desulfated CCK-7 (10-400 pmol/kg) induced a weak sphincter of Oddi contraction even with doses five times greater than the maximal dose of sulfated CCK-7. The denervated sphincter of Oddi did not respond to CCK-3 (10-80 nmol/kg) or CCK-2 (10-160 nmol/kg). Furthermore, a continuous proglumide infusion (5-20 mg/kg X min) and bolus doses of dibutyryl cyclic guanosine monophosphate (250-1000 micrograms/kg) blocked the effect of sulfated CCK-8 on the gallbladder and sphincter of Oddi. Higher doses of these antagonists were needed, however, to block the CCK effect on the sphincter of Oddi than on the gallbladder. In contrast, high doses of desulfated CCK-7 (100 pmol/kg) or CCK-3 (200 nmol/kg) did not antagonize the effect of sulfated CCK-8 (10-80 pmol/kg) on the gallbladder. These findings suggest the existence of three sets of specific CCK receptors with molecular configuration requirements determined by the type of cell where these receptors are located: on the postganglionic cholinergic neurons, on the smooth muscle cells of the gallbladder, and sphincter of Oddi, or on the postganglionic noncholinergic, nonadrenergic inhibitory neurons.

Proglumide peptides and CCK antagonistic action in hog duodenal circular muscle

New proglumide peptides were synthesized and their inhibitory activity against the cholecystokinin (CCK)-induced relaxation was tested in duodenal circular muscles of hogs in order to locate the active moiety. Isotonic tension is reported as a percentage of the relaxation induced by CCK-4 (4.23 microM) or by Ca-free EGTA (2 mM). In R1-CONHCH(CH2CH2CO-R2)CON(CH2CH2CH3)2, P2-II(R1 = PhCH2O, R2 = Phe33-NH2), its D isomer and P3-I (R1 = Ph, R2 = Asp32-Phe33-NH2) had potent antagonistic activity (IC50 = 47.9 (32.4-72.4) microM, 25.1 (10.0-61.7) microM and 186 (141-240) microM, respectively). Benzotript, from another group of CCK antagonists had an IC50 of 52.5 (40.7-67.6) microM. P2-II (49 microM) or its D isomer (19.6 microM) antagonized non-competitively, and P3-I (168 microM) and benzotript (58.4 microM) antagonized competitively the CCK-4-induced relaxation. P3-I (84 or 168 microM) also antagonized competitively the CCK-8-induced relaxation. The amino acids of Tyr27, Trp30 and Phe33, separately, play important roles for agonist activity for relaxation. Tyr27 is the main relaxing group, Trp30 an antagonistic one and Phe33 is another relaxing one. In the proglumide skeleton, N,N-dipropylglutaramic acid acts like Trp30. Agonist, partial agonist and antagonist activities are exerted by these three groups and bulky substituents.

Affinity labeling of a novel cholecystokinin-binding protein in rat pancreatic plasmalemma using new short probes for the receptor

Previous biochemical characterizations of the cholecystokinin (CCK) receptor have used the "long" probe 125I-Bolton-Hunter-CCK-33 since it was the only CCK analogue with high affinity and high specific radioactivity which possessed an amino group available for chemical cross-linking. These studies have consistently identified a major binding protein of approximately 81 kilodaltons and have identified several minor proteins which were obtained under different cross-linking conditions and in different laboratories. Because the receptor-binding region of CCK-33 (carboxyl-terminal heptapeptide) is so far removed from the radiolabel and from available amino groups (positions 1 and 11), this probe carries potential for proteolytic cleavage of label from receptor and for labeling "near neighbors" instead of the binding site. We therefore designed two "short" probes for the CCK receptor. 125I-Bolton-Hunter-Lys-Gly-CCK-8 has an epsilon-amino group available for cross-linking. 125I-Tyr-[Thr28,Nle31]CCK-25-33 has an alpha-amino group for cross-linking and has the major advantage of being labeled by oxidative means, unique for CCK derivatives. Both radioiodinated decapeptides were purified by reverse-phase high pressure liquid chromatography to yield specific radioactivity of 2,000 Ci/mmol; demonstrated saturable, specific, and high affinity binding to rat pancreatic plasma membranes; and retained full biological activity to stimulate amylase secretion. Using a variety of cross-linking methods, these probes each identified the same Mr = 85,000-95,000 protein in rat pancreatic plasmalemma, and CCK-8 competed for this labeling in a concentration-dependent manner (IC50 = 1 nM). No change in apparent mobility of this band was observed under reducing or nonreducing conditions, suggesting lack of covalent attachment to other subunits. The Mr = 85,000-95,000 species migrated differently on sodium dodecyl sulfate gels than any of the components previously identified using 125I-Bolton-Hunter-CCK-33, confirming the novel nature of this binding protein. These short probes should be very useful for further characterization of CCK receptors on this and other tissues.

Carbachol regulates cholecystokinin receptor on pancreatic acinar cells

We have examined the effect of carbamylcholine on the binding of cholecystokinin (CCK) to dispersed acini from rat pancreas. The CCK receptor on pancreatic acini possesses two classes of binding sites. Simultaneous addition of carbamylcholine inhibited binding of CCK to acini due to an apparent loss of high affinity CCK binding sites. Atropine prevented the inhibitory effect of carbamylcholine, whereas calcium ionophore A23187 did not alter binding of CCK. 12-O-tetradecanoylphorbol-13-acetate (TPA) inhibited binding of CCK in the same manner as carbamylcholine. Inhibition by carbamylcholine was reversible and the recovery was time dependent. By contrast, inhibition of binding of CCK by TPA did not reverse after a 60-min incubation without the agent. These findings, at least in part, account for the inhibition of the CCK-induced stimulation of amylase secretion by carbamylcholine. The action of TPA on binding of CCK suggests the possible involvement of the activation of protein kinase C in the inhibition of binding.

Regional and cellular heterogeneity of cholecystokinin receptors mediating muscle contraction in the gut

The contractile action of cholecystokinin (CCK) on smooth muscle of the gut is either direct (gallbladder and gastric fundus) or both direct and neurally mediated (small intestine). These regional differences were used to characterize pharmacologically CCK receptors on smooth muscle cells and neurons of the gastric fundus, gallbladder, and ileum of the guinea pig. In circular and longitudinal ileal smooth muscle, tetrodotoxin was used to separate direct from neurally mediated contractile effects. Cholecystokinin receptors on smooth muscle cells were found in all locations. The muscle cells displayed a decreasing order of sensitivity to the C-terminal octapeptide of cholecystokinin as expressed in the median doses, and to the selective cholecystokinin antagonist, proglumide, as expressed in the inhibitory dissociation constants. The median doses of the octapeptide of cholecystokinin ranged from 5.5 nM in gallbladder muscle to 185 nM in circular ileal muscle; the corresponding inhibitory dissociation constants of proglumide ranged from 180 to 437 microM [corrected]. Cholecystokinin receptors on cholinergic neurons were confined to circular and longitudinal ileal muscle; the neurons were 80-300 times more sensitive to the octapeptide of cholecystokinin (D50's 0.5 and 2.3 nM) than the corresponding muscle cells, and 19-21 times more sensitive to proglumide (inhibitory dissociation constants, 20 microM [corrected]). The results provide clear evidence of cellular heterogeneity of cholecystokinin receptors (i.e., difference in sensitivity between muscle cells and neurons from the same location) as well as regional heterogeneity (i.e., difference in sensitivity between muscle cells from various locations).

Possible involvement of the CCK receptor in the benzodiazepine antagonism to CCK in the mouse brain

In mice, intraperitoneally injected chlordiazepoxide and proglumide, both of which are regarded as cholecystokinin (CCK) receptor antagonists in the peripheral tissues, dose-dependently inhibited the satiety induced by 200 ng of intracisternally administered CCK octapeptide (CCK8). Intraperitoneally administered diazepam (1 mg/kg) and/or Ro 15-1788 (5 mg/kg), a benzodiazepine antagonist, both prevented the elevation in the pain threshold induced by 1 microgram of CCK8. However, Ro 15-1788 did not antagonize the effect of diazepam that reversed the CCK-induced antinociception. Ro 15-1788 also inhibited the satiety induced by CCK8. From these results, it was considered that the antagonism, which was observed in the present work, of benzodiazepines and proglumide to CCK8 seemed to occur at the CCK receptor and not at the benzodiazepine receptor in the brain.

Effects of calcium mediated secretagogues on the growth of pancreatic acinar cells in vitro

Caerulein, CCK8, and gastrin, hormones which interact with the cholecystokinin receptor increased the growth of mouse pancreatic acinar cells in vitro. In contrast, bombesin, substance P, and carbachol, factors which interact with separate receptors, and stimulate pancreatic secretion similarly to CCK by mobilising intracellular Ca2+, did not have any effect on the growth of pancreatic acinar cells in vitro. These results suggest both a unique role for cholecystokinin in the physiological regulation of the pancreas and that the mechanisms that mediate the trophic effects of cholecystokinin are different from those that mediate secretion.

Effect of hydrocortisone on the maturation of cholecystokinin (CCK) binding and CCK stimulated amylase release in pancreatic acini of neonatal rats

Neonatal rat pancreata are not responsive to stimulation by cholecystokinin (CCK) and this has been shown to be due primarily to low binding of CCK to pancreatic acinar cells of rats of this age group. To see if hydrocortisone has any effect on the maturation of CCK binding and enzyme secretion, day-old rat pups were injected three times intraperintoneally with hydrocortisone at a dose of 5 mg/100 g body weight per dose and sacrificed 48 h after the first injection. Control age-matched pups were injected with 0.9% saline at the same volume and schedule as the hydrocortisone injected pups. The pancreatic weight, protein, and DNA contents were found to be significantly lower in the pups from the hydrocortisone-treated group than in the pups from the control group. The protein content per unit weight of DNA, however, was not different between the two. The maximal output of amylase under stimulation by 3 X 10(-10) M CCK was significantly higher in the dispersed acini prepared from the hydrocortisone-treated group as compared to dispersed acini prepared from the control (575 +/- 50 vs. 390 +/- 40% when expressed as a percentage of basal release). The maximal binding to 125I-BH-CCK was also significantly higher in the dispersed acini from the hydrocortisone group when compared to the dispersed acini from the control group (2.6 +/- 0.5 vs. 1.4 +/- 0.4%). Hydrocortisone, therefore, induces the precocious maturation of the secretory apparatus of the pancreatic acini, specifically the increase in capacity to bind and the greater responsiveness of the acini to CCK.

Tifluadom, a kappa-opiate agonist, acts as a peripheral cholecystokinin receptor antagonist

Tifluadom, a benzodiazepine kappa-opiate agonist, stereoselectively inhibited the binding of 125I-CCK to pancreatic membranes (IC50 = 47 nM). Several other opiate agonists were ineffective. Scatchard analysis indicated the inhibition of CCK binding by tifluadom was competitive in nature. Tifluadom (1 microM) did not displace 125I-CCK binding to brain tissue or 125I-gastrin binding to fundic glands. In the isolated guinea pig gallbladder, tifluadom antagonized CCK-8 induced contractions with an estimated pA2 of 6.8. These data demonstrate that tifluadom is a peripherally selective CCK antagonist. This unique action could contribute to its reported analgesic and appetite stimulatory properties.

Beta-carbolines selectively antagonize the cholecystokinin action in isolated guinea-pig gallbladder muscle

Two beta-carbolines, methyl beta-carboline-3-carboxylate (beta-CCM) and ethyl beta-carboline-3-carboxylate (beta-CCE), caused the parallel shift of the dose-response curve for cholecystokinin (CCK) in isolated guinea-pig gallbladder muscle. The Schild plot regarding the parallel shift in the dose-response curves had a regression line with a slope of 1.03 and a pA2 value of 5.17 for beta-CCE, while the method of van Rossum gave a pA2 value of 5.24 for beta-CCE and 5.53 for beta-CCM. Both the beta-carbolines protected CCK receptors in the gallbladder muscle from alkylation by dibenamine, but beta-CCM did not protect acetylcholine receptors from dibenamine alkylation. These results suggest that beta-CCM and beta-CCE, so-called inverse agonists of benzodiazepines (BZP), antagonize the CCK action in the gallbladder muscle in a competitive manner, and the antagonism takes place at CCK receptor sites. No spare receptors for CCK were found in the guinea-pig gallbladder muscle.

Structural features of various proglumide-related cholecystokinin receptor antagonists

Thirteen proglumide derivatives that varied in the length of the di-n-alkyl group and in the substitutions on the benzoyl moiety were tested for their ability to interact with guinea pig pancreatic cholecystokinin (CCK) receptors. Each derivative was more potent than proglumide. There was a close correlation between their abilities to inhibit CCK-stimulated amylase release and to inhibit binding of 125I-CCK. For the di-n-alkyl derivatives the relative potency was n-pentyl greater than n-hexyl greater than n-butyl greater than n-propyl. For the benzoyl moiety, adding two electron-withdrawing groups increased potency more than adding a single electron-withdrawing group or adding electron-donating groups. The 3,4-dichloro-di-n-pentyl derivative of proglumide was 1,300 times more potent than proglumide, and its action was specific, competitive, and it functioned as a CCK receptor antagonist in rat, mouse, and guinea pig pancreas. For all proglumide derivatives there was a good correlation (r = 0.84, P less than 0.001) between their abilities to inhibit CCK-stimulated amylase release and that previously reported for their abilities to inhibit CCK-induced gallbladder contraction. However, certain proglumide derivatives had a much higher affinity for the pancreatic CCK receptor than for the CCK receptor mediating gallbladder contraction. For other proglumide derivatives the pattern was reversed. These results demonstrate that both the di-n-alkyl group and the substitution on the benzoyl moiety of proglumide are equally important determinants of affinity and that derivatives such as the di-n-pentyl 3,4-dichloro analogue can be produced that are 1,300 times more potent than proglumide.(ABSTRACT TRUNCATED AT 250 WORDS)

[Decreased sensitivity of cholecystokinin receptors in the brain as affected by the prolonged administration of haloperidol]

The authors have used behavioural and radioreceptor methods of investigation, that helped to find correlates of the behavioural phenomena on the receptor level.