Do antagonists of pancreatic cholecystokinin receptors interact with central nervous system cholecystokinin receptors?

Different effects of CCK antagonists on gastric-acid response to CCK and pentagastrin

The role of CCK receptor subtypes in peptide-stimulated acid secretion was assessed in six unanesthetized rats. The CCK-stimulated acid secretion was not blocked by L-365,260, a CCKB/gastrin receptor antagonist, and was significantly increased by devazepide, a CCKA receptor antagonist, given alone or together with L-365,260. L-365,260, but not devazepide, blocked pentagastrin-stimulated acid secretion, and, when given together, devazepide abolished the effect of L-365,260. We conclude: 1) pentagastrin stimulates acid secretion through a gastrin-type receptor, but CCK may not, and 2) pentagastrin and CCK can stimulate acid secretion despite simultaneous blockade of CCKB/gastrin and CCKA receptors.

Spinal co-administration of cholecystokinin antagonists with morphine prevents the development of opioid tolerance

The effects of intrathecal (i.t.) co-administration of the cholecystokinin (CCK) antagonists lorglumide or proglumide with a "low" (1 microgram) and "high" (10 micrograms) dose of i.t. morphine on the development of opioid tolerance were determined using the rat tail-flick assay. Although co-injection of 7 ng lorglumide or 20 ng proglumide (doses which have been demonstrated to acutely enhance 1 microgram morphine, i.t.) were without effect, co-administration of 70 ng lorglumide or 64 ng proglumide with 1 microgram morphine for 6 days inhibited development of tolerance to this dose of opioid. Higher doses of CCK antagonists (1400 ng lorglumide and 1280 ng proglumide) were required to prevent the tolerance induced by 10 micrograms morphine. These findings provide further evidence that CCK mediates, at least partially, tolerance which develops to the analgesic effect of opioids and indicate the involvement of CCK pathways in the spinal cord. The results are also consistent with a mechanism in which the level of activation of compensatory, anti-opioid CCK circuitry is increased in proportion to the functional level of opioid pathways.

Cholecystokinin increases intracellular Ca2+ concentration in cultured striatal neurons

Although it has been established that pancreatic cholecystokinin (CCK) receptors are coupled to phosphatidylinositol turnover, the events which follow activation of CCK receptors in the central nervous system have not received much attention. In this paper, changes in intracellular Ca2+ concentration ([Ca2+]1) in response to CCK peptides were measured in single cultured rat striatal neuron by fura-2 fluorometry. CCK peptides dose-dependently increased [Ca2+]i in a monophasic manner. The order of the potencies of CCK peptides to increase [Ca2+]i was as follows: caerulein greater than CCK-8 greater than desulfated CCK-8 greater than CCK-4. The effect of caerulein was completely blocked in a Ca2(+)-depleted medium. In addition, omega-conotoxin GVIA completely inhibited the effect of caerulein, while neither nifedipine nor verapamil affected it. Our results indicate that CCK receptors couple to N-type voltage-sensitive Ca2+ channels in cultured rats striatal neurons.

Chronic administration of cholecystokinin antagonists reverses the enhancement of spinal morphine analgesia induced by acute pretreatment

The effects of acute and chronic (22 days) treatment with the cholecystokinin (CCK) antagonists proglumide and lorglumide on antinociception induced by intrathecal (i.t.) morphine were determined at weekly intervals with the rat tail-flick assay. On day 1, acute pretreatment with either proglumide (20 ng, i.t.) or lorglumide (7 ng, i.t.) enhanced morphine (1 microgram, i.t.) analgesia compared to saline (1 microliter, i.t.) pretreatment, but this facilitation was absent on days 8 and 15 of CCK antagonist treatment and was replaced by attenuation of opioid antinociception on day 22. Following termination of daily proglumide or lorglumide injections, normal (control) morphine response was observed after pretreatment with either CCK antagonist on days 29 and 36. Weekly co-administration of either drug with morphine had similar effects: opioid antinociception was initially enhanced on day 1, but this amplification was lost by day 8 and remained absent for the duration of the study (i.e., up to day 36). Inhibition of morphine analgesia, however, was not observed with this treatment paradigm. Chronic daily administration of either CCK antagonist alone did not lower nociceptive thresholds; further, normal opioid response was retained throughout the study in saline treated controls receiving morphine weekly. This study demonstrates that whereas acute i.t. administration of CCK antagonists enhances i.t. morphine antinociception, chronic treatment causes loss of facilitation or attenuation of opioid antinociception, suggesting that (1) compensatory alterations in CCK-opioid interactions develop during chronic CCK blockade and (2) CCK antagonists may not be useful adjuncts to opioid analgesics in the management of chronic pain in man.

L364,718 antagonizes the cholecystokinin-induced suppression of locomotor activity

To determine the role of CCK-A receptors in the cholecystokinin (CCK)-induced suppression of locomotor activity in the rat, the ability of the selective CCK-A receptor antagonist L364,718 to block these responses was investigated. Cholecystokinin octapeptide (CCK8) (10, 100 micrograms/kg IP) and caerulein (1, 5, 10 micrograms/kg IP) produced marked reductions in locomotor activity whereas cholecystokinin tetrapeptide (CCK4) (100 micrograms/kg IP) was without effect. The reductions in activity produced by CCK8 (10 micrograms/kg) and caerulein (10 micrograms/kg) were antagonized by L364,718 (100 micrograms/kg IP). In an open field test CCK8 (10 micrograms/kg IP) reduced locomotor activity and total number of rears and increased pause duration. These effects of CCK8 on open-field behaviour were also antagonized by L364,718 (100 micrograms/kg IP). It is concluded that L364,718 is a potent antagonist of the actions of CCK8 and caerulein on locomotor activity, suggesting that the effects of these peptides are mediated by a CCK-A receptor.

Unsulfated CCK-8 not blocked by proglumide or CR 1409 in the mouse abdominal irritant-induced stretching assay: possible central site of action

Previous studies have shown that unsulfated cholecystokinin octapeptide (CCK-8-U) shares with the sulfated octapeptide (CCK-8-S) and the carboxyl-terminal tetrapeptide (CCK-4) the ability to block abdominal irritant-induced stretching when administered intracerebroventricularly. The effects of CCK-8-U, however, are not naloxone-reversible and do not appear upon systemic administration. To assess the hypothesis that the antistretching effects of CCK-8-U are mediated by central-type (CCK-B), rather than peripheral-type (CCK-A) receptors, the present experiments examined the reversal of these effects by CR 1409, a CCK receptor antagonist with in vitro selectivity for CCK-A receptors, and by proglumide. Both antagonists, when administered ICV, blocked the antistretching effects of CCK-8-S and CCK-4 (ICV), but not those of CCK-8-U. CR 1409 was approximately 40 times more potent against CCK-8-S by the ICV route than subcutaneously, indicating a likely action on CCK-A receptors in the brain. The effects of morphine, bombesin and neurotensin (ICV) were not blocked by CR 1409, indicating specificity for CCK receptor-mediated effects. The antistretching effects of CCK-8-U do not appear to be mediated by CCK-A receptors, and the possibility of a CCK-B receptor site of action must be considered.

Effects of cholecystokinin and pentagastrin on rat hippocampal neurones maintained in vitro

Extracellular and intracellular recordings from CA1 neurones of rat hippocampal slices were undertaken to assess the relative potencies of cholecystokinin fragments. The CCK peptides displayed a large variability in their effects on extracellularly recorded population spikes. Intracellular recordings from CA1 neurones revealed a more consistent excitant action of these compounds. The C-terminal octapeptide CCK-8S, the tetrapeptide CCK-4 and pentagastrin were all found to be agonists when applied to hippocampal CA1 neurones maintained in vitro. Repeated application of the peptide fragments to the same cell resulted in a loss of activity. Neurones pre-treated with a CCK peptide showed no response to an application of a second, different, CCK fragment indicative of receptor cross-desensitization. Depolarisations induced by the excitatory amino acid L-glutamate remained unaffected by peptide application. These data suggest that the CCK fragments are agonists at rat CA1 neurones and share a common mode of action distinct from that of the excitatory amino acid L-glutamate.

Proglumide has access to brain and antagonizes the central satiety effect of cholecystokinin octapeptide in the dog

Intra-third cerebroventricularly administered cholecystokinin octapeptide (CCK-8) decreased food intake through central mechanisms in the dog. Proglumide, administered intravenously, did enter into cerebrospinal (ventricular) fluid, and partially, but significantly, reversed this effect. CR1409, one of the newly synthesized glutaramic derivatives, blocked CCK-8-induced satiety more strongly than proglumide. These results indicate that systemic proglumide and CR1409 result in antagonism of the central CCK receptor for satiety in the dog.

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.

Pharmacological examination of cholecystokinin (CCK-8)-induced contractile activity in the rat isolated pylorus

The actions of cholecystokinin (CCK) in the production of a satiety-like state have been suggested to be mediated via receptors for CCK which are located in the pylorus. We investigated the actions of CCK and other pharmacological agents upon the isolated rat pylorus in vitro. We used the change in isometric tension of the tissue preparation (contraction amplitude) as the measure of the effects of the pharmacological agents. Cholecystokinin COOH-terminal octapeptide (CCK-8) was observed to elicit contraction in a dose-dependent manner, with the half-maximal dose (ED50) in the vicinity of 1 nM. Rapid desensitization to CCK was observed. The contraction amplitude was atropine-independent, and was not significantly antagonized by a wide variety of other pharmacological agents. The Na+-channel blocker tetrodotoxin was without effect upon contractile amplitude, as was the K+-channel blocker 4-aminopyridine, except at very high concentrations. Neurotensin, bombesin, and the substance P and bombesin antagonist spantide all elicited contraction in the isolated tissue; neurotensin had a similar potency to CCK-8 and bombesin was 10-15-fold less potent than CCK-8. Unsulfated CCK-8 was at least 170-fold less potent than sulfated CCK-8 and tetragastrin was at least 500-fold less potent than CCK-8. These results suggest that pyloric CCK receptors, which appear to have a pharmacological profile typical of peripheral CCK receptors, may have a physiological role in the peptidergic control of gastric emptying in the rat.

Phenylethylamide derivatives of the C-terminal tetrapeptide of gastrin. Potent inhibitors of gastrin-stimulated acid secretion

Peptide analogues of the C-terminal tetrapeptide of gastrin in which the phenylalanine had been replaced were synthesized and their biological activity on acid secretion evaluated. Compounds Boc-Trp-Leu-Asp phenylethylamide 6, Boc-beta-Ala-Trp-Leu-Asp phenylethylamide 9, Boc-Trp-Leu-Asp p-fluorophenylethylamide 19, Boc-Trp-psi(CH2NH)-Leu-Asp phenylethylamide 23, Boc-Trp-Leu-Asp 2,2-diphenylethylamide 15, and Boc-D Trp-Leu-Asp 2,2-diphenylethylamide 21, in which the phenylalanine had been replaced by phenylethylamine, p-fluorophenylethylamine or 2,2-diphenylethylamine were synthesized. None of these derivatives showed activity on acid secretion in the anaesthetized rat at doses as high as 5 mg/kg. However, they were potent inhibitors of gastrin-induced acid secretion, with ED50 varying from 0.1 to 0.6 mg/kg.

Proglumide (gastrin and cholecystokinin receptor antagonist) inhibits insulin secretion in vitro

CCK-8 and its desulfated analog (des-CCK-8) increase insulin secretion from isolated rat pancreatic islets in the presence of 8.3 mM glucose in a concentration-dependent manner. Proglumide (DL-4-benzamido-N,N-dipropylglutaramic acid), a gastrin and cholecystokinin (CCK) receptor antagonist, inhibits the synergistic effect of CCK on insulin release in the presence of 8.3 mM glucose; its EC50 (half-maximal effective concentration) was 1.2 +/- 0.4 mM. Its effect is specific in that it does not inhibit the glucose- or GIP (glucose dependent insulinotropic peptide) induced insulin secretion to a major degree. CCK-8, des-CCK-8 and proglumide compete for binding of 125I-CCK-33 to rat pancreatic islets; the IC50 of proglumide was 0.8 mM. The affinity of proglumide is in the range of both its EC50 for inhibition of insulin secretion and its IC50 in other in vitro systems tested so far (exocrine pancreas, gall bladder, cortex). Its inhibitory effect presumably is not a gastrin antagonizing effect since gastrin does not stimulate insulin secretion. The data therefore indicate that proglumide should be monitored for diabetic effects in vivo.