The CCKA receptor antagonist devazepide does not modify opioid self-administration or drug discrimination: comparison with the dopamine antagonist haloperidol

We previously reported that the selective cholecystokininA (CCKA) receptor antagonist, devazepide, blocked the acquisition of a morphine conditioned place preference (ref 28). An interpretation of this finding is that devazepide may either affect an opioid discriminative stimulus and/or modify the rewarding properties of opioids. The present study was designed to investigate these issues by determining the effect of equivalent doses of devazepide in a morphine drug discrimination paradigm and a model of heroin self-administration. In each case, devazepide (0.001-1 mg/kg) was ineffective, i.e there was no antagonism of a morphine discriminative cue, and in a separate group of rats trained to self-administer heroin (0.03 mg/kg/infusion, FR5 schedule, 1h per day), devazepide did not alter the pattern of heroin responding. Because of evidence implicating an interaction between accumbens CCK and dopamine (DA) systems and evidence suggesting an apparent differential involvement of DA in opioid place conditioning, self-administration and drug discrimination behaviour, the effect of the DA antagonist haloperidol was examined in the latter two paradigms. In each test, haloperidol produced an effect inconsistent with a direct DAergic involvement. In a final study the CCKB antagonist L365-260 was also found not to affect an opioid discriminative cue. The present results therefore cast doubt on the potential utility of selective CCKA antagonists as treatments for opioid abuse, and further suggest that CCKB antagonists may not potentiate the subjective effects of opioids, an important finding considering that such drugs have been proposed as adjuncts to opioid therapy for the treatment of pain relief.

CCK receptor activation may prevent tolerance to morphine in mice

Different groups of mice were treated with morphine (50 mg/kg s.c.) once daily for 1, 2, 3, 4 or 5 days, in order to develop tolerance to the drug. The antinociceptive effect of morphine (9 mg/kg s.c.) was tested 24 h after each dose of the drug administration. Tolerance to morphine reached its peak on the 4th day. Daily pretreatment of animals for a period of 4 days with different doses of cholecystokinin octapeptide (CCK-8; 0.001, 0.01, 0.05 and 0.1 mg/kg s.c.), caerulein (0.0001, 0.001, 0.005 and 0.01 mg/kg s.c.) but not unsulfated cholecystokinin octapeptide (0.001, 0.01 or 0.1 mg/kg s.c.) 30 min before daily administration of morphine (50 mg/kg s.c.) prevented the development of tolerance. A group of animals received a single dose of caerulein (0.005 mg/kg), CCK-8 (0.01 mg/kg) or unsulfated CCK-8 (0.01 mg/kg) 30 min before morphine injection (50 mg/kg s.c.) on the 3rd or 4th day. In these animals, which were tested for antinociception on the 5th day, tolerance to the drug (3, 6 and 9 mg/kg s.c.) was also decreased by caerulein, CCK-8 but not unsulfated CCK-8. In a group of mice in which peptides were administered 30 min prior to the doses of morphine (3, 6 or 9 mg/kg s.c.) on the 5th day, similar results were obtained. The results of the present study indicate that activation of both CCKB and CCKA receptors may prevent the development of tolerance to morphine, and the sulfate group in the CCK-8 molecule may be essential for the tolerance inhibition.

Caerulein changes morphine-induced antinociception depending on pretreatment times

1. In the present study, the effect of caerulein (CLN) on morphine analgesia has been tested. 2. Different doses of morphine produced antinociception in a dose dependent manner. When animals were pretreated with CLN 5 min before morphine administration, the morphine response was decreased. However, when CLN was injected 30 or 60 min prior to morphine, the drug effect was increased. 3. Naloxone, sulpiride, metergoline or proglumide decreased the potentiation of morphine response caused by CLN. CLN, proglumide, sulpiride, metergoline and naloxone alone did not exert any effect on tail-flick latency. 4. It is concluded that, depending on pretreatment times of CLN administration the response of morphine was decreased or increased and D-2 dopamine, serotonin and/or CCK receptors may be involved in the potentiation of morphine response induced by CLN.

Effects of BOC-CCK-4 and L 365.260 on cortical 5-HT release in guinea-pigs on exposure to the elevated plus maze

The elevated plus maze is a well-established model of anxiety, with previous results showing that guinea-pigs handled daily from birth exhibit behaviour in this test similar to rats. In the present microdialysis study exposure of the guinea-pig to the elevated plus maze increased extracellular 5-HT in the lateral prefrontal cortex. The CCK-B receptor agonist BOC-CCK-4 (10 micrograms/kg) produced 'anxious' behaviour and potentiated the rise in 5-HT observed on exposure to the X-maze. The basal release of cortical extracellular 5-HT was not affected by BOC-CCK-4. Pretreatment with the selective CCK-B antagonist L 365.260 (100 micrograms/kg) antagonized both the 'anxious' behaviour and the neurochemical changes induced by BOC-CCK-4 while L 365.260 alone produced 'anxiolytic' behaviour, decreased basal extracellular 5-HT and prevented the increase in extracellular 5-HT seen when the guinea-pigs were exposed to the X-maze. Our results show that CCK-B receptor stimulation and blockade induce changes in central extracellular 5-HT levels associated with 'anxious' and 'anxiolytic' behaviour, respectively.

Inhibition of pro-cholecystokinin (CCK) sulfation by treatment with sodium chlorate alters its processing and decreases cellular content and secretion of CCK 8

Pro-cholecystokinin (CCK) has three sulfated tyrosine residues. Sulfation of the tyrosine residue in CCK 8 is known to be important for its activity at CCK A receptors. The role of these sulfated tyrosines in the sorting and processing of pro-CCK was examined by treatment of CCK-secreting rat thyroid medullary carcinoma cells with 10 nM sodium chlorate (a non-toxic inhibitor of tyrosine sulfation). This treatment caused a 50% decrease in the cellular content of immunoreactive CCK and an 80% decrease in its secretion. Sephadex G-50 chromatography of cellular extracts and culture media showed a selective depletion of CCK 8. There was a comparative sparing of CCK 33 and larger molecular forms in cellular extracts which was not observed in the media. These results suggest that the sulfation of the tyrosines of pro-CCK is clearly important for the correct sorting and/or processing of pro-CCK. The pattern of immunoreactive CCK peptides seen with chlorate treatment is consistent with the substrate specificity of a recently identified putative CCK cleaving enzyme and suggests that unsulfated pro-CCK is not efficiently processed to CCK 8 in vivo. The large decrease in CCK content and secretion observed with sodium chlorate may also be due to inefficient sorting of unsulfated pro-CCK into secretory vesicles.

Antidepressant-like effects of CCKB antagonists in mice: antagonism by naltrindole

1. The effects of selective CCKB agonists, BC 264 and BC 197 were investigated in the conditioned suppression of motility test in mice, an animal model used to select antidepressant drugs. The results showed that both CCKB agonists at doses of 3 and 30 micrograms kg-1, accentuated the suppression of motility in shocked mice and did not modify the behaviour of non-shocked mice. The effects of BC 264 were suppressed by L-365,260. 2. L-365,260 alone, at doses of 0.2 and 2 mg kg-1 decreased motor inhibition in shocked mice and had no effect in non-shocked mice. 3. The effects of L-365,260 observed in shocked mice were suppressed by naltrindole, a selective antagonist for delta-opioid receptors, suggesting the occurrence of physiological adverse interactions between CCK and opioid systems. 4. Together, these results suggest that CCKB antagonists could block centrally located CCKB receptors to produce antidepressant-like effects which could indirectly involve delta-opioid receptor stimulation.

FPL 14294: a novel CCK-8 agonist with potent intranasal anorectic activity in the rat

Cholecystokinin octapeptide (CCK-8) induces satiety in many species including man. However, its therapeutic utility is restricted due to its short biological half-life and poor bioavailability. FPL 14294 [4-(sulfoxy)-phenylacetyl(MePhe6)CCK-6] is a CCK analog with enhanced metabolic stability that was comparable to CCK-8 in potency to contract isolated gallbladder and in affinity at the CCK-A and CCK-B receptor. However, FPL 14294 was more than 200 times more potent than CCK-8 in inhibiting 3-h feeding in 21-h fasted rats. FPL 14294 also possessed intranasal anorectic activity at 5 micrograms/kg, while CCK-8 was inactive at doses up to 500 micrograms/kg. Anorectic activity was inhibited by pretreatment with a CCK-A antagonist (MK-329) but not by a CCK-B antagonist (L365,260). The anorectic effects of CCK-8 and FPL 14294 were the result of a direct effect on feeding and not caused indirectly by effects on water intake. These results indicate that FPL 14294 is a potent, intranasally active, anorectic agent whose enhanced in vivo potency over that of CCK-8 may reflect differences in stability, bioavailability, or receptor kinetics.

Cholecystokinin octapeptide (CCK-8) injected into a cerebral ventricle induces a fever-like thermoregulatory response mediated by type B CCK-receptors in the rat

In conscious female Wistar rats with chronic lateral cerebroventricular cannula, the thermoregulatory effects of CCK-8, ceruletide and prostaglandin E1 (PGE1) were studied. In addition, the possible involvement of type A or type B receptors of CCK-8 in thermoregulatory effects of PGE1 and CCK-8 was also investigated. In the normothermic rat an intracerebroventricular (i.c.v.) injection of CCK-8 or ceruletide induced a thermogenic response with tail-skin vasoconstriction and a resulting rise in colonic temperature (Tc). There was a significant negative correlation between the starting level of Tc and the extent of rise in Tc following an i.c.v. administration of PGE1, CCK-8 or ceruletide. Subcutaneously injected CCK-8 caused decreases in Tc in a cool ambient temperature as also described by others. The fever-like response to i.c.v. injected CCK-8 was attenuated by a CCK type B receptor blocker, but not by a CCK type A receptor blocker. Conversely, the hypothermic response to peripherally administered CCK-8 was attenuated by a type A receptor blocker, but not by a type B receptor blocker. Neither of these CCK-receptor blockers influenced the fever caused by an i.c.v. injection of PGE1. It is concluded that in normothermic rats the thermogenic response observed after i.c.v. injection of CCK-8 and ceruletide is the most likely central thermoregulatory change mediated by CCK type B receptors, while the well-known hypothermic response observed after peripheral injection of these peptides might also be explained by their direct effect on variables influencing some of the thermoregulatory effector mechanisms at the periphery.

A quantitative structure-activity relationship study of ligands exhibiting agonist and antagonist actions with cholecystokinin-receptors

Observed biological activities of substituted phenyl urea/thiourea tetrapeptides as agonists with the cholecystokinin-alimentary canal (CCK-A) receptor, and (R)-4-benzamido-5-oxopentanoic acid derivatives with both peripheral (CCK-A) and the central (CCK-B) (brain) receptors have been shown to be correlated with various physicochemical, e.g. pi, sigma, and structural, e.g. Vw and dummy, I, parameters. These results were, then interpreted to predict promising criteria for having ligands with better affinity with the CCK receptors.

Cholecystokinin and neuropeptide Y receptors on single rabbit vagal afferent ganglion neurons: site of prejunctional modulation of visceral sensory neurons

A [125I]cholecystokinin (CCK) analog and [125I]peptide YY (PYY) were used to localize and characterize CCK and neuropeptide Y (NPY) receptor binding sites in the rabbit vagal afferent (nodose) ganglion. High concentrations of CCK and NPY binding sites were observed in 10.6% and 9.2% of the nodose ganglion neurons, respectively. Pharmacological experiments using CCK or NPY analogs suggest that both subtypes of CCK (CCK-A and CCK-B) and NPY (Y1 and Y2) receptor binding sites are expressed by discrete populations of neurons in the nodose ganglion. These results suggest sites at which CCK or NPY, released in either the nucleus of the solitary tract or a peripheral tissue, may modulate the release of neurotransmitters from a select population of visceral primary afferent neurons. Possible functions mediated by these receptors include modulation of satiety, opiate analgesia, and the development of morphine tolerance.

Subdiaphragmatic vagotomy does not prevent the anti-exploratory effect of caerulein in the elevated plus-maze

We compared the action of subdiaphragmatic vagotomy upon the anti-exploratory and motor depressant effects of caerulein, an agonist of cholecystokinin (CCK) receptors, in male rats. Vagotomized rats entered more frequently into the open arms of elevated plus-maze compared to intact control rats. Caerulein (1 microgram/kg subcutaneously (s.c.)) significantly suppressed the exploratory behaviour in vagotomized rats but not in intact and sham-operated rats. In contrast, subdiaphragmatic vagotomy did not change the locomotor activity of rats in open field compared to intact and sham-operated animals. At a higher dose (10 micrograms/kg s.c.), the caerulein pretreatment markedly decreased the number of line crossings, rearings and head-dippings of intact animals in open field. In sham-operated rats caerulein also suppressed the locomotor activity, whereas in vagotomized rats it only tended to reduce the frequency of rearings. Consequently, the present study revealed the different action of vagotomy upon the motor depressant and anti-exploratory effects of caerulein. These results support the view that CCKA receptors in the gastrointestinal tract are mediating the motor depressant, whereas CCKB receptors in the brainstem are involved into the mediation of anti-exploratory effect of caerulein.

Peptides and anxiety: a dose-response evaluation of pentagastrin in healthy volunteers

A large body of data suggest that brain cholecystokinin (CCK) systems are involved in the regulation of anxiety, and numerous studies have demonstrated that CCK-4, a CCKB agonist, reliably induces panic attacks in patients with panic disorder. Recently, pentagastrin, a commercially available CCKB agonist, has been reported to have similar anxiogenic properties. To further explore the utility of pentagastrin as a challenge agent and to determine whether its effects are dose-related, a dose-response study was conducted in ten healthy volunteers. Pentagastrin (0.2 microgram/kg, 0.6 microgram/kg and 1.0 microgram/kg) and inactive placebo were infused over one minute on four separate challenge days in a double-blind fashion. Subjects received pentagastrin while participating in a structured social interaction task. Repeated measures of anxiety, blood pressure, pulse, ACTH, and cortisol were taken at baseline and postinfusion. Pentagastrin administration led to increases in anxiety, pulse, ACTH, cortisol and physical symptoms of panic, in a dose-related manner. Participation in the social interaction task led to increases in measures of anxiety as well as increases in pulse and blood pressure. Few differences were found between the 0.2 microgram/kg dose of pentagastrin and placebo, or between the 0.6 microgram/kg and the 1.0 microgram/kg doses of pentagastrin. These findings support the notion that CCK systems are involved in the regulation of anxiety, and suggest that the 0.6 microgram/kg dose may be optimal for increasing symptoms of anxiety while minimizing unpleasant side effects. The powerful anxiogenic effects of the social interaction task underscore the importance of contextual variables in challenge studies.

Biological actions of cholecystokinin

Cholecystokinin (CCK) has emerged as an important mammalian neuropeptide, localized in peripheral organs and in the central nervous system. This review presents an overview of the molecular aspects of CCK peptides and CCK receptors, the anatomical distribution of CCK, the neurophysiological actions of CCK, release of CCK and effects of CCK on release of other neurotransmitters, and the actions of CCK on digestion, feeding, cardiovascular function, respiratory function, neurotoxicity and seizures, cancer cell proliferation, analgesia, sleep, sexual and reproductive behaviors, memory, anxiety, and dopamine-mediated exploratory and rewarded behaviors. Human clinical studies of CCK in feeding disorders and panic disorders are described. New findings are presented on potent, nonpeptide CCK antagonists, selective for the two CCK receptor subtypes, which demonstrate that endogenous CCK has biologically important effects on physiology and behavior.

Both low- and high-affinity CCK receptor states mediate trophic effects on rat pancreatic acinar cells

Cholecystokinin (CCK) stimulates the growth of pancreatic acinar cells. However, the molecular mechanisms involved in this trophic action are unknown. CCK binds to both high- and low-affinity receptor states, and these two states appear to activate separate sets of intracellular messengers and have opposite effects on amylase release. JMV-180 is a CCK analogue that interacts in the rat with the high-affinity state as an agonist and the low-affinity state as an antagonist. In the current study, CCK octapeptide (CCK-8) and JMV-180 were tested for their ability to stimulate the growth of rat pancreatic acinar cells in primary culture. CCK-8 stimulated [3H]thymidine incorporation into DNA in a dose-dependent manner. Effects were observed with 0.3 nM, and maximal increases were seen at 3 nM CCK-8 (442 +/- 53% of control, n = 5, P < 0.01). JMV-180 also stimulated DNA synthesis. Effects were noted with 10 nM, and a maximal increase of 267 +/- 82% (n = 4, P < 0.01) of control was stimulated by 100 nM JMV-180. These data with JMV-180 indicate that the high-affinity receptor state for CCK is capable of stimulating DNA synthesis. However, within the same experiment the effects of CCK were always significantly greater than those of JMV-180. To test whether CCK has an additional effect through interactions with the low-affinity state, the effects of a combination of JMV-180 with a maximal dose of CCK-8 were examined. JMV-180 inhibited the maximal effect of CCK-8 in a dose-dependent manner with a maximal inhibition occurring with 1 microM JMV-180. The effects of the combination of 3 nM CCK-8 and 1 microM JMV-180 were no greater than those of JMV-180 alone. Taken together these data indicate that CCK-mediated increases in DNA synthesis in rat pancreatic acinar cells in vitro occur by interactions with both high- and low-affinity receptor states.

Autoradiographic localization of CCK-8 binding sites in the rat brain: effects of chronic methamphetamine administration on these sites

The effects of chronic methamphetamine (MAP) administration (at a dose of 4 mg/kg for 14 days) on [3H]pCCK-8 binding sites in the rat brain were investigated by an in vitro quantitative receptor autoradiographic technique. The number of [3H]pCCK-8 binding sites was significantly reduced in layers III and IV of the medial frontal, anterior, and posterior cingulate cortices, in layers II-IV of the retrosplenial cortex, in layers III-VI of the dorsal insular cortex, and in the reticular nucleus of the thalamus, compared to these numbers in a control group of rats that received physiologic saline. Further, chronic methamphetamine administration led to a significant increase in the number of these binding sites in layer I of the entorhinal cortex. These findings indicate the CCK peptides in the limbic lobe may be closely related to the development of the behavioral changes associated with methamphetamine sensitization. In addition, these results provide supporting evidence for the involvement of the limbic system in the pathophysiology of schizophrenia.

C-terminal calcitonin gene-related peptide fragments and vasopressin but not somatostatin-28 induce miosis in monkeys

The miotic effects of C-terminal calcitonin gene-related peptide (CGRP) fragments, somatostatin-28 and vasopressin have been evaluated with special attention being paid to possible interactions with cholecystokinin (CCK)A receptors. The peptides were injected intracamerally to anesthetized monkeys pretreated with indomethacin and atropine. CGRP-(32-37) induced a miosis with a potency 1000 times lower than that previously found with sulphated CCK-8. Two other fragments, CGRP-(30-37) and CGRP-(31-37), also had miotic properties. The CGRP-(32-37)-induced miosis was antagonized by the CCKA receptor antagonist loxiglumide. No contractile effect was elicited by 67 pmol-7.4 nmol somatostatin-28. Vasopressin (360 pmol) caused a small reduction in pupil size. Loxiglumide pretreatment did not affect the reduction in pupil size but a vasopressin receptor antagonist partly inhibited the response. The results indicate that CGRP-(32-37) is a miotic with low potency but high efficacy in the monkey eye, probably interacting with CCKA receptors, and that vasopressin is a mitotic with low potency and efficacy, probably acting via vasopressin receptors.

Role of gastrin and cholecystokinin receptors in regulation of peptone-stimulated gastric acid secretion in conscious rats

With the availability of selective gastrin/CCKB (L365,260) and CCKA (L364,718) receptor antagonists the present study was designed to investigate the role of gastrin and cholecystokinin (CCK) receptors in meal-stimulated gastric acid secretion. Gastric acid output was measured by continuous intragastric titration in conscious rats. Vehicle (dimethylsulfoxide/saline, 3:1), L365,260 (3 or 9 mg/kg), or L364,718 (1 mg/kg) was given by i.v. bolus injection. Basal acid output was strongly inhibited by both doses of L365,260 while L364,718 had no effect. Intragastric peptone (4%, w/v) increased acid secretion 40-65% of the response to a maximal dose (2.5 nmol/kg per h) of gastrin-17. L365,260 completely abolished gastrin-17 stimulated acid secretion and partially inhibited peptone-induced acid secretion. Blockade of CCKA receptors by L364,718 did not affect peptone-stimulated acid output. This study demonstrates that gastrin/CCKB receptors are important in regulating basal acid secretion in the conscious rat while CCKA receptors do not appear to influence basal or peptone-stimulated gastric acid secretion. Blockade of gastrin/CCKB receptors partially inhibits intragastric meal-stimulated acid secretion indicating that the gastrin/CCKB receptor has a physiological role as mediator of food-stimulated acid secretory response in conscious rats.

Biomolecular advances in gastrointestinal hormones

Gastrointestinal hormones are chemical messengers that regulate a broad range of physiologic functions. Although primarily expressed within tissues of the gut, these peptide hormones are widely distributed throughout the body and act on multiple target tissues. Furthermore, these regulatory peptides can exist in multiple molecular forms that may bind to multiple cell-surface receptors coupled to one of several possible signal transduction systems leading to diverse biologic responses. With such an expansive field to study, it is not surprising that gut endocrinologists have embraced the new techniques that are emerging from the revolution of molecular biology. Beginning with the first construction of a recombinant DNA molecule by Paul Berg in 1971, molecular biology has developed many new techniques that have been rapidly adopted by gut endocrinologists to enable a more detailed understanding of gastrointestinal function. The merging of these two fields has led to a new area of research, molecular gut endocrinology, or the study of gut physiology and endocrinology at the level of individual molecules (ranging from polypeptide-surface receptors to small-molecule second messengers to DNA sequences). Gut cells are constantly bombarded by numerous hormones, and the tightly regulated physiologic status of each cell is becoming more clearly understood.

Voluntary intake and gastric emptying in pigs: effects of fat and a CCK inhibitor

The influence of the cholecystokinin (CCK) antagonist MK-329 (0.1 mg/kg) on short-term control of voluntary food intake and gastric emptying was studied in five pigs. Arterial injection of MK-329 abolished the inhibition of intake resulting from duodenal infusion of emulsified fat (Intralipid, 24 g/h). However, MK-329 only reduced the inhibition of dry matter (DM) and liquid emptying, and hence increased stomach volume at satiety. Intralipid infusion decreased the rise in gastric pressure during feeding. All these changes are consistent with endogenous CCK, released by Intralipid, inhibiting intake independent of the concomitant slowing of gastric emptying. MK-329 alone significantly increased intake using two different diets, but had no effect on gastric emptying so that gastric volume at satiety was significantly increased. These results suggest that endogenous CCK may be part of short-term satiety control in the pig.

Partial agonism by gastrin for a cholecystokinin receptor mediating pepsinogen secretion

Isolated gastric glands from rabbit were used to characterize the functional cholecystokinin (CCK)-like peptide receptors that mediate pepsinogen secretion. Pepsinogen secretion was stimulated by both CCK octapeptide sulfate (CCK-8) and A-71378, a selective CCK-A-type receptor agonist, with similar mean effective doses (1.0 and 0.8 nM, respectively). Compared with CCK-8, gastrin-17 (G-17-I) showed reduced potency and only partial efficacy for stimulation of pepsinogen secretion while inhibiting the maximal CCK-8-stimulated response. The nonpeptide inhibitors, asperlicin and L-364,718, inhibited pepsinogen secretion with identical pA2 values for antagonism of both CCK and gastrin, indicating that both peptides interact with the same functional receptor. Specific binding of [3H]CCK-8 to isolated chief cell membranes was displaced fully by both CCK and gastrin, indicating full receptor occupancy by both peptides. A novel synthetic peptide analogue, pseudogastrin [(Glu)5-Ala-Tyr-Nle-Gly-Trp-Nle-Asp-Phe-NH2], was used to investigate the structural basis for the lower potency and efficacy of G-17-I. The potency of CCK and gastrin analogues for pepsinogen secretion was found to be dependent on both sulfation of a tyrosine residue and the position of the tyrosine residue relative to the COOH-terminal phenylalanine amide. The efficacy appears to be determined partially by the extended NH2-terminal sequence of G-17-I. The results of the present study are interpreted to show that pepsinogen secretion is mediated by a CCK-A-type receptor and gastrin acts at the same receptor as a partial agonist.

A cloned CCK-A receptor transduces multiple signals in response to full and partial agonists

Chinese hamster ovary (CHO) cells, stably transfected with the cloned rat CCK-A receptor, were used to study signal transduction events initiated by cholecystokinin octapeptide (CCK-8) and the partial agonist JMV-180. In single CHO-CCK-A cells loaded with fura-2, superfusion of CCK-8 (10 pM-1 nM) resulted in an increase in intracellular Ca2+ concentration ([Ca2+]i). At CCK-8 concentrations < 100 pM, the signal consisted of [Ca2+]i oscillations. At higher concentrations, CCK-8 induced a typical biphasic response consisting of a large peak followed by a lower sustained plateau. Superfusion of JMV-180 also resulted in an increase in [Ca2+]i; in contrast to acinar cells this increase did not consist exclusively of [Ca2+]i oscillations. Both CCK-8 and JMV-180 increased polyphosphoinositide hydrolysis, although JMV-180 stimulated formation of only 10% as much [3H]inositol phosphates. [Ca2+]i signals stimulated by both CCK-8 and JMV-180 were blocked by the aminosteroid U-73122. CCK-8 (1-10 nM) increased formation of adenosine 3',5'-cyclic monophosphate (cAMP) and release of arachidonic acid in CHO-CCK cells. These increases were not mimicked by JMV-180 (10 microM). Furthermore, no cAMP formation or arachidonate release could be detected when cells were incubated with both JMV-180 and CCK-8. These data indicate that in CHO-CCK-A cells, unlike acinar cells, both CCK-8 and JMV-180 increase [Ca2+]i by similar mechanisms. However, the CCK-A receptor can differentially recognize and then activate discrete transduction pathways on binding of these two agonists.

The effect of cholecystokinin on intracellular Ca2+, membrane-associated protein kinase-C activity, and progesterone production in chicken granulosa cells

Nerve fibers immunoreactive for cholecystokinin (CCK) have been observed in the rat ovary, but the function of this gut peptide in the ovary is not known. These studies were designed to investigate the effects of the CCK C-terminal octapeptide (CCK-8) on the intracellular calcium ion concentration ([Ca2+]i), protein kinase-C (PKC) activity, and progesterone secretion in granulosa cells obtained from the two largest preovulatory follicles (F1 and F2) of hens. [Ca2+]i was measured in cells loaded with the Ca(2+)-responsive fluorescent dye fura-2. The resting [Ca2+]i in these cells was 96 +/- 5 nM. There was a rapid (i.e. within 5-10 sec) 2- to 4-fold increase in [Ca2+]i in 70% of the cells examined after the addition of 10(-7) M CCK-8. The CCK-8-triggered [Ca2+]i transient was not affected by incubating the cells in Ca(2+)-free medium containing 2 mM EGTA or by pretreating the cells with a Ca2+ channel blocker, such as La3+ (1 mM) or D600 (100 microM). The CCK-8-triggered [Ca2+]i surge was abolished by pretreating the cells with the inhibitor of inositol phospholipid hydrolysis, neomycin (1.5 mM), the CCK antagonists proglumide (1 mM) and benzotript (1 mM), or pertussis toxin (50 ng/ml for 12 h). Incubating granulosa cells with CCK-8 (2 x 10(-7) M) for 10 min stimulated a 1.60 +/- 0.04-fold increase in membrane-associated PKC activity over control levels. In 3-h incubations, CCK-8 (10(-6)-10(-8) M) did not affect basal or LH (20 or 100 ng/ml-stimulated progesterone production. These studies demonstrate that CCK-8 causes a transient increase in chicken granulosa cell [Ca2+]i through the release of Ca2+ from intracellular stores and activates membrane-associated PKC activity, but does not affect progesterone production. These results suggest the presence of G-protein-coupled phospholipase-C-activating CCK receptors on the surface of these cells.

N alpha-carboxyacyl analogues of CCK with a substituted Gly: interaction with pancreatic and gallbladder CCK receptors

It has been reported that certain N alpha-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 CCKA 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 alpha-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 (EC50): CCK-8 (0.09 nM) > Suc[Sar3]CCK-7 (0.23 nM) > des(SO3)CCK-8 (28 nM) > Suc[D-Trp4]CCK-8 (32 nM) > Suc[D-Trp3]CCK-7 (53 nM) > Pht[D-Trp3]CCK-7 (180 nM) > Glt[D-Trp3]CCK-7 (220 nM). 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 CCKA receptors in the pancreas and on gallbladder smooth muscle possess similar affinities for the various N alpha-carboxyacyl analogues of CCK-7 and CCK-8 with a substituted Gly and provide further evidence that the CCKA receptors in gallbladder and pancreas cannot be distinguished pharmacologically.