Behavioral effect of cholecystokinin octapeptide in vagotomized rats

Cholecystokinin octapeptide (CCK-8) was administered intracerebroventricularly (icv) or subcutaneously (sc) into subdiaphragmatically vagotomized and sham-operated rats, and the behavioral effects were quantified by an open-field test. Intracerebroventricularly injection of CCK-8 decreased locomotion and rearing to the same extent in both vagotomized and sham-operated rats, while sc injection produced behavioral changes only in sham-operated rats but not in vagotomized ones. The results indicate that CCK-8 affects both central and peripheral receptors, and the vagal nerve may be the major pathway causing behavioral effects from the visceral organs to the brain.     

Effects of cholecystokinin octapeptide sulphate ester and unsulphated cholecystokinin octapeptide on active avoidance behaviour in rats

The effects of peripherally administered cholecystokinin octapeptide sulphate ester and its unsulphated form on the active avoidance behaviour of rats were studied. The acquisition of avoidance behaviour was impaired, while extinction was facilitated, following cholecystokinin octapeptide sulphate ester or unsulphated cholecystokinin octapeptide treatment. These peptides had no action on open-field activity. It is concluded that peripherally administered cholecystokinin octapeptide influences acquisition and extinction of active avoidance behaviour and this effect is unrelated to general motor activity of the animals.     

Exocrine pancreatic secretion: effect of subarachnoidal application of cholecystokinin octapeptide in rats

Administration of cholecystokinin octapeptide (CCK-8) intravenously, or in the subarachnoidal surface of the olfactory lobe in rats, caused an increase in pancreatic protein and amylase secretion. It was observed that for subarachnoidal administration of CCK-8 both protein and amylase outputs were higher than that seen after i.v. injection. This result is consistent with the presence of central CCK receptors which when activated can enhance pancreatic exocrine secretion. The blockade of the effect of CCK by administration of CCK-8-specific antisera proves the specificity of the subarachnoidal CCK-8 stimulation.     

The effect of cholecystokinin octapeptide on pituitary-adrenal hormone secretion

The purpose of this investigation was to determine the influence of cholecystokinin octapeptide (CCK-OP) on pituitary-adrenal hormone secretion. CCK-OP at a dose of 5 μg/kg (i.p.) elevated plasma corticosterone from 27 to 43 μg/100 ml in one experiment and from 12 to 50 μg/100 ml in a second experiment: Lower doses of CCK-OP (0.5 μg/kg) elevated corticosterone from 12 μg/100 ml to 20 μg/100 ml. CCK-OP (1, 10, and 100 ng/ml) had no effect on ACTH-induced corticosterone released by isolated adrenal cells in vitro when tested in the presence of 50 pg of ACTH_1?24. 100 and 500 ng of CCK-OP resulted in an increased pituitary ACTH release equal to 123% (n.s.) and a 206% (P < 0.05) of control, respectively. In comparison, a $\text{3}\text{5}$ hypothalamic stalk median eminence equivalent increased ACTH release to 313% of control (P < 0.05). The exact mechanism of this CCK effect on pituitary ACTH release is unknown. Although it is likely that the direct effects on the pituitary in vitro represent a pharmacologic and not a physiologic effect of this peptide, in vivo doses are between doses used for pancreatic effects and satiety effects suggesting that there may be a physiologic stimulating action of this peptide on the hypothalamic-pituitary-adrenal axis but at a level above the adrenal and pituitary.     

Modulation of passive avoidance behaviour of rats by intracerebroventricular administration of cholecystokinin octapeptide sulfate ester and nonsulfated cholecystokinin octapeptide

The effects of intracerebroventricular administration of different doses of cholecystokinin octapeptide sulfate ester (CCK-8-SE) and nonsulfated cholecystokinin octapeptide (CCK-8-NS) were tested on the latency of passive avoidance behaviour in rats. Treatments were carried out prior to learning trial, immediately after electroshock and prior to testing 24 h retention. Both CCK-8-NS and CCK-8-SE enhanced the latency of passive avoidance after all forms of treatment while showing different dose-response patterns depending on time of administration. These data indicate that CCK-8-SE and CCK-8-NS might play a role in the regulation of memory consolidation and retrieval.     

Effects of intraventricular administration of cholecystokinin octapeptide sulfate ester and unsulfated cholecystokinin octapeptide on active avoidance and conditioned feeding behaviour of rats

The effects of cholecystokinin octapeptide sulfate ester (CCK-8-SE) and unsulfated cholecystokinin (CCK-8-NS) were studied following intraventricular administration on active avoidance and conditioned feeding behaviour of rats. In the CCK-8-NS and CCK-8-SE treated animals the acquisition of active avoidance and conditioned feeding behaviour were considerably impaired compared to the control; furthermore, these peptides caused a facilitated extinction of active avoidance and conditioned feeding behaviour. The data suggest that cholecystokinin octapeptide is capable of modifying the fear and hunger motivated behaviours of rats.     

In vivo and in vitro effects of cholecystokinin octapeptide on the release of prolactin in rats

The effect of cholecystokinin octapeptide (CCK-8) on the release of prolactin (PRL) in rats was studied in vivo and in vitro. Intravenous injection of 5 micrograms/100 g BW of CCK-8 resulted in significant increase in the plasma PRL level after 10 and 20 min. CCK-8 at concentrations of 10(-11) M to 10(-7) M also caused dose-dependent stimulation of PRL release from dispersed cells of rat anterior pituitary. On the other hand, dopamine inhibited PRL release from dispersed cells of rat anterior pituitary in a dose-related manner at concentrations of 10(-8) M to 10(-6) M. Release of PRL from the cells was increased by addition of K+ at high concentration (53 mM) in a Ca++-dependent manner. Addition of 10(-3) M verapamil to the incubation medium inhibited CCK-8-induced PRL release from the cells. Addition of dopamine (10(-7) M) to the incubation medium inhibited PRL release from the cells induced by CCK-8 or high K+ (53 mM). These results indicate that CCK-8 acts directly on the anterior pituitary cells to stimulate PRL release and that calcium ion is involved in the mechanism of this effect.     

Chronotropic actions of cholecystokinin octapeptide on the rat heart

Cholecystokinin octapeptide (CCK-8) administered i.v. to urethane-anaesthetized rats or added to the perfusion stream of isolated rat hearts produced an immediate bradycardia. The size of this response was dose-related. Studies in vivo and in vitro using atropine and propranolol indicated that the response to CCK-8 was largely due to a direct action of the peptide on the heart. N-carbobenzoxy-tryptophan (CBZ-Trp), a cholecystokinin receptor antagonist, abolished the response of the isolated heart to CCK-8. Gastrin I did not produce bradycardia. The receptors on rat heart were similar to the classes of cholecystokinin receptors found in brain and exocrine pancreas in that CCK-8 rather than cholecystokinin tetrapeptide (CCK-4) was the preferred agonist.     

In vivo and in vitro effects of cholecystokinin octapeptide on the release of growth hormone in rats

The effect of cholecystokinin octapeptide (CCK-8) on the release of growth hormone (GH) in rats was studied in vivo and in vitro. Intravenous injection of 5 micrograms/100 g BW of CCK-8 resulted in significant increase in the plasma GH level after 10 and 20 min. CCK-8 at concentrations of 10(-11)M to 10(-7)M also caused dose-dependent stimulation of GH release from dispersed cells of rat anterior pituitary. On the other hand, somatostatin (SRIF) inhibited GH release from dispersed cells of rat anterior pituitary in a dose-related manner at concentrations of 10(-7)M to 10(-9)M. Release of GH from the cells was increased by addition of K+ at high concentration (50 mM) in a Ca++-dependent manner. Addition of 10(-3)M verapamil to the incubation medium inhibited CCK-8-induced GH release from the cells. Addition of SRIF (10(-7)M) to the incubation medium inhibited GH release from the cells induced by CCK-8 or high K+ (50 mM). These results indicate that CCK-8 acts directly on the anterior pituitary cells to stimulate GH release and that calcium ion is involved in the mechanism of this effect.     

Repeated treatment with cholecystokinin octapeptide improves maze performance in aged Fischer 344 rats.

Previous studies have shown that sulfated cholecystokinin octapeptide (CCK-8S) can improve learning in adult rodents when administered systemically or into the central nucleus of amygdala. Here we analyzed the effect of repeated intraperitoneal (i.p.) injection of CCK-8S on the performance of 26-month-old Fischer 344 rats in different versions of the Morris water maze and in a rota-rod test of motor coordination. Old rats were injected daily with different doses of CCK-8S (0.32 to 8.0 microg/kg; IP) 10 min before the behavioral tests. Control groups included vehicle-injected old and adult (3-month-old) F 344 rats. To control for a possible development of tolerance to the behavioral effects of repeated CCK-8S administration, groups of aged rats were included which were subjected to an acute rather than a repeated CCK injection schedule. The repeated administration of CCK-8S did not influence the performance of the old rats in the hidden-platform version of the maze. In addition, the acute treatment with CCK-8S failed to modify navigation performance in this task, suggesting that drug-tolerance may not account for the lack of behavioral effects seen after repeated CCK-8S injection. During the "probe trial", the percentage of animals per group, which swam exactly across the former platform site, was markedly increased in aged rats treated repeatedly with 1.6 microg/kg CCK-8S. This might be indicative of improved retention of the prior platform location and/or a higher resistance of the learned escape response to extinction. The specificity of the effect of CCK-8S on processes related to spatial learning and memory is supported by the lack of effect on motor performance.     

Protective effect of cholecystokinin octapeptide on angiotensin II-induced apoptosis in H9c2 cardiomyoblast cells

Cholecystokinin (CCK) and its receptors are expressed in mammalian cardiomyocytes and are involved in cardiovascular system regulation; however, the exact effect and underlying mechanism of CCK in cardiomyocyte apoptosis remain to be elucidated. We examined whether sulfated CCK octapeptide (CCK-8) protects H9c2 cardiomyoblast cells against angiotensin II (Ang II)-induced apoptosis. The H9c2 cardiomyoblasts were subjected to Ang II with or without CCK-8 and the viability and apoptotic rate were detected using a Cell Counting Kit-8 assay, Hoechst 33342 staining, terminal deoxyribonucleotide transferase-mediated nick-end labeling assays, and flow cytometry. In addition, specific antiapoptotic mechanisms of CCK-8 were investigated using specific CCK1 (Devazepide) or CCK2 (L365260) receptor antagonists, or the PI3K inhibitor LY294002. The expression of CCK, CCK1 receptor, CCK2 receptor, Akt, p-Akt, Bad, p-Bad, Bax, Bcl-2, and caspase-3 were detected by Western blot analysis and real-time polymerase chain reaction. We found that CCK and its receptor messenger RNA (mRNA) and protein are expressed in H9c2 cardiomyoblasts. Ang II-induced increased levels of CCK mRNA and protein expression and decreased levels of CCK1 receptor protein and mRNA. Pretreatment of CCK-8 attenuated Ang II-induced cell toxicity and apoptosis. In addition, pretreatment of H9c2 cells with CCK-8 markedly induced expression of p-Akt, p-bad, and Bcl-2 and decreased the expression levels of Bax and caspase-3. The protective effects of CCK-8 were partly abolished by Devazepide or LY294002. Our results suggest that CCK-8 protects H9c2 cardiomyoblasts from Ang II-induced apoptosis partly via activation of the CCK1 receptor and the phosphatidyqinositol-3 kinase/protein kinase B (PI3K/Akt) signaling pathway.     

Effects of exogenous cholecystokinin octapeptide on acquisition of naloxone precipitated withdrawal induced conditioned place aversion in rats

Cholecystokinin octapeptide (CCK-8), a gut-brain peptide, regulates a variety of physiological behavioral processes. Previously, we reported that exogenous CCK-8 attenuated morphine-induced conditioned place preference, but the possible effects of CCK-8 on aversively motivated drug seeking remained unclear. To investigate the effects of endogenous and exogenous CCK on negative components of morphine withdrawal, we evaluated the effects of CCK receptor antagonists and CCK-8 on the naloxone-precipitated withdrawal-induced conditioned place aversion (CPA). The results showed that CCK2 receptor antagonist (LY-288,513, 10 μg, i.c.v.), but not CCK1 receptor antagonist (L-364,718, 10 μg, i.c.v.), inhibited the acquisition of CPA when given prior to naloxone (0.3 mg/kg) administration in morphine-dependent rats. Similarly, CCK-8 (0.1-1 μg, i.c.v.) significantly attenuated naloxone-precipitated withdrawal-induced CPA, and this inhibitory function was blocked by co-injection with L-364,718. Microinjection of L-364,718, LY-288,513 or CCK-8 to saline pretreated rats produced neither a conditioned preference nor aversion, and the induction of CPA by CCK-8 itself after morphine pretreatments was not significant. Our study identifies a different role of CCK1 and CCK2 receptors in negative affective components of morphine abstinence and an inhibitory effect of exogenous CCK-8 on naloxone-precipitated withdrawal-induced CPA via CCK1 receptor.     

Pharmacokinetics and organ catabolism of cholecystokinin octapeptide in pigs

The pharmacokinetics and organ catabolism of cholecystokinin octapeptide (CCK8) were studied in pigs. In conscious animals, intravenous infusion of increasing doses of CCK8 (2.9-232.3 pmol.kg-1.min-1) resulted in a linear increase of plasma CCK-like immunoreactivity (CCK-LI). At the cessation of infusion of the largest dose of CCK8, plasma CCK-LI promptly returned to near basal values. The half-disappearance time (t1/2), metabolic clearance rate (MCR) and distribution volume (DV) were estimated to be 0.55 +/- 0.03 min, 134.8 +/- 10.8 ml.kg-1.min-1 and 107.9 +/- 13.0 ml.kg-1, respectively. In another group of anesthetized animals, infusion of CCK8 at similar doses produced higher plateau plasma CCK levels and the t1/2, MCR and DV were calculated to be 0.68 +/- 0.06 min, 32.5 +/- 3.9 ml.kg-1.min-1 and 45.2 +/- 5.6 ml.kg-1, respectively. Estimates of first-pass immunological degradation through various vascular beds were in the range 27-66%, with in decreasing order the kidney, liver, hindleg, followed by the brain and gut. These results indicate that immunoreactive CCK8 is rapidly cleared from plasma during passage through several vascular beds. The peptide is only partly inactivated during hepatic transit and so may exert hormonal effects upon its release from intestinal stores.     

Protective effect of CR 1409 (cholecystokinin antagonist) on experimental pancreatitis in rats and mice

CR 1409, a glutaramic acid derivative with competitive cholecystokinin-antagonistic activity, was administered IP and evaluated in comparison with proglumide (the model CCK-receptor antagonist), gabexate (protease inhibitor) and PGE₂ (cytoprotective) on two different models of experimental pancreatitis. Acute pancreatitis was induced in mice by six IP injections of 50 μg/kg caerulein at hourly intervals. The drugs were administered 30 minutes before each caerulein administration. Blood samples and pancreata were collected 3 hours after the last caerulein injection. In the second experiment, pancreatitis was induced in rats by injecting 0.3 ml 6% sodium taurocholate interstitially into the pancreas. The drugs were administered twice, 30 minutes before and 3 hours after taurocholate. The animals were killed 6 hours after laparotomy and blood samples and pancreata were collected. CR 1409 exhibited on both pancreatitis models a protective effect in a dose range of 0.3–10 mg/kg. Proglumide exhibited a protective activity at higher doses (200–400 mg/kg). Gabexate and PGE₂ were effective only in pancreatitis induced by taurocholate in a dose range of 30–60 mg/kg and 60–130 μg/kg respectively. These results, showing a high protective effect of CR 1409 on different models of acute pancreatitis, suggest an important role of CCK in the pathogenesis of pancreatitis.     

Blocking of cholecystokinin octapeptide behavioral effects by proglumide

An open field apparatus was used to assess the effect of proglumide, a selective antagonist of cholecystokinin octapeptide (CCK-8), to block the behavioral effect of CCK-8 in rats. Intracerebroventricular (ICV) injection of CCK-8 (0.5 to 2 micrograms) was effective in suppressing general exploratory activities and this effect was blocked by proglumide at doses of 2 to 5 micrograms administered ICV or 1 mg/kg administered subcutaneously. The effect of peripherally administered CCK-8 (10 micrograms/kg) was blocked by peripherally administered proglumide at a dose of 2 mg/kg but not by centrally administered proglumide at a dose of 5 micrograms/rat. The behavioral effect of CCK-8 was thus clearly blocked by proglumide.     

Effect of cholecystokinin octapeptide sulphate ester on brain monoamines in the rat

The effect of different doses of intracerebro-ventricularly administered cholecystokinin octapeptide sulphate ester (CCK-8-SE) was studied on dopamine (DA), norepinephrine (NE) and serotonin (5-HT) contents in the hypothalamus, mesencephalon, amygdala, septum and striatum, 10, 20 and 60 min following administration. The DA and NE content increased and the 5-HT content decreased in the hypothalamus and mesencephalon. A biphasic action was observed in the amygdala of DA, NE and 5-HT depending upon the time and doses used. Similar action was seen on DA and NE in the septum. In the striatum, the DA and 5-HT content decreased while the NE level first increased and then decreased. The data indicate that the CCK-8-SE is able to modify the activity of DA, NE and 5-HT in different brain regions in a time and dose-dependent manner, with a local specific action.