CCK-A Receptor Antagonist Research Articles

Cholecystokinin receptors do not mediate the suppression of food-motivated behavior by lipopolysaccharide and interleukin-1 beta in mice

During the course of an infection, profound metabolic and behavioral changes are observed. The resulting decrease in food intake can be reproduced by administration of lipopolysaccharide (LPS) or the proinflammatory cytokines (e.g., interleukin-1 [IL-1] and tumor necrosis factor it induces. To test the possibility that cholecystokinin (CCK) mediates anorexia induced by IL-1β and LPS, mice trained to poke their noses in a hole to obtain a food reward according to a fixed ratio (1 reward per 20 actions) were pretreated with the CCK-A receptor antagonist L364,718 (at 1 mg/kg) or with the CCK-B receptor antagonist L365,260 (50 μg/kg) before being injected with LPS (100 μg/kg) or IL-1β (20 μg/kg). All injections were given via the intraperitoneal (i.p.) route. In spite of its ability to block the effects of exogenous CCK-8 on food-motivated behavior in mice, the CCK-A receptor antagonist did not block the depressive actions of LPS and IL-1β on food-motivated behavior. The CCK-B receptor antagonist was not more effective at blocking. These results do not support a role for CCK in the anorexic effect of LPS and IL-1β.

The role of long chain fatty acids in regulating food intake and cholecystokinin release in humans

BACKGROUND AND AIMSThe mechanism of intraduodenal fat induced inhibition of food intake is still unclear. Therefore, we tested the ability of duodenal fatty acids to suppress food intake at a...

Bradykinin induced contraction of human gallbladder muscle in vitro

Aim To examine the mechanisms of Bradykinin (BK)-induced contraction on human gallbladder muscle and to investigate possible receptors that may mediate this action. Methods A full-thickness segment from the anterior aspect of healthy and stone-hearing gallbladders was removed and placed in cold Krebs solution in an organ bath. Concentration-response curves (CRCs) were obtained for BK (0.1-100/LM). The BK response curves were repeated in the presence of a number of antagonists and channel blockers BI & B2 receptor antagonists, SR 27897 (0.5nM,a CCK-A receptor antagonist), mepyramine (l/LM, a histamine receptor antagonist), atropine (l/LM, a muscarinic receptor antagonist), prazosin (O.l/LM,a adrenoceptor blocker), tetrodotoxin (O.03/LM, a Na channel blocker), quinidine (l/LM, a K channel blocker) and indomethacin (3/LM, a cyclo-oxygenase inhibitor). Extracellular Ca involvement was examined by use of Ca free medium. Ryanodine (lO/LM) was used to examine intracellular involvement. Ethics committee approval for tissue sampling was obtained. Statistical significance was performed using t-test, P < .05 or less was considered as indicative of significance. Results Healthy (n=6) and stone-bearing (n=9) gallbladders showed similar and repeatable CRCs to BK (EDso=4.95 & 5.5/LM). The BK response was significantly reduced only in healthy strips by BI receptor blockade (EDso=31.5/LM) and in both tissue types by B2 receptor blockade (EDso=37.2 & 29./LM). Neither antagonist affected the maximum BK response. No significant rightward shift of the response to BK was observed in the presence of mepyramine (n=4), atropine (n=), prazosin (n=6), tetrodotoxin (n=), quinidine (n=7) or SR27897 (n=5). A significant rightward shift of the curve was noted in the presence of indomethacin (n=20,EDso=55/LM). BK-induced contraction was not modified in Ca-free medium (n=7), however the presence of ryanodine caused a significant rightward shift of the BK dose-response curve (n=7,EDso=46/LM. Conclusion Gallbladder strips contract to BK in a dose-dependent manner. A difference in receptor population seems to exist between normal and stone-bearing gallbladders. BK appears to have a direct myogenic effect on the human gallbladder and this may be mediated by a third BK receptor or a BK-independent mechanism. The contraction occurs independently of extracellular Ca but intracellular Ca is vital. In addition, part of this BK-induced contraction is probably mediated by the release of a cyclo-oxygenasc-dcrived product from the arachidonic acid pathway.

Inhibition of the hypothalamic-pituitary-adrenal axis in food-deprived rats by a CCK-A receptor antagonist.

The circadian activity of the hypothalamic-pituitary-adrenal (HPA) axis is regulated by caloric flow in rats. During the dark cycle, it has been shown that, in fasted rats, the time-course profile of plasma concentrations of adrenocorticotropin (ACTH) and corticosterone parallels the profile of food intake in ad libitum fed animals. Cholecystokinin (CCK) is involved in regulating food intake in rodents. CCK-8 reduces food intake by acting on CCK-A receptors subtype. This work aims at establishing an eventual relationship between the modulatory role of CCK on food intake and its effect on HPA axis activity during fasting. We studied the effect of CCK-A and CCK-B receptor antagonists on food intake during the first period of the dark cycle. Under these conditions we observed that the CCK-A receptor antagonist, SR-27897 (0.3 mg kg(-1)), but not the CCK-B receptor antagonist, L-365260 (1 mg kg(-1)), increases food-intake. In a second series of experiments we observed that the increase of both ACTH and corticosterone plasma level elicited by fasting, was prevented by SR-27897, but not by L-365260. These results indicate that CCK-A receptor blockade during fasting prevents the activation of the HPA axis.

CCK-A receptor activation induces Fos expression in myenteric neurons of rat small intestine

Cholecystokinin (CCK), a hormone secreted from endocrine cells of the small intestine, participates in the control of motility and secretion in the gastrointestinal tract, and in the control of food intake. At least some of the effects of CCK on intestinal function appear to be mediated via activation of intrinsic neurons in the myenteric plexus. However, the distribution of CCK-responsive enteric neurons within the rat small intestine is not known. Neither has the role of CCK-A receptors in the activation of rat myenteric neurons been investigated. Therefore, to determine the distribution of CCK-responsive neurons in the small intestinal myenteric plexus we utilized immunohistochemical detection of Fos, the protein product of the immediate early gene c-fos, to identify neurons that were activated by exogenous CCK. We also monitored Fos expression in the dorsal hindbrain, and examined CCK-induced Fos expression in the presence or absence of a receptor antagonist for the type-A CCK receptor. We found that CCK significantly increased Fos expression in the hindbrain and in myenteric neurons of the duodenum and jejunum, but not the ileum. Neuronal Fos responsiveness in both brain and myenteric neurons was mediated by CCK-A receptors, as CCK-induced Fos expression was eliminated in rats pretreated with a CCK-A receptor antagonist. We conclude that CCK activates small intestinal myenteric neurons, via CCK-A receptors. Activation of these intrinsic intestinal neurons may participate in reflexes and behaviors that are mediated by CCK.

Functional CCK-A and Y2 receptors in guinea pig esophagus

Effects of cholecystokinin octapeptide (CCK-8), peptide YY (PYY), neuropeptide Y (NPY) and their analogs on muscle contractions of esophageal strips were investigated. CCK-8-induced a tetrodotoxin and atropine-sensitive contraction. The relative potencies for CCK related peptides to induce contractions were CCK-8>desulfated CCK-8>gastrin-17-I. The CCK-A receptor antagonist L-364,718 was >300-fold more potent than the CCK-B receptor antagonist L-365,260 at inhibiting CCK-8-induced contraction. These indicate that neural CCK-A receptors mediate this contraction. PYY or NPY did not cause muscle contraction or inhibit muscle contraction induced by carbachol, endothelin-1 or KCl. However, both PYY and NPY concentration-dependently inhibited contraction induced by CCK-8. This inhibition was not affected by nitric oxide (NO) synthase inhibitors l-NMMA or l-NAME. The relative potencies for PYY related peptides to inhibit CCK-8-induced contraction were PYY>NPY>NPY13–36>[Leu 31, Pro 34]NPY>pancreatic polypeptide (PP). We conclude that CCK interacts with neural CCK-A receptors to cause esophageal muscle contraction. PYY and NPY interact with Y2 receptors to inhibit this CCK-induced muscle contraction by an effect not related to NO.

Pathophysiological role of cholecystokinin in humans.

Cholecystokinin (CCK) is a major gastrointestinal hormone that plays an important role in stimulation of pancreatic secretion and gall-bladder contraction, regulation of gastrointestinal motility and induction of satiety. Ingestion of fat and protein induces significant increases in plasma CCK. Intraluminal mediators of CCK secretion, luminal CCK releasing factor and diazepam-binding inhibitor, were purified from rat intestinal secretion. These CCK-releasing factors (RF) are secreted tonically by the small intestine and stimulate CCK release. Another kind of CCK-RF named 'monitor peptide' was purified from the rat pancreatic juice that stimulates CCK secretion when introduced into rat intestine. Bile exclusion from the duodenum causes an increase in basal CCK and enhances stimulated plasma CCK release, and bile salt replacement reverses these effects. Thus, the CCK-RF are spontaneously secreted into the intestinal lumen in humans, while the CCK-producing cells are under constant suppression by intraduodenal bile acids. In acute pancreatitis, plasma CCK levels are high in patients with gallstone pancreatitis, but not in patients with pancreatitis from other causes, such as alcoholic and idiopathic pancreatitis. A transient disturbance of bile flow into the duodenum by stones or oedema of the pancreas together with impairment of pancreatic exocrine function might cause the increase in plasma CCK release in gallstone pancreatitis. Patients with chronic pancreatitis with mild to moderate impairment of exocrine function and abdominal pain, had significantly higher plasma CCK concentrations, whereas patients with pancreatic insufficiency had a significantly lower plasma CCK response to a test meal than the healthy subjects. The increased CCK may further aggravate pancreatitis and worsen the prognosis of pancreatitis by stimulating the injured pancreas, resulting in the vicious circle via endogenous CCK release. The CCK-A receptor antagonist might be therapeutically useful in acute pancreatitis by stopping the vicious circle.

Involvement of CCK in the Paraventricular Nucleus of the Hypothalamus in the CNS Regulation of Colonic Motility

The effects of cholecystokinin octapeptide (CCK₈), the CCK-A receptor antagonist, MK-329, and the CCK-B receptor antagonist, L-365, 260, microinfused into the paraventricular nucleus of hypothalamus (PVN) on colonic motor function was investigated in awake rats, chronically implanted with a microinjection cannula into the PVN and a catheter into the proximal colon. In fasted rats, bilateral microinfusion of CCK₈ at doses of 1.5 and 3.0 μg/rat into the PVN stimulated colonic transit, as shown by a significant increase in the geometric center by 47 and 54%, respectively. This effect of CCK₈ was site-specific to the PVN, since microinjection of the peptide into sites outside of but adjacent to PVN had no effect. In non-fasted rats, L-365,260 bilaterally microinjected into the PVN at a dose of 1.5 μg/rat inhibited propulsive colonic motor function; colonic transit time significantly increased by 73% in comparison to the control condition. Microinfusion of the CCK-A antagonist into in the PVN did not affect colonic transit. These results show that the PVN is a responsive site for the central CCK₈-induced modulation of colonic motility. The data suggest, that endogenous CCK in the paraventricular nucleus of the hypothalamus unfolds a stimulatory effect on colonic transit through action on CCK-B receptors.

Diverse effects of phytohaemagglutinin on gastrointestinal secretions in rats

Kidney bean lectin phytohaemagglutinin (PHA) is known for its binding capacity to the small intestinal surface inducing marked hyperplasia and hypertrophy and an increased pancreatic function. Recent observations indicate that PHA is able to attach to gastric mucosal and parietal cells. Therefore, we compared the effects of PHA on gastric acid secretion, and pancreatic amylase secretion in rats. To study gastric secretion in conscious animals, rats were surgically prepared with chronic stainless steel gastric cannula and with indwelling polyethylene jugular vein catheter. Acid secretion was determined by titration of the collected gastric juice to pH 7.0. Similar studies were performed to investigate the effect of PHA on pancreatic enzyme secretion in conscious rats supplied with pancreatic cannula. Pancreatic enzyme secretion was also studied in rats anesthetized with either halothane or urethane. In conscious rats PHA significantly inhibited basal acid secretion when compared to vehicle-treated controls. The effect was dose-dependent and reversible. On the other hand, given in the same doses as in the acid-secretory studies, PHA stimulated pancreatic amylase secretion in rats prepared with chronic pancreatic cannula. This effect was blocked by devazepide, a CCK-A receptor antagonist. In halothane-anesthetized rats PHA administration increased pancreatic amylase secretion, too. During urethane anesthesia, however, the stimulatory effect of PHA was not observed. These results provide evidence that intragastric PHA treatment induces opposite effects on gastric acid secretion and pancreatic enzyme secretion: it is a potent inhibitor of acid output, and a stimulator of pancreatic enzyme discharge. Our data also show that the stimulatory effect of PHA on pancreatic enzyme secretion can be blocked by urethane, an anaesthetic that is known to turn off the negative pancreatic feedback control of pancreatic function in rats.

Dual CCK-A and CCK-B receptor antagonists (II). Preparation and structure activity relationships of 5-alkyl-9-methyl-1,4-benzodiazepines and discovery of FR208419.

In our continuing research for dual CCK-A and -B antagonists, according to our hypothesis that dual CCK-A and -B antagonists should be more efficacious than selective CCK-A antagonists for the treatment of pancreatitis, we have prepared various 5-alkyl-9-methyl-1,4-benzodiazepines. From the compounds prepared, 1-cyclohexyl-carbonylmethyl-5-ethyl-9-methyl-3- (m-tolylureido)-2-oxo-1,4-benzodiazepine, (40) was selected as a candidate for development due to its well-balanced high affinity for both receptors. The R-enantiomer of 40, (R)-40 (FR 208419), had 27-fold higher affinity for the CCK-A receptor and 8-fold more potent CCK-B receptor binding activity than (S)-40. The biological activity after p.o. administration of (R)-40, estimated from the ID50 value (0.23 mg/kg p.o.) obtained by preliminary evaluation by gastric emptying effects, is considered to be high enough for further development. This compound is now undergoing further biological evaluations with a view to clinical development.

コレシストキニンきっ抗剤の探索研究

Cholecystokinin (CCK) is a major gastrointestinal hormone with an important role in regulating various target organs such as pancreas, gallbladder and gut. CCK is also one of the most widely distributed neuropeptides in the brain and is considered as a putative central nervous system transmitter. The CCK receptors are divided into two CCK-A and CCK-B sub-type receptors. We have researched these respective receptor antagonists in the 1, 4-benzodiazepine derivatives and succeeded in discoveries of a selective CCK-A receptor antagonist, FK 480, a selective CCK-B receptor antagonist, FR 175985, and a dual CCK-A and -B receptor antagonist, FR 208419.This manuscript describes the syntheses and the structure-activity relationships of these respective CCK receptor antagonists.

Continuous Infusion of Cholecystokinin Leads to Down-Regulation of the Cholecystokinin-A Receptor in the Rat Pancreas

Infusion of sulphated cholecystokinin-8 (CCK-8S) in rats transiently increased the proliferation of pancreatic acinar cells, whereas the CCK-A receptor antagonist devazepide decreased such proliferation. This effect ceased after 3 days. CCK-8S or devazepide injected twice daily induced a persistent effect on the cell proliferation involving the major cells of the exocrine pancreas. The aim of this study was to examine the effect of continuous infusion of CCK-8S and devazepide on CCK-A receptor gene expression. Male Sprague-Dawley rats received subcutaneous continuous infusion of 5 microg/kg/h CCK-8S, 200 microg/kg/h devazepide, or 1% bovine serum albumin (BSA) by means of osmotic minipumps. The rats were killed after 4 days; I h before being killed they received 5-bromo-2-deoxyuridine (BrdU) intraperitoneally. Plasma was collected for analysis of CCK. The pancreas was dissected, and indirect immunofluorescence for BrdU and CCK-A receptor was performed. In situ hybridization to CCK-A receptor mRNA was performed for examination and semiquantification of receptor gene expression. Continuous infusion of CCK-8S led to a sixfold increase in plasma CCK and a 40% increase in pancreatic weight. Devazepide did not affect the CCK level but decreased the pancreatic weight by 24% compared with BSA-infused rats. The BrdU labeling indicated that CCK-8S had no effect on cell proliferation. Immunofluorescence for the CCK-A receptor showed a decreased labeling intensity after CCK-8S infusion. The mean optical density of in situ hybridization labeling of the sections from CCK-8S-treated rats was decreased to 37% +/- 3% of that in controls. Devazepide did not affect the CCK-A receptor gene expression. Continuous stimulation of the CCK-A receptor led to a downregulation of the receptor gene expression in pancreatic acinar cells and decreased labeling of the receptor at immunohistochemistry. The results suggest that down-regulation of the receptor is a protective mechanism against overstimulation.

Acute taurodeoxycholate-induced pancreatitis in the rat is associated with hyperCCKemia.

Cholecystokinin (CCK) has been suggested to be involved in the development and course of acute pancreatitis. In the present study we measured plasma CCK concentrations in acute experimental pancreatitis (AEP) in the rat, and evaluated the role of circulating CCK levels on the initial pancreatic damage in pancreatitis. Endogenous hyperCCKemia was induced by surgical biliodigestive shunt (BDS) and exogenous hyperCCKemia by infusion of CCK-8S. The CCK-A receptor antagonist devazepide was used to antagonize the effect of CCK. Pancreatitis was induced by pancreatic duct infusion of sodium taurodeoxycholate 4 wk after the BDS operation or 1 wk after the start of the infusions. Nonpancreatitic sham- and BDS-operated rats, respectively, were used as control animals as were groups of otherwise untreated rats with pancreatitis. The animals were sacrificed 6 h after induction of pancreatitis. Concentrations of CCK were determined in plasma as were protein and amylase levels in the pancreas and peritoneal exudates. The extent of pancreatic necroses was assessed microscopically. Pancreatitis caused an 11-20-fold increase of circulating CCK as measured after 6 h. In pancreatitic rats with induced hyperCCKemia, there was a further marked increase of plasma CCK. Pancreatic weight and edema, protein and amylase contents, and extent of necroses were the same regardless of the level of plasma CCK. Devazepide had no influence on the studied pancreatic parameters. We conclude that acute taurodeoxycholate-induced pancreatitis in the rat is associated with elevated plasma CCK concentrations. There seems, however, not to be any correlation between the degree of hyperCCKemia and the extent of initial pancreatic damage.

Small intestinal and pancreatic microstructures are modified by an intraduodenal CCK-A receptor antagonist administration in neonatal calves

The aim of the present study was to investigate the role of CCK on the upper gut and pancreas microstructure and on pancreatic juice secretion in neonatal calves assessed by a repetitive intraduodenal administration of FK480, a CCK-A receptor antagonist, during the first 6 days of life. The experiment was performed on 10 neonatal calves surgically fitted with a pancreatic accessory duct catheter and duodenal cannulas. Calves were sacrificed on day 7 for tissue sampling. Treatment with FK480 resulted in: reduction of preprandial pancreatic juice secretion at days 1–3, smaller size of pancreatic acini and number of cells per acinus, reduction in intestinal crypt depth (except in the duodenal bulb), numerous modifications of intestinal villi length and width, lower mitotic index of crypt cells, and increased number and size of enterocytes with ‘empty vacuoles’. In conclusion, the blockade of CCK-A receptors during early life both reduced pancreatic exocrine secretion and induced complex changes in pancreatic microstructure. The influence of CCK on the upper gut microstructure in neonatal calves could be either direct via activation of CCK-A receptors located in the mucosa of the upper gut or indirect by modulation of the secretion of pancreatic juice.

Secretion of pancreatic digestive enzymes induced in rats by first-time oral exposure to kidney bean E2L2 lectin is mediated only in part by cholecystokinin (CCK).

The acute effects of kidney bean (Phaseolus vulgaris) E2L2 lectins (PHA) given orally to conscious rats or continually infused into the duodenum of anesthetized rats on blood cholecystokinin (CCK), secretin, and gastrin and on secretion of pancreatic digestive enzymes have been evaluated. PHA increased circulating levels of CCK and secretin but did not alter gastrin. In addition, PHA induced dose-dependent secretion of trypsinogen, chymotrypsinogen, and alpha-amylase by the pancreas in vivo. This pancreas output appeared to be modulated only in part through CCK. Thus pretreatment of rats with a CCK-A receptor antagonist (L-364718) attenuated the immediate (< or = 90 min) pancreas secretory response to PHA but could not prevent a PHA-associated increase in digestive enzyme output in the longer term (after 90 min). In contrast, treatment of rats with L-364718 abolished the stimulatory effects of soyabean trypsin inhibitors on digestive enzyme secretion in both the short and long term. Additional mechanisms or hormones, such as secretin, may play a role in modulating later exocrine pancreas responses to PHA.

Inhibition of gastric emptying by bombesin-like peptides is dependent upon cholecystokinin-A receptor activation

The amphibian peptide bombesin (BN) and the related mammalian peptides gastrin-releasing peptide (GRP) and neuromedin B (NMB) inhibit gastric emptying in rats. Exogenous administration of BN stimulates the release of cholecystokinin (CCK), a gastrointestinal peptide that also potently inhibits gastric emptying. To determine whether the inhibition of gastric emptying by BN-like peptides is mediated by a CCK-dependent mechanism, we examined the ability of the CCK-A receptor antagonist, devazepide, to block the inhibition of saline gastric emptying produced by BN, GRP18–27 and NMB. Using the same dosages as in the gastric emptying experiment, we also evaluated the effect of devazepide on feeding suppression produced by systemically administered BN. Our results showed that devazepide completely blocked the suppression of gastric emptying produced by BN, GRP18–27 and NMB but had no effect on BN-induced suppression of food intake. These results suggest that BN-like peptides inhibit gastric emptying through an indirect mechanism that is dependent upon CCK-A receptor activation. In contrast, the suppression of food intake by BN, in this experimental paradigm, is independent of CCK-A receptors.

Duodenal loading with glucose induces fos expression in rat brain: selective blockade by devazepide.

The role of CCK in mediating neuronal activity in the brain in response to dietary carbohydrate was measured by detecting Fos immunoreactivity in response to duodenal glucose load in rats after administration of the CCK-A receptor antagonist devazepide. In adult, male Sprague-Dawley rats, infusion for 30 min of 545 mg (2.18 kcal) dextrose through a duodenal cannula induced Fos expression in the nucleus of the solitary tract (NTS), area postrema (AP), lateral division of the central nucleus of the amygdala (CeAL), and the external subnucleus of the lateral parabrachial nucleus (LPBE). Devazepide treatment (1 mg/kg) attenuated Fos expression in the NTS and AP by 81 and 78%, respectively, but not in the CeAL or LPBE. These results indicate that central neuronal activation is elicited by dietary glucose in the intestinal lumen and that activation of neurons in the NTS and AP is mediated by CCK-A receptors.

Evidence that cholecystokinin receptors are not involved in the hypothalamic-pituitary-adrenal response to intraperitoneal administration of interleukin-1beta.

The purpose of this study was to investigate a putative role for cholecystokinin (CCK) in the activation of the hypothalamic-pituitary-adrenal (HPA) axis following intraperitoneal (i.p.) administration of interleukin-1-beta (IL-1beta). Previous studies predict that CCKA receptors on vagal sensory afferents may be involved in the initiation of the stress response following an acute i.p. injection of IL-1beta. Adult male rats were given an i.p. injection of a specific CCKA (devazepide, 1 mg/kg) or CCKB (CI-988, 1 mg/kg) receptor antagonist, 30 min prior to an i.p. injection of rat recombinant IL-1beta (rrIL-1beta), 0.5 microg/kg in 0.9% sterile saline/0.01% rat serum albumin. Blood samples were obtained via an indwelling jugular vein catheter, and the plasma levels of the stress hormones ACTH (adrenocorticotropin hormone) and corticosterone analysed over time as an indicator of HPA axis activation. This dose of rrIL-1beta resulted in a significant release of ACTH and corticosterone, peaking at 30-60 min, and returning to basal levels by 2 h. Pretreatment with either devazepide or CI-988 had no effect on the rrIL-1beta induced ACTH or corticosterone release. In contrast, the same dose of devazepide completely inhibited the ACTH and corticosterone response to i.p. CCK (octapeptide, sulphated form, CCK-8S), 5 microg/kg. It is concluded that CCK receptors are not involved in the hormonal stress response to a submaximal i.p. dose of rrIL-1beta.

Cholecystokinin, acting through the A receptor subtype, stimulates the proliferative activity of adrenocortical cells and thymocytes in the rat.

Cholecystokinin (CCK) is a multifunctional regulatory peptide, which acts through two main subtypes of receptors, named CCK-A and CCK-B. Evidence indicates that CCK modulates cell proliferation in various tissues in a paracrine manner, and proofs are available of the presence of CCK in both adrenal glands and thymus. Hence, we have investigated the possible mitogenic action of this peptide on these two tissues, by evaluating the /1000 of metaphase-arrested cells after vincristin injection (mitotic index). The systemic administration of CCK (three subcutaneous injections of 20 nmol/kg, 28, 16 and 4 h before the sacrifice) increased the mitotic index in both the outer adrenal and thymus cortexes of immature (20-day-old) rats and the enucleated adrenal gland of adult (2-month-old) animals at day 5 and 8 of regeneration. The simultaneous administration of equimolar doses of a selective CCK-A receptor antagonist blocked the effect of CCK, while a CCK-B antagonist was ineffective. These findings indicate that CCK exerts a marked CCK-A-mediated proliferogenic effect on both adrenal cortex and thymus in the rat, the physiological relevance of which, however, remains to be demonstrated. In fact, the administration of the CCK-A antagonist alone was ineffective, thereby casting doubts on the role played by endogenous CCK in the maintenance and stimulation of adrenal and thymus growth.

Characterization of the binding of a novel radioligand to CCKB/gastrin receptors in membranes from rat cerebral cortex.

1. We have investigated the binding of a novel radiolabelled CCKB/gastrin receptor ligand, [3H]-JB93182 (5[[[(1S)-[[(3,5-dicarboxyphenyl)amino]carbonyl]-2-phenylethyla mino]-carbonyl]-6-[[(1-adamantylmethyl) amino]carbonyl]-indole), to sites in rat cortex membranes. 2. The [3H]-JB93182 was 97% radiochemically pure as assessed by reverse-phase HPLC (RP-HPLC) and was not degraded by incubation (150 min) with rat cortex membranes. 3. Saturation analysis indicated that [3H]-JB93182 labelled a homogeneous population of receptors in rat cortex membranes (pKD=9.48+/-0.08, Bmax=3.61+/-0.65 pmol g(-1) tissue, nH=0.97+/-0.02, n=5). The pKD was not significantly different when estimated by association-dissociation analysis (pKD=9.73+/-0.11; n=10). 4. In competition studies, the low affinity of the CCKA receptor antagonists, L-364,718; SR27897 and 2-NAP, suggest that, under the assay conditions employed, [3H]-JB93182 (0.3 nM) does not label CCKA receptors in the rat cortex. 5. The affinity estimates obtained for reference CCKB/gastrin receptor antagonists were indistinguishable from one of the affinity values obtained when a two site model was used to interpret [125I]-BH-CCK8S competition curves obtained in the same tissue (Harper et al., 1999). 6. This study provides further evidence for the existence of two CCKB/gastrin sites in rat cortex. [3H]-JB93182 appears to label selectively sites previously designated as gastrin-G1 and therefore it may be a useful compound for the further discrimination and characterization of these putative receptor subtypes.