Carbachol-induced down-regulation of receptors for pancreatic secretagogues

Pancreatic acini possess a high affinity class of cholinergic receptors and a low affinity class of cholinergic receptors. Carbachol occupation of high affinity cholinergic receptors produces a reduction in binding of [3H]N-methylscopolamine. First incubating acini with carbachol caused a complete loss of high affinity cholinergic receptors with no change in the number or affinity of low affinity cholinergic receptors. Carbachol occupation of low affinity cholinergic receptors appears to produce a reduction in binding of 125I-CCK-8 and 125I-[Tyr4]bombesin. Acini possess two classes of CCK receptors. One class has a high affinity for CCK-8; the other class has a low affinity for CCK-8. First incubating acini with carbachol caused a 60% decrease in the number of high affinity CCK receptors with no change in the number of low affinity receptors or the affinities of either class of receptors for CCK-8. Acini possess a single class of bombesin receptors and first incubating acini with carbachol caused a 40% decrease in the number of bombesin receptors with no change in their affinity for bombesin.

Gastrin modulates growth of a rat acinar pancreatic cell line: receptor analysis and signal transduction

Recent studies have demonstrated the presence of both CCKA and CCKB receptors on dog and guinea pig pancreas. Although CCKA receptors are implicated in enzymatic secretion, biological effects of CCKB receptors are still unknown. We have previously found that a rat acinar pancreatic cell line (AR4-2J) possesses both receptor subtypes. In this work we report the ability of various CCK/gastrin agonists and antagonists to bind with these receptors. We found that gastrin, pentagastrin and Gastrin/CCK4 induce ornithine decarboxylase activity, an early event involved in cell proliferation, as well as 3H-thymidine incorporation. Furthermore, these effects occur at doses at which these peptides interact only with the CCKB receptor subtype. In view of these data we propose that modulation of AR4-2J cell growth by gastrin agonists specifically involve occupation of the CCKB receptor.

Correlation between phospholipid breakdown, intracellular calcium mobilization and enzyme secretion in rat pancreatic acini treated with Boc-[Nle28, Nle31]-CCK-7 and JMV180, two cholecystokinin analogues

In this work in vitro pharmacological profiles of two analogues of the C-terminal heptapeptide of cholecystokinin (CCK) were evaluated. The analogue Boc-[Nle28, Nle31]-CCK-7, a stable analogue of CCK-8, has the same activity profile as CCK-8, and was found to be very potent in stimulating amylase secretion, phospholipid breakdown and [Ca2+]i mobilization from rat pancreatic acini. It can be used as a probe for studying CCK-actions. The CCK-analogue Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-Asp-2-phenylethylester, (JMV180), which stimulates amylase secretion without inhibition at supramaximal concentrations, has different effects on phospholipid hydrolysis and [Ca2+]i mobilization, compared to CCK-8 and Boc-[Nle28, Nle31]-CCK-7. Compound JMV180 was unable to significantly promote phospholipid breakdown, and was only 50%-60% as efficacious as Boc-[Nle28, Nle31]-CCK-7 in promoting [Ca2+]i mobilization. These findings suggest that low affinity CCK-receptors might be responsible for the supra-maximal inhibition of amylase secretion, and are correlated with phospholipid breakdown and maximal [Ca2+]i mobilization.

Cholecystokinin receptor antagonist loxiglumide: influence on bilio-pancreatic secretion and gastrointestinal hormones in man

We characterized the effect of the specific cholecystokinin (CCK) receptor antagonist loxiglumide (CR 1505) on gallbladder contraction, pancreatic enzyme output and plasma CCK concentrations determined by radioimmunoassay and bioassay. Gallbladder emptying and bilirubin output in response to the intraduodenal administration of a mixed liquid meal were completely inhibited by an intravenous infusion of loxiglumide (10 mg/kg/h). In contrast, meal-stimulated pancreatic enzyme secretion was diminished by only 30-40%. CCK concentrations in response to the test meal were 3-fold higher during infusion of loxiglumide, as determined by radioimmunoassay. In the absence of the antagonist, the bioassay measured CCK plasma levels identical to those determined by radioimmunoassay. In the presence of loxiglumide, CCK-like bioactivity was not detectable, indicating that the plasma concentrations of the CCK receptor antagonist were sufficient to abolish all circulating CCK-like bioactivity. We conclude that fasting volume and meal-induced contraction of the gallbladder are controlled by CCK. Postprandial pancreatic enzyme secretion, however, is mainly mediated by non-CCK-dependent mechanisms. Plasma CCK-like immunoreactivity is increased by loxiglumide, whereas plasma CCK-like bioactivity is zero in the presence of an CCK-receptor antagonist.

Anxiogenic-like action of caerulein, a CCK-8 receptor agonist, in the mouse: influence of acute and subchronic diazepam treatment

Effects of caerulein, a cholecystokinin octapeptide (CCK-8) receptor agonist, on exploratory activity of mice were investigated. Exploratory and locomotor activity of animals were measured using elevated plus-maze and open field tests. The systemic administration of caerulein at non-sedative doses (100 ng/kg-1 micrograms/kg i.p.) resulted in a significant decrease in the exploratory activity of mice. This effect was completely blocked by proglumide, a CCK-8 receptor. Acute treatment with low doses (0.1-0.75 mg/kg i.p.) of diazepam did not attenuate the anxiogenic-like effect of caerulein, but at more high doses of diazepam the coadministration depressed locomotor activity in mice. After subchronic diazepam treatment (2.5 mg/kg once a day, 10 days, i.p.) tolerance was developed toward the sedative effect of diazepam, and 72 h after withdrawal of the drug the animals showed increased anxiety in the plus-maze test. 30 min after the last injection procedure the anxiogenic-like effect of caerulein (500 ng/kg i.p.) on exploration was absent in both diazepam or vehicle groups. However, 72 h after the last pretreatment injection caerulein (500 ng/kg i.p.) reduced significantly the exploratory activity in control group, whereas it was inactive after diazepam withdrawal. The results obtained in this study support the hypothesis that endogenous CCK-8 an CCK-8 receptors are involved in the neurochemistry of anxiety and the anxiolytic action of benzodiazepine tranquillizers.

Cholecystokinin receptors and vagal nerves in control of food intake in rats

This study was designed to determine the specificity and physiological nature of short-term satiety effects of cholecystokinin (CCK) in rats with intact and transected vagal nerves. Rats with-the gastric fistulas, closed or open, were used for normal feeding or sham feeding of liquid meal offered for 30 min. CCK-8 (0.5-10 nmol/kg) injected intraperitoneally (ip) 15 min before feeding inhibited food intake dose dependently in both normal-fed and sham-fed rats at a minimal inhibitory dose of 1 nmol/kg. CCK-8 at the same doses caused a potent stimulation of pancreatic protein secretion, reaching maximum at a dose of approximately 0.5 nmol/kg. Pretreatment with a potent CCK receptor antagonist, L-364,718 (2.5 mg/kg ip), increased food intake during normal feeding (but not sham feeding) and almost completely blocked the satiety and pancreatic stimulatory effects of CCK. When feeding was preceded by intragastric administration of proteinase inhibitor (Foy-305, 200 mg/kg), food preload, or diversion of bile-pancreatic secretion to the exterior, there was a significant increase in the plasma level of CCK and an inhibition of food intake by about 36, 78, and 25%, respectively. Pretreatment with L-364,718 completely abolished this inhibition by Foy-305 and bile-pancreatic diversion and reduced that caused by food preload. Among other gut peptides given ip (10 nmol/kg) only bombesin reduced food intake, whereas gastrin, secretin, gastric inhibitory polypeptide (GIP), pancreatic polypeptide (PP), and peptide YY (PYY) were ineffective.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of CR 1409, a potent CCK receptor antagonist, on basal and stimulated pancreatic secretion in rat

The effect of a specific cholecystokinin (CCK) receptor blocker from Rotta Research Laboratorium (Monza/Milano, Italy), CR 1409 (Lorglumide), on pancreatic secretion was investigated. CR 1409 caused a rightward and parallel shift in the dose-response curve of CCK-8-stimulated pancreatic protein secretion in anesthetized rats, demonstrating a competitive mechanism of inhibition. The mean pA2 value, showing the 50% inhibitory dose of CR 1409, was 6.4. CR 1409 proved to be about 1,000 times more potent as a CCK receptor blocker than proglumide, the first glutaramic acid analogue with anti-CCK potential. In conscious rats, pancreatic protein and water secretion were significantly diminished for about 2 h in response to 300 micrograms/kg of CR 1409 given subcutaneously during diversion of pancreatic juice, demonstrating inhibition of endogenous CCK by this new glutaramic acid derivative. By contrast, during reintroduction of precollected pancreatic juice into the duodenum, when the release of CCK is almost totally eliminated, pancreatic secretion was not modified by the same dose.

Cholecystokinin in the inhibition of gastric secretion and gastric emptying in humans

Cholecystokinin (CCK) is known to inhibit gastric acid secretion and gastric emptying but its physiological role in the inhibition of gastric functions is not settled. In this study performed on 16 young male subjects, gastric acid secretion and emptying rate were determined after intragastric administration of 8% peptone meal alone or in combination with intravenous infusion of graded doses of CCK-8 (5-80 pmol/kg.h) or with addition of vegetable oil to meal without or with pretreatment with loxiglumide, a specific CCK antagonist. CCK-8 infusion at lower dose (5 pmol/kg.h) was ineffective but at higher doses (20-80 pmol/kg.h) it resulted in a significant reduction in acid output by 39 and 43% and a decrease in gastric emptying from 54% to 40 and 22%, respectively. Pretreatment with loxiglumide abolished almost completely the inhibition of both gastric acid and gastric emptying by CCK-8. Fat added to peptone meal reduced gastric acid secretion by 42-65% and decreased gastric emptying to 24-32%. The pretreatment with loxiglumide tended to reduce fat-induced inhibition of gastric acid secretion and gastric emptying but the difference in the inhibition of gastric functions between the tests without and with loxiglumide was not significant. This study provides evidence that exogenous CCK administered at pharmacological doses is a potent inhibitor of gastric acid secretion and gastric emptying and probably acts via specific CCK receptors. In contrast, fat induces inhibition of gastric acid secretion and gastric emptying that cannot be fully attributed to hormonally acting CCK.

Pancreatic receptors for cholecystokinin: evidence for three receptor classes

For inhibition of binding of 125I-Bolton-Hunter-labeled cholecystokinin octapeptide (125I-BH-CCK-8) to guinea pig pancreatic acini, the potencies for agonists were CCK-8 greater than desulfated [des(SO3)] CCK-8 greater than gastrin-17-I greater than pentagastrin greater than CCK-4 and for the antagonists L 364718 greater than proglumide analogue 10 greater than CBZ-CCK-(27-32)-NH2. For all non-sulfated agonists, the curves were biphasic with 20% of the tracer bound to sites with high affinity for these agonists with the following relative potencies: gastrin-17-I greater than pentagastrin greater than des(SO3)CCK-8 much greater than CCK-4; whereas 80% was bound to low-affinity sites with the following potencies: des(SO3)CCK-8 greater than gastrin-17-I = pentagastrin much greater than CCK-4. For L 364718 and proglumide analogue 10, 80% of 125I-BH-CCK-8 was bound to sites with high affinity for these antagonists and 20% to sites with low affinity. Analysis of the dose-inhibition curve for CCK-8 demonstrated two binding sites; however, comparison with the analysis in the presence of 0.1 microM gastrin-17-I suggested three binding sites. The gastrin-17-I dose-inhibition curve was significantly better fit by a three-site model than by a two-site model. The affinities of the various agonists and antagonists for the three sites were compared with their abilities to inhibit binding of 125I-gastrin-I and either stimulate or inhibit CCK-8-stimulated amylase release. These results demonstrate that 125I-BH-CCK-8 binds to three classes of receptors, not two as reported previously. Two classes are CCK-preferring, bind 83% of 125I-BH-CCK-8 at tracer concentrations, and comprise high- and low-affinity CCK-preferring sites that can be distinguished by all agonists but have equally high affinity for L 364718 and proglumide 10. A third class binds 17% of the tracer, cannot be differentiated from high-affinity CCK-preferring receptors by CCK-8, and has low affinities for L 364718 and proglumide 10. Future studies relating binding of 125I-BH-CCK-8 to biological activity or characterization of the CCK receptor by using radiolabeled agonists should consider CCK interaction with three receptors, not two as was done in the past.

Integrated actions of cholecystokinin on the gastrointestinal tract: use of the cholecystokinin bioassay

This article has centered on the hormonal actions of CCK on a variety of different target tissues. Until the development of specific assays for measuring plasma levels of the hormone, it was not possible to distinguish physiologic from pharmacologic effects. However, by the methods described earlier it now has become clear that CCK, in physiologic concentrations, stimulates gallbladder contraction, delays gastric emptying, potentiates insulin secretion, and may affect satiety. Actions of CCK that have been studied by radioimmunoassay methods and determined also to be physiologic include stimulation of pancreatic exocrine secretion. Other actions of CCK that may be physiologic but have not been thoroughly investigated include effects on bowel motility, relaxation of lower esophageal sphincter pressure, regulation of sphincter of Oddi pressure, effects on analgesia, and modification of behavior. Some of these actions may be attributable to endogenous, but neurally released CCK and, therefore, would not be hormonal actions. However, continued investigations with specific CCK receptor antagonists together with accurate measurements of circulating levels of CCK should make it possible to define the physiologic importance of CCK on these other potential sites of action. The variety of CCK's physiologic effects emphasizes its integrative function on both digestive and metabolic processes. After a meal, in a highly coordinated fashion, CCK (1) regulates the movement of nutrients through the gastrointestinal tract, (2) contracts the gallbladder and stimulates pancreatic exocrine secretion to facilitate digestion, and (3) potentiates amino acid-induced insulin secretion and delays gastric emptying to maintain euglycemia. An effect to reduce food intake following food ingestion would be a logical extension of these integrated actions. Thus, CCK appears to have an essential role in regulating the intake, processing, and distribution of essential nutrients.

Effects of gastrointestinal peptides on gastrointestinal cancer growth

The trophic effect of gut hormones may have important clinical applications for treatment of gut and pancreatic cancers. We now have developed methods by which we can quantitate gut hormone receptors in normal and neoplastic gut mucosa and pancreas. Analysis of gut and pancreatic tumors for gut hormone receptors may thus allow us to select patients with these cancers who would respond to treatment with hormones, antihormones, or hormone ablation in a manner similar to current strategies that are employed successfully for treatment of patients with breast cancer.

Effect of the novel cholecystokinin receptor antagonist CR-1392 on cholecystokinin-induced antroduodenal and pyloric motor activity in vivo

The effects of i.a. injected cholecystokinin (CCK)-octapeptide on pyloric and antroduodenal motility, measured with strain gauges and combined side hole-sleeve manometry, were investigated in 16 dogs in vivo. CCK-octapeptide (OP) induced strong pyloric contractions when injected into the pylorus (threshold of 2 x 10(-13) mol; ED50, 8 x 10(-13) mol). Similar responses were obtained in the distal antrum (threshold, 6 x 10(-13) mol; ED50, 3 x 10(-12) mol) and the proximal duodenum (threshold, 5 x 10(-13) mol; ED50, 3 x 10(-12) mol). The nonsulfated form of CCK-OP was about 2 to 3 log units less potent in eliciting these excitatory responses in the pylorus (threshold, 9 x 10(-10) mol). Atropine shifted the dose-response curve of CCK-OP in pylorus, duodenum and antrum to the right suggesting a neural action of CCK-OP. However, an excitatory effect of CCK-OP was still present after neural blockade with tetrodotoxin i.a. Therefore, there was probably a muscular as well as a neural site of action of CCK-OP in these tissues. Systemic application of the novel CCK-antagonist CR-1392 in a dose of 1.2 mg/kg i.v. plus 100 micrograms i.a. shifted the dose-response curve of CCK-OP 1 log unit to the right without affecting the dose-response curve to acetylcholine. This dose of CR-1392 did not interfere with the pyloric motor responses to duodenal field stimulation or to intraduodenal acid infusion. These results demonstrate the dual peripheral action on nerve and muscle of CCK-OP in the pylorus in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

Distinct requirements for activation at CCK-A and CCK-B/gastrin receptors: studies with a C-terminal hydrazide analogue of cholecystokinin tetrapeptide (30-33)

We describe here the properties of tert-butyloxycarbonyl-Trp-Leu-Asp-Phe-NHNH2 (A-57696), a C-terminal hydrazide analogue of tert-butyloxycarbonyl-CCK4 (Boc-Trp-Met-Asp-Phe-NH2), at four cholecystokinin (CCK) receptor-bearing tissues, the guinea pig pancreas and gall bladder (Type A), guinea pig cortex (Type B), and NCI-H345 cells, a human small cell lung cancer cell line that expresses CCK-B/gastrin receptors. Using 125I-Bolton-Hunter-cholecystokinin octapeptide (26-33) (125I-Bolton-Hunter-CCK8) as the radioligand, A-57696 was found to be selective for cortical CCK-B receptors (IC50 = 25 nM), compared with pancreatic CCK-A receptors (IC50 = 15 microM). A-57696 behaved as a competitive antagonist in reversing CCK8-stimulated pancreatic amylase secretion and phosphoinositide breakdown. By Schild analysis, its Kd was determined to be 4.7 and 6.8 microM in amylase and phosphoinositide assays, respectively. A-57696 (100 microM) did not elicit gall bladder contraction, and it inhibited contractions induced by CCK8. The Kd of A-57696 at gall bladder CCK-A receptors was 19 microM. In contrast, A-57696 behaved as a partial agonist (80% of maximal CCK8 response) in stimulating calcium mobilization at CCK-B/gastrin receptors on NCI-H345 cells. A-57696 and CCK8 inhibited each other in calcium mobilization experiments utilizing the fluorescent dye Indo-1. Stimulatory actions of CCK8 and A-57696 were reversed by the CCK-B-selective (R)-L-365,260 (100 nM), whereas at the same concentration, the CCK-A-selective (S)-L-365,260 was ineffective. Binding studies using 125I-Bolton-Hunter-CCK8 and 125I-gastrin indicated that binding sites labeled by these two ligands displayed similar affinities for CCK8, desulfated CCK8, gastrin, A-57696, and both enantiomers of L-365,260. A-57696 represents a new class of CCK-A peptide antagonist at guinea pig pancreas a new class of CCK-A peptide antagonist at guinea pig pancreas and gall bladder. Its contrasting functional activities at guinea pig CCK-A and CCK-B/gastrin receptors in a human tumor cell demonstrate that, in addition to the previously described differences in binding specificity for selective agonists and antagonists, CCK-A receptors and CCK-B/gastrin receptors have different requirements for activation.

Centrally administered CCK-8 suppresses activity in mice by a "peripheral-type" CCK receptor

Cholecystokinin octapeptide (CCK-8) administered either systemically (IP) or centrally (ICV) suppresses several types of behavior in mice including exploratory locomotion, rearing and grooming. At doses equimolar to those active for CCK-8, neither desulfated CCK-8 (CCK-8-DS), nor the protected C-terminus tetrapeptide fragment, BOC-CCK-4, is behaviorally active when administered either centrally or systemically. A potent and selective antagonist to the peripheral type (Type A) CCK receptor, A-65186, when given systemically, blocked the effects of systemically administered CCK-8, but failed to block the effects of ICV administered CCK-8. Central administration of A-65186 blocked the effects of ICV administered CCK-8. These results demonstrate that administration of exogenous CCK-8 to mice can suppress exploratory locomotion by acting either centrally or peripherally and that in either case the demonstrated behavioral effects are mediated via a "peripheral" type (Type A) CCK receptor.

Cholecystokinin receptor antagonism of stimulated pancreatic and gastric secretion

The effects of cholecystokinin receptor antagonist, dipentyl-3,4-dichloroproglumide (DDP), on stimulated pancreatic and gastric secretion were studied in the rat. DDP dose-dependently inhibited cholecystokinin-stimulated amylase release from dispersed acinar cells. In vivo, DDP inhibited cholecystokinin octapeptide-stimulated amylase and protein secretion. DDP also inhibited pentagastrin-stimulated gastric acid secretion in vivo. Meal-stimulated acid output was decreased by 34% (DDP 400 micrograms/kg/hr) but responsiveness to histamine or parachlorophenyl-gamma-aminobutyric acid was unchanged.

Experimental pancreatitis is mediated by low-affinity cholecystokinin receptors that inhibit digestive enzyme secretion

Rats infused with a supramaximally stimulating dose of the cholecystokinin (CCK) analog caerulein develop acute edematous pancreatitis. Using CCK-JMV-180, a recently developed CCK analog that acts as an agonist at high-affinity CCK receptors but antagonizes the effect of CCK at low-affinity receptors, we have determined that caerulein induces pancreatitis by interacting with low-affinity CCK receptors. Those low-affinity receptors mediate CCK-induced inhibition of digestive enzyme secretion from the pancreas. Our observations, therefore, suggest that this form of experimental pancreatitis results from the inhibition of pancreatic digestive enzyme secretion.

Effects of loxiglumide on gallbladder emptying in healthy volunteers

This study evaluates the effects of the specific cholecystokinin receptor antagonist loxiglumide on gall-bladder emptying after a meal or after intravenous infusion of caerulein in humans. Ten healthy male volunteers were studied five times on separate days. The following five studies were performed in randomized order: (a) caerulein was intravenously infused at doses increasing from 7.5 to 120 ng/kg.h without the antagonist; (b) in addition to increasing doses of caerulein, loxiglumide was given intravenously at doses of 0.2, 1.0, or 5.0 mg/kg.h; (c) a solid-liquid 800-kcal meal was given without loxiglumide; (d) the 800-kcal meal was given with simultaneous infusion of 1 or 5 mg/kg.h loxiglumide; and (e) loxiglumide (5 mg/kg.h) was given. without caerulein or the test meal. Gallbladder volume was measured by ultrasound. Loxiglumide dose-dependently inhibited gallbladder emptying induced by caerulein or the meal. High doses of the antagonist did not only abolish meal-induced gallbladder emptying but increased gallbladder volume after administration of caerulein or the meal when compared with prior fasting values. The antagonist given alone markedly increased gallbladder volumes compared with prior fasting values. In conclusion, given alone markedly increased gallbladder volumes compared with prior fasting values. In conclusion, cholecystokinin is the hormone primarily and mainly responsible for mediation of gallbladder emptying after a regular meal. Cholecystokinin might also play a physiologic role in the regulation of the fasting tone of the gallbladder.

[The effect of cholecystokinin antagonists on satiety induced by cholecystokinin octapeptide in dogs]

We administered two cholecystokinin antagonists to dogs intravenously (i.v.) and into the third cerebral ventricle (i.t.v.). Proglumide (3-300mg/kg/hr i.v. or 0.1-10mg/dog i.t.v.) reversed the satiety previously shown by mongrel dogs after i.t.v. CCK-8. A new glutaramic derivative, CR1409, blocked this satiety even more strongly when administered by either route. Proglumide increased proglumide levels in ventricular fluid, indicating its ability to cross the blood-brain barrier. However, i.t.v. proglumide did not appear in the blood during the observation period. These results suggest that systemic proglumide and CR1409 act as antagonists of the central CCK receptor concerning satiety in dogs; intravenously administered proglumide was found to cross the blood-brain barrier and partially but significantly reverse the satiety caused by CCK-8.

Synthesis and biological activity of some partially modified retro-inverso analogues of cholecystokinin

Syntheses of some partially modified retro-inverso analogues of the C-terminal octa- or heptapeptide of cholecystokinin are described. These analogues (in which the C-terminal carboxamide was deleted or not) were obtained by reverting one or several peptide bonds in the parent molecule. All these compounds were able to inhibit binding of labeled CCK-8 to rat pancreatic acini and guinea pig brain membranes and to stimulate amylase release from rat pancreatic acini with various potencies. Some of these derivatives reproduce only part of the biological response of CCK on amylase release.

Ornithine decarboxylase and polyamines in cholecystokinin-induced pancreatic growth in rats: effects of alpha-difluoromethylornithine and the CCK receptor antagonist L-364,718

Acute and long-term changes of ornithine decarboxylase and polyamines during pancreatic adaptation in response to cholecystokinin administration (1 microgram kg-1 body wt every 8 h) were studied in rats. alpha-difluoromethylornithine, an irreversible and specific inhibitor of ornithine decarboxylase, was applied simultaneously to elucidate the essential role of polyamines in pancreatic growth. In the cholecystokinin-treated animals ornithine decarboxylase activity was increased after 2 h, reached a maximum after 8 h (444.6 pmol 14CO2 h-1 mg-1 DNA, about 65-fold greater than controls, P less than 0.001) followed by a significant increase of putrescine after 6 h and spermidine after 24 h while spermine remained unchanged. The trophic parameters increased in the following time sequence: thymidine kinase (12 h), DNA polymerase (24 h), pancreatic weight (2 days), protein (2 days) and DNA (5 days). alpha-difluoromethylornithine significantly delayed the increase in ornithine decarboxylase, putrescine and spermidine as well as all trophic parameters. Increases in ornithine decarboxylase, polyamines and all trophic parameters were completely inhibited by simultaneous application of the CCK receptor antagonist L-364,718. These data indicate an important role for ornithine decarboxylase and polyamines in cholecystokinin-induced pancreatic growth in rats.

Effects of site-specific CNS microinjection of cholecystokinin on lordosis behavior in the male rat

We have previously demonstrated that intracerebroventricular injections of sulphated cholecystokinin octapeptide (sCCK-8) had a dramatic facilitatory effect on lordosis behavior in the gonadectomized, estrogen-primed male rat. In the female, sCCK-8 facilitates or inhibits lordosis when microinjected into the medial preoptic nucleus (MPN) or ventromedial nucleus of the hypothalamus (VMH), respectively. In order to identify sCCK-8 responsive sites that modulate lordosis behavior in gonadectomized males, sCCK-8 was microinjected into the MPN or VMH. Sulphated CCK-8 significantly increased lordosis behavior when microinjected into the MPN of estrogen-primed males, but had no significant effects when microinjected into the VMH. These results imply that CCK-sensitive neural substrates within the MPN may act to disinhibit lordosis in the gonadectomized, estrogen-primed male rat. The lack of an effect of VMH injection of sCCK-8 on lordosis in males is discussed in terms of possible sex differences in sCCK-8-sensitive lordosis-modulating circuits.

Effects of the CCK receptor antagonist L364,718 on pancreatic growth in adult and developing animals

Although exogenous administration of cholecystokinin (CCK) or dietary manipulation to increase circulating CCK have previously been shown to promote pancreatic growth, the role of CCK in controlling normal pancreatic development remains unclear. A potent CCK receptor antagonist, L364,718, was administered to rats, guinea pigs, and hamsters to block the effect of endogenous CCK. Animals were given continuous infusions of L364,718 (25 nmol.kg-1.h-1), CCK octapeptide [(CCK-8) 200 pmol.kg-1.h-1], or both CCK-8 and L364,718 for 14 and 28 days. Adult (4-mo-old) and young (4-wk-old) animals were used. CCK-8 and L364,718 were administered via separate, subcutaneously implanted mini-osmotic pumps. Infusions of CCK-8 alone for 28 days resulted in a 21.7% increase in wet pancreatic weight in 4-wk-old rats and a 22.7% increase in 4-wk-old guinea pigs (both P less than 0.001 compared with controls). Similar increases were found in DNA, RNA, and total protein contents. Coadministration of L364,718 totally blocked the trophic effects of exogenously infused CCK-8 in rats and guinea pigs. Administration of L364,718 alone in hamsters, guinea pigs, and rats for 14 and 28 days failed to alter the normal growth of the pancreas gland as measured by these parameters. Although elevated levels of CCK appear to promote a potent trophic response in the growing pancreas, this regulatory peptide does not appear to be an essential trophic factor for the normal growth of the exocrine pancreas in these animals.

A new CCK analogue differentiates two functionally distinct CCK receptors in rat and mouse pancreatic acini

Analysis of the competitive inhibition of 125I-labeled cholecystokinin octapeptide (CCK-8) binding to isolated rat or mouse pancreatic acini showed that in both species CCK-8 interacts with two different affinity sites. A newly synthesized CCK analogue modified at the COOH-terminal phenylalanine residue totally inhibited 125I-CCK binding. This interaction occurred with sites of a single affinity in rat acini but with two different affinity sites in mouse acini. When acini were incubated with increasing concentrations of CCK-8, a biphasic stimulation of amylase release was observed. By use of rat acini, the analogs stimulated amylase release but caused no inhibition at supramaximal concentrations. By contrast, in mouse pancreatic acini, analogues showed a biphasic stimulation of amylase release similar to CCK-8. Both CCK-8 and the analogue stimulated [3H]leucine incorporation into protein at low concentrations in rat pancreatic acini. Higher concentrations of CCK-8 profoundly inhibited [3H]leucine incorporation, whereas the analogue had no inhibitory effect. Moreover, the analogue at higher concentrations blocked the inhibition of [3H]leucine incorporation caused by CCK-8 but did not affect carbamylcholine-induced inhibition. In mouse acini, however, the CCK analogue inhibited [3H]leucine incorporation similar to the effect of CCK-8. The results support the concept that occupancy of distinct affinity sites or states of the CCK receptor is associated with specific biological actions. A model of the CCK receptor is proposed in which two interchangeable affinity states exist. By occupying all the receptors in only one state, the new CCK analogues serve as partial agonists of some and antagonists of other actions of CCK.

Postponement of satiety by blockade of brain cholecystokinin (CCK-B) receptors

Exogenous cholecystokinin (CCK) decreases food intake and causes satiety in animals and man. However, it has not been established that endogenous CCK causes satiety or whether the response is mediated by peripheral-type (CCK-A) or brain-type (CCK-B) receptors. The development of potent and selective antagonists for CCK-A (MK-329) and CCK-B (L-365,260) receptors now allows these issues to be addressed. The CCK-A antagonist MK-329 and the CCK-B antagonist L-365,260 increased food intake in partially satiated rats and postponed the onset of satiety; however, L-365,260 was 100 times more potent than MK-329 in increasing feeding and preventing satiety. These results suggest that endogenous CCK causes satiety by an agonist action on CCK-B receptors in the brain.