Doses Of Caerulein Research Articles

In vivo rat pancreatic acinar cell function during supramaximal stimulation with caerulein

Infusion of a supramaximal dose of caerulein results in acute interstitial pancreatitis in rats. We report studies of in vivo pancreatic acinar cell function during the initial 3.5 h of supramaximal stimulation with caerulein (5 micrograms X kg-1 X h-1). Amino acid [( 3H]phenylalanine) uptake was not altered, and there was no change in the rate or extent of protein synthesis or in intracellular transport of in vivo pulse-labeled proteins from microsome to zymogen granule-enriched fractions. However, the discharge of labeled protein was markedly inhibited. Radioautographic studies indicated that the pulse-labeled proteins retained in the gland were not located extracellularly but had accumulated within acinar cells, with a preferential distribution at the cell apex (presumably in zymogen granules) and in large vacuoles that form within the cell during hyperstimulation. Supramaximal stimulation with caerulein also caused increasing amounts of amylase and labeled proteins to be recovered in the postmicrosomal fraction. These findings suggest that supramaximal stimulation causes digestive enzymes to become localized in organelles that are fragile and subject to disruption during tissue homogenization. These organelles may be the vacuoles noted in morphological studies and believed to represent immature condensing vacuoles and/or crinophagic vacuoles.

Modulating effect of cerulein on benzodiazepine receptors

Subcutaneous administration of caerulein (100-500 micrograms/kg) significantly reduced the development of picrotoxin (8 mg/kg) seizures in male mice. The same doses of caerulein inhibited 3H-flunitrazepam binding in in vivo experiments. Proglumide, an antagonist of cholecystokinin receptors, in low dose (5 mg/kg) potentiated the effects of caerulein (100 micrograms/kg), whereas the administration of proglumide in high dose (25 mg/kg) reduced the action of caerulein on 3H-flunitrazepam binding and picrotoxin seizures. Caerulein (5-1000 nM) decreased 3H-flunitrazepam binding in in vitro experiments only after supplementation of the binding medium with 120 mM NaCl and 5mM KCl. The results suggest the possible interaction of caerulein with chloride ionophor. It seems probable that the direct interaction of caerulein with chloride ionophor in involved in the inhibitory effect of caerulein on picrotoxin seizures and 3H-flunitrazepam binding.

Caerulein-Induced Acute Necrotizing Pancreatitis in Mice; Protective Effects of Proglumide Benzotript, and Secretin

The onset, course, and regression of the biochemical and structural alterations associated with pancreatitis induced by various doses of caerulein were studied in the mouse. In addition, the protective effect of secretin was compared with that of the cholecystokinin-receptor antagonists proglumide and benzotript. Subcutaneous or intraperitoneal injections of caerulein induced increases in serum amylase concentration and pancreatic weight and histologic evidence of acute pancreatitis, all effects being dose-related. Cytoplasmic vacuoles were the earliest histologic alterations. As the pancreatitis progressed these vacuoles increased to an enormous size. Interstitial inflammation and acinar cell necrosis were prominent after 6 h, reached a maximum after 12 h, and mostly disappeared after 4 days. During the course of pancreatitis approximately 40% of the acinar cells showed signs of severe degeneration or necrosis at the most effective doses of caerulein. Electron microscopy showed both intact and degenerating granules inside the vacuoles. Signs of basolateral exocytosis of zymogen granules were not observed. During the regression of pancreatitis, focal atrophy was a remarkable histologic finding. Repetitive initiation of pancreatitis (six courses of caerulein injections over 5 wk) produced marked focal atrophy and early fibrosis. High doses of proglumide or benzotript markedly ameliorated both the biochemical and structural alterations induced by caerulein. Secretin, even at very high doses, had only minor protective effects. This study presents a model of acute necrotizing pancreatitis in which the severity of the induced pancreatitis ranges dose-dependently from mild interstitial inflammation to severe necrosis. The ultrastructural alterations described herein support the hypothesis that the trigger mechanism of acute pancreatitis appears to be a primary intracellular event rather than an interstitial event that secondarily damages the acinar cells.

Analysis of the Long-Lasting Antagonistic Effect of Caerulein on Amphetamine Hyperactivity in Rats

Caerulein (CLN), which is chemically related to cholecystokinin octa-peptide (CCK-8) and produces a short-lasting pharmacological effect when administered peripherally, caused a long-lasting antagonistic effect on amphetamine (AMP) hyperactivity in rats when given in combination with haioperidol (HLP). Briefly, rats were treated with a combination of CLN (0.3–40 μg/kg, s.c.) and HLP (0.1 mg/kg, s.c.) and exposed to AMP on the first day. The animals became less sensitive to AMP for 24 hr to about 2 weeks depending on the CLN dose, according to measurements of their ambulatory activities in an open field or with an Animex activity meter at low sensitivity. Examination of the properties of this long-lasting effect revealed that: 1) in animals treated with CLN and HLP, but without AMP on the first day, the susceptibility to AMP was not influenced on the next day; 2) in substitution experiments, the antagonistic effect of CLN could be reproduced by higher doses of CCK-8 (160 μg/kg) but not by nonsulfated CLN; 3) in the regimen of the treatment schedule, HLP could be replaced by chlorpromazine or sulpiride, but not by α-blocking agents like phenoxybenzamine or yohimbine; 4) apomorphine, nomifensine and tranylcypromine could not substitute for AMP. Thus, injection of CLN together with HLP and AMP on the first day might be necessary to produce the long-lasting anti-AMP effect. The possible mechanism of this CLN effect is discussed.

Structural and biochemical characterization of maximal and supramaximal hormonal stimulation of rat exocrine pancreas.

To study the regulation of the successive steps along the secretory pathway in the rat exocrine pancreas the model of in vivo infusion of synthetic caerulein in conscious rats for periods up to 72 h was combined with electron microscopy and in vitro analysis of protein synthesis, intracellular protein transport and enzyme discharge using isolated pancreatic lobules. Prolonged and maximal hormonal stimulation was obtained with 0.25 microgram kg-1 h-1 caerulein and resulted in a 80-90% depletion of enzyme stores within 1 to 3 h, followed by coordinate and anticoordinate changes in individual rates of (pro-)enzyme synthesis after a lag period of 3 h. One group (two amylases) revealed a decrease in synthesis to levels about 10-fold lower than controls. A third group of proteins (one trypsinogen, lipase, proelastase) did not show changes in synthesis with hormone stimulation. The sum of such alterations led to an increase in total rate of synthesis after 6 h, which was combined with acceleration of intracellular transport, packaging, and granule discharge, thus enabling a sustained rate of secretion over the period of stimulation. In contrast, infusion of a supramaximal dose of caerulein (5.0 micrograms kg-1 h-1) induced acute edematous pancreatitis and led to an almost complete reduction of volume and protein output from the cannulated main pancreatic duct. Using freeze-fracture techniques and thin-section electron microscopy, earliest structural alterations were observed at membranes of zymogen granules and the plasma membrane. Fusion of zymogen granules among each other led to formation of large membrane-bound vacuoles within the cytoplasm. These and individual zymogen granules fused with the lateral instead of the apical plasma membrane, discharging their content into the interstitial space. Vacuole formation was associated with activation of lysosomes and with cytoplasmic destruction of acinar cells. The findings indicated severe changes in the specificity of the intracellular membrane fusion process induced by supramaximal doses of caerulein, which finally resulted in autodigestion of the pancreas.

Caerulein peripheral injection: A study on the correlation with dopaminergic metabolism

Immunocytochemical and electrophysiological studies indicate the existence of a functional relationship between Cholecystokinin (CCK) and dopaminergic transmission. In order to gain more information on this relationship, the effect of Caerulein, a CCK stable analogue, on rat spontaneous locomotor activity and on biochemical markers of dopaminergic transmission were measured simultaneously. The concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC) and the spontaneous or K+ evoked release of dopamine were studied in rat striatum and nucleus accumbens immediately after testing for motor activity. An almost complete reduction in locomotor activity but not significant changes in DOPAC content and dopamine release were observed in rats injected with the peptide (0.25/microgram/Kg, intraperitoneally). DOPAC concentrations were slightly (30%) decreased by increasing 200 folds caerulein dose. In addition, a very minute dose of haloperidol (25 /microgram/Kg) potentiated the caerulein (0.25/microgram/Kg) induced hypomotility, while the parameters of dopaminergic metabolism were unaffected. Our results indicate the existence of a relevant pharmacological interaction between caerulein and dopamine antagonists, although it is not clear whether this interaction takes place at the dopamine terminals level.

Effect of proglumide, a cholecystokinin receptor antagonist, on caerulein-stimulated pancreatic enzyme secretion and pancreatic polypeptide release in the dog

In five conscious dogs we studied the effect of proglumide, a cholecystokinin (CCK) antagonist, on caerulein-stimulated pancreatic secretion and release of pancreatic polypeptide (PP). Graded doses of caerulein (15–240 ng/kg per h) were infused intravenously. Experiments were repeated with a fixed infusion of proglumide (40 mg/kg per h). Release of PP following increasing doses of caerulein was significantly inhibited by proglumide ( P < 0.01). However, proglumide did not significantly affect caerulein-stimulated pancreatic protein secretion. Proglumide might be useful in defining the physiological role of CCK.

Interaction between stimulants of exocrine pancreatic secretion in dogs.

We measured bicarbonate and protein secretory responses to graded doses of intravenous caerulein and bethanechol and intraduodenal L-phenylalanine alone or with background secretin; graded doses of secretin alone or with background caerulein or L-phenylalanine; and background secretin plus graded doses of caerulein or L-phenylalanine plus background atropine sulfate. Potentiation (more-than-additive response) occurred for bicarbonate secretion between secretin and caerulein, between secretin and L-phenylalanine, but not between secretin and bethanechol. The only potentiating interaction for protein secretion was between secretin and low doses of caerulein. Atropine abolished the potentiated bicarbonate response to secretin plus L-phenylalanine but had no effect on the response to secretin plus caerulein. Potentiation between secretin and cholinergic mechanisms and cholecystokinin for pancreatic bicarbonate secretion may be an important regulatory mechanism, while potentiation of protein secretion with these stimulants does not appear to be important in dogs. A cholinergic mechanism mediates much of the bicarbonate potentiation between secretin and intestinal L-phenylalanine.

Effect of caerulein on total and ionized calcium secretion in the duodenal juice of man.

Previous studies have demonstrated an increase of total calcium secretion in the duodenal juice of healthy subjects after cholecystokinin (CCK) administration superimposed on a continuous secretion infusion. In order to get more detailed information on the physiology of calcium secretion and its dependance on hormonal stimulation, ionized and total calcium were determined in the duodenal juice of 9 volunteers under constant stimulation with secretin and graded caerulein doses; bound calcium was calculated as the difference of total and ionized calcium. The results of total calcium were in good agreement with previously published data. We found that total calcium secretion is mainly determined by bound calcium and bound calcium is mainly secreted together with bile products. Since ionized calcium concentration was independent of caerulein administration it is suggested that its concentration in gallbladder bile must be in good accordance with that of hepatic bile and pancreatic juice together.

A caerulein-sensitive potentiation of the behavioral effects of apomorphine by dibutyryl-cAMP

The dopaminergic behavioral effects of apomorphine in rats were evaluated using a rating scale. Caerulein, a decapeptide physiologically similar to cholecystokinin, enhanced at lower doses and inhibited at higher doses the behaviors induced by apomorphine. Dibutyryl-cAMP, but not dibutyryl-cGMP, potentiated apomorphine behaviors. The potentiation was inhibited by a high dose of caerulein. These data provide evidence for an opposing effect of cAMP and caerulein or cholecystokinin in modulating dopaminergic systems.

Structure-activity and dose-effect relationships of the antagonism of picrotoxin-induced seizures by cholecystokinin, fragments and analogues of cholecystokinin in mice

Intraperitoneal administration of cholecystokinin octapeptide sulphate ester (CCK-8-SE) and nonsulphated cholecystokinin octapeptide (CCK-8-NS) enhanced the latency of seizures induced by picrotoxin in mice. Experiments with N- and C-terminal fragments revealed that the C-terminal tetrapeptide (CCK-5-8) was the active centre of the CCK octapeptide molecule. The analogues CCK-8-SE and CCK-8-NS (dose range 0.2–6.4 μmol/kg) and caerulein dose range 0.1–0.8 μmol/kg) showed bell-shaped dose-effect curves, with the greatest maximum inhibition for CCK-8-NS. The peptide CCK-5-8 had weak anticonvulsant activity in comparison to the octapeptides, 3.2 μmol/kg and larger doses of the reference drug, diazepam, totally prevented picrotoxin-induced seizures and mortality. The maximum effect of the peptides tested was less than that of diazepam. Experiments with analogues and derivatives of CCK-5–8 demonstrated that the effectiveness of the β-alanyl derivatives of CCK-5-8 were enhanced and that they were equipotent with CCK-8-SE. Of the CCK-2–8 analogues, Ser(SO 3H) 7-Ac-CCK-2-8-SE and Thr(SO 3H) 7-Ac-CCK-2-8-SE and Hyp(SO 3H)-Ac-CCK-2-8-SE were slightly more active than CCK-8-SE.

Pancreatic citrate and protein secretion of alcoholic dogs in response to graded doses of caerulein.

Previous studies have shown dissolution of human pancreatic stones in vitro by citrate solution which bind considerable amounts of ionized calcium. Pancreatic citrate secretion has been demonstrated in canine and human pancreatic juices. This study compares pancreatic citrate secretion of chronic alcohol-fed dogs with controls in response to graded doses of caerulein, in order to evaluate possible differences in factors favouring pancreatic lithogenicity. The dose-response-relation of citrate outputs after graded doses of caerulein revealed significantly reduced maximal secretory capacity of citrate in alcoholic dogs. Protein concentrations in juices from alcoholic dogs were reduced for all doses of caerulein but protein outputs were not different. Bicarbonate concentrations and outputs, as well as volumes, were significantly greater in alcoholic dogs. Linear relation were found between citrate and protein secretion. Chronic alcohol consumption in the dog leads to reduced citrate secretion, which is consistent with recent results in humans suffering from chronic calcifying pancreatitis, who secrete significantly less citrate than healthy subjects. The decrease of calcium-chelating citrate could be an additional factor causing increased calcium levels in the pancreatic juice of chronic alcoholics, a circumstance that might favour protein-plug formation and subsequently pancreatic stone formation.

Analysis of the antagonistic effect of caerulein on amphetamine hyperactivity

Caerulein (CLN), chemically related to cholecystokinin octapeptide (CCK-8), generally produces a short-lasting pharmacological effect (Folia Pharmacol. Japon., 81, p6, 1982). However, in rats pretreated with a combination of CLN (0.3-40 μg/kg, s.c.) and haloperidol (HLP, 001mg/kg, s.c.), a long-lasting antagonistic effect on amphetamine (AMP) hyperactivity was found. In brief, animals, pretreated with a combination of CLN and HLP and exposed to AMP on the first day, become less sensitive to AMP for 24 hr to 2 weeks depending on the dose of CLN, when ambulatory activities were measured in an open field of Hall’s type. Examination of the properties of this long-lasting effect showed that: 1) In animals treated with CLN and HLP, but without AMP on the first day, the susceptibility to AMP was not influenced on the next day. 2) When another peptide was substituted for CLN, the antagonistic effect could be sustained only by injecting higher doses of CCK-8 (l60μg/kg) but not by nonsulfated CLN or small doses of CCK-8 (40μg/kg). 3) The long-lasting change in AMP susceptibility could be achieved if chlorpromazine or sulpiride was employed instead ofHLP. However, α-blocking agents, phenoxybenzamine and yohimbine, could not produce the effect. 4) Apomorphine, nomifensine and tranylcypromine could not be substituted for AMP. These results show that injecting CLN together with HLP and AMP on the first day might be necessary to produce a long-lasting anti-AMP effect. The effect was also observed in vagotomized rats or after an intracerebroventricular injection of CLN (100, 1000ng). Injection of CLN (10, 100ng) into the nucleus accumbens produced no effect. These observations are discussed in relation to a possible mechanism.

Effect of Cholecystokinin-Octapeptide, Caerulein, and Pentagastrin on Epithelial Cell Proliferation in the Murine Gallbladder

The growth-promoting effect of cholecystokinin-octapeptide, caerulein, and pentagastrin on gallbladder mucosa was investigated in mice. The acute effects on deoxyribonucleic acid synthesis activity was explored with a [3H]thymidine pulse and autoradiography after subcutaneous injection of the polypeptides. The administration of a supramaximal dose of caerulein or of cholecystokinin-octapeptide induced a significant increase (p less than 0.01) in the nuclear uptake of [3H]thymidine by the gallbladder epithelial cells. The injection of pentagastrin had no effect. Implantation of osmotic minipumps was used for the chronic administration of submaximal doses of caerulein or pentagastrin. Using successive [3H]thymidine pulses and autoradiography, increases in labeling (p less than 0.01) and mitotic indices (p less than 0.05) were observed in the caerulein group, whereas pentagastrin had no effect. In addition, a morphometric method was used to determine the total epithelial cell number in the entire gallbladder after chronic administration of the peptides. A significant (p less than 0.01) epithelial cell hyperplasia was observed to occur after caerulein administration whereas pentagastrin given by the same route had no effect on the epithelial cell population. These data indicate that cholecystokininlike peptides promote epithelial growth in the gallbladder of mice.

Effects of caerulein on rat small and large intestinal fluid transport in vivo.

We have examined the effect of caerulein on intestinal fluid transport in vivo. Rat jejunal, ileal, and colonic segments were perfused with a physiologic buffer for a 60-min control period, followed by a 60-min period after caerulein, prostaglandin E2 (PGE2), or saline (0.9%, w/v) were given by intramuscular (i.m) injection. At a dose of 5 micrograms/kg caerulein had no effect on ileal fluid transport. Lower doses of caerulein (300 ng and 1 microgram/kg) also had no effect. PGE2 significantly (P less than 0.05) inhibited net ileal absorption by 94 +/- 24% from pre-dose levels. Caerulein (300 ng/kg) had no effect (P greater than 0.05) on jejunal or colonic fluid transport. Intestinal fluid accumulation assessed by the 'enteropooling' assay did not increase after 30 ng or 1 microgram/kg of caerulein, whereas in animals given PGE2 of (5 mg/kg) the fluid accumulation more than doubled (P less than 0.001): control 1.59 +/- 0.15 ml; cerulein (1 microgram/kg) 1.36 +/- 0.20 ml; and PGE2 4.7 +/- 0.50 ml. Serum levels of caerulein (after a 1 microgram/kg dose), measured by radioimmunoassay, were elevated up to 30 min after i.m. injection. The data indicate that caerulein has no direct effect on rat small or large intestinal fluid transport.

Effects of Caerulein on exocrine pancreatic secretion in sheep

caerulein administered by slow intravenous infusion at increasing dosage rates (0.1, 1.0, 5.0 and 10.0 ng/kg/min X 30 min) stimulated pancreatic juice production in sheep as well as the protein content, the amylolytic, the lipolytic and proteolytic activities of pancreatic juice samples collected at 30 min intervals. A long lasting (300 min) infusion of a high dose of Caerulein by subcutaneous route elicited stimulatory effects with reduced intensities, slower onsets but more sustained durations than those produced by the same dose level administered intravenously.

Comparison of the effect of caerulein and testmeal on exocrine pancreatic secretion in the dog

Small doses of caerulein (10, 20, 40, 100 ng/kg/h) were given to conscious dogs with chronic duodenal and gastric fistulas, and the exocrine pancreatic response was compared with that obtained by a testmeal. Maximal protein and bicarbonate secretion varied between 20 and more than 100 ng/kg/h, depending on the individual animal. Testmeal-stimulated pancreatic secretion was approximately equivalent to that achieved with 10 ng caerulein/kg/h. Plasma secretin levels did not change significantly during testmeal stimulation.

The effects of caerulein on food intake in the cat

The effects of physiological doses of caerulein, a pure cholecystokinin analog, was measured on food intake of cats. Food intake was increased by caerulein when infused at 400 ng/kg/hr. However, at the lowest dose, a slight decrease of intake was observed suggesting that low levels of caerulein may inhibit food intake in this species. Slow infusion of caerulein as compared to bolus injection may have opposite effects on food intake, that is, stimulation with infusion and inhibition with injection.

Effect of Caerulein on Exocrine and Endocrine Pancreas in the Rat

The secretion of insulin, glucagon, pancreatic juice, and amylase in response to a 20-min iv infusion of synthetic caerulein were studied simultaneously in the anesthetized rat. Caerulein, a chemical analogue of cholecystokinin, was used in doses of 1-1000 ng/kg.min. The maximum stimulatory effect of caerulein on pancreatic juice volume and amylase output was obtained with doses of 10 ng/kg.min. With increasing doses, the effect decreased progressively. On the other hand, the release of insulin and glucagon was stimulated only by supramaximal doses of caerulein, which had little or no effect on pancreatic exocrine secretions. These results raised the question of whether, under physiological conditions, cholecystokinin regulates the secretory activity of the endocrine pancreas.

Discrepancies between the Doses of Cholecystokinin or Caerulein-Stimulating Exocrine and Endocrine Responses in Perfused Isolated Rat Pancreas

The effects of highly purified natural porcine cholecystokinin (CCK) and synthetic caerulein on the rate of flow of pancreatic juice, the rate of output of amylase, and the rate of release of immunoreactive insulin (IRI) and immunoreactive glucagon (IRG) were simultaneously investigated in the isolated perfused rat pancreas. The maximal flow rate of pancreatic juice was obtained with concentrations of CCK ranging from 0.5 to 10 mU/ml, whereas amylase output was maximal at CCK concentrations from 1 to 10 mU/ml. Caerulein at concentrations of 0.05-1 ng/ml induced a similar maximal flow rate and amylase secretion. Supramaximal stimulatory concentrations of these peptides resulted in lower rates of release of fluid and amylase than with the maximally effective concentrations. Stimulation of IRI and IRG release was elicited only with concentrations of peptides supramaximal for effects on the exocrine responses. The demonstration of very similar discrepancies between the doses of caerulein required to elicit maximal exocrine responses and those required to elicit endocrine responses provide strong evidence that the pattern of the effect of the porcine CCK is accounted for by CCK itself. Although caerulein had no influence on IRI response when superimposed on 100 or 150 mg/100 ml glucose stimulation, preperfusion of caerulein led to a significant enhancement of IRI response to a subsequent glucose stimulation in both phases. The augmentation effect was completely separate from the direct IRI-stimulating effect of caerulein, because the CCK-like peptide requires no glucose for insulinotropic action. Because the concentrations of the peptides necessary for stimulation of endocrine responses were inhibitory in their effects on exocrine responses, it may be inferred that it is unlikely that the endocrine effect is physiologically important, though the results of caerulein for augmenting glucose-stimulated IRI release suggests a possible role for CCK in carbohydrate metabolism.