The action of scretin, cholecystokinin-pancreozymin and caerulein on pancreatic secretion in the rat

Pancreatic Crosstalk in the Disease Setting: Understanding the Impact of Exocrine Disease on Endocrine Function

The exocrine and endocrine are functionally distinct compartments of the pancreas that have traditionally been studied as separate entities. However, studies of embryonic development, adult physiology, and disease pathogenesis suggest there may be critical communication between exocrine and endocrine cells. In fact, the incidence of the endocrine disease diabetes secondary to exocrine disease/dysfunction ranges from 25% to 80%, depending on the type and severity of the exocrine pathology. Therefore, it is necessary to investigate how exocrine-endocrine "crosstalk" may impact pancreatic function. In this article, we discuss common exocrine diseases, including cystic fibrosis, acute, hereditary, and chronic pancreatitis, and the impact of these exocrine diseases on endocrine function. Additionally, we review how obesity and fatty pancreas influence exocrine function and the impact on cellular communication between the exocrine and endocrine compartments. Interestingly, in all pathologies, there is evidence that signals from the exocrine disease contribute to endocrine dysfunction and the progression to diabetes. Continued research efforts to identify the mechanisms that underlie the crosstalk between various cell types in the pancreas are critical to understanding normal pancreatic physiology as well as disease states. © 2024 American Physiological Society. Compr Physiol 14:5371-5387, 2024.

Repetitive Cerulein-Induced Chronic Pancreatitis in Growing Pigs-A Pilot Study

Chronic pancreatitis (CP) is an irreversible and progressive inflammatory disease. Knowledge on the development and progression of CP is limited. The goal of the study was to define the serum profile of pro-inflammatory cytokines and the cell antioxidant defense system (superoxidase dismutase-SOD, and reduced glutathione-GSH) over time in a cerulein-induced CP model and explore the impact of these changes on selected cytokines in the intestinal mucosa and pancreatic tissue, as well as on selected serum biochemical parameters. The mRNA expression of CLDN1 and CDH1 genes, and levels of Claudin-1 and E-cadherin, proteins of gut barrier, in the intestinal mucosa were determined via western blot analysis. The study showed moderate pathomorphological changes in the pigs' pancreas 43 days after the last cerulein injection. Blood serum levels of interleukin (IL)-1-beta, IL-6, tumor necrosis factor alpha (TNF-alpha), C-reactive protein (CRP), lactate dehydrogenase (LDH), gamma-glutamyl transpeptidase (GGTP), SOD and GSH were increased following cerulein injections. IL-1-beta, IL-6, TNF-alpha and GSH were also increased in jejunal mucosa and pancreatic tissue. In duodenum, decreased mRNA expression of CDH1 and level of E-cadherin and increased D-lactate, an indicator of leaky gut, indicating an inflammatory state, were observed. Based on the current results, we can conclude that repetitive cerulein injections in growing pigs not only led to CP over time, but also induced inflammation in the intestine. As a result of the inflammation, the intestinal barrier was impaired.

Expression of Adenosine Receptors in Rodent Pancreas

Adenosine regulates exocrine and endocrine secretions in the pancreas. Adenosine is considered to play a role in acini-to-duct signaling in the exocrine pancreas. To identify the molecular basis of functional adenosine receptors in the exocrine pancreas, immunohistochemical analysis was performed in the rat, mouse, and guinea pig pancreas, and the secretory rate and concentration of HCO₃⁻ in pancreatic juice from the rat pancreas were measured. The A_2A adenosine receptor colocalized with ezrin, an A-kinase anchoring protein, in the luminal membrane of duct cells in the mouse and guinea pig pancreas. However, a strong signal ascribed to A_2B adenosine receptors was detected in insulin-positive β cells in islets of Langerhans. The A_2A adenosine receptor agonist 4-[2-[[6-Amino-9-(N-ethyl-β-D-ribofuranuronamidosyl)-9H-purin-2-yl]amino]ethyl]benzenepropanoic acid (CGS 21680) stimulated HCO₃⁻-rich fluid secretion from the rat pancreas. These results indicate that A_2A adenosine receptors may be, at least in part, involved in the exocrine secretion of pancreatic duct cells via acini-to-duct signaling. The adenosine receptors may be a potential therapeutic target for cancer as well as exocrine dysfunctions of the pancreas.

Cholecystokinin (CCK) Regulation of Pancreatic Acinar Cells: Physiological Actions and Signal Transduction Mechanisms

Pancreatic acinar cells synthesize and secrete about 20 digestive enzymes and ancillary proteins with the processes that match the supply of these enzymes to their need in digestion being regulated by a number of hormones (CCK, secretin and insulin), neurotransmitters (acetylcholine and VIP) and growth factors (EGF and IGF). Of these regulators, one of the most important and best studied is the gastrointestinal hormone, cholecystokinin (CCK). Furthermore, the acinar cell has become a model for seven transmembrane, heterotrimeric G protein coupled receptors to regulate multiple processes by distinct signal transduction cascades. In this review, we briefly describe the chemistry and physiology of CCK and then consider the major physiological effects of CCK on pancreatic acinar cells. The majority of the review is devoted to the physiologic signaling pathways activated by CCK receptors and heterotrimeric G proteins and the functions they affect. The pathways covered include the traditional second messenger pathways PLC-IP3-Ca²⁺ , DAG-PKC, and AC-cAMP-PKA/EPAC that primarily relate to secretion. Then there are the protein-protein interaction pathways Akt-mTOR-S6K, the three major MAPK pathways (ERK, JNK, and p38 MAPK), and Ca²⁺ -calcineurin-NFAT pathways that primarily regulate non-secretory processes including biosynthesis and growth, and several miscellaneous pathways that include the Rho family small G proteins, PKD, FAK, and Src that may regulate both secretory and nonsecretory processes but are not as well understood. © 2019 American Physiological Society. Compr Physiol 9:535-564, 2019.

Cerebrospinal Fluid Secretion by the Choroid Plexus

The choroid plexus epithelium is a cuboidal cell monolayer, which produces the majority of the cerebrospinal fluid. The concerted action of a variety of integral membrane proteins mediates the transepithelial movement of solutes and water across the epithelium. Secretion by the choroid plexus is characterized by an extremely high rate and by the unusual cellular polarization of well-known epithelial transport proteins. This review focuses on the specific ion and water transport by the choroid plexus cells, and then attempts to integrate the action of specific transport proteins to formulate a model of cerebrospinal fluid secretion. Significant emphasis is placed on the concept of isotonic fluid transport across epithelia, as there is still surprisingly little consensus on the basic biophysics of this phenomenon. The role of the choroid plexus in the regulation of fluid and electrolyte balance in the central nervous system is discussed, and choroid plexus dysfunctions are described in a very diverse set of clinical conditions such as aging, Alzheimer's disease, brain edema, neoplasms, and hydrocephalus. Although the choroid plexus may only have an indirect influence on the pathogenesis of these conditions, the ability to modify epithelial function may be an important component of future therapies.

Lack of tolerance development with long-term administration of PEGylated cholecystokinin

Cholecystokinin (CCK) is a short acting satiating peptide hormone produced in the proximal small intestine. Daily CCK injection in rats initially inhibits food intake, but after several days, food intake is no longer affected, suggesting development of tolerance. Previously, we covalently coupled CCK to a 10kDa polyethylene glycol (mPEG-OH) and showed that this conjugate, PEG-CCK(9), produced a significantly longer anorectic effect than unmodified CCK(9). The present study examined whether tolerance to the anorectic effect develops during long-term administration of PEG-CCK(9). For 14 consecutive days, male Wistar rats (n=12) received a daily i.p injection of 8microgkg(-1) of PEG-CCK(9) and a control group received a daily control injection of mPEG-OH. Body weight and food intake were monitored daily during the experiment. Effects on the pancreas were investigated. On each day, injection of PEG-CCK(9) induced an anorectic effect lasting 3-6h, but failed to significantly reduce daily total food intake compared to controls. The body weight gain of the PEG-CCK(9)-treated animals was not different from controls. The PEG-CCK(9)-treated group had a significantly higher pancreas weight, mainly due to hyperplasia. In conclusion, PEG-CCK(9) continued to have a daily suppressive effect on food intake when administered for 14 consecutive days, showing there was no development of tolerance.

Dose-response effect of intraduodenal HCl on exocrine pancreatic secretion, portal secretin, and VIP plasma levels in anesthetized rats

In anaesthetized rats, a dose-dependent effect of different intraduodenal HCl loads (0.6, 1.2, 6 and 12 mmol/h) on exocrine pancreatic secretion and plasma levels of secretin and VIP has been observed. The flow rate of pancreatic juice showed a significant increase at all the doses used; the integrated percentage response (IPR) of flow were 359%, 595%, 894% and 1371% for, respectively, 0.6, 1.2, 6 and 12 mmol/h. The increase of protein output only achieved statistical significance at HCl loads of 6 mmol/h or more; the IPR of protein output were 153%, 305%, 320% and 420% for, respectively, 0.6, 1.2, 6 and 12 mmol/h HCl. Portal levels of secretin and VIP were measured by specific radioimmunoassays. Significant increase of secretin concentration was observed at HCl loads of 1.2 mmol/h or more, whilst VIP levels only increased significantly after intraduodenal HCl load of 6 mmol/h or more. The IPR of secretin release were 180%, 203%, 280% and 322% for, respectively, 0.6, 1.2, 6 and 12 mmol/h HCl and IPR of VIP release were 3%, 20%, 244% and 315% for, respectively, 0.6, 1.2, 6 and 12 mmol/h HCl. Our results suggest that secretin may play a more prominent role than VIP in stimulating exocrine pancreatic secretion in response to intraduodenal loads of acid in this species.

Transcriptional regulation by cholecystokinin-pancreozymin in rat pancreas

Cholecystokinin-pancreozymin (CCK-PZ) is involved in the regulation of pancreatic protein synthesis and secretion. We demonstrate here that CCK-PZ also stimulates RNA synthesis. Rats were killed 0, 30, 60, 120, 240 or 480 min after intraperitoneal injection of CCK-PZ (8 U/kg). Nuclei were prepared from pancreata and used for in vitro RNA synthesis ('run-on' experiments) in the presence of [alpha-32P]UTP. Total RNA synthesis increased after CCK-PZ with maximum UTP incorporation at 60 min. Contributions of RNA polymerase II, responsible for mRNA synthesis, and RNA polymerases I and III could be separately estimated by using alpha-amanitin. RNA polymerase I and III activities increased by 68% after CCK-PZ, whereas RNA polymerase II activity increased by 113%. Rates of synthesis of amylase, chymotrypsinogen B, trypsinogen I and actin mRNAs were estimated by quantitative hybridization of newly synthesized transcripts to specific cDNA clones. Synthesis of the four RNAs increased with a maximum between 60 and 120 min after CCK-PZ, stimulation being more important for the serine proteinases than for amylase. It was concluded that, in rat pancreas, CCK-PZ controls gene expression at the transcriptional level.

Pancreatic dose dependent effect of intraduodenal HCl in the anesthetized rabbit

1. A dose-response relationship between intraduodenal perfusion of different HCl loads (1.8, 4.5, 9, 18 and 45 mmol/hr) and volume, bicarbonate and protein outputs, from the exocrine pancreas of anaesthetized rabbits was observed. 2. This study also shows a dose-response relationship between the different HCl loads and the porta levels of secretin and VIP. 3. The secretin response showed a marked decrease during the stimulation period and this may suggest the involvement of a neural mechanism. 4. The plasma VIP responses were of a magnitude that might suggest a hormone role for VIP in this effect.

Effects of phorbol ester on cholecystokinin octapeptide-evoked exocrine pancreatic secretion in the rat

1. A comparative study was made of the effect of the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA) on cholecystokinin octapeptide-evoked exocrine pancreatic secretion in the anaesthetized rat and isolated permeabilized pancreatic acinar cells. 2. Cholecystokinin octapeptide (CCK8; 0.10-6.40 nmol (kg body weight)-1) induced dose-dependent increases in pancreatic juice flow, total protein output and amylase release in the anaesthetized rat. 3. Administration of TPA (10(-8) mol (kg body weight)-1) in combination with CCK8 resulted in marked attenuation of the CCK8-evoked secretory response. 4. Simultaneous injection of polymyxin B (10(-8) mol (kg body weight)-1), an inhibitor of protein kinase C, with TPA and CCK8 reversed the inhibitory effect of the phorbol ester on CCK8-induced pancreatic juice flow, total protein output and amylase release. 5. In permeabilized rat pancreatic acini CCK8 (10(-13)-10(-9) M) elicited dose-dependent increases in [3H]leucine-labelled protein secretion (3H-labelled protein release). Combining TPA (10(-8) M) with CCK8 resulted in an inhibition of the CCK8-induced 3H-labelled protein release especially at lower concentrations of CCK8. At higher concentrations of CCK8, TPA was unable to inhibit the CCK8-evoked 3H-labelled protein release. Again, polymyxin B reversed the TPA-induced inhibition of CCK8-evoked 3H-labelled protein output. 6. The results indicate that protein kinase C activation may play an important physiological role in modulating the CCK8-evoked secretory response in rat pancreas in vivo and in vitro.

Isolation, sequence and biosynthetic significance of a novel fragment of gastrin-releasing peptide from chicken proventriculus

The isolation of bombesin-related peptides in chicken proventriculus was monitored by radioimmunoassay using a C-terminal specific bombesin antibody. Two peptides were identified, one corresponded to the 27-residue, chicken gastrin-releasing peptide (GRP-27) previously identified; the other corresponded to its C-terminal hexapeptide. Chicken GRP-27 stimulated pancreatic and gastric acid secretion in anaesthetized turkeys, but the hexapeptide was inactive. No evidence could be found to suggest that the hexapeptide was an artifact of degradation generated during extraction or isolation. It is proposed that the hexapeptide is produced either by chymotryptic-like cleavage of GRP-27 or by trypsin-like cleavage followed by two cycles of dipeptidylaminopeptidase cleavage. This type of biosynthetic processing may be more common than formerly supposed.

Role of cholecystokinin in the regulation of pancreatic enzyme secretion in the rat

Whereas pancreatic exocrine secretion in the rat varies considerably depending on the condition under which a study is performed, it is of great importance to study pancreatic pathophysiology in vivo, while the rat is conscious. In recent years several studies were performed in the conscious rat with a cannulated pancreatic duct, and much progress was made in delineating the role of cholecystokinin (CCK) in the regulation of pancreatic enzyme secretion in more detail. This progress was mainly due to the development of specific and sensitive radioimmunoassays for CCK and the availability of specific CCK-receptor antagonists. In the rat it was shown that a negative feedback regulation mechanism of pancreatic enzyme and CCK secretion exists in which intraluminal trypsin and, to a lesser extent, bile acids and plasma CCK, plasma secretin, and the cholinergic system play important roles. Probably by interference with this feedback mechanism in the rat, casein is a stronger stimulant of plasma CCK release and pancreatic exocrine secretion than fat. Finally, CCK does not play an important role in bombesin-stimulated pancreatic enzyme secretion in the rat.

Effects of chronic alcohol intake and secretory stimulation on sodium taurocholate-induced pancreatic necrosis in the rat

The effects of long-term alcohol intake and pancreatic secretory stimulation on pancreatic necrosis were studied in rats with acute pancreatitis induced by an intraductal injection of sodium taurocholate. Neither alcohol nor pancreozymin alone influenced the extent of pancreatic tissue damage in this experimental model. However, when animals were exposed to both alcohol and pancreozymin, the tissue lesions induced by the bile salt were wider than those in the presence of either alcohol or secretory stimulation alone. The results indicate that secretory stimulation with pancreozymin superimposed on chronic alcohol intake sensitizes the pancreas to the injury caused by intraductal bile salt administration.

Agonist-induced changes in cell membrane capacitance and conductance in dialysed pancreatic acinar cells of rats

1. Single acinar cells enzymatically isolated from the rat pancreas were subjected to tight-seal whole-cell recordings. Changes in cell membrane capacitance and conductance were simultaneously recorded using a phase-sensitive detection method. 2. Acetylcholine (ACh, 0.05-0.5 microM) and cholecystokinin octapeptide (CCK-8, 10-50 pM) concomitantly induced transient increases in cell membrane current, capacitance and conductance only when cytosolic Ca2+ was weakly chelated by EGTA (70 microM). These responses were prolonged when the cells were dialysed with a solution containing GTP gamma S (a stable analogue of GTP, 50-100 microM), whereas they were inhibited by dialysing with that containing GDP beta S (a stable analogue of GDP). These results suggest that a type of guanine-nucleotide-binding protein (G-protein) could be involved in ACh- or CCK-receptor signalling. 3. The ACh- or CCK-induced responses (with or without GTP gamma S in the cytosol) were all abolished when a high dose of EGTA (1-2 mM) was injected into the acinar cells. In addition, A23187, a calcium ionophore, induced sustained responses when the cytosolic Ca2+ was weakly buffered by 70 microM-EGTA. These results suggest that the secretagogues regulate the changes in cell membrane capacitance and conductance via an increase and decrease of cytosolic Ca2+ concentration. 4. Oscillatory changes in cell membrane conductance and capacitance were consistently observed even without applying secretagogues when the cells were dialysed with a solution containing GTP gamma S (50-100 microM) and cytosolic free Ca2+ ions weakly buffered at about 10(-6) M with a low dose of EGTA and CaCl2. 5. The peak amplitude of changes in cell membrane capacitance induced by ACh or CCK-8, with or without GTP gamma S in the cytosol, varied between 200 and 1000 fF, thereby suggesting that 20-100 zymogen granules can fuse with the luminal cell membrane in response to these agonists in rat exocrine pancreatic acinar cells.

The cholecystokinin antagonist L-364,718 inhibits the action of cholecystokinin but not bombesin on rat pancreatic secretion in vivo

The action of an antagonist of peripheral CCK receptors, L-364,718 on CCK8 and bombesin-induced pancreatic exocrine secretion was studied in anaesthetized rats. Both CCK8 and bombesin increased the rate of flow and rate of enzyme secretion from the pancreas. Intravenous L-364,718 inhibited the actions of CCK8, but not those of bombesin. It is concluded that bombesin acts on the exocrine pancreas directly rather than through the release of CCK.

Time course and cellular site of mitotic activity in the exocrine pancreas of the rat during sustained hormone stimulation

Previous studies from our laboratory indicate that the adaptive response of the exocrine pancreas of the rat to prolonged stimulation with optimal doses of caerulein (0.25 microgram X kg-1 X h-1) follows a characteristic time course in which each step in the secretory pathway is activated. The immediate response is the depletion of zymogen-granule stores followed by coordinate and anticoordinate changes in individual rates of (pro-)enzyme synthesis after a lag period of 2 h. The sum of such changes leads to an increase in total rate of protein synthesis by 3 h which is combined with acceleration of intracellular transport packaging and granule discharge. In the present study the time course of DNA synthesis and the labeling index of five populations of pancreatic cells have been analyzed after caerulein stimulation for periods ranging from 6 to 72 h, using in vivo labeling with 1 mu Ci/g 3H-thymidine 1 h prior to sacrifice of the animals. DNA synthesis did not change during the initial 18 h in spite of persistent stimulation indicated by a 80% reduction on enzyme content. Following this lag period a sharp rise in DNA synthesis 20- to 25-fold above control levels was observed, which decreased by 48 h to reach control levels by 72 h. Increase in DNA synthesis was most pronounced in animals with lowest enzyme content in the pancreas. From the five cell populations studied by autoradiography interlobular duct cells and islet cells had no significant increase in labeling index at any time of stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Pancreatic secretion in the rat influenced by the low molecular weight serine proteinase inhibitor Gabexate mesilate

The effect of intravenous or intragastric administration of the synthetic proteinase inhibitor Gabexate mesilate (GM) on the pancreas of rats was investigated. Infused intravenously at 4 mg kg-1 h-1, GM inhibited both basal or cerulein (0.2 microgram kg-1 h-1)-stimulated pancreatic protein secretion. Intracellular transport and secretion of newly synthesized pancreatic enzymes was not influenced by intravenous infusion of GM. Intragastric administration of GM (400 mg kg-1) on four consecutive days increased pancreatic wet weight, protein and enzyme content of the gland. A preferential increase of proteinases above glucosidases was observed. Pancreatic lobules from inhibitor-treated rats released 30% less amylase in response to cerulein or carbachol when the rate of discharge was expressed in percent of initial content. Expressed in ku amylase/microgram DNA secretion rate was two-fold higher than in controls. In pancreatic duct cannulated rats GM (400 mg kg-1 h-1), introduced intragastrically on five consecutive days, stimulated volume-bicarbonate and protein secretion rate, the secretory response on the fifth day being significantly higher than on the first day. Enzyme pattern in pancreatic juice changed characteristically: mainly the amount of acidic proteinases increased, whereas the amount of the basic isoforms was altered only slightly.

A difference in stimulatory effects on pancreatic exocrine secretion between ursodeoxycholate and trypsin inhibitor in the rat

We previously reported that intraduodenally infused ursodeoxycholate produced hypersecretion of pancreas in bicarbonate and fluid secretion in the rabbit (Digestive Diseases and Sciences, 28:942, 1983). Since trypsin inhibitor stimulates pancreatic secretion in the rat whose pancreatic exocrine secretion is regulated by a luminal feedback mechanism, in the present study we examined the stimulatory effect of ursodeoxycholate in comparison to Trasylol in unanesthetized rats with both the presence and the absence of returning bile-pancreatic juice. Under the condition in which bile-pancreatic juice were continuously returned to the intestine, the intraduodenally infused ursodeoxycholate produced significant increases in juice flow and bicarbonate and protein outputs, while Trasylol significantly increased protein output only. After an 8- to 10-hr period of bile-pancreatic juice diversion, Trasylol no longer affected pancreatic secretion, whereas ursodeoxycholate still stimulated the bicarbonate output significantly. Trypsin activities in the proximal half of the small intestine were not decreased by the infusion of UDCA. The mechanism of stimulatory effect of ursodeoxycholate on pancreatic secretion is independent of luminal feedback regulation and appears to differ from that of trypsin inhibitor.

Cholecystokinin interacts with prefeeding to impair runway performance

Previous experiments demonstrated the ineffectiveness of the C-terminal octapeptide of cholecystokinin (CCK-8) for impairing runway performance by food-deprived rats. These results were consistent with the proposal that CCK-8 does not reduce food intake by inhibiting appetitive motivation but instead acts late in the meal to prematurely trigger satiety. For further evaluation of this hypothesis, the effect of CCK-8 on runway performance was assessed after 21 h food-deprived rats consumed a partial meal of 30% sucrose. Injection of 1.0 micrograms/kg CCK-8 after rats were allowed 3 min (6.2 ml consumed) or 5 min (9.7 ml) access to 30% sucrose produced significant reductions in running speed of 43% and 70%, respectively. After 5 min prefeeding, 0.25 and 0.50 micrograms/kg CCK-8 also produced significant decreases in speed of 20% and 59%, respectively. By contrast, CCK-8 had little or no effect without prefeeding. Doses of 0.25 and 0.50 micrograms/kg failed to affect running speed on these tests and 1.0 micrograms/kg produced a small (7%) though significant decrease. These results suggest that inhibition of feeding motivation after CCK-8 administration develops during the course of the meal through interaction with signals generated by the ingestion of food.

Partial restoration of pancreatic function by exogenous secretin in rats with ceruletide-induced acute pancreatitis

Pharmacological doses of ceruletide administered intravenously to unconscious rats uniformly induces acute pancreatitis (AP) as well as a striking reduction in pure pancreatic juice (PPJ) and protein output. High-dose intravenous secretin administered to rats with ceruletide-induced AP effects a reestablishment of PPJ flow and a significant increase in PPJ protein output. Light microscopy of the pancreas in ceruletide-induced AP rats revealed marked acinar cell vacuolization and intense interstitial edema. By contrast, pancreatic histology in AP rats treated with high-dose secretin revealed a distinct lessening of acinar cell vacuolization and interstitial edema. We have established that high-dose intravenous secretin given to rats with ceruletide-induced AP is (1) not harmful, (2) reestablishes PPJ flow and evokes a partial restoration of protein output, and (3) appears to reduce pancreatic histopathology when compared to non-secretin-treated rats with AP.

In-vivo stimulation of rat pancreatic acinar cells by infusion of secretin. I. Changes in enzyme content, pancreatic fine structure and total rate of protein synthesis

Infusion of synthetic secretin in conscious unrestricted rats for periods up to 24 h was used to study the structural and functional adaptation of pancreatic acinar cells to this secretagogue. Initial dose-response studies established 16 clinical units (CU) per kg and h (corresponding to 4.64 micrograms X kg-1 X h-1) as optimal dose for persistent stimulation of enzyme discharge. Infusion of this dose led to a slow but progressive depletion of enzyme stores with minimal content by 12 h stimulation. As a result of persistent stimulation total protein synthesis in the acinar cells increased after a lag period of 3 h and reached maximal values 90% above controls by 6 and 12 h secretin infusion. No structural equivalent for pronounced fluid and bicarbonate secretion was observed for either acinar or duct cells over the entire dose range (1 to 64 CU X kg-1 X h-1) and infusion period (1-24 h), except an increased number of coated vesicles in duct cells. Discharge of enzymes from acinar cells was paralleled by a high frequency of exocytotic images at the luminal plasma membrane and was accompanied by the occurrence of membrane fragments in the luminal space, especially after 3 and 6 h secretin infusion. An increased number of lysosomal bodies at these time points especially in the vicinity of the Golgi complex was interpreted in relation to membrane recycling following massive exocytosis. This pattern of structural and functional adaptation of acinar cells following secretin infusion corresponds to previously described changes following caerulein and carbamylcholine stimulation.

Effect of aging on pancreatic secretion in rats

We have characterized the effects of aging on the pancreatic exocrine secretory response to the normal stimulatory hormones, secretin, and cholecystokinin. Young (6 month old) and aged (26 months old) male Sprague-Dawley rats were prepared with pancreatic fistulas and challenged with different doses of secretin (0.03, 0.06, and 0.12 nmol/kg) and cholecystokinin-8 (0.3, 0.6, and 1.2 nmol/kg) intravenously. The pancreatic secretion was measured for volume and bicarbonate and protein outputs. Our results show that in aged rats, the basal pancreatic secretion volume and protein and bicarbonate outputs were significantly reduced, and the pancreatic secretion volume and protein and bicarbonate responses to graded doses of secretin or cholecystokinin-8 were significantly reduced. This study demonstrates that pancreatic exocrine function in rats diminishes with age.

Effect of secretagogues on pancreatic exocrine secretion in the monkey and the dog

The effects of secretin, cholecystokinin, dopamine, histamine and acetylcholine on the secretion of pancreatic juice were investigated in the monkey and the dog. In the resting state, bicarbonate concentration and the volume of pancreatic juice in the monkey were greater than those in the dog. However, the protein concentration of pancreatic juice in the monkey was less than that in the dog. Intravenous administration of secretin, cholecystokinin, histamine and acetylcholine caused a dose dependent increase in pancreatic secretion in both species. The responses in the monkey were greater than those in the dog. Dopamine caused pancreatic secretion only in the dog. The increase in bicarbonate concentrations of pancreatic juice induced by secretin and histamine in the monkey were greater than that in the dog. Increase in protein concentrations of the juice induced by cholecystokinin and acetylcholine in the monkey were less than that in the dog. However, pancreatic juice pH in both species was the same and was not affected by the secretagogues in the resting state or during the stimulation by secretogogues. From these results, it is concluded that there is a species difference in the secretory actions of the secretagogues in the monkey and the dog.

Immunoreactive cholecystokinin in human and rat plasma: correlation of pancreatic secretion in response to CCK

Immunoreactive cholecystokinin (CCK) levels in human and rat plasma are described using a radioimmunoassay specific for the biologically active sulfated end of CCK. This assay detected significant changes in plasma cholecystokinin levels during intrajejunal administration of amino acids and intravenous infusions of CCK-8 which were followed by increased pancreatic secretion. In humans, the concentration (pg/ml) of plasma cholecystokinin increased from 10.8 to 18.9 following intrajejunal amino acid instillation and from 15.4 to 31.1 during CCK infusion, while pancreatic trypsin secretion increased more than 15 fold. Ingestion of a test meal also caused a rapid and significant elevation (P less than 0.05) in both plasma CCK (14.5-21.7 pg/ml) and gastrin (50-160 pg/ml) levels. In the rat, an injection of 46 ng of CCK-8 produced a 300% increase in immunoreactive plasma CCK levels (2 min) and caused peak pancreatic protein secretion within 5 min; 4 fold lower doses (11.5 ng) elevated plasma CCK by 38% and pancreatic protein secretion to a small but significant extent. The ability of this assay to detect various forms of sulfated CCK in human plasma was also determined. Following gel chromatography on Sephadex G-50, at least three different immunoreactive peaks were found in plasma from fasted subjects and after intrajejunal amino acid stimulation. While the lower molecular weight CCK peptides (CCK-8 and CCK-12) were detected in plasma from both fasted and stimulated subjects, the larger form (CCK-33) was only present in measurable concentrations after amino acid infusion. The simultaneous measurement of increased plasma CCK levels and pancreatic secretion and the changes in the distribution of CCK peptides following amino acid infusion provides strong support that this assay detects physiologically relevant changes in biologically active CCK peptides.

Action of secretin on pancreatic enzyme secretion in man. Studies on pure pancreatic juice

The action of pure, natural secretin on the pancreatic secretion of enzymes was investigated in six patients with external transduodenal drainage of the main pancreatic duct performed after biliary tract surgery. Secretin infused for five successive 50 minute periods at increasing doses of 0.03, 0.1, 0.3, 0.9 and 2.7 clinical units (CU)/kg/h, produce a dose dependent increase in protein and lipase output. A weak but significant (p less than 0.02) increase of enzyme output above the fasting level was already observed with the lowest dose. The maximal output of protein and lipase, observed with the highest dose of secretin infused, corresponded to about 50% of that induced by maximal doses of cerulein (100 ng/kg/h) plus secretin (1 CU/kg/h). As far as bicarbonate is concerned, the lowest dose of secretin (0.03 CU/kg/h) significantly (p less than 0.001) stimulated bicarbonate output. The dose of 0.9 CU/kg/h of secretin evoked a bicarbonate output of 526 +/- 49 micromol/min; trebling the dose of secretin did not significantly increase the output of bicarbonate above this value. Increasing doses of secretin induced a dose related increase in calcium output. There was a close parallel between calcium and protein outputs, suggesting that the increase in calcium output reflected primarily an increase in the enzyme-associated fraction of pancreatic juice calcium. It is concluded that secretin stimulates pancreatic enzyme secretion in man probably by a direct action on the acinar cells.

The Golgi apparatus and lysosomes of rat pancreatic acinar cells following refeeding

The short term effects of refeeding on the Golgi apparatus and lysosomes of the rat exocrine pancreas were evaluated by ultrastructural, morphometric and cytochemical methods. Ten minutes after refeeding, there was a significant enlargement of Golgi cisternae and a significant increase, compared with the controls, in the number of condensing vacuoles and lysosomes. These modifications were accompanied by the appearance of acid phosphatase activity in stacked Golgi cisternae (as well as GERL) of some cells. One hour after refeeding, there were about the same numbers of condensing vacuoles and lysosomes as in the controls; Golgi cisternae were still significantly enlarged, compared with the controls, but they were no longer reactive for acid phosphatase. In both fasting and refed animals, acid phosphatase activity was demonstrable in tubular lysosomes. The data are interpreted in terms both of membrane disposal and recycling, leading to enhanced formation of zymogen granules, during physiologically stimulated secretion.

The role of nicotinic receptors in dog pancreatic exocrine secretion

1 The effects of pentamethonium, an autonomic ganglion blocker, were studied on the exocrine pancreatic secretion of six conscious dogs given intravenous infusions of urecholine, caerulein or pentagastrin on a background of submaximal doses of secretin. 2 Urecholine-induced protein secretion was not affected but both caerulein- and to a smaller extent, pentagastrin-induced protein secretions were depressed by pentamethonium. 3 These results indicate that intravenous caerulein and pentagastrin, but not urecholine, act at least partially via nicotinic receptors. 4 Volume and bicarbonate output were depressed by pentamethonium when stimulated by intravenous caerulein with a background of secretin, but not when stimulated by pentagastrin on a background of secretin. 5 From these data it is suggested that caerulein and pentagastrin may potentiate secretin-stimulated hydrelatic secretion by different mechanisms.

Pharmacology, clinical uses, and adverse effects of ceruletide, a cholecystokinetic agent

Ceruletide, a decapeptide, is a potent cholecystokinetic agent with a direct spasmogenic effect on the gallbladder muscle and bile ducts in humans and animals. It was recently approved by the Food and Drug Administration for use as an adjunct in x-ray examination of the gallbladder and small bowel. The drug causes a coordinated propulsive activity from the duodenum to the ileum and segmenting activity in the colon. Because of this stimulatory effect, ceruletide is useful not only diagnostically as an aid in x-ray examination of the small bowel, but also therapeutically for treatment of postoperative ileus, intestinal atonia, and chronic fecal statis. Because of its pancreatic stimulatory action, it is useful in evaluation of exocrine pancreatic function. In therapeutic doses the adverse effects noted are mild, transient extensions of the drug's pharmacologic actions and are manifest as nausea, vomiting, abdominal pain, and rarely hypotension and tachycardia. On the basis of current evidence, ceruletide is a safe and effective cholecystokinetic agent and small bowel and exocrine pancreatic stimulant.

The effect of extracellular calcium deprivation on amylase secretion and 45Ca efflux from rat pancreas

1. The role of extracellular Ca(2+) in pancreatic enzyme secretion and (45)Ca efflux evoked by acetylcholine (ACh) and caerulein has been assessed in the incubated, uncinate pancreas of young rats.2. In a medium containing 2.5 x 10(-3)m-Ca(2+), the maximal rates of amylase secretion evoked by optimal doses of each secretagogue were similar. However, the time courses of amylase release during prolonged stimulation of the gland were different.3. The time course of amylase secretion in response to an optimal dose of ACh (10(-5)m) was characterized by an initial rapid increase followed by a slow sustained rise. For caerulein (10(-8)m), an initial rapid rise was followed either by a plateau or slight decline in the rate of amylase secretion.4. Both secretagogues produced similar increases in the rate coefficient of (45)Ca efflux from the gland.5. With supra-optimal doses of the secretagogues, amylase secretion, but not the rate coefficient of (45)Ca efflux, was depressed.6. Reducing the extracellular Ca(2+) concentration did not have a marked effect on basal amylase secretion but inhibited the action of both secretagogues. When the Ca(2+) concentration was 10(-6)m or lower, these inhibitory effects were irreversible. Amylase secretion stimulated by ACh was more sensitive to extracellular Ca(2+) deprivation than that stimulated by caerulein, the concentration required for half-maximal secretion being about 9-fold greater for ACh.7. Decreasing the extracellular Ca(2+) concentration increased both the basal and stimulated rate coefficients of (45)Ca efflux.8. Our results support the hypothesis that pancreatic enzyme secretagogues act by releasing bound Ca(2+) from sites within the acinar cell. Furthermore, they suggest that the site utilized by ACh is more amenable to depletion, via changes in extracellular Ca(2+) concentration, than that employed by caerulein.

The effect of long-term feeding of soya-bean flour diets on pancreatic growth in the rat

1. Pancreatic growth was measured in rats by changes in pancreatic weight, nucleic acid content and protein content after feeding diets of heated soya-bean flour (HSF), raw soya-bean flour (RSF), 200 g raw soya-bean flour + 800 g heated soya-bean flour/kg (80 HSF) and 400 g raw soya-bean flour + 600 g heated soya-bean flour/kg (60 HSF) for periods up to 36 weeks. Control rats of comparable age to soya-bean flour-fed rats were continued on rat cubes during the 36-week study. 2. Cube-fed rats remained significantly heavier than rats fed on soya-bean flour diets. Analysis of variance showed rats fed on HSF were significantly heavier than RSF-fed rats and rats fed on 80 HSF significantly heavier than those fed on 60 RSF. 3. Pancreatic indices in HSF-fed rats were similar to comparable control rats. 4. Hypertrophy was found in rats fed on the RSF-containing diets with the extent of enlargement corresponding to the RSH content. Hyperplasia was also found in rats fed on RSF and 60 HSF. 5. The greatest pancreatic growth was seen in RSF-fed rats with all the indices peaking at 8 weeks followed by a decline and then a rise again at 36 weeks. 6. The fall in pancreatic indices in rats fed on RSF for 12 and 24 weeks is most likely an effect of general malnutrition due to the multiple deficiences in amino acids which occur in animals fed on RSF. The rise at 36 weeks may reflect increased body growth or the beginning of adenomatous changes.

Effect of acetylcholine, gastrin, and glucagon alone and in combination with secretin and cholecystokinin on the secretion of the isolated perfused rat pancreas

Dose-response curves of acetylcholine (ACh), gastrin, and glucagon given alone or in combination with a submaximal dose of secretin (S;' 5.0 U/h) plus cholecystokinin (CCK; 1.0 U/h) were studied in the isolated perfused rat pancreas. ACh (25 x 10-9 mol/h) increased the basal secretory flow ( mean +/- SEM: 1.19 +/- 0.22 microliter/min) by 693% and protein output (2.7 +/- 0.2 microgram/min) by 1726%. The protein secretion evoked by S plus CCK was further increased by ACh to a maximum of 26% whereas the volume secretion remained unaltered. Gastrin (100 ng/h) stimulated the protein output by 352% and, when combined with S and CCK, up to further 23% and the secretory flow by 37%. Glucagon evoked a significant (P less than 0.005) increase of the protein output, but decreased the volume as well as the protein output (by 43% and 32%, respectively; P less than 0.05) when it was combined with the tested doses of S and CCK.

The release of rat intestinal cholecystokinin after oral trypsin inhibitor measured by bio-assay

The distribution, molecular form and release of cholecystokinin (CCK)-like activity in extracts of rat small intestine was studied with an in vitro gall-bladder bio-assay. In contrast to the reported heterogeneity of CCK-like immunoreactivity in the intestine, only a single molecular form of CCK-like activity was detected using the bio-assay. 2. The CCK-like activity eluted from Sephadex G50 with a Kav of 0.69, after the triacontriapeptide of cholecystokinin (CCK33) and before cholecystokinin octapeptide 2500, may represent the 22 amino acid peptide of CCK (CCK22). The bio-assay peak of CCK-like activity had pancreozymin activity and CCK/gastrin C terminal immunoreactivity. The CCK-like activity weas readily extracted from the small intestine at neutral pH, but subsequent treatment with cold 0.5 M-acetic acid extracted further CCK-like activity of the same molecular form as that recovered under neutral conditions. 3. The bio-assay detected no CCK-like activity, nor was pancreozymin-like activity found in fractions corresponding to CCK33 or CCK8 after Sephadex G50 chromatography of rat intestinal extracts. 4. Oral trypsin inhibitor was a potent stimulus for the release of CCK-like activity from the upper small intestine of the rat. After oral trypsin inhibitor release, CCK-like activity was rapidly resynthesized.

Evidence for a cyclic AMP system highly sensitive to secretin in gastric glands isolated from the rat fundus and antrum

The effects of secretin and vasointestinal peptide (VIP) on the production of cyclic AMP have been studied in gastric glands isolated by means of EDTA from rat fundic and antral mucosa. (1) In gastric fundus, secretin and VIP caused a time- and temperature-dependent stimulation of cyclic AMP production that was maximal when the test agents were incubated for 60 min at 20 degrees C in the presence of 0.5 mM 3-isobutyl-1-methylxanthine as a phosphodiesterase inhibitor. The dose-response curve was monophasic for both peptides, the production of cyclic AMP being sensitive to 10(-10) M secretin and to 5 . 10(-8) M VIP. Half-maximal stimulation was obtained with 2.9 10(-9) M secretin or 2 . 10(-7) M VIP and the maximal stimulation represented a 21-fold and a 19-fold increase above control for secretin and VIP, respectively. Histamine also stimulated cyclic AMP production, with a Km of about 5 . 10(-4) M. No additive effect on cyclic AMP production was oberved when secretin and VIP were simultaneously added at maximally active concentrations, while an additive effect was observed when secretin and histamine were added together. (2) In gastric antrum, the characteristics of the secretin- and VIP-stimulated cyclic AMP production were similar to those observed in gastric fundus. Histamine nevertheless failed to stimulate the formation of cyclic AMP in antral mucosa. (3) These data demonstrate the existence of a cyclic AMP system highly sensitive to secretin in gastric glands isolated from the rat fundus and antrum and suggest that VIP operates through this system. (4) It is proposed that the pepsinogen- and/or mucous-secreting cells are implicated in the regulation of cyclic AMP production by secretin in gastric glands of the rat.

Exogenous and endogenous stimulations during different phases of pancreatic secretion in conscious rats

The effects of stepwise increasing doses of intravenous caerulein, secretin, urecholine and intraduodenal oleic acid were investigated in conscious rats. a) Basal water, bicarbonate, and protein secretion significantly augmented after diversion of pancreatic juice. On the basis of protein secretory pattern of basal secretion 3 stable stages have been recognised: 1. The most physiological basal stage during return of pancreatic juice. 2. The first, highly elevated plateau from the 4th to 7th 30-min period after diversion of pancreatic juice. 3. The second, delayed and less elevated plateau after 270 min. b) The following patterns of stimulated secretion were observed: 1. Caerulein stimulated protein and bicarbonate secretion during return of juice and the first plateau but it failed to elicit a significant response during the second, delayed plateau. 2. Secretin and urecholine showed similar protein responses during return of pancreatic juice but after diversion, they stimulated water and bicarbonate secretion only. 3. During the second plateau oleic acid stimulation resulted in a significant increase in water and bicarbonate secretion but no significant increase occured in protein output. The delayed inhibition of protein secretion, previously described in our laboratory, was unchanged. 4. Supramaximal doses of exogenous stimuli caused an inhibition in pancreatic secretion.

Potent stimulation of the avian exocrine pancreas by porcine and chicken vasoactive intestinal peptide

1. The actions of chicken and porcine secretins and vasoactive intestinal peptides (VIPs) were compared on the rate of flow and rate of protein secretion from the exocrine pancreas in urethane anaesthetized turkeys and rats. 2. Chicken VIP was about twice as potent as porcine VIP and 100-150 times as potent as chicken and porcine secretins in stimulating the flow of pancreatic juice in the turkey. 3. Porcine secretin was a strong stimulant of the flow of pancreatic juice in the rat, but chicken secretin and the two VIPs were only active in doses 20-50 times higher than those of porcine secretin. 4. Neither the two VIPs nor the two secretins significantly stimulated the rate of pancreatic protein secretion in the turkey or rat. 5. In the turkey I.V. infusion of graded doses of chicken VIP produced graded increases in the flow of pancreatic juice; in the presence of an infusion of a low dose of CCK8 the flow of juice secreted in response to the highest dose of chicken VIP was significantly lower compared with the infusion of VIP alone, and responses to the other doses of VIP were lower but not significantly so. The infusion of chicken secretin reduced the flow of juice in response to infusions of chicken VIP, but the differences were not significant. There was no significant difference in either the rate of flow, or rate of protein secretion from the turkey pancreas in response to an infusion of chicken secretin and CCK8, compared with CCK8 alone. 6. The results cast doubt on the importance of secretin for regulation of the avian pancreas, and suggest instead that VIP might have a physiological role in regulating the flow of pancreatic juice in birds.