Pancreatic Weight Research Articles

Incidence of apoptosis in the pancreas of young and old rats

We reported previously that the pancreatic protein responses to the high dose of cholecystokinin (CCK) or bile–pancreatic juice diversion were impaired in old rats of both sexes, whereas the basal secretion was comparable to that in young animals. To examine the mechanism of the attenuated response in old rats, we examined the incidence of apoptosis of the pancreatic acinar cells and the plasma CCK concentrations produced by bile–pancreatic juice diversion, which is a potent endogenous stimulator of pancreatic secretion, in young (4–8 months old) and old (25–29 months old) rats of both sexes. Apoptosis was examined by electron microscopic examination and the nick end-labeling method for detecting cells with DNA strand breaks. The plasma CCK level was determined by RIA with OAL-656 antibody. The incidence of nick end-labeling-positive cells (apoptotic index) was slightly higher in old rats of both sexes. Apoptosis coincided with the acinar cell loss in old male rats, in which apoptotic index was much greater than that in young animals. The plasma CCK levels produced by bile–pancreatic juice diversion were lower in old than in young male rats, whereas no age difference was observed in females. The basal plasma CCK levels were comparable regardless of age and sex. The pancreatic wet weights were higher in old than in young rats of both sexes. These observations suggested that although impaired CCK functions in old male rats might have some role in the increase in apoptosis in the pancreas, the increase in apoptosis could not fully explain the attenuated pancreatic response in old rats.

Pathophysiologic studies of experimental chronic pancreatitis in rats induced by injection of zein-oleic acid-linoleic acid solution into the pancreatic duct.

An experimental model of chronic pancreatitis was induced by a retrograde injection of a viscous solution consisting of zein-oleic acid-linoleic acid (0.05 ml/100 g body weight) into the rat pancreatic duct. Histologic and biochemical changes were investigated over a period of 6 months after induction of this model. The treated rats gained weight, but pancreatic weight decreased with time. Histologically, the widening of acinar lumen and cellular vacuolization occurred within 24 h at the parenchyma neighboring the small ducts filled with the injected solution. Degenerative parenchyma, interstitial edema, and inflammatory cell infiltration were pronounced 1 week later. Thereafter, duct-like tubular complex formation progressed, and the exocrine tissue exhibited marked atrophy of the gland with irregular fibrosis and fat replacement over a period of 6 months. Pancreatic contents of protein, amylase, DNA, and RNA markedly decreased, as did pancreatic weight, whereas hydroxyproline content increased. Oral administration of camostat did not affect pancreatic weight and contents of enzyme in this model. Urinary para-aminobenzoic acid (PABA) excretion in the BT-PABA test decreased to 54% at 6 weeks and 22% at 6 months. Although three quarters of pancreatic immunoreactive insulin (IRI) content was lost after 6 months, overt diabetes did not occur. The results suggest that an obstructive mechanism in the small ducts plays an important role in the genesis and development of chronic pancreatitis.

Reduced reactivity of pancreatic exocrine secretion in response to gastrointestinal hormone in WBN/Kob rats

We compared pancreatic exocrine secretion in 5-month-old WBN/Kob rats, a model of chronic pancreatitis, with that in Wistar rats of the same age in a conscious state. Basal pancreatic secretion and pancreatic wet weight in WBN/Kob rats were lower than the values for Wistar rats. There was no difference in plasma cholecystokinin (CCK) concentration between the two types of rats. When CCK-8 was intravenously administered, the stimulation of pancreatic protein secretion in WBN/Kob rats was weaker than that in Wistar rats. When bile and pancreatic juice were diverted from the duodenum, the resulting increase in the plasma CCK concentration was similar in both types of rats, but stimulation of the volume and protein output of pancreatic juice in WBN/Kob rats was weaker than that in Wistar rats. In addition, WBN/Kob rats exhibited little increase in pancreatic wet weight because of this diversion. When secretin was intravenously administered, the stimulation of fluid secretion in WBN/ Kob rats was also weaker than that in Wistar rats. The binding of CCK-8 to pancreatic membrane fractions in WBN/Kob rats was much weaker than that in Wistar rats. Histological findings in WBN/Kob rat pancreas showed proliferation of fibrous tissue and atrophy of acinar cells. In conclusion, pancreatic exocrine secretion in response to the gastrointestinal hormones, CCK and secretin, was lower in WBN/Kob rats than in Wistar rats. These findings suggest that the hyposecretion of pancreas in WBN/Kob rats is hyporeaction of pancreatic membrane to gastrointestinal hormones.

CCK administration after CCK receptor blockade accelerates recovery from cerulein-induced acute pancreatitis in rats.

We examined the effects of treatment with cholecystokinin (CCK) octapeptide (CCK-8) and the CCK receptor antagonist loxiglumide on the recovery of exocrine pancreas in post-acute pancreatitic rats. Acute pancreatitis was induced in rats by intravenous infusion of 20 microg/kg/h cerulein for 4 h. At 24 h after the start of cerulein infusion, rats were divided into nine treatment groups: oral administration of saline (control), or oral administration of 10 or 50 mg/kg body weight loxiglumide twice daily for the first 3 days, followed by saline administration (Loxi-1 and Loxi-2), 10 or 50 mg/kg body weight loxiglumide twice daily for 6 days (Loxi-3 and Loxi-4), oral administration of saline or 10 or 50 mg/kg body weight loxiglumide twice daily for the first 3 days, followed by subcutaneous injection of 2.5 microg/kg body weight CCK-8 twice daily for the next 3 days (CCK-1, CCK-2, and CCK-3), and subcutaneous injection of 2.5 microg/kg body weight CCK-8 twice daily for 6 days (CCK-4). Pancreatic wet weight and biochemical changes were evaluated on day 8 at 12 h after the last treatment. Treatment with loxiglumide (Loxi-3 and Loxi-4) or CCK-8 for 6 days (CCK-4) or with a high dose of loxiglumide for the first 3 days (Loxi-2) significantly suppressed the recovery of pancreatic weight and DNA content compared to saline treatment or to the untreated normal control rats. However, when loxiglumide treatment was followed by 3 days of CCK-8 injections (CCK-2 and CCK-3), pancreatic protein and DNA content recovered to levels comparable to or above the control levels. The most remarkable increase in enzyme content was obtained in postpancreatitic rats treated with high-dose loxiglumide for the first 3 days, followed by CCK-8 injection (CCK-3). On the other hand, 6 days of CCK-8 treatment (CCK-4) had no significant influences on pancreatic enzyme contents. These results suggest that the most favorable strategy for the treatment of acute pancreatitis is to give high-dose loxiglumide during the early stage for only a short period, followed by CCK-8 administration.

Role of cholecystokinin-A (CCK-A) receptor in pancreatic regeneration after pancreatic duct occlusion: a study in rats lacking CCK-A receptor gene expression.

We examined the role of the cholecystokinin-A (CCK-A) receptor in acute inflammatory and regenerative stages of experimental pancreatitis using a rat model lacking the CCK-A receptor [Otsuka Long-Evans Tokushima Fatty (OLETF) rats]. OLETF and control [Long-Evans Tokushima Otsuka (LETO)] rats were prepared with an internal bile fistula and with obstruction of pancreatic flow and were sacrificed 1-14 days later. Histological examination was performed, and changes in pancreatic wet weight, protein concentration, CCK-A and -B receptor mRNA levels, tyrosine kinase activities, and plasma amylase and CCK levels were determined. The plasma amylase level showed a transient increase on day 1, the CCK level remained at high levels throughout, and tyrosine kinase activity was increased significantly on day 3 but declined thereafter. These parameters were comparable for both strains during the acute inflammatory stage. However, no regenerative findings were observed by histological examination and the protein concentration in the pancreas was significantly lower in OLETF rats on days 7-14, during which time regeneration was completed in LETO rats. These observations indicate that the absence of the CCK-A receptor did not modify the acute phase of pancreatitis but significantly retarded regeneration of the pancreatic tissue.

Long-Term Effects of CCK-Agonist and -Antagonist on Food Intake and Body Weight in Zucker Lean and Obese Rats

Meereis-Schwanke, K., H. Klonowski-Stumpe, L. Herberg and C. Niederau. Long-term effects of CCK-agonist and -antagonist on food intake and body weight in Zucker lean and obese rats. Peptides 19(2) 291–299, 1998.—The present study evaluates long-term effects of the CCK-agonist caerulein and the CCK-A antagonist loxiglumide in obese and lean Zucker rats. Caerulein and loxiglumide altered food intake neither in obese nor in lean rats. By as yet unknown mechanisms, however, weight increase was accelerated by loxiglumide and reduced by caerulein in obese and lean rats. Caerulein increased pancreatic weight only in lean but not in obese rats. Thus, obese rats show a resistance of pancreatic CCK-A receptors. The failure of CCK-agonist and -antagonist to alter food intake suggests that this CCK-resistance is not responsible for obesity in the genetically altered rats.

Effects of Epidermal Growth Factor, Cholecystokinin, and Secretin on Growth of the Alimentary Tract in the Neonatal Guinea Pig

Gut hormones and growth factors are likely to be involved in the functional changes and substantial growth of the alimentary tract that occurs during early neonatal life. The present experiments investigated the effects of continuous subcutaneous infusion of cholecystokinin (CCK), secretin, and epidermal growth factor (EGF) in neonatal guinea pigs for 4 or 15 days. At doses of 20, 100 or 500 pmol/kg/h, CCK and secretin had no effect on alimentary tract organs except for an increase in pancreatic weight at 4 days with the highest dose of CCK and an increase in stomach weight at 4 days with the highest dose of secretin. In contrast, EGF showed dose-dependent and time-dependent effects on all the alimentary tract organs when infused at 70, 210 and 630 pmol/kg/h. These results suggest that EGF, but not CCK or secretin, is likely to be an important trophic factor during the neonatal period.

Effect of chronic oral administration of the CCK receptor antagonist loxiglumide on exocrine and endocrine pancreas in normal rats.

In normal adult rats, administration of a low dose of loxiglumide for 7 d had no significant effect on exocrine and endocrine pancreatic function, whereas a high dose of loxiglumide decreased pancreatic enzyme output without inducing insulin resistance and diabetes mellitus. There is a possibility that chronic administration of cholecystokinin receptor antagonists not only inhibits the growth of the pancreas but also alters exocrine and endocrine pancreatic function. Loxiglumide at a dose of 50, 100, or 200 mg/kg body weight, or the same volume of saline, was given by an orogastric tube twice daily for 7 d (13 successive times). Biochemical and functional changes were determined on d 8 at 24 h after the last administration of loxiglumide and 18 h fasting. Pancreatic exocrine and endocrine function was simultaneously determined following an intravenous injection of a mixed solution of 0.5 g/kg body weight glucose plus 100 ng/kg body weight cerulein. Pancreatic weight and protein content were dose-dependently decreased by loxiglumide, whereas DNA content was decreased only by the highest dose of loxiglumide. Loxiglumide caused dose-dependent decreases in pancreatic fluid and protein output. Total pancreatic insulin content in rats treated with loxiglumide was not significantly different from that in the control rats. However, insulin concentration relative to DNA content was significantly increased in rats treated with 200 mg/kg body weight loxiglumide compared with that in other groups of rats. Glucose-stimulated insulin release was significantly low in rats treated with the highest dose of loxiglumide compared with that in other groups of rats, although there was no difference of serum glucose concentrations among these four groups of rats.

Postnatal development of the rat exocrine pancreas. II. Effects of protein-calorie malnutrition on amylase secretion and CCK receptor binding.

Malnutrition induces pancreatic atrophy and intracellular derangement, but its effects on cholecystokinin (CCK) receptors and the CCK-induced secretory response remain unclear. We used a rodent model to study the developmental effects of protein-calorie malnutrition on exocrine pancreatic function. Simultaneous experiments evaluated postnatal alterations in CCK-induced amylase response and receptor binding of pancreatic acini. At all postnatal ages, somatic and pancreatic weight of the malnourished rats was significantly below age-matched controls (p < 0.01). The malnourished rats showed a higher secretory response to CCK at 1 day of age and increased acinar sensitivity at 2 days. Maximal amylase secretion was significantly higher at 5 and 18 days (p < 0.05), but remained similar to that of the age-matched controls at 36 days. CCK receptor binding showed no significant changes at 1 and 2 days postnatally in comparison with controls. At 5 and 18 days, the affinity of the high-affinity state showed a twofold increase, while the capacity of the high-affinity state decreased by 40-55%. At the same time, the affinity of the low-affinity state increased significantly (p < 0.05), but the capacity of the low-affinity state was essentially unchanged. The acinar sensitivity of malnourished rats was consistently reduced between 5 and 36 days, which coincided with a reduction in spare receptors in the malnourished rats. In conclusion, the increased amylase secretory response at 1 and 2 days of age may be due to an adaptive response of endocrine function to maternal metabolic stress. The increased affinities of CCK receptors at 5 and 18 days may be associated with a higher secretory responsiveness, while the decreased spare receptors may contribute to a reduction in the acinar sensitivity. These results demonstrate that malnutrition induces changes in CCK binding and its secretory response.

Long-Term Blockade of Cholecystokinin (CCK)

To determine the effect of long-term blockade of cholecystokinin (CCK) on both pancreatic storage and secretion processes, L 364,718 (a CCK receptor antagonist) was administered to rats at 0.1 mg/kg/day for 3, 7, and 15 days. Zymogen granules were analyzed by flow cytometry to determine their light scattering properties-forward scatter and side scatter-as well as their amylase content measured by a specific antiserum. The mean number of zymogen granules per cell was counted on pancreatic sections using electron microscopy. DNA content, pancreatic weight, and enzyme secretion were also studied under both basal conditions and CCK infusion at a dose of 1.25 micrograms/kg/h, which is able to displace the CCK receptor antagonist. Two subpopulations of zymogen granules (Z1 and Z2) were identified on the basis of their light scattering parameters, in both control and L 364,718-treated rats. L 364,718 administered for 3, 7, and 15 days induced a significant reduction in the amylase content of individual zymogen granules, for both Z1 and Z2 zymogen granule subsets. In contrast, the number of zymogen granules per cell increased from day +3 of treatment onward, the highest values being detected at day +7. Hyperplasia was observed only at day +15. Basal enzyme secretion decreased significantly in rats treated with L 364,718 for 3 and 7 days but recovered to control values after 15 days of treatment. No significant differences in CCK-stimulated amylase secretion were observed between control and L 364,718-treated rats. At day +15 of L 364,718 treatment a significant increase in enzyme secretion was observed with respect to shorter treatment periods; this was associated with a significant increase in both the number of cells and the number of zymogen granules per cell. Our results indicate that chronic administration of L 364,718 induces a biphasic effect on pancreatic function. Interestingly, although enzyme secretion reached recovery after long-term treatment (15 days), the storage process is altered since the mean enzyme content in each individual zymogen granule remains significantly reduced.

Effect of Irsogladine on gap junctions in cerulein-induced acute pancreatitis in rats.

The capacity for intercellular communication (IC) via gap junctions is found in normal pancreatic acinar cells. The major role of IC is considered to be the maintenance of tissue homeostasis and the regulation of signal transmissions. Up to now, the participation of IC via gap junctions in acute pancreatitis has not been reported. We investigated the role of IC in cerulein (Cn)-induced acute pancreatitis in rats using irsogladine, an enhancer of IC via gap junction. Acute edematous pancreatitis was induced in rats by two intraperitoneal injections of 40 micrograms/kg Cn. Rats received various doses (25, 50, or 100 mg/kg body weight) of irsogladine orally, 15 and 2 h before the first Cn injection. The normal control group received only vehicle. The severity of pancreatitis was evaluated enzymatically and histologically 5 h after the first Cn injection. In Cn-induced acute pancreatitis, irsogladine significantly lowered the serum amylase level, the pancreatic wet weight, and the pancreatic amylase and DNA contents, in a dose-dependent manner. Particularly, the amylase content improved to the level of the normal controls. Histologically, the severity of pancreatitis was reduced significantly by treatment with irsogladine and no discernible vacuolization was seen in the group with 100 mg/kg irsogladine treatment. By immunofluorostaining pancreata with anti-connexin 32 (Cx32; a gap junction protein) antibody, we found that pancreatic acini were diffusely positive for Cx32 in the control group, but the number of Cx32-positive grains decreased markedly, to 19%, in the pancreatitis group. With 100 mg/kg irsogladine treatment, the number of Cx32 grains recovered to 70% of the normal control value. These findings indicate that IC via gap junction is disturbed in Cn-induced pancreatitis, which may result in the breakdown of tissue homeostasis and the progression of acute pancreatitis.

Evidence That A8947 Enhances Pancreas Growth via a Trypsin Inhibitor Mechanism

A8947 is a member of the sulfonyl urea class of compounds and is the active ingredient in a commercial broad leaf herbicide. This compound has been shown to produce pancreatic hypertrophy in rats, mice, and dogs. The objectives of this study were to investigate the mechanism(s) for the A8947 induction of pancreatic acinar cell hypertrophy and proliferation and to evaluate whether these pancreatic changes are reversible. A8947 was fed to male Crl:CD BR rats for up to 28 days (0, 300, 10,000, 30,000 ppm) or 56 days (0, 30,000 ppm). Rats were terminated on Test Days 7, 14, and 28 to assess the time course and dose response for the A8947-induced pancreatic changes, while rats terminated on Test Day 56 were used to assesss the reversibility of the pancreas effects at 30,000 ppm A8947. A8947 produced significant increases in pancreatic weight and acinar cell proliferation and diffuse acinar cell hypertrophy in 7 days at 10,000 and 30,000 ppm dose levels. By Day 14, absolute pancreas weights in the 10,000 and 30,000 ppm groups were maximally increased and remained at these levels throughout the study. In contrast, acinar cell proliferation in the 30,000 ppm group was still elevated at Test Day 14, but attenuated relative to the 7-day response, and returned to control levels by Test Day 28. No effects were observed at 300 ppm after a 28-day exposure period, while complete reversibility of A8947-induced pancreatic effects was demonstrated at 30,000 ppm following a 1-month recovery period (Test Day 56). Cholecystokinin (CCK) levels were increased by A8947 and closely followed the time course for pancreatic changes. MK-329, a specific CCKAreceptor antagonist, completely ablated the ability of 30,000 ppm A8947 to increase pancreas weight following 7 days of exposure. A8947 did not bind the CCKAreceptor in a receptor competition assay, negating any potential agonist mechanism. A8947 did, however, inhibit trypsinin vitro,suggesting a mechanism of action similar to that of raw soy protein, in which trypsin inhibitionin vivoresults in increased CCK levels followed by pancreatic acinar cell hypertrophy and proliferation.

Total parenteral nutrition influences both endocrine and exocrine function of rat pancreas.

The aim of this study was to examine the effect of total parenteral nutrition (TPN) on the endocrine and exocine function of the pancreas. Endocrine function was investigated using an intravenous glucose tolerance test (IGTT) in rats with TPN for 7 or 14 days. Exocrine function was evaluated by measuring amylase secretion from isolated acini as well as pancreatic weight, water content, protein, and enzymes after 7 days of TPN. When the TPN rats were compared with the controls, the glucose tolerance curve after an IGTT was unchanged, the basal plasma insulin levels were slightly lower and the insulin secretory response to intravenous glucose was markedly impaired. No differences could be seen between the insulin response after 7 days and that after 14 days of TPN. The weight of pancreas, the total content and concentration of pancreatic protein, and the total amylase content of the pancreas were lower, whereas the total content of both chymotrypsin and trypsin was higher. The concentration of DNA remained intact, whereas the total DNA content decreased. The levels of lipolytic enzymes, except for carboxylesterlipase, were unaffected. After TPN treatment, the insulin secretory response to glucose is impaired, the exocrine pancreas is hypoplastic and the storage pattern of pancreatic exocrine enzymes is altered.

Mechanisms for the Pancreatic Oncogenic Effects of the Peroxisome Proliferator Wyeth-14,643

Several peroxisome proliferators have been shown to produce pancreatic acinar cell hyperplasia/adenocarcinomas in 2-year bioassays with rats: ammonium perfluorooctanoate (C8), clofibrate, methylclofenapate, HCFC-123, and Wyeth-14,643 (WY). We have usedin vitro(C8, WY) andin vivo(WY) approaches to examine several possible mechanisms of pancreatic tumorigenesis by peroxisome proliferating compounds. These mechanisms include cholecystokinin receptor agonism (CCKA), trypsin inhibition, alterations in gut fat content, cholestasis, and altered bile flow/composition. All of these mechanisms enhance pancreatic growth either by binding to the CCKAreceptor or by increasing plasma CCK levels.In vitroexperiments using a receptor competition binding assay demonstrated that WY and C8 do not bind directly to the CCKAreceptor. In a continuous spectrophotometric assay, WY and C8 also failed to inhibit trypsin, a common mechanism for increasing plasma CCK levels. Thesein vitroresults suggested that WY was not acting via the two most common mechanisms for modulation of pancreas growth. Two types ofin vivoexperiments were conducted. The subchronic study (2-month duration) was designed primarily to detect early changes in pancreatic growth such as those mediated by compounds that inhibit trypsin or act as CCKAreceptor agonists. The chronic study (6 months) was designed primarily to evaluate whether the pancreatic lesions were secondary to hepatic changes such as cholestasis and/or altered bile flow/composition. In thein vivoexperiments, male Crl:CDBR rats were fed diets containing 0 or 100 ppm WY. In the subchronic study WY-treated rats had a twofold increase in mean relative liver weights, an eightfold increase in hepatic peroxisomal proliferation, and a fourfold increase in hepatocyte cell proliferation after 1 week which remained elevated throughout the 2 months of treatment. In contrast, no pancreatic weight effects, increases in plasma CCK, or acinar cell proliferation was seen through 2 months in the WY group when compared to the control group. Fecal fat concentrations were also measured at 2 months and demonstrated no difference between control and WY-treated animals. The absence of any early pancreas changes in the subchronic study is consistent with thein vitrodata which demonstrated that WY is not a CCKAagonist or a trypsin inhibitor. The chronic study demonstrated increases in pancreatic weights at 3 months (6% above control) and 6 months (17% above control), as well as increased CCK plasma levels in the WY-treated group. Liver effects in the chronic study paralleled those of the subchronic time points. Clinical pathology endpoints including increased serum concentrations of bile acids, alkaline phosphatase, and bilirubin were indicative of cholestasis in the chronic WY-treated group. The cholestasis may be responsible for the downward trend in total bile acid output, both of which may contribute to the modest increases in plasma CCK levels. These results indicate that chronic exposure to WY causes liver alterations such as cholestasis, which may increase plasma concentrations of CCK. Hence, WY may induce pancreatic acinar cell adenomas/adenocarcinomas via a mild but sustained increase in CCK levels secondary to hepatic cholestasis.

Recombinant leptin exchanges between parabiosed mice but does not reach equilibrium.

Parabiosis experiments suggest that ob/ob mice are deficient in a circulating "lipostatic" signal but respond to such a signal when it is delivered in the cross circulation from their parabiotic partner. Identification of leptin as the mutation in ob/ob mice leads to the assumption that leptin is the lipostatic signal. The objective of these experiments was to determine the circulating half-life of leptin and to demonstrate whether it exchanged between parabiosed mice. Measurement of disappearance of recombinant leptin from serum in SWRJ mice indicated a circulating half-life of approximately 36 min. Single ob/ob mice or one member of a parabiosed pair of ob/ob mice received 50 micrograms recombinant murine leptin in two intraperitoneal injections a day for 10 days, starting 40 days after parabiosis surgery. Control mice and pairs received equivalent injections of vehicle. In single mice, leptin significantly reduced food intake, body weight, serum insulin, and pancreatic and liver weight. Leptin treatment of one member of a parabiosed pair of ob/ob mice reduced serum insulin, gut content (an index of food intake), and body fat in both partners. The injected parabiont lost more fat than its partner, and body temperature was increased only in the injected mouse, indicating that leptin did not reach equilibrium in the two animals. This was confirmed by Western blot analysis of serum leptin measured 2 h after injection. Therefore, although leptin can exchange between parabionts, its half-life is inadequate to allow equilibrium when a large concentration gradient exists between partners.

Effect of a new CCK-A receptor antagonist, dexloxiglumide, on the exocrine pancreas in the rat

The effect of dexloxiglumide, a new potent cholecystokinin (CCK) antagonist, on pancreatic enzyme secretion and growth was studied in the rat. Pancreatic exocrine secretion was studied both in vitro (isolated and perfused pancreatic segments) and in vivo (anaesthetized animals with cannulation of the common bile duct) whereas the trophic effect was investigated after short-term (7 days) administration of the CCK-agonist, caerulein, or camostate (a potent trypsin inhibitor), with or without dexloxiglumide. CCK-8 stimulated amylase release from in vitro pancreatic segments in a concentration-dependent manner. Dexloxiglumide displaced the concentration response curves to CCK-8 to the right without affecting the maximum response, suggesting a competitive antagonism. The Schild plot analysis of data gave a straight line with a slope (0.90±0.36) not significantly different from unity. The calculated pA 2 for dexloxiglumide was 6.41 ± 0.38. In vivo experiments confirmed results from in vitro studies since intravenous dexloxiglumide reduced pancreatic exocrine secretion induced by submaximal CCK-8 stimulation (0.5 nmol/kg/h) in a dose-dependent manner, the ID 50 being 0.64 mg/kg. Both exogenous and endogenous (released by camostate) CCK increased the weight of the pancreas, the total pancreatic protein and DNA, trypsin and amylase content. Dexloxiglumide (25 mg/kg), administered together with caerulein (1 μg/kg), reduced the peptide-induced increase in pancreatic weight, protein and enzyme content. Similarly, when dexloxiglumide was given together with camostate (200 mg/kg), all the observed changes were reduced by concomitant administration of the antagonist. These results demonstrate the ability of dexloxiglumide to antagonize the effects of CCK on pancreatic secretion and growth, suggesting that this compound is a potent and selective antagonist of CCK-A-receptors in the pancreas.

Retardation of pancreatic regeneration after partial pancreatectomy in a strain of rats without CCK-A receptor gene expression.

This study extends a recent observation that Otsuka Long-Evans Tokushima Fatty (OLETF) rats show no expression of the cholecystokinin (CCK)-A receptor gene in the pancreas because of a genetic abnormality. We compared the changes in pancreatic regeneration in terms of wet weight and protein and DNA contents after partial pancreatectomy (30% resection) in OLETF and control (Long-Evans Tokushima Otsuka: LETO) rats and examined whether the CCK-B receptor has a role in pancreatic regeneration after pancreatectomy. The pancreatic wet weight increased significantly with age in both OLETF and LETO rats regardless of surgical procedure, but the increase with respect to time was significantly less in OLETF than in LETO rats. The protein and DNA concentrations in the pancreas (mg/g wet tissue) were comparable for both strains after sham operation. However, they were significantly lower than pancreatectomy in OLETF rats compared to those after sham operation, whereas they were comparable in LETO rats regardless of surgical procedure. The ratio of protein content/DNA content (cell size) was significantly lower in OLETF than LETO rats under all conditions. CCK-B receptor gene expression was not enhanced after pancreatectomy. In conclusion, the CCK-A receptor is not an absolute requirement for pancreatic normal growth but is important for pancreatic regeneration.

Effect of ageing on pancreatic hyperplasia after 90% proximal small bowel resection.

The present study was performed to examine the effect of ageing on pancreatic hyperplasia observed after proximal small bowel resection (PSBR). Young and old Wistar rats were randomly assigned to two groups, which underwent either an approximate 90% PSBR or a jejunal and ileal transection (TRC). One week after the operation, the pancreatic wet weight and the protein, DNA and RNA content of the pancreas were all significantly higher in young PSBR rats than in young TRC rats. However, no differences were seen in the old rat groups. Plasma enteroglucagon levels were elevated in both young and old PSBR rats, but the ratio of increase between the PSBR and TRC groups was significantly higher in young rats. Plasma cholecystokinin and gastrin levels did not increase after PSBR in either the young or old rats. These findings suggest that pancreatic hyperplasia observed after PSBR is attenuated by ageing, probably due to an insufficient increase in plasma enteroglucagon levels.

Apoptosis Participates in the Remodeling of the Endocrine Pancreas in the Neonatal Rat

In rodents, shortly after birth a lack of increase in pancreatic weight and in islet mass have been reported during a time of overall body weight increase. To understand this regulation of the neonatal growth of the β cell mass, we studied Sprague Dawley rats at 2, 9, 13, 17, 20, 24, and 31 days of age for β cell replication, β cell mass, and cell size and for the presence of β cell apoptosis. β cell mass was stable from 2–20 days (range: 0.91 ± 0.2 to 1.33 ± 0.23 mg) and increased thereafter. β cell replication progressively decreased. Condensed apoptotic nuclei were identified and counted on paraffin sections using the fluorescent dye propidium iodide. Apoptoticβ cell nuclei were found at a basal rate (1.54 ± 0.22%) at 2, 9, and again after 20 days of age. However, at 13 and 17 days, the incidence of apoptosis was significantly increased (3.64 ± 0.45%). The decreased replication and the increased incidence of apoptosis in the β cells strongly suggest a wave of neogenesis of β cells to maintain the constant β cell mass. These data show that the endocrine pancreas undergoes significant modification during neonatal life and that apoptosis is an important mechanism in this remodeling of the β cell mass. Whether a selective deletion of some population ofβ cells occurs is unclear, but a dysregulation of this remodeling process could have important effects on the pancreatic β cell mass.

Gastrin effects on growth and exocrine secretion in the neonatal rat pancreas.

In adult rats, cholecystokinin (CCK) binds to pancreatic CCK-A receptors and stimulates exocrine secretion and pancreatic growth. In newborn rats there is very little mature intestinal CCK and few pancreatic CCK-A receptors. However, there is an abundant source of the related peptide gastrin, and in addition, there are pancreatic CCK-B/gastrin receptors. In this study, we have explored the hypothesis that gastrin may "deputise" for CCK in the neonate and cause pancreatic exocrine secretion, growth, and maturation. Newborn rats were injected intraperitoneally with the gastrin antagonist, C1-988, or placebo for 5 days and sacrificed on day 6. Body weight (CI-988, 8.25 +/- 0.48 g; placebo, 10.17 +/- 0.93 g) and pancreatic weight (19.41 +/- 1.5 vs. 21.58 +/- 1.72 mg) were the same. Protein (1,202 +/- 78 vs. 1,254 +/- 56 micrograms), amylase (22.3 +/- 0.9 vs. 19.2 +/- 1.00 U), RNA (117 +/- 7 vs. 126 +/- 5 micrograms), and DNA (95 +/- 8 vs. 100 +/- 7 micrograms) contents of the pancreas were similar in the two groups. The weight of the stomach was reduced (p = 0.04) in the treated group (50.8 +/- 2.5 mg) compared to the placebo group (59.8 +/- 3.7 mg). In both neonates and adults, CCK-8 was approximately 1,000 times more potent than gastrin-17 in stimulating amylase release from isolated pancreatic acini. This suggests that enzyme release is probably mediated by the same receptors in both adults and neonates, and in adults previous work has shown this to be the CCK-A receptor. In conclusion, these data show that gastrin has very weak effects on neonatal pancreatic exocrine secretion, and furthermore, gastrin is not essential for growth and maturation of the neonatal pancreas. The role of gastrin and CCK-B/gastrin receptors in the neonatal pancreas remains speculative.