Inhibitory effect of a cholecystokinin antagonist on the proliferative response of the pancreas to pancreatobiliary diversion

Carcinoid syndrome misdiagnosed as a malabsorptive syndrome after biliopancreatic diversion

A case is reported of a woman who developed untreatable diarrhea after a prior biliopancreatic diversion (BPD), attributed to the malabsorptive component. Abdominal ultrasound incidentally found focal liver lesions. On fine needle aspiration biopsy, atypia was found, and these hepatic lesions were resected with free margins. The specimen showed liver metastases of an aggressive malignant neuroendocrine neoplasm. The primary site was subsequently identified to be in the pancreas. The physician and surgeon must realize that non-related diseases can develop after bariatric surgery, as in the general population.

Gastric gland degeneration induced in monkeys by the CCK-B/gastrin receptor antagonist CI-988

Gastric effects of subchronic treatment with the cholecystokinin-B (CCK-B)/gastrin receptor antagonist CI-988 were investigated in cynomolgus monkeys. In preliminary range-finding studies, CI-988 was given orally to 1 monkey per sex for 14 days at doses of 50, 100, 200, and 500 mg/kg/day. Subchronic studies of CI-988 were subsequently conducted using 5 monkeys per sex at doses of 0, 5, 25, and 75 mg/kg for 4 or 13 wk. High-dose monkeys were dosed initially at 100 mg/kg, but the dose was not well tolerated and was decreased to 75 mg/kg after 8 days of treatment. One male monkey at 75 mg/kg was euthanatized in extremis on day 23. In the range-finding study, minimal to moderate, multifocal to diffuse degeneration of gastric glands, primarily in the fundic region, was observed at 100 mg/kg and above, with frank gastric mucosal atrophy occurring at 200 and 500 mg/kg. Minimal to mild gastric gland degeneration was also observed in the subchronic study after 4 wk at 25 and 75 mg/kg, but histopathologic gastric changes were remarkably absent after 13 wk. Mucosal height in the stomach fundus was decreased 19.8% in 75-mg/kg males at week 4, and although gastric mucosa appeared histologically normal after 13 wk, mucosal height remained 28.6% less than that of controls. In females at 75 mg/kg, fundic mucosal height was decreased 7% and 5% at weeks 4 and 13, respectively, but decreases were not statistically significant. Mean serum gastrin concentrations were increased 10-fold in males only after 4 wk at 75 mg/kg, but were comparable to controls during week 13. CI-988-induced gastric gland degeneration is consistent with antagonism of gastrin's trophic activity toward gastric mucosa. Notwithstanding decrements in gastric mucosal height, disappearance of mild histopathologic findings despite continued treatment with the ligand suggests some degree of adaptation to subchronic CCK-B/gastrin inhibition, although the mechanism of accommodation has yet to be delineated.

Stimulation of pancreatic growth. Distal small bowel resection mediated by increased levels of cholecystokinin

SUMMARY BACKGROUND DATA

Distal, but not proximal, resection of the small bowel induces growth of rat pancreas, but the mechanism of this phenomenon is poorly clarified. The release of cholecystokinin (CCK), a trophic hormone for the pancreas, is regulated by a negative-feedback control of bile salts. The ileum is a major site for reabsorption of bile salts. Thus, unsuppressed release of CCK due to deleted reabsorption of bile salts after distal small bowel resection may be a cause of pancreatic growth. In this study, the authors have examined whether pancreatic growth after distal small bowel resection was mediated by endogenous CCK and have determined whether the mechanism of this pancreatic growth required biosynthesis of polyamine.

METHODS

Male Fischer 344 rats underwent 70% distal small bowel resection or transection of the ileum. Beginning 48 hours after surgery, CR1409 (a CCK-receptor antagonist) or saline was injected subcutaneously every 8 hours. All animals were pair-fed and killed 14 days after surgery. The pancreas from each rat was excised, weighed, and assayed for DNA, RNA, protein, and polyamine content.

RESULTS

Distal small bowel resection increased pancreatic weight, DNA, RNA, and protein, as well as polyamine levels; all of these increases were significantly suppressed by CR1409. Postprandial release of CCK into the circulation was significantly increased after distal small bowel resection.

CONCLUSIONS

Pancreatic growth after distal small bowel resection was associated with the stimulation of polyamine biosynthesis; growth appeared to be mediated by endogenous CCK.

Effects of short-term administration of the CCK receptor antagonist, KSG-504, on regeneration of pancreatic acinar cells in acute pancreatitis in rats

Cholecystokinin (CCK) receptor antagonists have been reported on have an inhibitory effect on acute experimental pancreatitis, but their long-term administration is also reported to block pancreatic regeneration. We examined whether the short-term administration of KSG-504 (KSG), a synthetic CCK-A receptor antagonist, inhibited the regeneration of pancreatic acinar cells after ethionine-induced acute pancreatitis in rats. KSG (50 mg/kg), given 12 times by subcutaneous injection at 6-h intervals, prevented the reduction of protein, amylase, and trypsinogen levels, and the DNA content of the pancreas and facilitated the recovery of these values. Ornithine decarboxylase activity in pancreatic tissue and a 5-bromo-2'-deoxyuridine labeling study indicated that DNA synthesis was accelerated in rats treated with KSG. These findings suggest that the short-term administration of KSG inhibits the development of ethionine-induced acute pancreatitis and facilitates the regeneration of acinar cells.

The role of gastrin and cholecystokinin in normal and neoplastic gastrointestinal growth

Gastrin and cholecystokinin (CCK) act as growth factors for the gastric mucosa and the pancreas, respectively. CCK is also responsible, via the CCK-A receptor, for the pancreatic hyperplasia observed following the feeding of protease inhibitors or pancreaticobiliary diversion. Hypergastrinaemia does not increase the incidence of spontaneous gastrointestinal carcinoma, but does stimulate the proliferation of gastric enterochromaffin-like cells via the gastrin/CCK-B receptor, with a consequent increase in the incidence of gastric carcinoids. Whether gastrin influences mutagen-induced gastrointestinal carcinogenesis is still controversial, but CCK clearly enhances the induction by carcinogens of acinar tumours in the pancreas. While gastrin increases xenograft growth of 50% of gastrointestinal tumours tested, effects on the proliferation of gastrointestinal tumour cell lines in vitro have been more difficult to demonstrate, perhaps because many cell lines are already maximally stimulated by autocrine gastrin. Gastrin mRNA and progastrin, but not mature amidated gastrin, have been detected in all gastrointestinal cell lines tested. Although cell proliferation is inhibited by gastrin/CCK receptor antagonists, the spectrum of antagonist affinities is not consistent with binding to either CCK-A or gastrin/CCK-B receptors. Definition of the molecular structure of the receptor involved in the autocrine loop may lead to novel therapies for gastrointestinal cancer.

Enteroglucagon, but not CCK, plays an important role in pancreatic hyperplasia after proximal small bowel resection

The present study was performed to examine the role played by pancreatotrophic factors, especially enteroglucagon and cholecystokinin (CCK), in the compensatory pancreatic hyperplasia observed after proximal small bowel resection (PSBR). Male Wistar rats were randomized into two groups, receiving either PSBR or transection (TRC). Five animals from each group were randomly selected for treatment with FK-480, a novel CCK antagonist. Four weeks after the operation, plasma levels of gastrin, CCK and enteroglucagon were measured. Pancreatic wet weight and protein, DNA, RNA and enzyme content were also determined. The wet weight and content of protein, DNA and RNA were significantly higher in PSBR rats than in TRC rats, regardless of whether they received FK-480. FK-480 had no suppressive effects on adaptive pancreatic growth after PSBR. Plasma enteroglucagon levels rose significantly in PSBR rats, and there were positive correlations between plasma enteroglucagon levels and pancreatic protein, DNA and RNA content. These findings demonstrated that plasma CCK was not the major trophic factor operating in the pancreas after PSBR, and showed that enteroglucagon plays an important role in the pancreatic hyperplasia that occurs after PSBR.

Stimulation of in vivo pancreatic growth in the rat is mediated specifically by way of cholecystokinin-A receptors

BACKGROUND/AIMS

Cholecystokinin (CCK) and gastrin stimulate growth of rodent pancreas in vivo. However, it remains unclear whether these growth effects are mediated specifically by CCK-A receptors, CCK-B receptors, or both. To clarify this issue, the present study examined the effect of highly selective and biologically active CCK agonists on pancreatic growth.

METHODS

Rats were subcutaneously injected with either (1) CCK-8, a nonselective CCK agonist (2.50 micrograms/kg body wt); (2) A-71623, a selective CCK-A agonist, tert-butyl-oxycarbonyl-Trp-Lys (epsilon-N-2-methylphenylaminocarbonyl)-Asp-(N-methyl)-Phe-NH2 (1.84 micrograms/kg body wt); (3) SNF-8815; a selective CCK-B agonist, [(2R,3S)-beta-MePhe28, N-MeNle31]CCK26-33 (2.40 micrograms/kg body wt); or (4) saline (control) for 21 days. Rats were killed, and pancreatic weight, protein content, RNA content, DNA content, protein-DNA ratio, RNA-DNA ratio, pancreatic area per nucleus, and number of mitoses per 10,000 acinar cells were determined.

RESULTS

Nonselective CCK agonist significantly increased pancreatic weight, protein, RNA, and DNA contents, and number of mitoses per 10,000 acinar cells. Likewise, selective CCK-A agonist significantly increased pancreatic weight, protein, RNA, and DNA contents, protein-DNA ratio, RNA-DNA ratio, pancreatic area per nucleus, and number of mitoses per 10,000 acinar cells. In contrast, selective and biologically active CCK-B agonist had no effect.

CONCLUSION

These findings indicate that pancreatic growth is mediated specifically by CCK-A receptors in the rat in vivo.

Enteroglucagon. A putative humoral factor inducing pancreatic hyperplasia after proximal small bowel resection

The present study evaluated pancreatotrophic factors after massive small bowel resection. Specifically, we examined the role of enteroglucagon in compensatory pancreatic hyperplasia after proximal small bowel resection (PSBR) by using rats fed a fiber-free elemental diet or an elemental diet containing pectin. PSBR increased the net pancreatic weight as well as the protein, DNA, RNA, and amylase contents, and elevated plasma enteroglucagon levels. Pectin addition to the diet provoked a further increase in these parameters and significant positive correlations were found between the plasma enteroglucagon levels and the protein, DNA, and RNA contents of the pancreas. Plasma gastrin and CCK levels were not affected by the small bowel resection. These results indicate that enteroglucagon may exert a potent trophic effect on the pancreas after PSBR.

Pancreatic trophism in experimental liver cirrhosis

Pancreatic trophism and pancreatic enzyme composition, and plasma levels of cholecystokinin, insulin, glucagon, and glucose in liver cirrhosis induced by chronic thioacetamide administration (0.02% in the drinking water for 12 mo) were studied in rats. Advanced liver cirrhosis was evident in all thioacetamide-treated rats. The weight of the pancreas and its contents of DNA, protein, trypsinogen, chymotrypsinogen, proelastase, secretory trypsin inhibitor, and amylase were significantly increased as compared to the controls. The pancreatic secretory enzyme content changes showed a nonparallelism, characteristic of a cholecystokinin effect. Light and electron microscopy revealed a normal pancreatic architecture. Bioassayed plasma cholecystokinin levels in both fed and 24-h-fasted cirrhotic rats were significantly higher than in the corresponding controls. The plasma glucose, insulin, and glucagon levels demonstrated hypoglycemic tendencies with a glucagon predominance. These findings indicate that advanced liver cirrhosis in the rat is accompanied by pancreatic hypertrophy and hyperplasia, which might be attributed, at least in part, to elevated circulating cholecystokinin levels.

Time-dependent changes in enterochromaffin-like cell kinetics in stomach of hypergastrinemic rats

BACKGROUND

Hypergastrinemia has been claimed to cause first hyperplasia and then dysplasia/neoplasia of enterochromaffin-like (ECL) cells in rat stomach. The growth is thought to reflect an accelerated self replication rate of mature ECL cells. The cytokinetics and the histidine decarboxylase (HDC) activity of the ECL cells were investigated during sustained hypergastrinemia.

METHODS

Hypergastrinemia was evoked by omeprazole (400 mumol.kg-1 x day-1 orally) for up to 1 year. Immunocytochemistry for histamine was used to determine the ECL cell density and combined with [H3]-thymidine autoradiography to establish the labeling index (LI), i.e., the proportion of the ECL cells that has incorporated [H3]thymidine.

RESULTS

The ECL cell density increased progressively for 10-20 weeks in response to the hypergastrinemia and remained at a plateau for the remainder of the study. The hyperplasia was diffuse with additional micronodules at 52 weeks. The ECL cell Ll was maximally elevated after 1-2 weeks and declined to control values after 10-20 weeks of treatment. In contrast, the HDC activity remained elevated for the duration of the study.

CONCLUSIONS

The ECL cell hyperplasia reflects the transiently elevated ECL cell Ll during the early phase but is not associated with an accelerated rate of mitosis during the 10-52 weeks period. Even though with time gastrin seems to loose its ability to sustain a high ECL cell Ll it retains its ability to maintain a high HDC activity.

Experimental pancreatic hyperplasia and neoplasia: effects of dietary and surgical manipulation

Several studies carried out during the past two decades have investigated the effect of dietary and surgical manipulation on pancreatic growth and carcinogenesis. Diets high in trypsin inhibitor stimulate pancreatic growth and increase the formation of preneoplastic lesions and carcinomas in the rat pancreas. Cholecystokinin (CCK) is the key intermediary in this response, since both natural and synthetic trypsin inhibitors increase circulating levels of the hormone and CCK antagonists largely prevent these changes. Fatty acids enhance pancreatic carcinogenesis in both rats and hamsters, whereas protein appears to have a protective role in the rat, but to increase tumour yields in the hamster. Several surgical operations affect the pancreas. Pancreatobiliary diversion and partial gastrectomy stimulate pancreatic growth and enhance carcinogenesis, probably by means of increased CCK release. Complete duodenogastric reflux has similar effects on the pancreas but the gut peptide involved is gastrin. Although massive small bowel resection increases pancreatic growth, the marked reduction in caloric absorption probably explains its failure to enhance carcinogenesis. CCK and enteroglucagon might work in concert to modulate the tropic response of the pancreas to small bowel resection. In the pancreas, as in the large intestine, hyperplasia appears to precede and predispose to neoplasia.

Inhibitory effect of a cholecystokinin antagonist on pancreatic carcinogenesis after pancreatobiliary diversion

The role of cholecystokinin (CCK) has been explored in pancreatic carcinogenesis following pancreatobiliary diversion (PBD), using the specific CCK receptor antagonist CR-1409. Male Wistar rats (n = 80) weighing 70-100 g were given weekly i.p. injections of azaserine (30 mg kg-1 week-1) for 3 consecutive weeks. One week later animals were randomised to receive either PBD or sham PBD and thereafter to receive s.c. injections of either saline or CR-1409 (10 mg kg-1 day-1, 5 days a week). Six months after operation surviving rats were killed as follows: sham + saline 20, PBD + saline 19, sham + CR-1409 14, PBD + CR-1409 11. Cardiac blood was taken for CCK assay and the pancreas was excised for wet weight measurement and quantitative estimation of atypical acinar cell foci (AACF), the precursor of carcinoma. PBD reduced median body weight (3-20% less than shams) but trebled the absolute and relative pancreatic weights (P < 0.001). CR-1409 blunted this adaptive response to PBD, reducing absolute pancreatic weight by 35% (P < 0.005). PBD quadrupled circulating CCK concentrations, regardless of the antagonist treatment. Acidophilic AACF occurred only in rats with PBD. CR-1409 markedly reduced the number of observed acidophilic AACF by 90% (P < 0.001) and the number of foci per pancreas by 93% (P < 0.001). Moreover, CR-1409 reduced the mean focal diameter of each lesion by 18% (P < 0.005), the mean focal volume by 58% (P < 0.05) and the percentage of pancreas occupied by acidophilic foci by 95% (P < 0.001). PBD enhances pancreatic carcinogenesis by causing hypercholecystokininaemia, and CR-1409 largely inhibits this enhancement.

Duodenogastric reflux enhances growth and carcinogenesis in the rat pancreas

Surgery for peptic ulcer disease may increase the risk of pancreatic cancer. The effect of duodenogastric reflux on pancreatic carcinogenesis was tested, and changes in the circulating levels of cholecystokinin (CCK) and gastrin were measured. Male Wistar rats (n = 40) weighing 250-300 g were randomized to undergo gastrotomy (control) or split gastrojejunostomy (to produce complete duodenogastric reflux) and then to receive azaserine (30 mg/kg/week intraperitoneally) or saline injections for 3 weeks. At 6 months, blood CCK was assayed and the pancreas was excised for quantitative estimation of atypical acinar cell foci (AACF), the precursor lesions of carcinoma. Rats that had undergone split gastrojejunostomy weighed 15-19 per cent less than controls (P < 0.05), but their relative pancreatic weight (mg pancreas per 100 g body-weight) was 52-60 per cent greater (P < 0.001). Acidophilic AACF occurred only in azaserine-treated rats with duodenogastric reflux. Although plasma CCK concentrations were unchanged, split gastrojejunostomy increased basal and postprandial gastrin levels by 98-175 per cent (P < 0.05). Duodenogastric reflux produces sustained hypergastrinaemia and promotes experimental pancreatic carcinogenesis.

Role of cholecystokinin in pancreatic adaptation to massive enterectomy

Since pancreatic adaptation to massive proximal small bowel resection (PSBR) may be modulated through cholecystokinin (CCK) secretion, we tested the effect of the CCK antagonist CR-1409 on this response. Male Wistar rats (n = 72) weighing 220-225 g were randomised to receive either PSBR or transection/resuture followed by saline or CR-1409 (12 mg/kg daily subcutaneously). Rats were killed one, two, and three weeks post-operatively, at which time blood was obtained for CCK assay and the pancreas was assessed for proliferative activity by three parameters: nucleic acid and protein content, bromode-oxyuridine (BrdUrd) labelling index, and proliferating cell nuclear antigen (PCNA) expression. PSBR increased plasma CCK concentration by 83-102% at 1-3 weeks, irrespective of CR-1409 administration. Total pancreatic DNA content per 100 g body weight increased by 34% at two weeks (p less than 0.05) and by 82% at three weeks (p less than 0.05), while RNA content increased by 60% and 178% (p less than 0.001) and protein content by 20% and 57% (p less than 0.05). PSBR increased the BrdUrd labelling index and the percentage of PCNA immunoreactive cells. CR-1409 completely abolished this proliferative response and also prevented the rise in nucleic acid and protein contents. Apart from growth stimulation, PSBR also enhanced pancreatic exocrine function, as shown by ultrastructural evidence of an appreciable decrease in zymogen granules; CR-1409 also inhibited this functional effect of hypercholecystokininaemia. The results confirm the tropic role of CCK after PSBR, and CR-1409 prevents this pancreatic adaptation.

Enhancing effect of partial gastrectomy on pancreatic carcinogenesis

The controversial issue of enhanced pancreatic carcinogenesis following partial gastrectomy has been explored in male Wistar rats (n = 40) weighing 250-300 g. Animals were randomised to receive either 60% distal gastrectomy with Roux-en-Y reconstruction or gastrotomy and resuture (control). Immediately after operation each group was further divided into two subgroups, receiving i.p. injections of either saline or azaserine (30 mg kg-1 wk-1 for 3 weeks). At 15 months blood was obtained at 0, 5, 15 and 30 min after a fatty meal for cholecystokinin (CCK) assay; rats were then killed. Pancreatic wet weight was measured, and histological sections were examined for atypical acinar cell foci (AACF), the putative precursor lesion of carcinoma. There were no significant differences in body weight or pancreatic weight between controls and rats with gastrectomy. Only azaserine-treated rats had acidophilic AACF. Partial gastrectomy substantially increased the number of acidophilic AACF per pancreas (median 26.05 vs 2.09; P less than 0.005), with a 9-fold increase in their volume (P less than 0.005). Basal and postprandial plasma CCK concentrations were higher after gastrectomy than in controls (P less than 0.05). Partial gastrectomy has an enhancing effect on azaserine-induced pancreatic carcinogenesis, probably by means of increased CCK release.