Proliferative response of different exocrine pancreatic cells after surgical pancreaticobiliary diversion in the rat

Hormonal control of pancreatic growth during fetal, neonatal and adult life

This review article has for major objective to summarize the old and latest developments on the hormonal controls of pancreatic growth. The article deals with hormonal controls during the fetal, neonatal and adult periods of pancreas development, growth and regeneration. During the fetal period, comparisons were made between studies performed with pancreatic explants and those designed in vivo. After birth, the effects of glucocorticoids, thyroxine, gastrin, bombesin, secretin, cholecystokinin alone or with secretin are reported. In the adults, similar studies were reported on hormones with addition of the effects of neuropeptides, the cell types targeted by hormones and the hormonal control after pancreatectomy and pancreatitis.

Effects of human platelet-derived growth factor-AB on sarcoma growth in vitro and in vivo

Platelet-derived growth factor (PDGF) has been proposed to play an important role in the growth of tumors. In order to study the effects of PDGF-AB on tumor growth in vivo, sarcoma-bearing mice were treated with PDGF-AB. The tumors, a malignant fibrous histiocytoma and an osteosarcoma, had functional PDGF receptors in vitro, as demonstrated by stimulation of PDGF-AB using a [3H]thymidine incorporation assay. Immunohistochemistry also revealed that both sarcoma xenografts expressed PDGF receptors. The tumor-bearing mice were given human PDGF-AB for 14 days, either continuously by an intraperitoneally placed mini-osmotic pump, or by daily injections. No effects on tumor growth in vivo were observed, as measured by tumor volume, autoradiography or cell cycle distribution. The histological appearance and ploidy of the tumors remained unaltered. The results indicate that, although the tumor cells are stimulated by PDGF-AB in vitro, the in vivo milieu or tumor growth pattern may render the tumors less susceptible to exogenously administered PDGF-AB in vivo.

Proliferation of parenchymal epithelial cells enhanced in chronic pancreatitis

This study was performed to determine whether pancreatic parenchymal epithelial cells in human chronic pancreatitis tissues retain a biologically significant capability to proliferate and, if so, within which epithelial compartment proliferation occurs. The techniques of immediate per-operative in vitro labelling with bromodeoxyuridine (BrdU) and conventional immunohistochemistry for Ki-67 antigen expression were used to identify proliferating cells. Concordance between the two techniques was confirmed in all tissues examined. In normal pancreas, proliferation was restricted to acinar epithelial cells, with no activity in the ductules. In chronic pancreatitis of both chronic obstructive and chronic calcifying types, the number of proliferating cells in the acini was significantly increased. A small population of proliferating cells was also apparent within ductules in chronic calcifying pancreatitis, but not in chronic obstructive pancreatitis. This investigation has shown that loss of parenchymal epithelium occurring in chronic pancreatitis is not caused by a primary failure of pancreatic 'stem-cell' proliferation, but is due to disproportionate attrition of differentiated parenchymal epithelial cells by a mechanism, possibly stromal in origin, which remains hitherto unidentified. The presence of proliferating ductular cells in chronic calcifying pancreatitis, but not chronic obstructive pancreatitis, suggests that distinct pathogenic processes may be operating in the former condition, which is classically regarded as secondary to ductal obstruction by stones, and in this single respect might be considered to be identical to chronic obstructive pancreatitis. Preservation of 'stem-cell' function supports the belief that regeneration of pancreatic parenchymal tissue could be a feasible proposition if biologically appropriate management strategies were developed to treat chronic calcifying pancreatitis.

Total parenteral nutrition affects the tropic effect of cholecystokinin on the exocrine pancreas

BACKGROUND

Cholecystokinin (CCK) exerts trophic effects on the exocrine pancreas. Total parenteral nutrition (TPN) results in hypotrophy of the pancreas. The present study aimed to examine the effect of exogenous and endogenous CCK during TPN.

METHODS

Seventy-two Sprague-Dawley rats were orally fed or given TPN after pancreaticobiliary diversion (PBD) and were infused with CCK-8S or the CCK-receptor antagonist devazepide for 7 days.

RESULTS

Infusion of CCK and PBD caused hyperCCKemia, whereas TPN did not influence the concentration of plasma CCK. The reduced pancreatic contents during TPN could be reversed by CCK but not by PBD. The hyperplastic response to CCK in orally fed rats was abolished during TPN. Devazepide did not influence the pancreatic variables in orally fed and TPN-treated rats.

CONCLUSION

TPN reduces the hyperplastic response of the exocrine pancreas to CCK, and CCK reverses the hypotrophy seen during TPN. The effects of CCK on the exocrine pancreas seems to need enteral nutrition for the full expression.

The changes in the rat parotid glands following total parenteral nutrition and pancreatico-biliary diversion are not mediated by cholecystokinin

CONCLUSIONS

The results of the present study suggest that the pancreas and parotid glands both respond with hypoplasia during absence of food in the digestive tract and with hyperplasia following pancreatico-biliary diversion (PBD). Factors other than cholecystokinin (CCK) are, however, involved in the effects on the parotid glands, since infusion of CCK-8S and devazepide was without influence.

BACKGROUND AND AIM

Total parenteral nutrition (TPN) causes reduced pancreatic weight, whereas PBD evokes hyperCCKemia and enlargement of the rat pancreas. The pancreas and parotid glands have in part similar morphology and function. Therefore, we studied the possible presence of alterations also in the parotid glands during TPN, after PBD and during infusion of sulfated cholecystokinin (CCK-8S) and the CCK-A receptor antagonist devazepide, respectively.

MATERIALS AND RESULTS

Rats either received TPN for 7 d, or were kept under otherwise identical conditions with free access to food and water. TPN markedly reduced both pancreatic and parotid wet weight and thereby also the protein and amylase contents, and pancreatic DNA content was decreased. There was a significant correlation between the pancreas and parotid glands when comparing these parameters. The concentration of plasma CCK was unaffected by TPN. PBD caused a sevenfold increase in plasma CCK and a three fold increase in the pancreatic weight compared to control rats 28 d after the operation. The protein and DNA contents in the pancreas were found to be increased. The parotid glands increased twofold in weight, but their protein and amylase contents were not affected. There was a significant correlation between the pancreas and parotid glands when comparing weight, and protein and amylase concentrations. Infusion of CCK-8S during 28 d caused a marked increase in pancreatic wet wt and protein and DNA contents. The CCK-A receptor antagonist devazepide induced a reduction in protein and DNA contents in the pancreas. The parotid glands were not affected by either treatment. No effect on the labeling index of serous and ductal cells of the parotid gland was seen at 36 h, 3, 7, and 28 d of infusion with CCK-8S or devazepide.

Profound duodenogastric reflux causes pancreatic growth in rats

Although duodenogastric reflux is a physiological event, excessive reflux may be a pathogenetic factor in several diseases of the foregut, including cancer. Long term profound duodenogastric reflux produces pancreatic and gastric tumours in rats. The trophic effect of surgically induced duodenogastric reflux on the pancreas was investigated and the mechanisms involved were examined. Rats with profound reflux from a split gastroenterostomy were compared with sham operated and unoperated controls after two and six weeks. In the six week experiment, one reflux and one sham group were given the cholecystokinin (CCK) receptor antagonist devazepide (25 nmol/kg/h). Duodenogastric reflux caused a significant increase in pancreatic weight, DNA, and plasma CCK and gastrin concentrations at both two and six weeks. Devazepide substantially reduced the pancreatic weight increase after six weeks but did not abolish it completely. CCK and gastrin were not affected by devazepide. These results suggest that CCK is largely responsible for the pancreatic growth induced by reflux but another factor may also be involved. The trophic effect of duodenogastric reflux may contribute to the increased incidence of pancreatic cancer reported after gastric surgery.

Colonic mucosal proliferation after pancreaticobiliary diversion in the hamster

The effect of pancreaticobiliary diversion (PBD) on the colonic mucosa was studied in hamsters over 5, 10, and 24 days. Sham-operated animals served as controls. At all three time intervals, experimental animals had increased plasma cholecystokinin concentrations and decreased gastrin concentrations. Five days after PBD, there was an increase in scintigraphically measured [3H]thymidine incorporation into colonic tissue. Correspondingly, there was an increase in the [3H]thymidine DNA labeling index of goblet cells in the colonic mucosa. The total number of cells in the colonic crypt columns were significantly increased on days 5, 10 and 24. Whether this proliferative response in the colon is due to increased release of cholecystokinin, enteroglucagon, other aberrations of hormones or growth factors, or simply an increased bile load on the colonic mucosa remains to be clarified. Such further studies may reveal an alternative animal model for studies on risk factors in colonic carcinogenesis.

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.

Effects of gastric fundectomy and antrectomy on the exocrine pancreas in the hamster

The effect of gastric fundectomy and antrectomy on growth of the exocrine pancreas was studied in hamsters over 5 and 25 d. Sham-operated animals served as controls. After 5 d, basal plasma gastrin concentrations were significantly increased in fundectomized animals (80.3 +/- 20.6 pmol/L) and significantly decreased in antrectomized animals (11.6 +/- 1.1 pmol/L) as compared with the controls (20.0 +/- 1.7 pmol/L). Similar differences were present among the 25-d groups, whereas basal plasma cholecystokinin (CCK) concentrations did not differ significantly between any groups at any time. At 5 d after fundectomy, there was a significant increase in pancreatic tissue [3H]-thymidine uptake and total DNA content, both of which were reduced 5 d after antrectomy. Autoradiography showed significantly increased [3H]-thymidine labeling index of acinar, intralobular duct, and centroacinar cells of the pancreas at 5 d after fundectomy. The increased intralobular duct cell labeling index persisted 25 d after fundectomy. Labeling indexes after antrectomy did not differ significantly from those in the controls, although antrectomized animals had the lowest values in all three cell compartments at 25 d. At 25 d, pancreatic wet wt and total DNA and protein content were significantly increased after fundectomy and significantly reduced after antrectomy. These findings indicate that fundectomy in the hamster induces pancreatic exocrine tissue hyperplasia and hypertrophy, whereas antrectomy leads to retardation of pancreatic growth.

The importance of the centroacinar region in cerulein-induced mouse pancreatic growth

Early proliferation events within different exocrine pancreatic cell compartments were studied in mice with or without cerulein administration. A technique with 3H-thymidine labeling of DNA-synthesizing cells was used. Groups of five animals were given either cerulein (20 micrograms/kg/24 h) or saline subcutaneously twice daily. 3H-thymidine was given as a single injection, 300 microCi intraperitoneally, on the 3rd and 8th day of cerulein or saline administration, and the fraction of labeled cells in each cell compartment (3H-thymidine labeling index, TLI) was calculated on the basis of autoradiographic analyses of the tissue. In a second set of experiments the distribution of the tracer between cell compartments, when given on the 3rd day of cerulein (saline) administration, was followed over a 5-day period. The highest proliferative rate was observed in the centroacinar cell compartment (TLI, 6%), and newly formed cells were accumulated during the 5-day 'chase' period. During the same time the relative amount of labeled centroacinar cells increased and comprised 40% of all labeled exocrine cells. The relative size of the compartment did not increase, indicating increased cell turnover with loss of or possibly migration of centroacinar cells into other pancreatic cell compartments. Weak and no trophic effects of cerulein were seen on the acinar and ductal cell populations, respectively. In the control group labeled ductal cells were significantly reduced during the chase period. This was not observed in the cerulein group, indicating addition of labeled cells to this compartment from other sources. A significant non-cerulein-dependent relative increase and decrease of the ductal and acinar cell compartments, respectively, were observed during the chase period.(ABSTRACT TRUNCATED AT 250 WORDS)