Trophic effects of gastrin on the exocrine pancreas in rats

Effect of hypergastrinemia on pancreatic carcinogenesis

BACKGROUND

Previous studies in our laboratory demonstrated that pancreatic carcinomas in rodents express receptors for the peptide hormone gastrin that are not present in normal adult pancreas. In view of an abundant literature suggesting that gastrin may promote growth of various gastrointestinal tissues and tumors, the effect of hypergastrinemia on the process of pancreatic carcinogenesis was evaluated.

METHODS

Rats received subcutaneous injections of the pancreatic carcinogen azaserine at 19 and 26 days of age. Starting at 12 months of age, animals were randomized to treatment with the proton pump inhibitor lansoprazole or vehicle by gavage for 6 months. At autopsy, pancreatic wet weight normalized to body weight was recorded, as well as the number of benign and malignant pancreatic lesions.

RESULTS

Serum gastrin levels were determined by radioimmunoassay and showed a greater than two-fold increase in lansoprazole-treated animals. Pancreatic wet weight in hypergastrinemic rats was increased compared to controls (p <0.05). Premalignant lesions such as acidophilic atypical acinar cell foci, adenomas, heterogeneous phenotypic populations of nodules within nodules, and carcinoma-in-situ were not increased in the hypergastrinemic group. Likewise, there was no difference in the incidence of invasive carcinoma in hypergastrinemic animals (10%) compared to controls (5.7%).

CONCLUSION

Hypergastrinemia stimulated an increase in pancreatic weight, but did not stimulate development of premalignant lesions or progression to cancer in the azaserine model of rat pancreatic acinar cell carcinoma.

The gastrin receptor promotes pancreatic growth in transgenic mice

INTRODUCTION

We demonstrated previously, in two different rodent models of pancreatic cancer, that the gastrin receptor is present on malignant pancreatic tumors in spite of the fact that the normal adult rat and mouse pancreas does not express gastrin receptors.

AIMS AND METHODOLOGY

To determine whether gastrin receptors mediate pancreatic growth or promote carcinogenesis or both, we created a transgenic mouse that constitutively expresses gastrin receptors in the exocrine pancreas. The transgene construct contained the full-length rat gastrin receptor cDNA sequence under the control of the rat elastase promoter.

RESULTS

Receptor presence and function on exocrine pancreatic tissue of transgenic but not control mice were confirmed by (125)I-gastrin-I binding studies and by gastrin stimulation of intracellular calcium release. Eighteen-month-old transgenic animals had larger pancreas-to-body weight ratios than their nontransgenic littermate controls (p < 0.001 for females; p < 0.01 for males); however, histopathologic examination revealed no neoplasms or other abnormalities.

CONCLUSION

In both female and male transgenic mice, the expression of the gastrin receptor in the exocrine pancreas is associated with a significant increase in pancreas weight, but it does not appear to promote the development of spontaneous pancreatic tumors.

Role of endogenous hypergastrinemia in regenerating endocrine pancreas after partial pancreatectomy

We studied the possible role of endogenous gastrin in the regenerating pancreas. Male Wistar rats underwent sham operation or 90% partial pancreatectomy (Px). Lansoprazole (30 mg/kg body wt), a proton pump inhibitor (PPI), was given p.o. for 3 weeks after surgery. Plasma glucose levels were higher in Px rats than in shams. Lansoprazole lowered plasma glucose levels in the Px rats. In addition, integrated insulin secretion during an oral glucose tolerance test (2 g/kg body wt) was significantly (p < 0.01) higher in lansoprazole-treated Px rats than in control Px rats, while lansoprazole did not affect insulin secretion in shams. Fasting serum gastrin levels were higher (p < 0.01) in lansoprazole-treated animals than in controls both in sham rats and in Px rats. Furthermore, lansoprazole increased the pancreas weight per body weight and elevated the insulin content of the pancreas in Px rats. These results suggest that endogenous hypergastrinemia has a trophic effect on endocrine pancreas during regenerating processes and that administration of PPI may be clinically beneficial to the remnant pancreas after pancreatectomy if the whole stomach is preserved.

Gastrin does not stimulate growth of the rat pancreas

BACKGROUND

Gastrin is thought to stimulate growth of the pancreas via gastrin/cholecystokinin (CCK)-B-type receptors. The aim of the present study was to examine the trophic response of the pancreas to exogenous gastrin or to hypergastrinemia of endogenous origin and to hypogastrinemia with or without concomitant hyperCCKemia.

METHODS

Hypergastrinemia was induced in male Sprague-Dawley rats by continuous infusion of human Leu15-gastrin-17 (5 nmol/kg/h, subcutaneously), by removal of the acid-producing part of the stomach (fundectomy), or by treatment with omeprazole (400 mumol/ kg/day, orally). Hypogastrinemia was induced by antrectomy or by gastrectomy. HyperCCKemia was induced by pancreaticobiliary diversion (PBD). The rats were killed 10 days or 8 weeks after the operations or treatments. The concentrations of circulating gastrin and CCK were measured by radioimmunoassay. The pancreatic weight and DNA content were determined.

RESULTS

Gastrin infusion, omeprazole treatment, and fundectomy greatly increased the serum gastrin concentration. The resulting levels were very similar in the three groups and probably represent the maximum attainable physiologic serum gastrin concentration. Whereas gastrin infusion or omeprazole treatment (hypergastrinemia) and antrectomy (hypogastrinemia) were without effect on the weight and DNA content of the pancreas, gastrectomy (hypogastrinemia) and fundectomy (hypergastrinemia) increased the weight and DNA content. PBD (hyperCCKemia) greatly increased the weight and DNA content of the pancreas. PBD plus fundectomy, PBD plus gastrectomy, PBD plus antrectomy, and PBD plus omeprazole increased the weight and DNA content of the pancreas, as did PBD alone.

CONCLUSION

CCK is a physiologically important trophic stimulus for the rat pancreas, but gastrin is not. The increase in pancreatic weight and DNA content after fundectomy and gastrectomy cannot be explained by means of either gastrin or CCK.

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.

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.

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.

Exocrine pancreatic function in obstructive jaundice rats: studies with isolated dispersed pancreatic acini

This study was conducted to investigate pancreatic exocrine function and pancreatic growth in rats with obstructive jaundice (OJ). OJ was produced in adult male Sprague-Dawley rats by bile duct ligation; control rats underwent laparotomy only. Induction of OJ was associated with significant hyperplasia and hypertrophy of the pancreas in rats as shown by increased DNA and RNA contents of pancreatic tissue. Factors associated with pancreatic growth in OJ rats were further examined in isolated dispersed pancreatic acini from OJ rats and the data were compared with those for control rats. Studies with isolated dispersed acini from OJ rats showed that pancreatic growth was accompanied by significant increases in total cellular amylase content; however, amylase release (percentage of initial) in response to cholecystokinin octapeptide was significantly decreased in OJ rats compared to control rats. Total amylase output in response to 100 pM cholecystokinin (CCK) was higher in the OJ group when compared to the control group (8.6 U/mg protein versus 6.4 U/mg protein), as calculated from the total amylase content and percentage of amylase released. Receptor binding data showed that the capacity of CCK receptors in OJ rats was significantly lower when it was compared with control. In addition, plasma levels of CCK were significantly elevated in OJ rats when compared to controls. These results suggest that obstructive jaundice induces pancreatic growth that is associated with alteration of exocrine pancreatic function. Abnormally high levels of stored amylase in pancreatic acini may be implicated in the development of pancreatitis as often seen in obstructive jaundice patients.

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.

Tropic role of enteroglucagon in pancreatic adaptation to subtotal enterectomy

Proximal small bowel resection causes pancreatic hyperplasia, presumably via a humoral mechanism. Although cholecystokinin can stimulate pancreatic growth, its proximal distribution in the gut makes it an unlikely intermediary after proximal small bowel resection. The potential roles of neurotensin and enteroglucagon were studied, since these hormones are mainly secreted from the ileum and proximal colon. Male Wistar rats (n = 50) weighing 200-250 g were randomized to receive 90 per cent proximal small bowel resection or jejunal transection and resuture (control). Rats were killed at 1 week or 1 month, when plasma was obtained for hormone assay and the pancreas was excised for protein and nucleic acid measurement. Proximal small bowel resection increased circulating enteroglucagon levels by 150 per cent at 1 week (P less than 0.002) and by 83 per cent at 1 month (P less than 0.005); neurotensin levels were unchanged. Pancreatic wet weight was 21 per cent greater 1 month after proximal small bowel resection (P less than 0.001). Proximal small bowel resection increased protein, RNA and DNA contents of the pancreas both at 1 week and at 1 month. Since plasma enteroglucagon correlated with these indices of pancreatic mass, enteroglucagon may have a pancreatotropic role (in addition to its enterotropic role).

Effect of tetragastrin on azaserine-induced carcinogenesis in rat pancreas

The effect of tetragastrin on pancreatic tumors induced by azaserine was investigated in Wistar rats. Rats were given 25 weekly injections of 10 mg/kg body weight of azaserine and 1 mg/kg body weight of tetragastrin as a suspension in olive oil every other day. Carcinogen-induced pancreatic lesions were examined by histochemical techniques, and were classified as ATPase-positive or ATPase-negative. In week 62, quantitative histological analysis showed that prolonged administration of tetragastrin had little or no influence on the number and size of the carcinogen-induced pancreatic lesions, although it caused significantly increased cell proliferation, indicated by a greater labelling index of the pancreatic acinar cells.

Effect of gastrin on liver regeneration after partial hepatectomy in rats

Gastrin has been shown to be an important trophic hormone for the mucosa of the stomach and the proximal intestine. In the present study the effect of gastrin on liver regeneration after partial hepatectomy in rats was investigated. After partial hepatectomy a significant rise in the concentration of gastrin in portal venous blood was found six, 12, and 18 hours after 70% hepatectomy. The effect of changes in the endogenous gastrin concentration on the liver regeneration was investigated in rats subjected to antrectomy or to fundectomy. Partial hepatectomy was done three weeks after the primary surgery. We found antrectomy to decrease liver regeneration, whereas fundectomy had no effect. Administration of pentagastrin 300 micrograms/kg sc three times daily for two and four days after partial hepatectomy significantly increased the rate of liver regeneration compared with controls. This study suggests that gastrin has a hepatotrophic effect. Whether this effect is caused by a direct action of gastrin on the hepatocytes or it is an indirect effect mediated by for instance insulin, glucagon or epidermal growth factor has to be further investigated.

Cholecystokinin influences pancreatic trophism following total gastrectomy in rats

In rats, total gastrectomy (TG) has been shown to induce pancreatic hyperplasia and increased tissue concentrations of pancreatic trypsin and amylase, whereas lipase concentration was decreased. We performed total gastrectomy with the additional insertion of a duodenal tube in 17 rats. A central venous catheter was placed after 3 wk. The control groups consisted of sham-operated rats with a gastrotomy plus duodenal tube and a group of rats with only a duodenal tube. The rats received meal stimulation with a 6 mL liquid diet (3 mL oil, 2 mL amino acid solution, and 1 mL glucose) via duodenal tube upon recuperation. Blood samples were taken before as well as 5, 15, 30, and 60 minutes after the meal and analyzed for insulin, pancreatic glucagon, gastrin, and CCK by specific RIA techniques. Glucose tolerance was found to be impaired after total gastrectomy. Though insulin release was delayed compared to the controls, the integrated postprandial output was unchanged. The pancreatic glucagon release after the meal increased 83% in TG rats, compared to control rats. The baseline and postprandial gastrin values diminished 70% compared to control animals. Neither group exhibited a postprandial increase in gastrin levels. TG led to an increased postprandial CCK output of 72% compared to controls. The trophic changes of rat exocrine pancreas following total gastrectomy, therefore, could be based on an elevated postprandial release of CCK.

Gut peptide-mediated adaptive response of the exocrine pancreas

The gastrointestinal system is substantially involved in the regulation of exocrine pancreatic secretion, and it is therefore not surprising that intestinal diseases have been shown to affect exocrine pancreatic function. In rat experiments gastrectomy, truncal vagotomy, and subtotal colectomy stimulated pancreatic growth and altered pancreatic enzyme composition. Focusing on two main hormones supposed to be involved in the regulation of pancreatic adaptation, we studied basal and stimulated gastrin and cholecystokinin (CCK) pattern after the operative procedures. After total gastrectomy basal CCK values were unchanged, whereas postprandial CCK plasma values and the integrated postprandial CCK release were significantly increased. After subtotal colectomy CCK levels, both basal and postprandial, were significantly increased. In both of these conditions gastrin levels were either decreased (total gastrectomy) or unchanged (subtotal colectomy). CCK may therefore be the major humoral candidate to promote the observed pancreatic adaptive response. After truncal vagotomy CCK values remained unchanged, whereas basal and postprandial gastrin was significantly increased. Gastrin may be a candidate involved in the stimulation of pancreatic trophism after vagisection.

Pancreatic trophism after truncal vagotomy in rats

Thirty-two rats had truncal vagotomy either with or without pyloroplasty. After 2 or 4 weeks, respectively, the pancreas was excised and weighed. Measurements of amylase, trypsin, lipase, total protein, and DNA were obtained from the homogenated pancreatic tissue. Isolated pancreatic lobules were incubated with and without ceruletide (5 X 10(-10) g/ml) during a 60 minute period. Amylase values were determined four times in the incubation medium. Morphometry was performed by light microscopy analysis. There was a significant increase in pancreatic weight, DNA content, and trypsin concentration 2 weeks after vagotomy with and without pyloroplasty. These changes were accelerated after 4 weeks. DNA, amylase, and total protein concentrations were unchanged. Lipase concentration decreased 2 weeks after vagotomy and pyloroplasty, whereas at 4 weeks, it decreased in both experimental groups. The in vitro incubation study revealed a significantly decreased amylase discharge under basal conditions, whereas the stimulated amylase discharge was unchanged in both experimental groups compared with the control group. Morphometry did not detect differences in exocrine cellular size. We conclude that vagotomy in rats induces pancreatic hyperplasia, enzyme dissociation, and decreased basal amylase discharge in vitro.

Additive interaction of pentagastrin and secretin on pancreatic growth in rats

The role of gastrin in regulating pancreatic growth and its interaction with secretin is unclear. We determined the dose-response relationships of pentagastrin for gastric and pancreatic secretion. Doses that stimulated gastric and pancreatic secretion were given every 8 h for 3 or 5 days; trophic responses of pancreas, oxyntic gland area, duodenum, and colon were compared. Interaction of secretin and pentagastrin on pancreatic growth was measured after 5 days of treatment. Pentagastrin was 250 times less potent for stimulation of pancreatic versus gastric secretion. A submaximal dose of pentagastrin for stimulating pancreatic enzyme secretion doubled pancreatic deoxyribonucleic acid synthesis after 3 days. Pentagastrin caused dose-related increases in pancreatic weight after 3 and 5 days. Pentagastrin had no effect on weight, deoxyribonucleic acid synthesis, or deoxyribonucleic acid content of oxyntic gland area, duodenum, or colon. Secretin had additive effects on pentagastrin-induced pancreatic growth. The pancreas appears to be more sensitive than other organs to trophic effects of pentagastrin. Secretin has additive rather than inhibitory effects on pentagastrin-induced pancreatic growth.

Effect of somatostatin on the growth of gastrointestinal mucosa and pancreas in rats. Role of endogenous gastrin

This study was undertaken to determine the influence of somatostatin on the growth of gastric, duodenal, and pancreatic tissue in rats placed on liquid diet. In the first part of the study animals were fed an elemental liquid diet for 10 days and then killed, and the growth of the oxyntic gland area of the stomach, 2 cm segments of duodenum and pancreatic tissue was determined. Feeding an elemental diet caused a decrease in organ weight, nucleic acid contents and serum gastrin level. Subsequent addition of pentagastrin prevented this reduction in organ weight and RNA and DNA contents while somatostatin failed to affect the decrease in growth parameters or serum gastrin level in tests with or without addition of pentagastrin. In a second part of the study, sham operated and antrectomised rats were used. Antrectomy caused a significant decrease in serum gastrin concentration and resulted in a significant reduction in the weight and RNA and DNA contents of the tissue tested. As in liquid diet, subsequent administration of pentagastrin prevented the reduction in the growth parameters both in tests with and without somatostatin. These results suggest that somatostatin inhibits the growth of the gastroduodenal mucosa by a mechanism involving, at least in part, the suppression of gastrin release.

Influence of obstructive jaundice on pancreatic growth and on basal plasma levels of cholecystokinin and gastrin in rats

Obstructive jaundice was produced in rats by ligation and transection of bile duct outside the liver; the control group underwent laparotomy alone. Pancreatic wet weight, amylase, lipase, protein, DNA, RNA, RNA/DNA ratio, and weight/100 micrograms DNA were significantly increased in jaundiced rats when compared to control rats. Histologic evaluation of pancreatic tissue obtained from jaundiced rats revealed the appearance of large or multiple nuclei in pancreatic acinar cells. Basal plasma levels of immunoreactive CCK were significantly increased in jaundiced rats at two weeks and four weeks but, when compared to the levels obtained in laparotomized controls at those time intervals, CCK levels were not significantly different. In jaundiced rats, plasma immunoreactive gastrin was found to be significantly decreased at two and four weeks. Plasma gastrin levels were also found significantly decreased when the jaundiced group was compared with laparotomized control group. The results suggest that obstructive jaundice induced enlargement of the pancreas, probably due to hyperplasia and hypertrophy of pancreatic cells. Whether or not this phenomenon is related to changes in gastrin and CCK is not known.

Effect of liquid diet on nude mouse gastrointestinal tract

The nude (athymic) mouse is currently used to study the effect of gastrin on cancer xenografts. We sought to develop a hypogastrinemia nude mouse model for use in evaluating the effect of hypogastrinemia on such xenografts. Thirty-six non-tumor-bearing nude mice were studied. Eighteen received a nutritionally complete liquid diet; eighteen received standard chow. Six mice from each group were weighed and killed (nonfasting) on days 2, 8, and 15. Mean serum gastrin levels (+/- SEM) for the control group were 118.7 +/- 7.5, 118.7 +/- 8.7, and 118.0 +/- 7.5 pg/ml on days 2, 8, and 15, respectively. Serum gastrin levels for the liquid diet group significantly decreased to 87.0 +/- 7.6, 88.0 +/- 9.7, and 66.7 +/- 9.6 pg/ml on the same days. Animals in both groups gained weight normally; there were no significant weight differences between the two groups at any point. No histological abnormalities were seen in stomach, small intestine, colon, cecum, liver, pancreas, spleen or kidney. However, the liquid diet group showed atrophic changes in colon: significant reductions in colon weight and RNA content on days 8 and 15, and significant reduction in colon protein content on day 8. This model of hypogastrinemia is reliable and inexpensive. The nonsurgical nature of the preparation allows excellent survival in this immunodeficient animal.

Long-term comparative effect of cholecystokinin and gastrin on mouse stomach, antrum, intestine, and exocrine pancreas

Mice were injected three times a day for 12 days with 300 micrograms/kg body weight of gastrin G17 or 37.5 Ivy dog U/kg body weight of CCK or saline. Other mice were also injected four times an hr for 1 hr with 7.5 micrograms/kg of gastrin, nine Ivy dog U/kg of CCK or saline; 1 hr before killing, they were injected with tritiated thymidine to evaluate the labelling indices in peptic, antral, duodenal, jejunal, and ileal mucosae. Four hours after the first injection of the two peptides, the peptic labelling indices increased while those of intestinal mucosa increased 8 hr after these injections. Long-term injections of CCK had a trophic effect on secretory cells of the digestive tract: the number of gastric zymogenic cells, Paneth cells, and the mucous cells of Brünner glands were hypertrophied. The pepsin, amylase, chymotrypsin, and lysozyme activities increased in stomach, exocrine pancreas, and intestine, respectively. Neither parietal cells nor intestinal enterocytes and hydrolase activities were affected. The trophic effect of long-term injections of gastrin is confirmed on parietal cells and exocrine pancreatic parenchyma and is demonstrated in Paneth cells. Confirming cytological results, pancreatic lipase and amylase activities and intestinal lysozyme activity were increased after gastrin. Although CCK and gastrin have a structural analogy, these two peptides did not affect the same cellular types. A specific action of CCK on the main secretory cells of the digestive mucosa is demonstrated.

Gastrin modulation of pancreatic growth

Gastrin has been proposed as a trophic factor for the pancreas. Extensive small-bowel resection increased transiently plasma gastrin levels in the rat and produced pancreatic growth. This growth was characterized by an increased pancreatic weight, protein and DNA content, and the occurrence of mitotic figures in acinar cells. In order to determine if gastrin is implicated in pancreatic hyperplasia, we induced endogenous variations of gastrin 3 weeks before small-bowel resection or transection. Hypogastrinemia was produced by antrectomy and hypergastrinemia by vagotomy plus pyloroplasty. Pyloroplasty alone was without any effect. All gastric operations alone enhanced though not significantly the weight of the pancreas and its content in protein and DNA. When performed before intestinal resection, they did not modify the hyperplastic response of the pancreas to the resection. Our findings do not support the views that antral gastrin exerts a trophic action on the rat pancreas and that gastrin is implicated in postresectional hyperplasia of the gland.

Effect of acid secretory capacity and chronic endogenous hypergastrinemia on pancreatic secretion and intestinal morphology in the rat

To study the trophic effects of gastrin on the gastrointestinal tract, chronic endogenous hypergastrinemia was produced in rats by implantation of the gastric antrum into the colon. Rats were sham-operated (normal gastrin, normal acid) or were prepared with BII gastrojejunostomy and antral resection (low gastrin, low acid), or BII gastrojejunostomy and antral implantation into colon (high gastrin, acid present). To separate effects of hypergastrinemia from those of acid hypersecretion, two additional groups were prepared with total gastrectomy and either resection of the antrum (low gastrin, no acid) or antral implantation into colon (high gastrin, no acid). After 12 weeks, the pancreatic secretory response to secretin was measured. The animals were then sacrificed, and liver, pancreas, small intestine, and colon were weighed. In separate groups of animals villous height and width and crypt depth of small intestine and transverse colon were measured. Serum gastrin concentrations increased three- to fivefold in fasting and fed antral implant animals. Serum gastrin levels in the fed state were lower in antrectomy rats compared to controls but did not differ in the fasting rats. Pancreas and colon were heavier in all hypergastrinemic rats. Liver weights did not differ between hypergastrinemic animals and controls. Stimulated pancreatic bicarbonate secretion following secretin infusion was elevated only in hypergastrinemic, hyperacidic rats. Hypertrophy of the small bowel was seen in antral implant rats only when the gastric remnant was preserved (ie, when acid was present). Colonic mucosal thickness was increased in antral implant rats with or without gastrectomy. No significant increases in small-bowel villous height or crypt depth were found in antral implant rats. Thus, chronic endogenous hypergastrinemia caused pancreatic and colonic hypertrophy independent of acid secretion. In addition to hypergastrinemia, gastric hyperacidity was also needed for enlargement of small bowel or increase in secretin-stimulated pancreatic bicarbonate secretion.

Hyperplasia of the exocrine pancreas after small bowel resection in the rat

The effect of a 90% small bowel resection on the exocrine pancreas was investigated over a three month period in adult Wistar rats. Control animals underwent a sham-resection consisting of a transection and reanastomosis of the small intestine. After jejunoileal resection, the wet weight of a gland increased significantly (52%) from the 15th day. The parallel increase in total protein, DNA and RNA content without any modification in the ratios of pancreatic weight, protein, and RNA to DNA suggests that there is cellular hyperplasia but not hypertrophy. Small intestinal resection decreased significantly the amount of amylase when expressed per unit pancreatic weight; it reduced slightly but not significantly that of chymotrypsin, while it did not modify the amount of lipase. However, the total amount of these enzymes in the pancreas remained unaltered when compared with controls. It is concluded that a massive resection of the small bowel induces cellular hyperplasia in the rat exocrine pancreas; this could compensate that reduced level of enzymes in acinar cells.

The effects of endogenous hypergastrinemia and hypogastrinemia on the exocrine and endocrine rat pancreas

The effects of endogenous hypergastrinemia and hypogastrinemia on the exocrine and endocrine pancreas were studied in the rat. Hypergastrinemia was induced by antral exclusion, and hypogastrinemia by antral resection. The studies were made 14 weeks after surgery. The total weight of the pancreas was increased both in hypergastrinemic and hypogastrinemic animals, due to hypertrophy of the exocrine cells. In contrast, the volume and total weight of the pancreatic islets were decreased. There was no numerical difference in the A-, D-, PP-cells between the hyper- and hypogastrinemic animals, respectively, and the controls. The number of insulin-producing (B-) cells was certainly reduced after the induction of hypogastrinemia. There was, however, signs of increased B-cell activity, which might contribute to an underestimation of the number of B-cells with the technique used. These findings do not support the hypothesis that antral gastrin has trophic influence on either exocrine or endocrine pancreas.