Effects of portacaval shunt on the rat stomach

Clinical parameters associated with gastric portal hypertensive polyps

OBJECTIVES

Portal hypertensive polyps (PHPs) are incompletely characterized lesions that can be found in the distal stomach of patients with portal hypertension. We aimed to delineate clinical factors associated with the appearance of these rare polyps.

MATERIAL AND METHODS

We conducted a cross-sectional study of a cohort with 513 cirrhotic patients comparing patients with and without PHP using descriptive analyses and multivariable logistic regression. To address the problem of missing values, in particular for HVPG and liver stiffness, we used multiple imputation of missing values.

RESULTS

The prevalence of macroscopically diagnosed PHP was 3.3% (95% confidence interval 2.0 - 5.4%). In 53% of cases, the correct classification was missed on index gastroscopy. Patients with PHP were older at gastroscopy (65 years vs. 59), had higher hepatic venous pressure gradients (HVPG, 28 mmHg vs. 19 mmHg), higher transient elastography (TE) measurements (50.7 kPa vs. 21.8 kPa) and more often had previous rubber band ligations (RBL, 64.7% vs. 25.8%). The multivariable logistic regression on the outcome macroscopically diagnosed PHP estimated an odds ratio (OR) for HPVG of 1.13 (CI 0.95-1.34), increased liver stiffness of 1.03 (1.00 - 1.07) and previous RBL of 3.84 (1.24 - 11.88), respectively.

CONCLUSION

The prevalence of PHPs in the stomach was higher than assumed in previous studies and misclassification was commonly observed. The appearance of these rare polyps is associated with previous RBL and may correlate with severity of PH. Thus, PHPs may be regarded as marker for relevant PH, but clinical significance of these polyps is still uncertain.

Clinical analysis of surgical treatment of portal hypertension

AIM: To review the experience in surgery for 508 patients with portal hypertension and to explore the selection of reasonable operation under different conditions.

METHODS: The data of 508 patients with portal hypertension treated surgically in 1991-2001 in our centers were analyzed. Of the 508 patients, 256 were treated with portaazygous devascularization (PAD), 167 with portasystemic shunt (PSS), 62 with selective shunt (SS), 11 with combined portasystemic shunt and portaazygous devascularization (PSS+PAD), 9 with liver transplantation (LT), 3 with union operation for hepatic carcinoma and portal hypertension (HCC+PH).

RESULTS: In the 167 patients treated with PSS, free portal pressure (FPP) was significantly higher in the patients with a longer diameter of the anastomotic stoma than in those with a shorter diameter before the operation (P<0.01). After the operation, FPP in the former patients markedly decreased compared to the latter ones (P<0.01). The incidence rate of hemorrhage in patients treated with PAD, PSS, SS, PSS+PAD, and HCC+PH was 21.09% (54/256), 13.77 (23/167), 11.29 (7/62), 36.36% (4/11), and 100% (3/3), respectively. The incidence rate of hepatic encephalopathy was 3.91% (10/256), 9.58% (16/167), 4.84% (3/62), 9.09% (1/11), and 100% (3/3), respectively while the operative mortality was 5.49% (15/256), 4.22% (7/167), 4.84% (3/62), 9.09% (1/11), and 66.67% (2/3) respectively. The operative mortality of liver transplantation was 22.22% (2/9).

CONCLUSION: Five kinds of operation in surgical treatment of portal hypertension have their advantages and disadvantages. Therefore, the selection of operation should be based on the actual needs of the patients.

Increased expression of cholecystokinin-A receptor mRNA in pancreas and cholecystokinin-B receptor mRNA in oxyntic mucosa after porta-caval shunting in rats

Porta-caval shunting enhances the trophic effects of cholecystokinin (CCK)-A receptor activation on the pancreas and of CCK-B receptor activation on the ECL cells in the oxyntic mucosa of the rat. The aim of the present study was to study the expression of CCK-A and CCK-B receptor mRNA after porta-caval shunting. Different doses of sulfated CCK-8 (CCK-8s) were administered to porta-caval shunting rats and sham-operated rats, 4 weeks after the operations. The pancreatic wet weight and DNA content were measured and the ECL cells in the oxyntic mucosa were counted after four days of continuous subcutaneous infusion. Total RNA was isolated from pancreas and oxyntic mucosa for Northern blot analysis of CCK-A and CCK-B receptor mRNA. Porta-caval shunting per se did not affect plasma CCK level nor the weight or DNA content of the pancreas, but resulted in increased number of ECL cells despite the fact that the serum gastrin concentration was reduced. The trophic response of the pancreas to low doses of CCK-8s was greater in porta-caval shunted rats than in sham-operated rats. Porta-caval shunted rats displayed an increased CCK-A receptor mRNA concentration in the pancreas (after stimulation with CCK-8s) and an increased CCK-B receptor mRNA concentration in the oxyntic mucosa. In conclusion, the porta-caval shunting-evoked enhancement of the trophic effect of CCK-A receptor activation on the pancreas and of CCK-B receptor activation on the ECL cells is associated with enhanced expression of CCK-A receptor mRNA in the pancreas and of CCK-B receptor mRNA in the oxyntic mucosa.

Endogenous gastrin and cholecystokinin do not promote growth of rat liver

BACKGROUND

The purpose of the study was to evaluate the trophic effects of endogenous hypergastrinemia and hypercholecystokininemia on intact and regenerating rat liver. We also examined the effects on the liver of portacaval shunting (PCS) alone or together with hypergastrinemia or hyperCCKemia. PCS is known to enhance the trophic effects of gastrin on the so-called enterochromaffin-like cells of the stomach and of CCK on the pancreas.

METHODS

Hypergastrinemia was induced by treatment with omeprazole (400 mumol/kg/day) or extirpation of the acid-producing part of the stomach (fundectomy). HyperCCKemia was induced by pancreaticobiliary diversion (PBD). After 4 weeks half of the rats were killed; the rest underwent partial hepatectomy and were killed 60 h later. PCS rats were killed 4 weeks after start of omeprazole treatment or after PBD. The concentrations of circulating gastrin and CCK were measured by radioimmunoassay. The liver weight and DNA content were analyzed.

RESULTS

Endogenous hypergastrinemia and hyperCCKemia failed to stimulate growth of either intact or regenerating liver. There were no differences in liver weight and DNA content between rats subjected to PCS and to combinations of PCS and omeprazole treatment, on the one hand, and PCS and PBD, on the other.

CONCLUSION

Gastrin and CCK are unlikely to be physiologically important in the regulation of liver growth and regeneration in the rat.

Hypercholecystokininemia produced by pancreaticobiliary diversion causes gastrin-like effects on enterochromaffin-like cells in the stomach of rats subjected to portacaval shunting or antrectomy

Gastrin and possibly cholecystokinin (CCK) control the activity and growth of the histamine-containing endocrine cells, the enterochromaffin-like (ECL) cells, in the oxyntic mucosa of the rat. Portacaval shunting (PCS) is known to activate the ECL cells through as yet unknown mechanisms. PCS also exaggerates the ECL cells' response to gastrin, whereas antrectomy causes hypotrophy and hypoplasia of the ECL cells. A recent study showed that the ECL cells failed to respond to sustained hyperCCKemia caused by pancreaticobiliary diversion (PBD). In the present study we investigated whether PBD-produced hyperCCKemia influenced the effects of PCS or antrectomy on the ECL cells. The results show 1) that hyperCCKemia raised the histidine decarboxylase (HDC) activity of the ECL cells in PCS rats but not in control rats, and the CCK-A receptor blockade failed to prevent the enzyme activation; and 2) that PBD prevented the ECL cell hypoplasia and the decrease in HDC activity induced by antrectomy. The findings suggest that under special circumstances endogenous CCK may stimulate the ECL cells.

Effect of omeprazole-evoked hypergastrinemia on ultrastructure of enterochromaffin-like cells in the stomach of portacaval-shunted rats

The histamine-producing enterochromaffin-like (ECL) cells in the acid-producing portion of the rat stomach responded to long-standing hypergastrinemia (omeprazole treatment daily for 8-10 weeks) with hypertrophy (and hyperplasia) and with a reduced number of granules and vesicles per unit cytoplasm. There was a reduction in the ratio of electron-dense granules versus vesicles and an increase in the profile diameter of the vesicles. Also, portacaval shunting (PCS) induced changes in the ECL cells, manifesting (i) as an increase in cell number and size, and (ii) as a reduced number of granules and vesicles per unit area. The cytoplasmic granules and vesicle profiles were enlarged, and the ratio of granules versus vesicles was reduced. The combination of PCS and long-standing hypergastrinemia (omeprazole treatment) produced a greatly enhanced ECL cell hypertrophy (and hyperplasia) and a marked reduction in the number of granules. The ratio of granules versus vesicles was markedly reduced while the profile diameters of both granules and vesicles were increased. The relative predominance of very large vesicles (vacuoles) was a prominent feature of the ECL cells in these rats.

Portacaval shunt increases the trophic effect of cholecystokinin on the rat pancreas

The trophic effect of cholecystokinin (CCK) on the pancreas was examined in portacava-shunted (PCS) rats. Exogenous CCK-8s and the CCK-A receptor antagonist devazepide were infused continuously by means of osmotic minipumps. HyperCCKemia of endogenous origin was induced by pancreaticobiliary diversion (PBD), which is known to cause growth of the pancreas. The results showed that PCS as such was without a trophic effect on the pancreas, whereas the combination of CCK-8s and PCS or PBD and PCS increased the trophic effects on the pancreas compared with CCK-8s or PBD alone. Moreover, the trophic effects of PBD and of the combination of PBD and PCS could be prevented by CCK-A receptor blockade (devazepide infusion). The results suggest that the capacity of the pancreas to respond to CCK is exaggerated--for as yet unknown reasons--after PCS.

Somatostatin cells in the oxyntic mucosa of hypo- or hypergastrinemic rats

The present report describes the long-term effects of antrectomy, antrum exclusion, portacaval shunt, omeprazole treatment, or the combination of omeprazole treatment and portacaval shunt on the number and density of somatostatin cells in the oxyntic mucosa of the rat. Antrectomy, which is associated with hypogastrinemia, raised the number and density of the somatostatin cells, whereas antrum exclusion and omeprazole treatment, which are associated with hypergastrinemia, reduced the number and density of the somatostatin cells. Portacaval shunt, which is associated with hypogastrinemia, increased both the number and the density. Omeprazole treatment of portacaval--shunted rats suppressed or even reversed the somatostatin cell hyperplasia after portacaval shunt alone. From these findings it is unlikely that gastrin stimulates the proliferation of somatostatin cells in the oxyntic mucosa. In fact, there seems to be an inverse relationship between the serum gastrin concentration and the somatostatin cell number.

Neuroendocrine cell hyperplasia and neuroendocrine carcinoma of the rodent fundic stomach

Certain substances when given orally to rats have effects on the neuroendocrine cells of the fundic stomach. Such compounds also have effects on acid or its secretion, which is to a greater or lesser extent suppressed, with a consequent rise in serum gastrin, followed by an increase in the number of histamine-secreting ECL cells. These changes are seen with the histamine H2 receptor antagonists loxtidine, SKF 93479, ICI 162,846 and ranitidine; with the hypolipidaemic agents clofibrate, ciprofibrate and benzofibrate; with sodium bicarbonate and pentagastrin; and with omeprazole, a potent inhibitor of the parietal cell proton pump mechanism. Changes in the pH of the rat stomach stimulate the neuroendocrine G cells of the pylorus to secrete gastrin, which acts on the ECL cells of the fundus causing the production of histamine, which in turn stimulates the parietal cell. This sequence leads to an excess of circulating gastrin, which is detectable within 5 days. Subsequently increases in the number of ECL cells occur, the hyperplasia being related to hypergastrinaemia and the degree of acid suppression. The hyperplastic response is rapid, being so obvious with loxtidine at 39 days that there is good reason to suppose it could well be detected earlier. Using omeprazole, hyperplasia was found at 28 days after oral doses of 140 mg/kg/day. In order to get an equivalent degree of acid suppression with ranitidine it was necessary to deliver 420 mg/kg/day by subcutaneous infusion using an osmotic minipump, when hyperplasia occurred. Interestingly, only omeprazole produced a hyperplastic response of G cells. Such results reflect the covalent binding of omeprazole to the proton pump as opposed to the competitive binding of ranitidine to the histamine H2 receptor site. In addition to ECL cell hyperplasia there is ample evidence from lifetime studies in rats and mice that neoplasia may result. Neuroendocrine carcinomas (carcinoids) of the rat fundic stomach have been observed with loxtidine, omeprazole, SKF 93479 and ICI 162,846. They are seen late in the 2-year rat studies and are most unlikely to have arisen purely as an extension of the hyperplastic response. It is possible that the prolonged disturbance of gastric homoestasis resulting from achlorhydria result in the production of a carcinogen or carcinogens, in which event it is not too surprising, in view of the neuroendocrine hyperplasia, that the tumours seen are neuroendocrine carcinomas.(ABSTRACT TRUNCATED AT 400 WORDS)

Enterochromaffin-like cells and gastric argyrophil carcinoidosis

The relevance of enterochromaffin-like (ECL) cells in gastric pathobiology has generated considerable interest particularly since the recent description of a pathological state characterized as gastric argyrophilic carcinoidosis. The morphological and biofunctional properties of these cells are distinct from other gastric endocrine cells. It is probable that ECL cells have a major role in the regulation of parietal cell function. Other possible functions may include a trophic regulatory influence. Of particular interest is the recent observation that agents which result in profound and sustained acid inhibition may cause ECL cell hyperplasia. This phenomenon has also been noted in human disease states in which a significant decrease in acid section is evident (pernicious anemia/atrophic gastritis). In patients with gastrinomas of the multiple endocrine neoplasia type I group, therapeutically induced acid inhibition may result in gastric ECL hyperplasia and even neoplasia (gastric carcinoid or ECLoma). Similarly, in the rodent species mastomys, which is genetically predisposed to the formation of gastric carcinoids, exposure to acid inhibitory agents results in rapid (90-120 days) development of gastric carcinoids. The pathobiological relevance of ECL cells and the mechanisms of their inducible hyperplasia and neoplasia may be of considerable significance in understanding the regulatory role of gastric endocrine cells.

Enhanced hyperplasia of gastric enterochromaffinlike cells in response to omeprazole-evoked hypergastrinemia in rats with portacaval shunts. An immunocytochemical and chemical study

The histamine-storing enterochromaffinlike cells, which are numerous in the oxyntic mucosa of the rat stomach, are known to proliferate in response to long-lasting hypergastrinaemia. In addition, portacaval shunting, which is not associated with elevated serum gastrin, causes an increase in enterochromaffinlike cell density. The present study shows that the combination of portacaval shunting and omeprazole-evoked, long-lasting hypergastrinemia results in enhanced enterochromaffinlike cell hyperplasia despite the fact that the hypergastrinemia was not significantly greater than in intact omeprazole-treated rats. The mechanism behind the enhanced response to gastrin of the enterochromaffinlike cells in rats with portacaval shunts is unknown. When results from untreated and omeprazole-treated rats were plotted, there was a linear correlation between the serum gastrin concentration and the enterochromaffinlike cell density in both sham-operated rats and rats with portacaval shunts. We conclude that gastrin plays a role in the development of enterochromaffinlike cell hyperplasia following omeprazole treatment in rats with portacaval shunts but that other as yet unidentified agents may also promote the response.

[The portacaval anastomosis in the liver cirrhosis model in the rat--significance of special preoperative preparation for decreasing surgical fatalities]

Following portocaval anastomosis a high lethality (87%) can be observed in a standardized micronodular liver cirrhosis model. By a special preoperative regimen this lethality can be reduced to 10%.

Porcine ileal polypeptide causes an increase in cytoplasmic Ca2+ in both parietal and chief cells resulting in acid and pepsinogen secretion

Porcine ileal polypeptide, an enterooxyntin isolated from distal small intestinal mucosal epithelium, has been observed to stimulate gastric acid secretion in vivo as well as in vitro (Wider, M.D. et al. (1984) Endocrinology 115, 1484-1491, Wider M.D. et al. (1986) Endocrinology 118, 1546-1550). We report here that porcine ileal polypeptide stimulates both acid (aminopyrine accumulation) and pepsinogen secretion in isolated, enriched populations of guinea pig parietal and chief cells in a dose-dependent manner. Further, 10(-9) M porcine ileal polypeptide caused an increase in cytoplasmic Ca2+ concentration in both parietal and chief cells similar in magnitude to that observed with gastrin-17 (10(-8) M) (as measured by both fura-2 and aequorin) and cholecystokinin octapeptide (CCK-OP) (10(-8) M), respectively. Porcine ileal polypeptide has been observed to cause no stimulation of cAMP production in gastric glands from guinea pigs (Gespach, C., personal communication) nor is there any effect of medium Ca2+ depletion on acid production observed with guinea pig gastric mucosal sections. It is concluded that porcine ileal polypeptide, at concentrations similar to circulating levels observed in plasma of normal pigs (5 x 10(-9) M), acts directly on the parietal and chief cells to cause the mobilization of intracellular Ca2+ from the stores resulting in acid and pepsinogen secretion. These experiments demonstrate that this peptide is a potent enterooxyntin and chief cell secretagogue which acts via the same signal transduction mechanisms as gastrin and cholecystokinin.

Gastrin and the trophic control of gastric mucosa

Gastrin is a trophic stimulant of the acid producing gastric mucosa. Experiments have been carried out in rats, in which chronic states of either low or high serum gastrin levels were induced by surgical manipulation or drug treatment. A relationship between circulating gastrin and a trophic effect could be demonstrated in the oxyntic mucosa, but not in the pancreas and small intestine. Endocrine cells in the oxyntic mucosa (the ECL cells and A-like cells) are among the target cells for the trophic action of gastrin. The functional significance of these two cell populations is unknown. There is much experimental evidence indicating that they are under functional as well as tropic control of gastrin. The vagus nerve also exerts trophic control on the oxyntic mucosa, including the endocrine cells within it. This could be demonstrated by one-sided truncal vagotomy which caused atrophy of the mucosa and hypoplasia of endocrine cells (notably the ECL cells) on the denervated side of the stomach. Conversely, portacaval shunt greatly increased the number of ECL cells. There was no hypergastrinaemia after portacaval shunt, and no trophic effect on other cell types in the oxyntic mucosa. The factors responsible for the ECL cell proliferation after portacaval shunting remain unknown. Tumours may arise spontaneously from the ECL cells. Such neoplasias have been described in Mastomys (Praomys natalensis) and in man. ECL cell hyperplasia and neoplasia in man, but not in Mastomys, are usually associated with hypergastrinaemia either as a result of a gastrin producing tumour or as a result of achylia (sometimes associated with pernicious anaemia). It is unlikely that gastrin alone is responsible for the neoplasia, though it is quite likely that long-standing hypergastrinaemia triggers or facilitates a sequence of events that ultimately leads to tumour formation, via diffuse ECL cell hyperplasia.

Mechanism of hypergastrinaemia after nephrectomy in the rat

Bilateral nephrectomy in the rat is followed by hypergastrinaemia and by activation of gastric histidine decarboxylase. The enzyme activity is thought to reflect the concentration of circulating gastrin. While there is general agreement that post-nephrectomy hypergastrinaemia is primarily the result of loss of renal elimination of gastrin, it remained to be determined whether gastrin secretion could be stimulated in the hypergastrinaemic state and whether it contributed to the hypergastrinaemia. Histamine, but not pentagastrin, is known to evoke gastric acid secretion in the nephrectomized rat, and histamine, but not pentagastrin, was found to lower the serum gastrin level and the gastric histidine decarboxylase activity, indicating that after nephrectomy gastrin was still secreted and that the secretion could be suppressed by increased acid output. The importance of gastrin secretion for post-nephrectomy hypergastrinaemia was assessed further by investigating the effect of nephrectomy on the serum gastrin concentration in rats previously subjected to operations that had either reduced (e.g. antrectomy) or raised (e.g. antrum exclusion) the serum gastrin concentration. Post-nephrectomy serum gastrin levels co-varied with the levels before nephrectomy. Thus, the capacity to secrete gastrin was not abolished by nephrectomy. Finally, nephrectomy greatly affected the linear correlation between the serum gastrin concentration and the gastric histidine decarboxylase activity in a manner suggesting the operation of a gastrin-independent factor capable of activating the enzyme.