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.     

Focal adhesion kinase and paxillin: novel regulators of brain sexual differentiation?

Steroid-mediated sexual differentiation of the brain is a developmental process that permanently organizes the brain into a male or female phenotype. Previous studies in the rodent have examined the steroid-mediated mechanisms of male brain development. In an effort to identify molecules involved in female brain development, a high-throughput proteomics approach called PowerBlot was used to identify signaling proteins differentially regulated in the neonatal male and female rat hypothalamus during the critical period for brain sexual differentiation. Focal adhesion kinase (FAK) and paxillin, both members of the focal adhesion complex family of proteins, were significantly elevated in the newborn female compared with the male hypothalamus. Sex differences in these proteins were not detected in brain regions that are not subject to substantial organizational effects of steroids. Estrogens, the aromatized products of testosterone in the male, can both masculinize and defeminize the male brain. Daily estradiol administration to neonatal females significantly reduced FAK and paxillin in the hypothalamus, and aromatase inhibition increased paxillin in males to levels comparable with females. Androgens also appear to modulate paxillin levels in combination with estrogen action. Across development, hypothalamic levels of FAK were significantly elevated in females compared with males on postnatal d 6. Synaptic circuits in the hypothalamus develop sex differences perinatally. Estradiol treatment of cultured hypothalamic neurons significantly enhanced axon branching (P<0.01), consistent with the phenotype of FAK-deficient neurons. Together, these data implicate FAK and paxillin as regulators of sex differences in neuronal morphology.     

Pancreatic polypeptide and other pancreatic hormones in spontaneously diabetic BB/W rats

The BB/W strain of rats develop spontaneous insulin-dependent diabetes. Diabetic BB/W rats have a marked insulinopenia and greatly diminished levels of insulin in their pancreas. Using a radioimmunoassay for rat pancreatic polypeptide (PP), we have examined the content of PP in extracts of the total pancreas and also the regional PP concentration of the three pancreatic lobes. Radioimmunoassays for glucagon, somatostatin (SRIF) and insulin were also made on these extracts. Compared with nondiabetic BB/W rat pancreas, pancreatic extracts from severely diabetic BB/W rats contained 30% as much PP, 31% as much glucagon, 19% as much SRIF, and 0.5% as much insulin. The rat PP radioimmunoassay was used to determine the elution pattern of PP-like antigens in gel chromatography fractions and to measure in vitro secretion of PP from perifused pancreatic slices obtained from diabetic and nondiabetic animals. PP-like immunoreactivity was observed in two zones in the elution from the gel columns when extracts from normal or diabetic rats were chromatographed. The major zone of immunoreactivity eluting at the volume expected for intact monometric rat PP accounted for 67% of the PP-like immunoreactivity in the case of nondiabetic rats and greater than 80% of the PP-like immunoreactivity found in extracts from severely diabetic rats. The minor zone of PP-like immunoreactivity eluted at a volume similar to the position of tetradecapeptide SRIF contained the remainder of detected PP-like immunoreactivity. Tissue slices from diabetic rats secreted more PP and glucagon than slices from nondiabetic rats when slices were perifused with a medium containing leucine, carbachol, and cholecystokinin, even though diabetic pancreas has smaller amounts of PP, glucagon, SRIF, and insulin. Stimulated insulin secretion was virtually absent when tissue slices from diabetic rats were perifused. These results indicate that in the BB/W diabetic rat: (a) pancreatic glucagon, PP, and SRIF are moderately decreased and insulin levels are drastically reduced, (b) lower levels of degraded or low molecular weight form of immunoreactive PP occurs in the diabetic rat pancreas compared to the normal rat, (c) the diabetic pancreas secretes more PP and glucagon and much less insulin than pancreas from nondiabetic rats when perifused under stimulating conditions. The diabetes occurring in the BB/W appears to be a severe type I diabetes characterized by reduced content of insulin, glucagon, SRIF, and PP in the pancreas of these animals. However, secretion of glucagon and PP were not reduced in this in vitro system.     

Effect of endothelin and endothelin receptor blockade on capillary permeability in experimental pancreatitis

BACKGROUND: Capillary leakage with fluid loss into the third space contributes to many of the early systemic complications in severe acute pancreatitis. There has been increasing interest in endothelin as one of the factors affecting capillary permeability. AIM: To elucidate further the role of endothelin in the development of capillary leakage in acute pancreatitis by investigating the effect of exogenous endothelin administration and endothelin receptor blockade in sham operated animals and two models of acute pancreatitis. METHODS: Determination of capillary permeability in the pancreas and colonic mucosa by quantifying extravasation of fluorescein labelled dextran using a novel computer assisted video image analysis system. RESULTS: Pancreatic and colonic capillary permeability increased stepwise from mild to severe acute pancreatitis. Endothelin increased pancreatic and colonic capillary permeability in healthy animals and animals with mild acute pancreatitis but had no additional adverse effect in severe acute pancreatitis. Endothelin receptor blockade decreased pancreatic capillary permeability in sham operated rats but had no effect on the colon. In mild and severe acute pancreatitis, endothelin receptor blockade stabilised increased capillary permeability in both the pancreas and colon. CONCLUSIONS: Endothelin plays an important role in mediating capillary permeability in the pancreas. In severe pancreatitis, it increases capillary permeability even outside the pancreas, thereby contributing to capillary leakage. Endothelin receptor blockade significantly reduces capillary permeability in acute pancreatitis both in and outside the pancreas, suggesting a therapeutic approach to counteract capillary leakage in severe acute pancreatitis.     

Continuous enteral feeding has an attenuating effect on the exocrine pancreas in rats

INTRODUCTION: Recent clinical observations suggest that continuous enteral feeding (CEF) may exert a beneficial effect in the management of inflammatory pancreatic diseases. Its effects on the exocrine pancreas, however, remain only partially investigated. AIM: To examine the effects of CEF on the exocrine pancreas in rats. METHODOLOGY: Eight male Wistar rats were intrajejunally cannulated, and CEF was started on postoperative day 6. In 10 control animals, laparotomy was followed by intragastric feeding (GF) with the same nutriment (Osmolite, Abbott) from postoperative day 6. The daily discharge was 24 kcal in both groups. After 5 days of feeding, the pancreas was removed; its weight and its protein, DNA, trypsin, and lipase contents were determined; and the exocrine pancreas was also examined for structural changes. RESULTS: The results revealed no significant difference in body weight loss between the two groups of animals, whereas the pancreas weight/body weight ratio was lower (p < 0.01) in the CEF group. The pancreatic protein, DNA, and enzyme contents were decreased (p < 0.01) after CEF as compared with the values for the GF group. Histologic examinations demonstrated clear decreases in acinar size and in the zymogen content of the pancreas in the CEF animals. CONCLUSION: This study clearly indicates that CEF reduces the enzyme production of the pancreas.     

Role of the actin cytoskeleton in G-protein-coupled receptor activation of PYK2 and paxillin in vascular smooth muscle

Dynamic remodeling of the actin cytoskeleton occurs during agonist-induced smooth muscle contraction. Tyrosine phosphorylation of the adaptor protein paxillin has been implicated in regulation of actin filament formation and force development. We have investigated the role of the actin cytoskeleton in noradrenaline (NA)-induced and endothelin (ET)-induced activation of the calcium-dependent nonreceptor tyrosine kinase PYK2 and subsequent phosphorylation of paxillin in rat small mesenteric arteries. NA and ET induced a rapid and prolonged activation of PYK2, as shown by increased phosphorylation at Y402 and Y881, and a concomitant association of the kinase with a Triton X-100 insoluble membrane (cytoskeleton) compartment. Both agonists also increased phosphorylation of paxillin at Y31 and Y118 with a similar time course as PYK2 phosphorylation, and induced its association with the same membrane compartment as PYK2. Treatment of arteries with cytochalasin D disrupted stress fibers and inhibited NA-induced and ET-induced force in a myosin light chain 20 phosphorylation independent and reversible manner. However, cytochalasin D treatment had no effect on NA-induced and ET-induced phosphorylation of either PYK2 or paxillin but did prevent their association with the TritonX-100 insoluble membrane compartment. These results show that in mesenteric arteries an intact cytoskeleton and force development are not prerequisites for G-protein--coupled receptor--induced activation of PYK2 and paxillin, by tyrosine phosphorylation, in vascular tissue, but are necessary for the translocation of PYK2 and paxillin to the membrane.     

Ontogeny of thyrotropin-releasing hormone and histidyl proline diketopiperazine in the rat central nervous system and pancreas

The ontogeny of TRH and of a proposed TRH metabolite, histidyl proline diketopiperazine (His-Pro DKP), was determined in the rat central nervous system and pancreas as a means of studying the interrelationship of these peptides. Various regions of the rat brain, spinal cord, and pancreas were dissected from animals ranging in age from prenatal day 17 to adult. The tissues were extracted for TRH and His-Pro DKP, and tissue levels of the two peptides were measured by specific RIAs. We found increasing TRH levels in the hypothalamus, spinal cord, and multiple extrahypothalamic brain regions in the developing rat [e.g. from 21 +/- 3 (+/- SE) pg/hypothalamus on prenatal day 17 to 2606 +/- 296 pg/hypothalamus in the adult]. In the rat pancreas, however, TRH levels initially increased from 354 +/- 37 pg/pancreas on prenatal day 21 to 749 +/- 68 pg/pancreas on postnatal day 7, but from day 7 to adulthood, the TRH content fell dramatically, being undetectable in the adult rat pancreas. The His-Pro DKP content increased in nearly all tissues studied, with peak values occurring on postnatal days 10 and 28 and in the adult. There was little apparent correlation, however, between the anatomical distribution and ontogeny of TRH compared with those of His-Pro DKP. We conclude that His-Pro DKP and TRH have widespread distributions involving the hypothalamus, extrahypothalamic brain, spinal cord, and pancreas in the developing rat. TRH and His-Pro DKP, however, have differing patterns of ontogeny in the rat, suggesting that His-Pro DKP may be derived from sources other than just TRH.     

Thyroxine induces pancreatic beta cell apoptosis in rats

AIMS/HYPOTHESIS: Thyroid hormones reduce glucose tolerance in animals and humans. This effect is accompanied by a reduction in the beta-cell volume of the pancreas. METHODS: We studied the underlying mechanism using terminal UTP nick end labelling (TUNEL) and caspase-3 to analyse apoptosis and BrdU labelling of beta-cell proliferation. RESULTS: The reason for the reduction of the beta-cell volume of the pancreas after thyroxine treatment is apparently an increased rate of beta-cell apoptosis by an increase of TUNEL and caspase-3 positive rat beta cells. In parallel, thyroxine treatment increased the rate of apoptosis in rat pancreatic ductal cells which are considered to contribute to the pool of stem cells from which insulin-producing beta cells originate. The effects of thyroid hormone treatment are reversible through an increase of the beta-cell replication rate when thyroxine is withdrawn as documented by an increase of the BrdU labelling index. CONCLUSION/INTERPRETATION: An increased rate of beta-cell death due to apoptosis causes a decrease of insulin content and glucose-induced insulin secretion from the pancreas in hyperthyroidism. The resulting reduction of beta cells in the pancreas can provide an explanation for the decrease of glucose tolerance in hyperthyroidism.     

PTEN下调paxillin的表达抑制胃癌转移

目的检测PTEN(phosphatase and tensin homolog deleted on chromosome10,10号染色体缺失的磷酸酶与张力蛋白同源物)及桩蛋白(paxillin)在胃癌细胞系BGC823中的表达,并探讨PTEN对paxillin的调节作用及其在胃癌的发生、发展中的意义。方法体外培养胃癌细胞BGC823,利用脂质体介导法瞬时转染pEAK8及pEAK8-PTEN质粒,获得pEAK8-BGC823(pE-B)和pEAK8-PTEN-BGC823(pE-P-B)细胞,采用免疫印迹法检测PTEN、paxillin及actin蛋白水平的表达,免疫荧光检测paxillin在细胞内的定位。结果 Western blot显示,pE-P-B细胞PTEN蛋白表达水平(1.013±0.074)明显高于pE-B细胞(0.513±0.006)和BGC823细胞(0.506±0.015),而paxillin的蛋白表达水平(0.883±0.032)明显低于后两者(2.747±0.047,2.663±0.096),BGC823与pE-B相比,PTEN和paxillin蛋白表达差异均无统计学意义(P>0.05),Sperman等级相关分析证明PTEN蛋白与paxillin蛋白的表达呈负相关(r=-0.12,P<0.05);免疫荧光显示,paxillin在pE-B细胞伸出伪足处聚集,在pE-P-B细胞中较少。结论过表达PTEN可能通过下调paxillin的表达从而抑制胃癌的转移。     

Nitric oxide induction in a rat model of selective pancreatic ischemia and reperfusion

BACKGROUND/AIMS: Ischemia and reperfusion of the pancreas may be important in aggravating the course of acute pancreatitis. In a rat model of selective pancreatic ischemia and reperfusion, we studied plasma levels of nitric oxide and expression of nitric oxide synthase in the pancrease and lung. METHODOLOGY: Pancreatic ischemia was achieved by occlusion of the 4 main pancreatic arteries for 40 min; this was followed by a 7-hour reperfusion period (group A, 10 rats). Outcome measures were compared with those of animals undergoing a sham operation (group B, 10 rats). RESULTS: Pancreatic damage in group A animals was demonstrated by increased serum alpha-amylase and by macroscopic and microscopic evidence. Total nitric oxide synthase activity in pancrease and lung was higher than in shams [median: 0.73 vs. 0.54 pmol/mg protein/min in the pancreas (P = 0.0082); 1.38 vs. 0.68 pmol/mg protein/min in the lung (P = 0.023)]; this was mainly due to activation of the inducible isoform of the enzyme. There was an associated 58.2% increase in plasma levels of nitric oxide metabolites [from mean 55.0 to 131.6 mumol/L (P < 0.001)]. Immunohistochemistry confirmed expression of inducible nitric oxide synthase and nitric oxide-mediated oxidative damage (nitrotyrosine) in both pancreas and lung. CONCLUSIONS: Ischemia and reperfusion of the pancreas induces pancreatic damage, overexpression of inducible nitric oxide synthase and oxidative damage within the pancreas and lung.     

Small bowel bypass prevents the trophic action of cholecystokinin on the rat pancreas

The effect of a chronic administration of cholecystokinin (CCK) on the rat pancreas has been studied in rats subjected to a 90% jejunoileal bypass or an intestinal transection (controls). Jejunoileal bypass, when compared to transection, did not modify the size of the pancreas but decreased its enzyme content, especially for amylase, and reduced the number of zymogen granules. These structural and biochemical changes were maintained when bypassed animals were treated three times daily and for six days with cholecystokinin (20 Ivy Dog Units (IDU)/kg). In contrast, CCK treatment in transected animals induced growth of the pancreas due to cellular hypertrophy and hyperplasia; pancreatic enzyme content, especially for chymotrypsin, and the population of zymogen granules in acinar cells were also enhanced. It is concluded that jejunoileal bypass prevents the trophic action of chronic CCK on the pancreas.     

异丙肾上腺素预处理对大鼠胰腺移植后缺血再灌注损伤的抑制作用

目的:探讨减轻大鼠胰腺移植后缺血再灌注损伤的保护作用机制.方法:IPC后动态检测大鼠胰腺组织热休克蛋白表达.建立大鼠胰腺移植缺血再灌注模型,选择表达热休克蛋白高峰时段供体大鼠胰腺移植作为实验组,未预处理供体大鼠胰腺移植作为对照组.移植后6 h,采集静脉血及移植胰腺.热休克蛋白70(HSP70)分别用Western blot法及免疫组织化学法检测.免疫组织化学法测定肿瘤坏死因子-α(TNF-α)表达.流式细胞仪检测胰腺细胞凋亡率.碘淀粉比色法检测血淀粉酶水平.结果:IPC后供体大鼠胰腺中HSP70的表达在24 h达到高峰,与其他各时段比较具有显著差异(0.92±0.25 vs 0.24±0.04,0.34±0.06,0.58±0.07,0.62±0.11,0.25±0.09,均P<0.05),IPC后6 h,12 h,24 h,36 h大鼠胰腺中HSP70的表达与未预处理组相应时段比较差异也显著(0.34±0.06 vs 0.28±0.07,0.58±0.07 vs 0.25±0.04.0.92±0.25 vs 0.27±0.05,0.62±0.11vs 0.25±0.06,均P<0.05),48 h恢复到原来水平.而未预处理组各时段间比较差异无统计学意义(P>0.05).HSP70主要表达于胰腺腺泡细胞及血管壁.对照组胰腺组织中TNF-α、细胞凋亡率、中性粒细胞、血淀粉酶的水平明显升高,与假手术组相比差异显著(均P<0.01).实验组降低了胰腺组织中TNF-α、细胞凋亡率、白细胞数、血淀粉酶的水平,与对照组比较差异具有统计学意义(11 929±1220vs46 111±3127,26.7%±4.5%vs 37.4%±4.7%,3 308±531 vs 6668±1506,1057 IU/L±148IU/L vs 1 408 IU/L±195IU/L,均P<0.05).结论:IPC减轻了大鼠胰腺移植后缺血再灌注损伤,IPC保护作用与HSP70的诱导生成有关.     

桩蛋白表达下调对结直肠癌细胞SW480侵袭力的影响

目的:探讨下调桩蛋白(paxillin)的表达对结直肠癌细胞SW480体外侵袭的影响.方法:筛选常见结直肠癌细胞株中paxillin 的表达,发现SW480中表达最多.构建干扰paxillin表达的特异性短发夹RNA(shRNA),转染结直肠癌细胞SW480.将SW480细胞分为3组:正常SW480组、阴性对照组及pa...     

Endogenous somatostatin inhibits interaction of insulin and cholecystokinin on exocrine secretion of isolated, perfused rat pancreas

INTRODUCTION: Although somatostatin inhibits pancreatic exocrine secretion, the inhibitory mechanism of endogenous somatostatin is not clearly understood. AIM: To investigate the effect of endogenous somatostatin on the interaction between endogenous insulin and exogenous cholecystokinin (CCK) in exocrine secretion of the totally isolated, perfused rat pancreas. METHODOLOGY: Endogenous releases of somatostatin and insulin were induced by 18 mM glucose. Streptozotocin (75 mg/kg) or cysteamine (300 mg/kg) was injected into rats 24 hours before the experiment to deplete insulin or somatostatin in the pancreas. RESULTS: Glucose (18 mM) enhanced CCK (10 pM)-stimulated secretions of fluid and amylase in the normal pancreas, which was further elevated by a somatostatin antagonist. Exogenous insulin (100 nM) also enhanced CCK-stimulated secretions in the streptozotocin-treated pancreas, which was also markedly increased by the somatostatin antagonist. The glucose (18 mM)-enhanced CCK-stimulated secretions were much higher in the cysteamine-treated pancreas than in the normal pancreas, which was dose-dependently reduced by exogenous somatostatin (30, 100 pM). However, endogenous or exogenous somatostatin did not modify the pancreatic responses to CCK alone. CONCLUSION: Endogenous somatostatin inhibits the interaction of endogenous insulin and CCK on pancreatic exocrine secretion in the rat rather than reducing the action of CCK alone or endogenous release of insulin.