Experimental pancreatitis in the rat. Light and electron microscopical observations on early pancreatic lesions induced by intraductal injection of trypsin, phospholipase A2, lysolecithin and non-ionic detergent

Pancreatic Blood Flow with Special Emphasis on Blood Perfusion of the Islets of Langerhans

The pancreatic islets are more richly vascularized than the exocrine pancreas, and possess a 5- to 10-fold higher basal and stimulated blood flow, which is separately regulated. This is reflected in the vascular anatomy of the pancreas where islets have separate arterioles. There is also an insulo-acinar portal system, where numerous venules connect each islet to the acinar capillaries. Both islets and acini possess strong metabolic regulation of their blood perfusion. Of particular importance, especially in the islets, is adenosine and ATP/ADP. Basal and stimulated blood flow is modified by local endothelial mediators, the nervous system as well as gastrointestinal hormones. Normally the responses to the nervous system, especially the parasympathetic and sympathetic nerves, are fairly similar in endocrine and exocrine parts. The islets seem to be more sensitive to the effects of endothelial mediators, especially nitric oxide, which is a permissive factor to maintain the high basal islet blood flow. The gastrointestinal hormones with pancreatic effects mainly influence the exocrine pancreatic blood flow, whereas islets are less affected. A notable exception is incretin hormones and adipokines, which preferentially affect islet vasculature. Islet hormones can influence both exocrine and endocrine blood vessels, and these complex effects are discussed. Secondary changes in pancreatic and islet blood flow occur during several conditions. To what extent changes in blood perfusion may affect the pathogenesis of pancreatic diseases is discussed. Both type 2 diabetes mellitus and acute pancreatitis are conditions where we think there is evidence that blood flow may contribute to disease manifestations. © 2019 American Physiological Society. Compr Physiol 9:799-837, 2019.

Pancreatite aguda experimental induzida pela L-arginina: avaliação histológica e bioquímica

RACIONAL: Doses excessivas de aminoácidos básicos como a L-arginina têm a capacidade de lesar o pâncreas de ratos. OBJETIVO: Descrever e avaliar as características bioquímicas e histológicas da pancreatite aguda induzida pela L-arginina em ratos durante a instalação, desenvolvimento e reparação do processo inflamatório pancreático. MATERIAL E MÉTODOS: A amostra constituiu-se de 105 ratos machos, da linhagem Wistar. Aos ratos do grupo experimento (n = 70) administrou-se injeção intraperitonial de 500 mg/100 g de peso corporal de L-arginina. No grupo controle (n = 35) foi injetada solução salina isotônica. Analisaram-se 10 animais do grupo experimento e 5 do grupo controle em cada período de 6 h, 12 h, 24 h, 48 h, 72 h, 7 dias e 14 dias. Durante os tempos determinados coletou-se sangue para exames laboratoriais e o pâncreas para análise em microscopia óptica. RESULTADOS: Doze a 24 horas após a injeção de L-arginina os níveis séricos de amilase atingiram valores máximos, comparados àqueles dos ratos controle, decrescendo gradualmente, alcançou-os na 48ªhora sendo significativamente menor após 72 horas e 7 dias. A atividade enzimática retornou a níveis basais após 14 dias. Os valores de amilase estavam normais em todos os tempos avaliados nos animais do grupo controle. Na microscopia óptica, após injeção de L-arginina, observou-se arquitetura pancreática histologicamente preservada no período de 6 horas, evidenciando-se em 24 horas importante edema intersticial. Após 48 horas, a arquitetura acinar estava parcialmente destruída com necrose celular focal, atingindo sua máxima severidade ao ultrapassar 72 horas. No 7º dia a necrose tecidual e o edema haviam diminuído, iniciando-se a regeneração da arquitetura acinar. Observou-se a reconstrução estrutural pancreática após 14 dias. No grupo controle não se encontraram alterações histológicas pancreáticas. CONCLUSÃO: A pancreatite aguda experimental induzida pela L-arginina induz a necrose pancreática, apresentando evolução auto-limitada com regeneração do pâncreas em 2 semanas.

Pancreatic capillary blood flow in an improved model of necrotizing pancreatitis in the rat

INTRODUCTION

The development of acute pancreatitis is characterized by profound changes in pancreatic microcirculation. Using in vivo microscopy with fluorescent-labeled erythrocytes as tracers we studied changes in pancreatic microcirculation in an improved rat model of necrotizing pancreatitis (NP) in comparison to edematous pancreatitis (EP) and healthy controls.

METHODS

Twenty-one male Wistar rats had their pancreatae exteriorized in a temperature-controlled immersion chamber followed by intravenous administration of fluorescent-labeled autologous erythrocytes. EP was induced by intraductal saline and intravenous caerulein (5 microg/kg/h) for 6 h (n = 7) and NP by controlled intraductal infusion of glycodeoxycholic acid (10 mmol/L) followed by intravenous caerulein (n = 7). Control animals received intraductal and intravenous saline (n = 7). The determination of pancreatic microcirculation was performed before as well as 1, 3, and 6 h after intraductal infusion by correlating the number of passing labeled erythrocytes/capillary/min with their concentration per microliter of arterial blood.

RESULTS

Pancreatic capillary flow in control animals remained constant over the 6-h observation period. Pancreatic capillary flow in the EP group rapidly increased to 188% of baseline after 3 h and remained significantly elevated throughout the experiments (P = 0.0001). In contrast, pancreatic capillary flow decreased significantly in the group suffering NP with values 46.7% of baseline after 6 h (P = 0.0001). Complete capillary stasis developed in 38% of investigated capillaries in the NP group compared to 0-1% in both other groups (P = 0.0001).

CONCLUSION

Pancreatic microcirculation in mild edematous pancreatitis is significantly increased while the evolution of necrotizing pancreatitis in the model studied herein is characterized by a dramatic reduction in pancreatic capillary flow in conjunction with areas of capillary stasis. These results underline the pathophysiologic relevance of the model and of therapeutic measures aimed at an improvement of pancreatic microcirculation in clinical necrotizing pancreatitis.

Microvasculature of the pancreas. Relation to pancreatitis

Local or generalized alteration of microcirculation may be expected in diseases of the pancreas. Changes may range from increased permeability of capillaries to hemorrhage. Tissue necrosis may result from prolonged ischemia owing to intravascular coagulation and severely impaired blood flow. It is possible to observe early microvascular changes by intravital microscopy. Klar and coworkers have demonstrated by this method that isovolemic hemodilution improves blood flow under conditions that would otherwise lead to tissue damage. This paper presents the basic microcirculation of the pancreas and the changes that accompany pancreatic disease. It emphasizes that concentration on the changes in microcirculation that accompany the early manifestations of pancreatic diseases, particularly pancreatitis, may reveal important clues to their pathogenesis.

The role of phospholipase A2 in pancreatic acinar cell injury

The integrity of rat pancreatic acinar cells under the influence of human phospholipase A2 (PLA2) was studied. Isolated pancreatic acini showed no increased discharge of aspartylaminotransferase (ASAT) when incubated either in solutions containing human pancreatic PLA2 or the bile salt sodium deoxycholate (DEC), the latter in concentrations that augment PLA2 activity but have no destructive detergent effect. When human pancreatic PLA2 was injected into the rat pancreatic duct, uneven distribution was observed at 15 min and 3 h in immunohistochemical sections. Edema and a mild inflammatory reaction were the main changes in the pancreas. The necrotic areas seen by light and electron microscopy were quite small and located mostly at the periphery of lobules corresponding the spread of the injected material. Necrosis was of the coagulation type and showed equal extent after the injection of PLA2 with or without DEC. Internalized human pancreatic PLA2 was present already 15 min after the injection in the cytoplasm of some intact acinar cells, indicating a functioning protective mechanism. It was concluded that pancreatic acinar cells are quite resistant to PLA2-catalyzed hydrolysis of membrane phospholipids in vitro, but additional trauma, e.g., pressure caused by intraductal injection, and tissue related factors, such as the mediators of the inflammatory reaction, make acinar cells susceptible to the effect of PLA2.

Pancreatic ischaemia in experimental acute pancreatitis: mechanism, significance and therapy

Much clinical and experimental evidence suggests that pancreatic ischaemia in the early phase of acute pancreatitis is important in the development of pancreatic necrosis. While depletion of intravascular volume has often been assumed to be the main circulatory defect, an additional disturbance of pancreatic microcirculation has been demonstrated experimentally. Possible contributory mechanisms include chemical-induced vasoconstriction, direct injury of vessel wall, intravascular coagulation and increased endothelial permeability resulting in pancreatic oedema, haemoconcentration and impaired venous drainage. Pancreatic ischaemia as a consequence of these local effects seems to be responsible for the transition of mild pancreatitis to parenchymal necrosis. In experimental models the beneficial effect of various drugs and of sympathetic blockade has been ascribed to an improvement in pancreatic perfusion. Although effective volume therapy is generally accepted as the mainstay of conservative treatment in acute pancreatitis, the efficacy of different fluid preparations is still controversial, and simple fluid resuscitation has not been shown to prevent the development of parenchymal necrosis. The specific impairment of pancreatic microcirculation cannot be prevented merely by replenishment of intravascular volume with crystalloids, albumin or plasma despite normalization of macrohaemodynamics. In contrast, partial replacement of blood by dextran preparations has been shown to increase pancreatic perfusion by improving blood fluidity. Isovolaemic haemodilution in conjunction with conventional fluid therapy may provide a new and effective means of protecting the pancreas from secondary injury due to the early ischaemic phase of acute pancreatitis.

Pancreatic acinar cell necrosis with intact storage of digestive enzymes in selenomethionine treated rats

Morphological and biochemical changes were observed in the pancreas and serum of rats after the intraperitoneal administration of selenomethionine, sodium selenite and methionine. Selenomethionine caused rapidly developing acinar cell necrosis. The first pathological changes were mitochondrial swelling and flocculent densities, and dilatation of cisternae of the endoplasmic reticulum. Zymogen granules appeared disrupted only in disintegrated acinar cells. Signs of autodigestive pancreatic inflammation with fat necrosis, elevation of pancreatic phospholipase A2 and serum amylase activities, as well as pulmonary oedema were present. Sodium selenite caused similar histologic changes to those produced by selenomethionine, but no changes were seen after methionine administration. Destruction of pancreatic acinar cells by an intraductal oleic acid injection that resulted in exocrine atrophy did not prevent systemic selenomethionine toxicity. Our results show that selenomethionine causes pancreatic acinar cell necrosis and that intracellular transport and storage of digestive enzymes is not primarily altered by this chemical.

Experimental acute pancreatitis--a quantification of dynamics at enzymic and histomorphologic levels

To study the dynamics of pathomorphologic alterations in the development of acute pancreatitis (AP) and the corresponding changes of the patterns of pancreatic enzymes in rats AP was induced by: 1) combination of a pancreatic juice edema and temporary pancreatic ischemia, ii) by intraductal instillation of trypsin, and iii) by trypsin instillation in combination with ischemia. At 4, 8 and 24 h postoperatively the histologic findings and the activities of lipase and alpha-amylase in the pancreas and the serum were analyzed. The histologic sum score of the individual rats did not correlate with their enzymic patterns in pancreas and in serum. In all three models there was a development of parenchymal necrosis independent of the existence of pancreatic fat necrosis. Therefore, it is not probable that fat necrosis represents an obligatory precondition for the initiation of autodigestion.

Involvement of oxygen radicals and phospholipase A2 in acute pancreatitis of the rat

The purpose of this study was to assess the involvement of oxygen radicals and phospholipase A2 in acute pancreatitis. Acute pancreatitis was induced in rats by the CCK-analogue cerulein (5 micrograms/kg.h) for 30 min, 3.5 h, and 12 h. At the end of the infusion, serum enzymes and the lipid peroxidation products conjugated dienes and malondialdehyde in the tissue were measured. Moreover, tissue samples underwent lightmicroscopical examination. After 3.5 h cerulein, an interstitial edema and a beginning accumulation of granulocytes in the pancreatic gland is observed. These changes are aggravating within 12 h, leading to tissue necrosis and migration of the granulocytes into the tissue. Concomitantly amylase and lipase increased by 15 and 35 times, respectively. Conjugated dienes and malondialdehyde increase already after 30 min cerulein and reach their highest levels after 3.5 h cerulein. At the same time the tissue activity of phospholipase A2 is elevated three fold. Rats were treated with superoxide dismutase and catalase before cerulein infusion. Treatment significantly prevents tissue necrosis, granulocyte accumulation, and edema formation. The enhanced activity of phospholipase A2, however, is unaffected by the treatment. Oxygen radicals seem to be instrumental in the development of the disease.

The role of phospholipase A2 in human acute pancreatitis

Several studies suggest that the activation of pancreatic phospholipase A2 (PLA2) and its release from injured acinar cells play an important role in the pathogenesis of acute pancreatitis. Elevated catalytic activity of PLA2 in serum is associated especially with severe forms of the disease. PLA2 has been purified from human cadaver pancreas and an antiserum raised against the enzyme in rabbits. Immuno-histochemical localization of PLA2 in pancreatic tissue was abnormal in acute pancreatitis. A time-resolved fluoroimmunoassay for human pancreatic PLA2 has been developed. Increased serum concentrations of immunoreactive PLA2 were found in acute pancreatitis during the first week after hospital admission. The values returned to normal somewhat more slowly than corresponding serum amylase values. The immunochemical determination of PLA2 in serum provides a fast and specific detection of injury to pancreatic acinar cells. The pancreas is not the only source of PLA2 in acute pancreatitis. The nonpancreatic PLA2 may originate from various inflammatory cells, but this hypothesis remains to be proven.

Raised plasma thromboxane B2 levels in experimental acute necrotizing pancreatitis in rats. The effects of flunarizine, dazoxiben, and indomethacin

The possible role of thromboxane A2 (TXA2) in acute necrotizing pancreatitis (ANP) was investigated in rats. After ANP was induced by injecting sodium taurocholate (5% w/v) into the pancreatic duct, the thromboxane B2 (TXB2) levels in plasma increased significantly. The effects of indomethacin, a general blocker of prostaglandin synthesis, on survival time and on plasma TXB2 levels were compared with those of dazoxiben, a more specific blocker of TXA2 synthesis, and Flunarizine, a calcium entry blocker known to inhibit the effects of TXA2. In a test group without any treatment, all animals died within 30 h of ANP induction. Although TXB2 levels were lowered by the administration of indomethacin, dazoxiben, and Flunarizine, survival times were not significantly altered. Indomethacin pretreatment had no beneficial effect, whereas 30% and 40% of the animals survived for 36 h after treatment with Flunarizine and dazoxiben, respectively. The results of the present study indicate that inhibition of TXA2 synthesis alone does not dramatically alter survival time. However, a potential role for other arachidonate metabolites in ANP cannot be ruled out by this study.

Morphometric evaluation of the turnover of autophagic vacuoles after treatment with Triton X-100 and vinblastine in murine pancreatic acinar and seminal vesicle epithelial cells

Large numbers of autophagic vacuoles were found in murine pancreatic acinar and seminal vesicle epithelial cells following the administration of Triton X-100 or vinblastine for 4 h. The autophagic vacuoles disappeared rapidly from the cells after the administration of cycloheximide to animals pretreated with Triton X-100. The decay in seminal vesicle cells appeared to follow first-order kinetics with an estimated t1/2 of 8.7 min. The regression in pancreatic cells was equally rapid and less than half the initial volume of autophagic vacuoles was found at the 12th min after cycloheximide injection. This time, the decay curve appeared to be linear rather than exponential. Our data, together with the work of others, support the view that the average half-life of autophagic vacuoles is a fairly constant parameter kept within the range of 6-9 min in various types of mouse and rat cell when the late steps of autophagocytosis (i.e. the fusion of autophagosomes and lysosomes and the degradation within lysosomes) are not affected. The regression of autophagic vacuoles was slow in mice pretreated with vinblastine (t1/2 of about 27-30 min) suggesting that this drug slows down the turnover of autophagic vacuoles. Morphometric evaluation of the regression of the autophagic vacuole compartment after cycloheximide treatment can be used as a tool to distinguish between treatments which elevate the amount of autophagic vacuoles within the cells by increasing the rate of sequestration from those which expand the autophagic vacuole compartment by causing accumulation of autophagic vacuoles as a result of blockade of the late steps of the autophagic process.

Ultrastructure of human acute pancreatitis

Few studies have been published on the ultrastructural changes which accompany human acute pancreatitis, and these have concentrated primarily on parenchyma. The present study concentrates on extraparenchymal changes, compares acute pancreatitis occurring alone with that on a background of chronic pancreatitis, and tests for similarity with observations made previously in an experimental model. Pancreatic tissue came from 16 patients undergoing surgery for pancreatic disease and five subjects without pancreatic disease. Regressive changes in parenchymal cells were consistent with ischemia, and with previously described studies. Polymorphonuclear leukocytes infiltrated into stroma and parenchyma. Platelets accumulated intra- and extravascularly. Fibrin deposits were common in the connective tissue, and could be observed in intercellular spaces at the base of acini, mingled with degenerating acinar cells and secretion product. Microthrombi occurred in blood vessels. These alterations were consistent with those in experimental acute pancreatitis. Similar changes were observed whether or not acute pancreatitis occurred on a background of chronic pancreatitis. The vascular component is important in acute pancreatitis, and altered epithelial barriers allow interaction between blood-borne material and pancreatic exocrine secretions.

Fat necrosis in human acute pancreatitis. An immunohistological study

Localization of phospholipase A2, lipase and colipase immunoreactivity were studied in paraffin embedded tissue sections. The samples were taken from the pancreas of 12 patients suffering from acute haemorrhagic necrotizing pancreatitis, and from diseased adipose tissue of 7 patients suffering from traumatic mammary fat necrosis. Peroxidase-antiperoxidase immunohistology revealed consistent positive reaction against phospholipase A2, lipase and colipase at the border of fat necrosis in pancreatic interlobular adipose tissue and in peripancreatic, mesenterial and retroperitoneal fat. The fat necroses of the breast were devoid of reaction. The results support the idea that in addition to lipase colipase and phospholipase A2 participate in the development of fat necrosis in acute pancreatitis. Pancreatic lipolytic enzymes are not present in the adipose tissue in mammary fat necrosis.

Experimental pancreatitis in the rat. Ductal factors in sodium taurocholate-induced acute pancreatitis

Spreading of injected material and ductal resistance were studied in the rat pancreas after intraductal injection of Indian ink, human serum or sodium taurocholate. Indian ink filled the main pancreatic duct and small ductules revealing the lobular structure in macroscopic preparation. Escape into the interstitium was observed both in the macroscopic preparations and in histologic sections. Human IgG was demonstrated immunohistochemically in single acinar cells and around acinar cells after intraductal injection of human serum. The changes were most pronounced at 15 min and at 6 h after the injection but were almost resolved at 24 h. The intraductal pressure was registered during sodium taurocholate infusion. The pancreatic duct ruptured at the pressure of 82 mm Hg in average. It was concluded that in the ductal model of experimental acute pancreatitis the infusion causes ruptures in pancreatic ducts and the infusate escapes into the interstitium where it remains for several hours.