Effects of endothelin on microcirculation of the pancreas

Randomized controlled trial using bosentan to enhance the impact of exercise training in subjects with type 2 diabetes mellitus

In type 2 diabetes patients, endothelin (ET) receptor blockade may enhance blood flow responses to exercise training. The combination of exercise training and ET receptor blockade may represent a more potent stimulus than training alone to improve vascular function, physical fitness and glucose homeostasis. We assessed the effect of an 8 week exercise training programme combined with either ET blockade or placebo on vasculature, fitness and glucose homeostasis in people with type 2 diabetes. In a double-blind randomized controlled trial, brachial endothelium-dependent and ‑independent dilatation (using flow-mediated dilatation and glyceryl trinitrate, respectively), glucose homeostasis (using Homeostasis Model Assessment for Insulin Resistance (HOMA-IR)) and physical fitness (maximal cycling test) were assessed in 18 men with type 2 diabetes (60 ± 6 years old). Subjects underwent an 8 week exercise training programme, with half of the subjects receiving ET receptor blockade (bosentan) and the other half a placebo, followed by reassessment of the tests above. Exercise training improved physical fitness to a similar extent in both groups, but we did not detect changes in vascular function in either group. This study suggests that there is no adaptation in brachial and femoral artery endothelial function after 8 weeks of training in type 2 diabetes patients. Endothelin receptor blockade combined with exercise training does not additionally alter conduit artery endothelial function or physical fitness in type 2 diabetes.

Differential effects of endothelins on histological and ultrastructural changes and trypsinogen activation in the secretagogue-induced acute pancreatitis in rats

The role of endothelins in acute pancreatitis remains obscure. To assess the effects of endothelins (ETs) in early (4 h) caerulein-induced acute pancreatitis (AP) in rats, ET-1, ET-2 and ET-3 (0.5 or 1.0 nmol/kg) were applied twice with i.p. caerulein (2×40 μg/kg) at 1h interval. Histological and ultrastructural examinations of pancreases and the assay of trypsinogen activation in whole homogenate were performed. All ETs, especially ET-1 at the higher dose, decreased inflammatory cell infiltration despite an increase in the edema score. The vacuolization and necrosis of acinar cells were slightly increased after the lower dose of ET-1 and ET-2. Ultrastructural changes were generally improved after the higher dose of ETs. Trypsinogen activation increased from 4.8±1.3% in control to 18.4±3.8% in AP (p<0.01). It was attenuated to 6.4±1.3% (p<0.01) by the higher dose of ET-1 and to 8.8±1.5% (p<0.05) by the lower dose of ET-3. In summary, ETs, especially ET-1 at the higher dose, were found to have some beneficial effects on morphological changes and trypsinogen activation in the pancreas in early caerulein-induced AP.

Pathophysiological role of platelets and platelet system in acute pancreatitis

The most successful approach for restoring normal long-term glucose homeostasis in type I diabetes mellitus is whole-organ pancreas transplantation. Graft pancreatitis is observed in up to 20% of patients and may lead to loss of the transplanted organ. Several pathophysiological events have been implicated in this form of pancreatitis. The most important cause of early graft pancreatitis is ischemia/reperfusion (I/R)-related disturbance of microvascular perfusion with subsequent hypoxic tissue damage. Recently, considerable evidence accumulated that, among a variety of other pathophysiological events, the activation of platelets can contribute to I/R injury in the course of acute pancreatitis experimentally and clinically. This review summarizes the events affecting platelet function and, therefore, pancreatic microcirculation leading to acute pancreatitis. Therapeutic approaches and own results are presented.

Endothelin-1 and pancreatic islet vasculature: studies in vivo and on isolated, vascularly perfused pancreatic islets

Endothelin-1 (ET-1) is a potent endothelium-derived vasoconstrictor, which also stimulates insulin release. The aim of the present study was to evaluate whether exogenously administered ET-1 affected pancreatic islet blood flow in vivo in rats and the islet arteriolar reactivity in vitro in mice. Furthermore, we aimed to determine the ET-receptor subtype that was involved in such responses. When applying a microsphere technique for measurements of islet blood perfusion in vivo, we found that ET-1 (5 nmol/kg) consistently and markedly decreased total pancreatic and especially islet blood flow, despite having only minor effects on blood pressure. Neither endothelin A (ET(A)) receptor (BQ-123) nor endothelin-B (ET(B)) receptor (BQ-788) antagonists, alone or in combination, could prevent this reduction in blood flow. To avoid confounding interactions in vivo, we also examined the arteriolar vascular reactivity in isolated, perfused mouse islets. In the latter preparation, we demonstrated a dose-dependent constriction in response to ET-1. Administration of BQ-123 prevented this, whereas BQ-788 induced a right shift in the response. In conclusion, the pancreatic islet vasculature is highly sensitive to exogenous ET-1, which mediates its effect mainly through ET(A) receptors.

Endothelin(A) receptor blockade reduces ischemia/reperfusion injury in pig pancreas transplantation

OBJECTIVE

The effect of prophylactic administration of a selective endothelin(A) receptor antagonist (ET(A)-RA) on ischemia/reperfusion injury in an experimental model of graft pancreatitis after pancreas transplantation was evaluated.

SUMMARY BACKGROUND DATA

It is well established that endothelin-1 (ET-1), a powerful vasoconstrictor, plays an important role in the development of pancreatitis. Recent studies have shown a beneficial effect of endothelin receptor antagonists in the therapy for experimental pancreatitis.

METHODS

Relevant ischemia/reperfusion injury was induced in pig pancreas transplants after 6 hours hypothermic preservation in University of Wisconsin solution. The recipients were randomized into 2 groups: control pigs received isotonic saline and the treated group received the selective ET(A)-RA BSF 208075 at the beginning of reperfusion. On postoperative days 2 and 5, animals were relaparotomized to obtain tissue specimens. Blood monitoring included lipase, amylase, C-reactive protein, trypsinogen-activation peptide, thiobarbituric acid-reacting substances, and ET-1. Partial oxygen tension (p(ti)O(2)) was measured by a Clarke-type electrode and blood flow by laser doppler. A semiquantitative score index was used for assessment of histologic injury and for immunohistochemical analysis of ET-1 and ET(A) receptor expression. Tissue mRNA levels of prepro ET-1, ET(A) receptor, pro-interleukin (IL)-6, and pro-IL-1beta were quantified using TaqMan real-time reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Prophylactic treatment with ET(A)-RA significantly reduced the severity of graft pancreatitis evidenced by C-reactive protein. The finding of transient capillary perfusion at the beginning of reperfusion supports the application of the ET(A)-RA during this period. The dramatic increase of plasma ET-1 in the therapy group is a clear evidence of effective receptor blockade. Mean trypsinogen-activation peptide levels from the portal venous effluent, but not mean systemic plasma TAP values were significantly lower in the treated group. Analysis of p(ti)O(2) and blood flow revealed a significant improvement of capillary perfusion and blood flow in the treated group and was associated with relevant reduction of tissue injury. Intrapancreatic ET-1 and IL-6 mRNA expression and ET-1 protein levels were significantly lower in the therapy group as compared with the control group. In contrast, ET(A) mRNA showed a marked up-regulation by ET(A) receptor blockade.

CONCLUSION

Application of a ET(A)-RA reduces ischemia/reperfusion induced graft pancreatitis in a pig transplantation model by improving microcirculation and reducing tissue injury.

Production and effects of endothelin-1 in rat pancreatic stellate cells

INTRODUCTION

Proliferation and matrix synthesis of activated pancreatic stellate cells (PSCs) participate in the development of chronic pancreatitis. Besides other substances, endothelin-1 (ET-1) may influence the activation process of PSCs. Until now, ET-1 has not been studied in this particular cell type.

AIMS

To characterize PSCs in rat pancreas with respect to expression of ET(A)-receptors, production of ET-1, and physiological effects induced by ET-1 during PSC activation.

METHODOLOGY

Immunocytochemical and ELISA techniques and cDNA microarray analysis were used. Physiologic effects were characterized by single cell measurements of free cytosolic Ca2+-concentration and of PSC contractility on collagen lattices.

RESULTS

Activation of PSCs in vitro, as assessed by alpha-smooth muscle actin expression, was accompanied by the de novo expression of ET(A)-receptors and synthesis of ET-1 mRNA and protein. Cytosolic Ca2+-concentration was increased upon ET-1 stimulation in activated but not in quiescent PSCs. Contractility of activated PSCs was significantly reduced by the selective ET(A)-receptor antagonist BQ123 but not by the ET(B)-receptor antagonist IRL-1038.

CONCLUSIONS

The results suggest that ET-1 may act as a paracrine and autocrine factor for activated PSCs and may mediate contractions of activated, but not quiescent, PSCs.

Further evidence for endothelin as an important mediator of pancreatic and intestinal ischemia in severe acute pancreatitis

INTRODUCTION

Severe acute pancreatitis is occasionally associated with pancreatic and intestinal necrosis. Mesenteric vasoconstriction is one of the most probable types of pathogenesis of these complications.

AIM

To investigate the involvement of endothelin-1 (ET-1), a potent vasoconstrictor.

METHODOLOGY AND RESULTS

Plasma ET-1 concentrations were extremely high in patients with pancreatic and/or diffuse intestinal necrosis. ET-1 mRNA was demonstrated in the rat pancreas, and the production of ET-1 protein by human umbilical vein endothelial cells was enhanced by tumor necrosis factor-alpha, thrombin, and protease-activated receptor-2-activating peptide. Administration of ET-1 in vivo induced mesenteric arterial spasm and decreased pancreatic and intestinal blood flow.

CONCLUSION

These results suggest the following: ET-1 is produced in and around the pancreas, mainly by endothelial cells, in severe acute pancreatitis; in the inflammatory setting, cytokines, activated thrombin and trypsin, may stimulate ET-1 production in a paracrine fashion; produced ET-1 may exaggerate the splanchnic microcirculation; and progressive ischemia may lead to necrosis of the pancreas and intestine.

Endothelin A but not endothelin B receptor blockade reduces capillary permeability in severe experimental pancreatitis

INTRODUCTION

Microcirculatory disorders, in particular increased capillary permeability (CapPerm), contribute to the multiple organ dysfunction syndrome in severe acute pancreatitis (AP). Endothelin receptor antagonists (ET-RA) have been shown to stabilize capillary leakage and improve organ function in AP.

AIM

To find out which endothelin receptor subtype (ET-A or ET-B) mediates the changes in CapPerm.

METHODOLOGY

Severe AP was induced in rats by intraductal bile salt infusion and i.v. cerulein. Animals were randomized to receive (1) saline; (2) selective ET-A-RA (LU-135252; 30 mg/kg); (3) selective ET-B-RA (A-192621); (4) nonselective ET-RA (LU-135252; 120 mg/kg); or (5) combined ET-A/B-RA (30 mg/kg LU-135252 + A-192621). Capillary blood flow (CBF) and CapPerm in the pancreas and colon and leukocyte rolling in mesenteric venules were determined.

RESULTS

Selective ET-A-RA increased CBF and decreased CapPerm in the pancreas and colon by 90-147% and reduced leukocyte rolling in AP but had no effect in healthy controls. Selective ET-B-RA increased pancreatic CBF (2.3 +/- 0.03 versus 2.1 +/- 0.04 nL/min) and enhanced CapPerm in the pancreas and colon by 24-35% in healthy controls but had no effect in AP. Blockade of both receptors produced effects similar to but less pronounced than those of selective ET-A-RA.

CONCLUSIONS

Blockade of ET-A and ET-B receptors has different effects on CapPerm in healthy animals and those with AP. This may explain the inconclusive results reported with nonselective ET-RA. In severe AP, blockade of ET-A but not ET-B receptors reduces CapPerm.

Comparison of Celsior and UW solution in experimental pancreas preservation

BACKGROUND

The University of Wisconsin solution (UW) is the gold standard for pancreas preservation. Celsior (CEL) was formulated specifically for heart preservation. Recently, experimental and clinical experience has been reported on the application of CEL to abdominal organs. In this animal study, pancreas preservation with CEL was compared with that in UW solution.

PATIENTS AND MATERIALS

Heterotopic, allogeneic pancreaticoduodenal transplantation was performed in female Göttingen Minipigs (n = 12 donors, n = 12 recipients). The grafts were flushed and stored for 6 h at 4 degrees C in UW or CEL. The recipients were randomized into two groups receiving either UW (n = 6)- or CEL (n = 6)-preserved grafts with a follow-up of 5 days. Blood flow (laser Doppler), partial oxygen tension, histological changes, endothelin-1 (plasma, immunohistochemistry), lipase, amylase, trypsinogen activation peptide, and C-reactive protein (CRP) were measured.

RESULTS

Partial oxygen tension was lower in the CEL group (P < 0.05). However, blood flow did not differ between UW- and CEL-preserved organs. The histomorphologic analysis of the pancreatic grafts revealed significantly less edema in the UW-preserved organs. Serum levels of amylase, lipase, CRP, and TAP taken from the central venous blood were comparable in the two groups, except for higher amylase values 36 h after reperfusion in the CEL group compared to the UW group (P < 0.05). Likewise, TAP taken from the portal venous effluent of the graft was found to be higher in the CEL group than in UW (P < 0.05). Endothelin-1 serum levels rose significantly during reperfusion without differences between the two groups. ET-1 immunohistochemistry revealed increased local ET-1 during reperfusion in all grafts. However, the ET-1 immunostaining in the CEL group was more pronounced than that in the UW group (P < 0.05).

CONCLUSIONS

Our results suggest that CEL solution is not as effective in preventing pancreatic ischemia/reperfusion damage as the standard UW solution in experimental pancreas transplantation. Increased ET-1 immunostaining and reduced p(ti)O(2) in the CEL group indicate increased microcirculatory damage in the CEL group.

Endothelin mediates local and systemic disease sequelae in severe experimental pancreatitis

Endothelin-1 has been shown to reduce pancreatic blood flow and cause focal acinar cell necrosis similar to those seen in acute pancreatitis (AP), whereas therapy with endothelin receptor antagonists enhanced pancreatic capillary blood flow (PCBF) and decreased mortality rates. The current study evaluated the role of endothelin in the development of severe AP. Trypsinogen activation peptides, acinar cell necrosis, and PCBF were used as local indicators of disease severity, fluid sequestration, cardiorespiratory and renal parameters, and colonic capillary blood flow as systemic disease indicators. The following groups of animals were examined: 1) rats with mild edematous AP and 2) severe necrotizing AP treated with and without endothelin, 3) transgenic rats overexpressing endothelin with severe AP, and 4) rats with severe AP prophylactically treated with endothelin receptor antagonists. The following observations were made: endothelin superimposed on mild AP caused hemoconcentration, a decrease in PCBF, and necrosis and ascites not seen in this model without endothelin exposure. Endothelin superimposed on severe AP had no significant effects. After induction of severe AP, less PCBF and more acinar cell necrosis were observed in transgenic rats than in their normal littermates. Prophylactic endothelin receptor antagonists improved local (acinar necrosis, PCBF) and systemic parameters (ascites, urine production, colonic capillary blood flow) of disease severity in animals with severe AP. These observations underscore the role of endothelin as a mediator of disease severity in AP and suggest that endothelin receptor blockade may become a promising therapeutic tool in this disease.

Endothelin receptor blockade in severe acute pancreatitis leads to systemic enhancement of microcirculation, stabilization of capillary permeability, and improved survival rates

BACKGROUND

We previously demonstrated that therapy with a new endothelin A receptor antagonist (ET-RA) significantly reduced mortality rates in severe acute pancreatitis (AP) in the rat without attenuating local signs of disease severity (intrapancreatic protease activation, acinar cell necrosis). This raised the question as to why ET-RA was so effective. The purpose of this study was to assess the effect of ET-RA on microcirculation (particularly capillary permeability) within and outside of the pancreas on intravascular fluid loss and extravascular fluid sequestration and on distant organ function.

METHODS

Severe AP was induced in rats by standardized intraductal bile acid infusion and cerulein hyper-stimulation. Starting 6 hours (n = 24 rats) and 12 hours (n = 30 rats) after the onset of AP, animals randomly received either the ET-RA (LU-135252) or saline solution with fluid resuscitation (6 mL/kg/h Ringer's lactate). At 24 hours, animals were relaparotomized for intravital microscopic determination of capillary blood flow, leukocyte rolling, and capillary permeability in the pancreas and colon. Further monitoring included cardiorespiratory and renal parameters, hematocrit levels and quantification of ascites and pleural effusions, and acinar cell necrosis at autopsy. Groups of sham-operated healthy animals (n = 6 animals each) that had been treated according to the same protocol served as control animals.

RESULTS

ET-RA treatment that was started 6 hours after AP-induction significantly decreased hematocrit levels (38% +/- 1% vs 45% +/- 2% with saline solution treatment), reduced ascites and pleural effusions (6.7 +/- 1.3 mL vs 11.9 +/- 1.3 mL), and improved urine production (4.8 +/- 0.5 mL vs 2.9 +/- 0.6 mL) and respiratory parameters. Moreover, all microcirculatory parameters were improved; in particular, capillary permeability was stabilized (158% +/- 9% vs 248% +/- 8% in the colon). These beneficial effects were also seen when therapy was delayed until 12 hours after AP induction. Pancreatic necrosis was not significantly reduced. The overall mortality rate was 12% in ET-RA-treated animals and 42% in saline solution-treated control animals (P <.05). In healthy animals ET-RA did not significantly alter the target parameters, except for a reduction of capillary permeability in the pancreas.

CONCLUSIONS

Improved microcirculation and stabilized capillary permeability in ET-RA-treated animals together with reduced intravascular fluid loss and extravascular fluid sequestration and improved renal and pulmonary function (1) may explain improved survival in this model, (2) support the hypothesis that systemic disease sequelae significantly contribute to outcome in AP, and (3) suggest that ET-RA may be a promising therapeutic tool in AP because it counteracts microcirculatory disorders that contribute to pancreatitis-associated organ dysfunction even when therapy is delayed to a point at which pancreatic injury may no longer be influenced.

Dynamic study of the distribution of microcirculatory blood flow in multiple splanchnic organs in septic shock

OBJECTIVES

To study dynamic distribution of microcirculatory blood flow in multiple splanchnic organs during septic shock; to test the hypothesis that changes in microcirculatory blood flow in splanchnic organs correlate with changes in regional flow during septic shock.

DESIGN

A prospective, controlled, animal study.

SETTING

Animal laboratory in a university medical center.

SUBJECTS

Nine anesthetized and mechanically ventilated domestic pigs.

INTERVENTIONS

Systemic flow (cardiac output) was measured with thermodilution and regional (superior mesenteric artery) flow with transit time flowmetry. Local blood flow (microcirculatory flow) was continuously measured in splanchnic organs (gastric, jejunal, and colon mucosa, liver, and pancreas) and the kidney with multichannel laser Doppler flowmetry. Septic shock was induced with fecal peritonitis. After 240 mins of sepsis, intravenous fluids were administered to alter hypodynamic shock to hyperdynamic septic shock.

MEASUREMENTS AND MAIN RESULTS

In this severe septic shock model, systemic and regional flows decreased by approximately 50% during the first 240 mins. Similar reductions were recorded in microcirculatory flow in the mucosa of the stomach (-41%; p < .001) and colon (-47%; p < .001). In the jejunal mucosa, on the other hand, flow remained virtually unchanged. Microcirculatory flow was also significantly decreased in the liver (-49%; p < .001), pancreas (-56%; p < .001), and kidney (-44%; p < .001). Administration of intravenous fluids at 240 mins was followed by three-fold increases in systemic and regional flows (approximately 70% above baseline). In the jejunal mucosa, flow also increased significantly above baseline (42%; p < .001), whereas in the stomach and the colon, it barely reached baseline. Kidney blood flow increased to baseline, whereas pancreas and liver flows remained 26% (p < .05) and 34% (p < .001), respectively, below baseline.

CONCLUSION

Changes in microcirculatory blood flow in the splanchnic organs are heterogeneous, both in early hypodynamic and in hyperdynamic septic shock, and cannot be predicted from changes in systemic or regional flows. Microcirculatory blood flow in the jejunal mucosa remains constant during early septic shock, whereas pancreatic blood flow decreases significantly more than regional flow.

The endothelin antagonist bosentan does not improve survival in severe experimental pancreatitis in rats

BACKGROUND

Severity of pancreatitis seems to be aggravated by impairment of vascular perfusion of the gland. Early mortality occurs within the first few days from the acute consequences of pancreatic injury with subsequent inflammatory response. Because vasoactive substances, including endothelin, seem to contribute to early mortality in acute pancreatitis, we tested the hypothesis that the inhibition of endothelin action could alter the outcome after severe experimental pancreatitis.

METHODS

In two groups of rats, pancreatitis was induced by intraductal infusion into the pancreatic duct of 1 microL/g body weight (b.w.) of either a 4% or a 5% sodium taurocholate solution. The mixed endothelin A and endothelin B receptor antagonist bosentan (20 mg/kg b.w.) or vehicle was injected intravenously in 12-h intervals for 3 d starting 1 h after induction of bile acid pancreatitis. This dose of bosentan is known to completely inhibit the effect of exogenous endothelin. The survival rate was monitored for 7 d. Thereafter, the surviving rats were sacrificed and the pancreas was prepared for histological and biochemical evaluation.

RESULTS

Irrespective of the treatment protocol (bosentan versus saline), survival was not different in animals challenged with either 4% or 5% sodium taurocholate. The corresponding survival rates were 62% with bosentan and 77% without bosentan in the 4% sodium taurocholate group. In the 5% sodium taurocholate group, the survival rates were 20% with and 27% without bosentan. Morphological and biochemical alterations were identical in control as well as in endothelin-antagonist-treated rats.

CONCLUSION

Therapy with the mixed endothelin A and endothelin B receptor antagonist bosentan does not influence the outcome after severe experimental pancreatitis. Therefore, blockade of endothelin A and B receptor subtypes may not be of major importance as a therapeutic principle in this model of experimental pancreatitis.

Evolution of streptozotocin-pancreatic damage in the rat: modulatory effect of endothelins on the nitridergic and prostanoid pathway

Many lines of evidence indicate that an increased pancreatic production of nitric oxide (NO) and prostaglandins (PGs) is found in the pancreas of streptozotocin-diabetic rats and that endothelins (ETs) are closely related to the nitridergic and prostanoid pathway in several tissues. In the present study the relationship between NO, ETs, and PGs has been explored in isolated pancreatic tissue from streptozotocin-diabetic rats. Pancreatic ET levels are higher in pancreatic tissues from diabetic (D) rats compared to control (C) animals. The addition of nitric oxide synthase (NOS) inhibitors (1 mM N(G)-nitro-l-arginine methyl ester, 600 microM N(G)-monomethyl-l-arginine) in the incubating medium reduces and NO donors (SIN-1, 300 microM spermine suppress, NONOate 100 microM) increases ET levels in pancreatic slices from C and D animals. PGE(2) (10(-7) M) increases and indomethacin (10(-6) M) decreases ET pancreatic production only in D but not in C tissues when added into the incubating bath. When tissues are incubated in the presence of endothelin 1 (ET-1) (10(-7) M), NOS activity is higher in C pancreas, while the ET-receptor antagonist bosentan (B) decreases NOS levels in D but not in C tissues. When pancreatic arachidonic acid (AA) conversion to prostaglandins was explored, ET-1 increased PGF(2alpha), PGE(2), and TXB(2) levels in C but not in D tissues. B abolishes TXB(2) increment due to the diabetic state, but failed in modulating AA conversion to 6-keto PGF(1alpha), PGF2(alpha) and PGE(2) in D pancreas. Our results show an alteration in AA metabolism, ET production, and NO increment associated with pancreatic damage due to streptozotocin.

Minoxidil and male-pattern alopecia: a potential role for a local regulator of sebum secretion with vasoconstrictive effects?

Regulation of the hair cycle takes place at the pilo-sebaceous unit with the sebaceous gland as a sex hormone-dependent part. Although minoxidil stimulates proliferation of follicular cells and activation of prostaglandin endoperoxide synthase-1, it was suggested that other mechanisms, such as an increase in the local blood flow, might mediate the drug effect on hair growth. If that is the case, it is possible that minoxidil counteracts some vasoconstrictive mediator of male-pattern alopecia. This hypothetical vasoconstrictive mediator X would have to meet some criteria: (I) vasoconstriction both in the general circulation and in the hair-growing skin; (II) local vasoconstrictive activity in the hair growing skin should be related to the circulating testosterone level; (III) only an increase in the local mediator X activity causes male-pattern alopecia, since hypertensive patients are not balder than expected. The sebaceous gland is a possible place of the mediator X secretion since it is a sex-hormone-dependent part of the pilo-sebaceous unit. ET-1 might be a suitable candidate for the mediator X, since male hormones raise ET-1 plasma levels and female hormones lower them. The speculation presented here is that ET-1, beside vasoconstriction in the general circulation, might also regulate the sebum secretion, by triggering contractions of the myoepithelial cells. This hypothetical mechanism would normally remain confined to the sebaceous gland. During puberty, sex hormones stimulate growth of sebaceous glands in both sexes. In women hypertrophied sebaceous glands under estrogen control would not increase its ET-1 content, while in men, testosterone would increase ET-1 secretion that might affect the neighboring arterioles. Induced vasoconstriction might reduce the hair growth and promote hair loss. If ET-1 plays the described role, then an ET-1 antagonist, i.e. bosentane, should also have some hair-growing properties.

ET-1 induces pancreatitis-like microvascular deterioration and acinar cell injury

Using in vivo microscopy red blood cell (RBC) velocities, functional capillary density (FCD) and capillary diameters were estimated after inducing acute pancreatitis by intraductal infusion of sodium taurocholate (0.8 ml; 4%) or after topical superfusion of the pancreas with ET-1 (100 pmol). Sodium taurocholate mediated a significant decrease in RBC velocities between 50 and 70%, transient decrease in capillary diameters by 10%, and a sustained decrease in FCD between 60 and 70% paralleled by a dramatic heterogeneity in blood flow. Topical superfusion of the exteriorized pancreas with ET-1 caused a significant decrease in RBC velocities between 65 and 75%, a sustained decrease in capillary diameters by 10%, and a decrease in FCD by 45% accompanied by an increase in flow heterogeneity. Following sodium taurocholate infusion pancreas histology revealed a severe edema and sublobular acinar cell necrosis, while topical ET-1 application displayed a severe edema of the pancreas with focal acinar cell necrosis. Thus, ET-1 mediated a deterioration of the pancreatic microcirculation, which is similar to the microcirculatory failure found in sodium taurocholate-induced experimental pancreatitis and was associated with focal acinar cell necrosis. We are thus inclined to hypothesize that endothelin released by injured endothelial cells during acute biliary pancreatitis promotes microcirculatory failure and ischemia in acute pancreatitis, eventually leading to acinar cell necrosis.

Effect of diaspirin cross-linked hemoglobin on normal and postischemic microcirculation of the rat pancreas

Microcirculatory alterations with reduced nutritive supply to the pancreas could be the cause of hyperamylasemia, which occurs in some patients receiving the vasoactive oxygen carrier diaspirin cross-linked hemoglobin (DCLHb) in clinical studies. Therefore, the effects of DCLHb on rat pancreas microcirculation were evaluated. Anesthetized Sprague-Dawley rats received one of the following treatments during baseline conditions (n = 7 rats/group): 10% hydroxyethyl starch (HAES) (0.4 ml/kg), DCLHb (400 mg/kg), or DCLHb (1,400 mg/kg). After 1 h of complete, reversible pancreatic ischemia, other animals received 10% HAES (0.4 ml/kg) or DCLHb (400 mg/kg) during the onset of reperfusion. The number of red blood cell-perfused capillaries (functional capillary density, FCD) and the level of leukocyte adherence in postcapillary venules in the pancreas were assessed by means of intravital microscopy during 2 h after treatment. In the nonischemic groups, FCD was 18% greater after DCLHb (1,400 mg/kg) than after 10% HAES treatment without any increase in leukocyte adherence. In the inschemia-reperfusion (I/R) 10% HAES group, FCD was significantly (P < 0.05) lowered, leukocyte adherence enhanced, and mean arterial pressure (MAP) reduced by 31% compared with nonischemic animals. DCLHb treatment in the I/R group resulted in a slight increase in FCD, a significant (P < 0.05) reduction of leukocyte adherence, and a complete restoration of MAP compared with the animals of the I/R control group. Thus our data provide no evidence for a detrimental effect on the pancreatic microcirculation or an enhanced risk of postischemic pancreatitis by DCLHb.

Endothelin receptor blockade improves fluid sequestration, pancreatic capillary blood flow, and survival in severe experimental pancreatitis

OBJECTIVE

To evaluate the effect of a new endothelin receptor antagonist (ET-RA) on the course of severe experimental pancreatitis.

BACKGROUND

Endothelin-1 has been shown to reduce regional blood flow in various organs, including the pancreas, and to aggravate cerulein-induced mild pancreatitis.

METHODS

Acute necrotizing pancreatitis (ANP) was induced in rats by standardized intraductal bile acid infusion and cerulein hyperstimulation. Serum trypsinogen activation peptides (TAP) were measured to verify comparable disease severity. Starting 6 hours after the onset of ANP, animals randomly received either saline or the new ET-RA LU-135252. Monitoring included cardiorespiratory parameters, urine output, hematocrit, and TAP levels. After 24 hours, animals were relaparotomized to determine pancreatic capillary blood flow and to assess the amount of free intraabdominal fluid and acinar cell necrosis. Survival was determined in a second set of experiments on 24 animals observed for 48 hours after pancreatitis induction and treatment with either normal saline or ET-RA.

RESULTS

Comparable TAP increases confirmed equally severe ANP in both groups before treatment. Treatment with ET-RA significantly reduced the mortality rate, from 50% in untreated animals to 8%. Improved survival was associated with significantly decreased hematocrit, improved urinary output, decreased ascites, and increased pancreatic capillary blood flow. There were no significant differences in plasma TAP and acinar cell injury in the surviving animals of the two treatment groups.

CONCLUSION

Therapy with the new ET-RA reduces the early mortality rate in experimental ANP, probably by reducing fluid sequestration and improving microcirculation.

Endothelin-1 infusion inhibits plasma insulin responsiveness in normal men

OBJECTIVES

Elevated plasma endothelin (ET)-1 levels have been described in insulin-resistant states such as syndrome X, obesity, non-insulin-dependent diabetes mellitus, and in some studies in essential hypertension. To investigate whether increases in circulating ET-1 to levels observed in insulin-resistant states can modulate insulin levels and/or insulin sensitivity in humans, we assessed these variables during low, non-pressor-dose ET-1 compared with placebo infusion.

DESIGN

In a randomized, single blind, crossover design, 10 lean normotensive male subjects received either an intravenous infusion of subpressor doses of ET-1 dissolved in polygeline or a control infusion of polygeline only (placebo). Using dynamic assessment by the minimal model approach with the modified frequent sampling intravenous glucose tolerance test (FSIGT) the following and other parameters were measured: insulin sensitivity; acute insulin response to glucose (AIR(G)) calculated as the average of the three peak values between 2 and 5 min after injection of glucose from which the basal insulin levels were subtracted; the initial area under the curve (AUC(1-19)) from insulin values between time 0 and 19 min and the first-phase insulin secretion (phi1) from insulin kinetics parameters.

RESULTS

ET-1 infusion reduced AIR(G) (to 34.85 +/- 4.27 compared with 49.3 +/- 6.9 microU/ml during placebo, P=0.017) and the acute C-peptide response to glucose (to 2.33 +/- 0.41 compared with 3.1 +/- 0.44 ng/ml, P=0.018), decreased plasma insulin levels during the FSIGT compared with placebo (analysis of variance P<0.0001) and decreased the AUC(1-19) (to 2.1 +/- 0.2 compared with 2.9 +/- 0.3 U/l per 20 min, P<0.01) while phi1 tended to be lower. S1 measured during ET-1 infusion was unaltered (11.11 +/- 1.91 x 10(-4) versus 10.88 +/- 2.11 10(-4)/min per mU per l, NS).

CONCLUSIONS

These findings demonstrate that an increase in circulating ET-1 to levels observed in insulin-resistant states acutely diminishes the insulin secretory response but does not significantly modify insulin sensitivity.

Endothelin-1 mediates the alcohol-induced reduction of pancreatic capillary blood flow

Increased plasma endothelin-1 (ET-1) levels in rats after alcohol administration and increased endothelin receptor expression in the pancreas in chronic alcoholic pancreatitis have led to the hypothesis that ET-1 may play a critical role in the pathogenesis of ethanol-induced pancreatic injury through impairment of perfusion. To further test the hypothesis that ET-1 mediates an alcohol-induced reduction of pancreatic perfusion, the present study compares the effect of intravenous alcohol and ET-1 on pancreatic capillary blood flow (PCBF) and investigates whether endothelin receptor blockade prevents the alcohol-induced reduction in PCBF. Anesthetized rats were randomly assigned to receive one of the following: a 1-hour infusion of 2 g/kg alcohol or the volume equivalent of saline solution plus ET-1 (1.25 microgram/kg), a specific endothelin-A receptor antagonist (50 mg/kg), or saline solution (volume equivalent). The pancreas was exposed for intravital microscopy; PCBF was determined at the same location before the test solutions were given, after the infusion, and 1 hour thereafter. Alcohol and ET-1 significantly decreased PCBF from 2.0 nl/min/cap to 1.7 nl/min/cap. The reduction in PCBF was even more pronounced when alcohol and ET-1 were combined (1.5 nl/min/cap), whereas the ET receptor antagonist increased PCBF in saline-treated rats to 2.2 nl/min cap and maintained stable PCBF in alcohol-treated animals. The observation that PCBF is reduced by both alcohol and ET-1 and that the alcohol-induced reduction of PCBF can be aggravated by ET-1 and prevented by a specific endothelin-1 antagonist supports the hypothesis that ET-1 is the mediator of the alcohol-associated reduction of pancreatic perfusion.

An ETa/ETb endothelin antagonist ameliorates systemic inflammation in a murine model of acute hemorrhagic pancreatitis

BACKGROUND

Endothelin peptides are polykines with strong vasoconstrictor properties. We have previously shown that endothelin antagonism (PD145065) reduces the local severity of acute pancreatitis. We now investigated the effect of endothelin antagonism on systemic inflammation in a model of acute hemorrhagic pancreatitis.

METHODS

Forty-two mice were divided into four groups. Group 1 was fed standard food plus PD145065 every 8 hours. Group 2 was fed a choline-deficient ethionine (CDE) supplemented diet and given saline every 8 hours. Group 3 was fed a CDE diet and treated with PD145065 every 8 hours from initiation of diet. Group 4 was fed a CDE diet and given PD145065 from 48 hours after initiation of diet. Animals were killed at 70 hours. Serum was collected. Pancreata and lung tissue were harvested.

RESULTS

Histology score, serum amylase level, lung myeloperoxidase, and interleukin (IL)-10 were all significantly reduced in both treatment groups (groups 3 and 4) (p < 0.05). IL-6 levels were reduced in group 3 only (p < 0.05). The mortality rate did not differ among any of the groups.

CONCLUSIONS

Endothelin antagonism decreased the severity of acute pancreatitis and reduced markers of systemic inflammation. Late treatment at 48 hours failed to prevent the rise in IL-6. Mortality rates were unaffected by treatment.

Expression of endothelin-1 in pancreatic tissue of patients with chronic pancreatitis

Chronic pancreatitis is characterized by the presence of an inflammatory infiltrate, progressive destruction of acinar cells, and fibrosis. The finding that endothelin-1, an endothelium-derived peptide with vasoconstrictive and mitogenic properties, reduces pancreatic blood flow in normal rats suggested that the peptide may be associated with the reduced pancreatic flow seen in animal models of chronic pancreatitis and in the morphological abnormalities of the disease. The aim of this study was to investigate sites of endothelin-1 expression in the pancreas of normal subjects and patients with chronic pancreatitis. The techniques of immunohistochemistry, in situ hybridization, and Northern blotting were used. Endothelin-1-like immunoreactivity was localized predominantly to islet cells both in normal subjects and in patients with chronic pancreatitis. Semi-quantitative analyses of immunostaining showed that endothelin-1-like immunoreactivity in islet cells of patients with chronic pancreatitis was greater than in normal subjects. Co-localization studies with glucagon, insulin, somatostatin, and pancreatic polypeptide showed that endothelin-1-like immunoreactivity co-exists with glucagon and insulin. There was no apparent co-existence of endothelin-1-like immunoreactivity with somatostatin or pancreatic polypeptide. Endothelin-1 mRNA was expressed in sites similar to those of the immunostaining, as well as in vascular endothelial cells. Northern blot analysis showed an increase in the expression of endothelin-1 mRNA in the patient population. There was a significant correlation between intensity of endothelin-1 immunostaining and severity of fibrosis in the patients with chronic pancreatitis. These findings suggest that an elevation in local expression of endothelin-1 may be associated with the morphological and haemodynamic changes of chronic pancreatitis.

Protective effects of endothelin-1 on acute pancreatitis in rats

Endothelin-1, a 21-residue peptide isolated from vascular endothelial cells, has a broad spectrum of actions. To clarify the involvement of endothelin-1 in acute pancreatitis, we examined the effects of endothelin-1 and its receptor antagonist BQ-123 on cerulein-induced pancreatitis in rats. Rats were infused intravenously with heparin-saline (control), endothelin-1 (100 pmol/kg/hr), cerulein (5 micrograms/kg/hr), or cerulein plus endothelin-1 for 3.5 hr. In another experiment, cerulein or cerulein plus BQ-123 (3 mg/kg/hr) was infused. Infusion of cerulein caused hyperamylasemia and pancreatic edema. Endothelin-1, when infused with cerulein, decreased the extent of pancreatic edema with a significant increase in the pancreatic dry- to wet-weight ratio. Histological changes induced by cerulein were markedly attenuated when endothelin-1 was given with cerulein. In contrast, endothelin-receptor blockade with BQ-123 further augmented pancreatic edema caused by cerulein. The extent of inflammatory cell infiltration was greater than BQ-123 was given with cerulein. Endothelin-1 or BQ-123 had no influence on hyperamylasemia. This study suggests that endothelin-1 has protective effects on experimental acute pancreatitis.

Effect of endothelin-1 on the development of hemorrhagic pancreatitis in rats

BACKGROUND

It has been hypothesized that microcirculatory disturbance plays an important role in the development of severe pancreatitis. In this study we investigated the effects of exogenous endothelin-1 on the development of severe pancreatitis in rats.

METHODS

Acute pancreatitis was induced by two intraperitoneal injections of cerulein (10 micrograms/kg body weight). Endothelin-1 was administered via an abdominal aortic catheter as a bolus of 250-750 pmol/kg BW every hour for 4 h.

RESULTS

Remarkable morphologic changes in the pancreas, including hemorrhage, and increases in serum amylase level and active elastase content in pancreatic tissue were observed in rats treated with cerulein plus endothelin-1 in a dose-dependent manner 5 h after the first cerulein injection. Local pancreatic blood flow decreased significantly, and microcirculatory disturbances in the pancreas were demonstrated.

CONCLUSIONS

These results suggest that endothelin-1 causes pancreatic microcirculatory disturbance and might be a contributing factor in the aggravation of acute pancreatitis.