Decrease In Functional Capillary Density Research Articles

Pathophysiological Role of Endothelins in Pulmonary Microcirculatory Disorders Due to Intestinal Ischemia and Reperfusion

Background. This study was conducted to investigate pulmonary microcirculatory disorders caused by intestinal ischemia reperfusion (IIR), and the pathophysiological roles of endothelin (ET) in acute lung injury (ALI).Methods. Male rats were pretreated with normal saline or a nonselective ET receptor antagonist (TAK-044) and subjected to IIR (60 min of intestinal ischemia and 180 min of reperfusion). The right upper lobe of the lung was examined by intravital confocal microscopy.Results. The size of arterioles and venules was not significantly reduced during IIR, but the functional capillary density (FCD) decreased significantly. TAK-044 improved the pulmonary microhemodynamics, inhibiting the accumulation of leukocytes, the pulmonary edema, and the decrease of FCD.Conclusions. In the early stage of IIR, pulmonary microhemodynamics seemed more likely to be disturbed by the decrease of FCD, than by arteriolar or venular vasoconstriction. ETs decrease the FCD, promoting the interaction between leukocytes and pulmonary vessels.

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.

Exocrine, but not endocrine, tissue is susceptible to microvascular ischemia/reperfusion injury following pancreas transplantation in the rat.

While post-transplant pancreatitis is still a frequently occurring complication of whole pancreas transplantation, dysfunction of the endocrine tissue is rarely observed. Given that microcirculatory disorders play a major role in the pathogenesis of pancreatitis, we hypothesized a dissociation of endocrine and exocrine microvascular control in pancreas transplantation (cold ischemia-reperfusion) and studied this dissociation quantitatively, analyzing the pancreatic microcirculation after heterotopic isogeneic pancreaticoduodenal transplantation in rats by means of fluorescence microscopy. Functional capillary density (FCD) of both exocrine and endocrine tissue of pancreatic grafts after 1 h of cold storage in HTK solution did not differ when compared to sham-operated, time-matched controls. Intermittent capillary perfusion, which is absent under sham control conditions and which is proposed to be operative as a compensatory mechanism to counteract malperfusion, was observed in 52% of the exocrine, but in only 8% of the endocrine, tissue studied (p < 0.05). In contrast, cold storage of pancreatic grafts for 6 h in HTK resulted in a complete loss of intermittent capillary perfusion in exocrine tissue and, consequently, marked exocrine perfusion failure (decrease in FCD), while FCD of pancreatic endocrine tissue was preserved without any significant change in the incidence of intermittent capillary perfusion. Thus, our results indicate a higher susceptibility of the exocrine pancreas to cold ischemia/reperfusion events that is associated with significant alterations in nutritive perfusion and, thus, with limitations of the oxygen supply to the tissue. This may lead to inflammatory tissue reactions in the clinical setting of pancreas transplantation.

Somatostatin attenuates microcirculatory impairment in acute sodium taurocholate-induced pancreatitis.

Using in vivo microscopy, red blood cell (RBC) velocities, functional capillary density (FCD), and overall changes in capillary blood flow (PI) were estimated following intraductal infusion of sodium taurocholate (0.8 ml; 4%) alone or in combination with systemic administration of somstostatin (single bolus SMS 100 microg/100 g body wt). Sodium taurocholate mediated a significant transient decrease in RBC velocities and a sustained decrease in FCD, which were paralleled by dramatic flow heterogeneity. Therefore, a significant reduction in overall capillary blood flow was calculated. Additional SMS treatment reduced microcirculatory impairment as expressed by reduction of blood flow heterogeneity, a less rarified functional capillary density, and a recovery of RBC velocities and acinar capillary overall perfusion to control values. As a result of this microcirculatory improvement, pancreas histology revealed slightly less severe tissue damage compared to the non-SMS-treated pancreatitis group. These findings demonstrate that exogenous SMS infusion can improve microcirculatory failure in acute biliary pancreatitis, which should have a beneficial effect on the course of the disease.

Acute pancreatitis in rats: effects of sodium taurocholate, CCK-8, and Sec on pancreatic microcirculation.

With use of in vivo microscopy, pancreatic duct permeability, red blood cell (RBC) velocities, functional capillary density (FCD), and overall changes in capillary blood flow (perfusion index) were estimated after intraductal infusion of sodium taurocholate (0.8 ml, 4%) alone or in combination with systemic administration of cholecystokinin (CCK, 0.3 microg/100 g body wt) or secretin (Sec, 10 microg/100 g body wt). Sodium taurocholate mediated a significant increase in pancreatic duct and capillary permeability within 105 +/- 26 s followed by a transient decrease in RBC velocities and a sustained decrease in FCD, which were paralleled by dramatic flow heterogeneity. Therefore, a significant reduction in overall capillary blood flow was calculated. CCK stimulation aggravated the microcirculatory failure due to a decrease in RBC velocities, which was accompanied by an increase in acinar cellular necrosis. Sec stimulation attenuated microcirculatory failure due to a more moderate reduction of FCD. The enhanced pancreatic duct and capillary permeability, which enables free diffusion of pancreatic digestive enzymes into the parenchyma, is the initiating event in acute biliary pancreatitis, causing microcirculatory failure and tissue damage. The microcirculatory changes are secondary and a propagating factor for the development of acini necrosis. Stimulation with CCK worsened the course of acute biliary pancreatitis.

Hemorrhagic hypotension induces arteriolar vasomotion and intermittent capillary perfusion in rat pancreas.

Hemorrhage-induced intermittent capillary perfusion and its relation to arteriolar vasomotion was studied in rat pancreatic acinar tissue using intravital fluorescence microscopy. During prehemorrhage conditions, microscopic analysis of the pancreatic microcirculation displayed neither arteriolar vasomotion nor intermittency of capillary perfusion (n = 22 animals). Hemorrhage-induced hypotension of 40 mmHg provoked arteriolar vasomotion in 18 of 22 animals and 59 of 115 arterioles studied. The maximum relative amplitude of arteriolar vasomotion was 44 +/- 8% (range 12-81%), and vasomotion frequency averaged 4.73 +/- 0.11 cycles/min. Hemorrhagic hypotension was further accompanied by 1) a decrease of functional capillary density [length of red blood cell-perfused capillaries per area of tissue under investigation (cm/cm2)] from 515 +/- 3 cm-1 at baseline to 386 +/- 3 cm-1 (P < 0.05) and 2) the instantaneous occurrence of intermittency of capillary perfusion in all observation areas (N = 220) of the 22 animals studied. The frequency of intermittency of capillary perfusion (4.72 +/- 0.14 cycles/min) did not differ from the frequency of arteriolar vasomotion, which implies a causal relationship between these two hemorrhage-induced microvascular mechanisms with the probable aim to counteract the decrease of functional capillary density.

Buflomedil hydrochloride attenuates tourniquet-induced microvascular reperfusion injury in striated muscle.

With the use of intravital fluorescence microscopy and the dorsal skinfold chamber model we studied the effect of buflomedil hydrochloride on microvascular reperfusion injury after 4 h of tourniquet-induced ischemia in hamster striated muscle. Animals (n = 15) received 3 mg/kg buflomedil (i.v. bolus) 5 min before onset of reperfusion, and 3 mg/kg buflomedil (continuous i.v. infusion) during the first 20 min of reperfusion. Animals (n = 13) receiving equivalent volumes of saline served as controls. Tourniquet-induced ischemia resulted in (a) a marked decrease of functional capillary density and (b) accumulation and adherence of leukocytes in postcapillary venules after 30 min and 2 h of reperfusion. This was associated with an increased microvascular permeability (leakage of macromolecules), reflecting the alteration of endothelial cell integrity. Treatment with buflomedil significantly reduced both post-ischemic capillary perfusion failure and leukocyte adherence in venules. Concomitantly, the increase of microvascular permeability in postcapillary venules was almost prevented, indicating the beneficial effect of buflomedil on the manifestation of microvascular reperfusion injury following tourniquet ischemia in striated muscle.