Capillary Cross-sectional Area Research Articles

The vascular footprint in cardiac homeostasis and hypertensive heart disease-A link between apelin receptor, vascular endothelial growth factor, and neuronal nitric oxide synthase.

Recent studies have suggested a connection between disturbances of the apelin system and various cardiac pathologies, including hypertension, heart failure, and atherosclerosis. Vascular endothelial growth factor is crucial for cardiac homeostasis as a critical molecule in cardiac angiogenesis. Neuronal nitric oxide synthase is an essential enzyme producing nitric oxide, a key regulator of vascular tone. The present study aims to shed light upon the complex interactions between these three vital signaling molecules and examine their changes with the progression of hypertensive heart disease. We used two groups of spontaneously hypertensive rats and age-matched Wistar rats as controls. The expression of the apelin receptor, vascular endothelial growth factor, and neuronal nitric oxide synthase were assessed immunohistochemically. We used capillary density and cross-sectional area of the cardiomyocytes as quantitative parameters of cardiac hypertrophy. Immunoreactivity of the molecules was more potent in both ventricles of spontaneously hypertensive rats compared with age-matched controls. However, capillary density was lower in both ventricles of the two age groups of spontaneously hypertensive rats compared with controls, and the difference was statistically significant. In addition, the cross-sectional area of the cardiomyocytes was higher in both ventricles of the two age groups of spontaneously hypertensive rats compared with controls, and the difference was statistically significant. Our study suggests a potential link between the apelin receptor, vascular endothelial growth factor, and neuronal nitric oxide synthase in cardiac homeostasis and the hypertensive myocardium. Nevertheless, further research is required to better comprehend these interactions and their potential therapeutic implications.

In Situ Microscopy Studies of Infused Megakaryocytes: Implications in Thrombopoiesis

The questions of whether thrombopoiesis - the release of platelets from megakaryocytes - occurs both as megakaryocytes emerge from the intramedullar space or occurs as well in the pulmonary vascular bed remains unanswered. Studies by Lefrançais E, et al, (Nature, 2017) demonstrated by in situ microcopy that perhaps 50% of all platelet release in mice occurs from megakaryocytes released from the marrow and traveled to the lungs where they undergo thrombopoiesis over a 20- to 60-minute time-period. We examined whether CD34+-derived human megakaryocytes infused into immunocompromized NSG mice would also shed platelets in the lungs in a similar fashion. We differentiated CD34+-derived hematopoietic stem-progenitors for 12 days in culture using conditions previously described (Wang Y, et al., Blood 2015). We found that unlike platelet-like-particle (PLP) formation in in vitro cultures of CD34+ hematopoietic progenitor cell (HPC)-derived (CD34+) megakaryocytes, which undergo asynchronous shedding of the PLPs, that over 95% of infused CD34+ megakaryocytes shed their platelets within the first 40 minutes much as has been observed for endogenous murine megakaryocytes. The average number of cytoplasmic extensions per megakaryocytes was ~2.7, again very similar to what was seen with endogenous murine megakaryocytes. In contrast, CD34+ cells grown in culture into megakaryocytes for a shorter period of time of only 7 days, poorly shed any cytoplasmic fragments. We also studied human megakaryocytes grown from immortalized megakaryocyte progenitor cell lines (imMKCLs) from induced pluripotent stem cells (iPSCs) generated by the Eto laboratory and kindly provided by Dr. Koji Eto, Kyoto University). These cells were grown and differentiated into terminal megakaryocytes as described (Nakamura S, Cell Stem Cell, 2014) for 4 days in culture. These cells have been proposed to be useful for large-scale preparation of PLPs in vitro for clinical use in place of donor-derived platelets. The resultant infused human imMKCL-derived megakaryocytes also synchronously shed platelets, but only 50% of the infused cells shed their cytoplasm in contrast to >95% of CD34+ megakaryocytes. Moreover, cytoplasmic extensions were decreased to an average of ~1.1 per megakaryocyte. We had proposed that in vitro-generated megakaryocytes might be directly infused into patients in place of further manipulating the megakaryocytes to release functional platelets in vitro using a bioreactor. However, such megakaryocytes will likely be contaminated with a higher level of HPCs than anticipated from in vitro-prepared platelets, and concern exists that they may lead to unacceptable graft versus host complications. We, therefore, examined whether irradiating megakaryocytes as one strategy to eliminate this concern results in megakaryocytes that are still functional and found that megakaryocytes irradiated with up to 25 Gy retain platelet yield per infused megakaryocytes with the platelets having the same half-life. If irradiated and kept in culture, these megakaryocytes begin to shed platelets and undergo apoptosis notably by 24 hours. We also examined whether the pulmonary bed differs from other vascular beds, and infused CD34+ megakaryocytes both intravenously and intra-arterially in parallel studies and found that following intra-arterial infusion, megakaryocytes were mostly entrapped in various organs, but shed few platelets. Thus, our studies suggest that the pulmonary bed is unique for platelet shedding from entrapped megakaryocytes. Whether this is due to the structural organization of the pulmonary beds, its endothelial lining, its reverse exchange in oxygen, carbon dioxide and pH from other capillary beds or the mechanical forces of inhalation and exhalation that expand and contract the capillary cross-sectional area needs to be examined. Our studies show that infused human megakaryocytes synchronously release platelets over a 40-minute window and can do so even after being irradiated and that this occurs specifically in the lungs not only has potential clinical application, but also raises biological questions about what determines thrombopoiesis-readiness and what are the features of the pulmonary bed that allows this synchronous release. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Muscle characteristics in chicks challenged with Salmonella Enteritidis and the effect of preventive application of the probiotic Enterococcus faecium

ABSTRACTThe present study was conducted to assess the effects of the probiotic Enterococcus faecium AL41 (EF) and of the enteric pathogen Salmonella Enteritidis PT4 (SE) on the development of posthatch pectoralis major muscle (PM) of broiler chicks. The four experimental groups were control (CON), EF, SE, and EF+SE (EFSE). EF and SE were given per os from days 1 to 7 and at day 4 posthatch, respectively. Muscle samples from 6 chicks per group were taken at day 8 (D8) and day 11 (D11) to evaluate PM myofiber growth, capillarization, DNA, RNA, and protein content, as well as enzyme activities (isocitrate dehydrogenase, lactate dehydrogenase, creatine kinase). PM growth rate was 7.45 ± 2.7 g/d in non-SE groups (CON, EF) and 5.10 ± 1.82 g/d in SE-infected groups (P < 0.02). Compared with group CON, application of bacteria (groups EF and SE) reduced the fiber cross-sectional area (246 and 262 vs. 347 ± 19 μm2) and the number of myonuclei per fiber (0.66 and 0.64 vs. 0.79 ± 0.03). At D11, hypertrophic myofiber growth normalized in the EF group, but negative effects persisted in SE and EFSE birds contributing to lower daily PM gain. In addition, SE infection strongly disturbed PM capillarization. Negative effects on capillary cross-sectional area and on the area (%) covered by capillaries persisted until D11 in the SE group, whereas pre-feeding of EF restored capillarization in the EFSE group to control levels. We conclude that supplementation of the probiotic bacteria EF AL41 had positive effects on PM capillarization and, thus, on delivery of O2, supply of nutrients, and removal of metabolites. Supplementation of probiotic bacteria might therefore reduce energetic stress and improve muscle health and meat quality during SE infection.

Improved diffusivity of NaOH solution in autohydrolyzed poplar sapwood chips for chemi-mechanical pulp production

This work investigated the changes in the physical structure of autohydrolyzed poplar sapwood chips and the effect on the subsequent alkali liquor diffusion properties for chemi-mechanical pulping (CMP). An alkali impregnation process was conducted by using the autohydrolyzed poplar sapwood with different levels of autohydrolysis intensity. The results showed that the volume porosity, water constraint capacity, and saturated water absorption of the autohydrolyzed poplar sapwood chips increased. Also, the effective capillary cross-sectional area (ECCSA) in the radial direction and the diffusion coefficients of NaOH solution in both the radial and axial directions all increased. Autohydrolysis pretreatment enhanced the alkali liquor diffusion properties in poplar sapwood chips, and the diffusion coefficient was increased more greatly in the radial direction than that in the axial direction.

Mixed-Mode Acrylamide-Based Continuous Beds Bearing tert-Butyl Groups for Capillary Electrochromatography Synthesized Via Complexation of N-tert-Butylacrylamide with a Water-Soluble Cyclodextrin. Part II: Effect of Capillary Size and Polymerization Conditions on Morphology and Chromatographic Efficiency

In this series, we investigate the impact of the complex formation constant of the hydrophobic monomer with respect to statistically methylated-β-cyclodextrin (Me-β-CD) on the electrochromatographic properties of highly crosslinked amphiphilic mixed-mode acrylamide-based monolithic stationary phases. In the first part, we investigated the retention properties. In the present study, we optimize the synthesis parameters with respect to obtainable morphology and separation efficiency. For this purpose, a series of mixed-mode acrylamide-based continuous beds bearing tert-butyl groups is synthesized under systematic variation of (i) the concentration of the lyotropic salt ammonium sulfate in the polymerization mixture and (ii) the dimension of the capillary. The impact of these parameters on the chromatographic efficiency is studied under isocratic conditions for alkylphenones in the reversed-phase mode via capillary electrochromatography with varied electric field strength. As expected, there is a strong impact of the concentration of ammonium sulfate in the polymerization mixture on the morphology (examined via scanning electron microscopy) and on the chromatographic efficiency, while there is only a minor influence when varying the size or the shape of the capillary cross-sectional area. Morphology and chromatographic efficiency of this new type of stationary phase are compared to those reported in our previous series. The studies reveal a significant influence of the formation constant of the formed inclusion complex on the morphology and the chromatographic efficiency for those monoliths having a large domain size, while there is an insignificant influence for those monoliths having a small domain size.

Effect of melatonin or maternal nutrient restriction on vascularity and cell proliferation in the ovine placenta

Previously we reported increased umbilical artery blood flow in ewes supplemented with melatonin from mid- to late-pregnancy, while maternal nutrient restriction decreased uterine artery blood flow. To further unravel these responses, this study was designed to assess placental cell proliferation and vascularity following supplementation with melatonin or maternal nutrient restriction. For the first experiment, 31 primiparous ewes were supplemented with 5mg of melatonin per day (MEL) or no melatonin (CON) and allocated to receive 100% (adequate fed; ADQ) or 60% (restricted; RES) of their nutrient requirements from day 50 to 130 of gestation. To examine melatonin receptor dependent effects, a second experiment was designed utilizing 14 primiparous ewes infused with vehicle, melatonin, or luzindole (melatonin receptor 1 and 2 antagonist) from day 62 to 90 of gestation. For experiment 1, caruncle concentrations of RNA were increased in MEL–RES compared to CON–RES. Caruncle capillary area density and average capillary cross-sectional area were decreased in MEL–RES compared to CON–RES. Cotyledon vascularity was not different across dietary treatments. For experiment 2, placental cellular proliferation and vascularity were not affected by infusion treatment. In summary, melatonin interacted with nutrient restriction to alter caruncle vascularity and RNA concentrations during late pregnancy. Although melatonin receptor antagonism alters feto-placental blood flow, these receptor dependent responses were not observed in placental vascularity. Moreover, placental vascularity measures do not fully explain the alterations in uteroplacental blood flow.

Fluorescence Microangiography for Quantitative Assessment of Peritubular Capillary Changes after AKI in Mice

AKI predicts the future development of CKD, and one proposed mechanism for this epidemiologic link is loss of peritubular capillaries triggering chronic hypoxia. A precise definition of changes in peritubular perfusion would help test this hypothesis by more accurately correlating these changes with future loss of kidney function. Here, we have adapted and validated a fluorescence microangiography approach for use with mice to visualize, analyze, and quantitate peritubular capillary dynamics after AKI. A novel software-based approach enabled rapid and automated quantitation of capillary number, individual area, and perimeter. After validating perfusion in mice with genetically labeled endothelia, we compared peritubular capillary number and size after moderate AKI, characterized by complete renal recovery, and after severe AKI, characterized by development of interstitial fibrosis and CKD. Eight weeks after severe AKI, we measured a 40%±7.4% reduction in peritubular capillary number (P<0.05) and a 36%±4% decrease in individual capillary cross-sectional area (P<0.001) for a 62%±2.2% reduction in total peritubular perfusion (P<0.01). Whereas total peritubular perfusion and number of capillaries did not change, we detected a significant change of single capillary size following moderate AKI. The loss of peritubular capillary density and caliber at week 8 closely correlated with severity of kidney injury at day 1, suggesting irreparable microvascular damage. These findings emphasize a direct link between severity of acute injury and future loss of peritubular perfusion, demonstrate that reduced capillary caliber is an unappreciated long-term consequence of AKI, and offer a new quantitative imaging tool for understanding how AKI leads to future CKD in mouse models.

The Morphological Changes in the Capillary Architecture of the Tibial Nerve Associated with Spontaneous Aging and Aerobic Exercise Intervention during Aging in Rats

[Purpose] Peripheral nerve degradation associated with aging is linked to failure of interactions in capillary metabolism. The aim of this study was to morphologically investigate the age-related changes in the capillary architecture of the tibial nerve in spontaneous aging and with aerobic exercise intervention in rats. [Subjects] Male Sprague-Dawley rats (n=15) were used in the present study. [Methods] The rats were divided into control (Cont, n=5), elderly (Elder, n=5), and elderly with aerobic exercise (Elder+Ex, n=5) groups. Aerobic training of low intensity was performed for 10 weeks using a treadmill starting at 96 weeks of age by the Elder+Ex group. The capillary diameter, cross-sectional area and number of microvascular ramifications in the tibial nerve were compared among the Cont (20-week-old), Elder (106-week-old) and Elder+Ex groups using three-dimensional images gained from confocal laser scanning microscopy. [Results] The capillary diameter, cross-sectional area and number of microvascular ramifications in the Elder group were significantly smaller than those observed in the Cont and Elder+Ex groups. [Conclusion] These findings suggest that the capillaries in the peripheral nerve degrade with spontaneous aging and that aerobic exercise of low intensity promotes angiogenesis, and protects the capillary from oxidative stress.

Correction to Klinkenberg slip theory for gas flow in nano-capillaries

Using a lattice Boltzmann (coarse grain) simulation of gas dynamics we show that the apparent permeability values of nano-scale capillaries could be significantly higher than those predicted by the Klinkenberg slip theory. The difference is due to kinetic effects of gas molecules that have gone through inelastic collisions with the capillary walls on those molecules that make up the bulk fluid in the capillary. The kinetic energy that the bouncing-back molecules have and the associated momentum carried to the bulk fluid is not a trivial matter in capillaries with diameter, h , less than 100 nm. Momentum carried by bouncing-back molecules amplifies the velocity profile developing across the diameter of the capillary. In a sense, it is not only the molecules interacting with the capillary wall that slip but also those interacting with the bulk fluid, i.e., double‐slip. The double-slip effect is shown using measured permeability data of two crushed nano-porous samples, Pyrophyllite, and three different shale samples at varying pore pressures. Using the simulation results, we propose a modification to the Klinkenberg equation. Our new double-slip Klinkenberg equation includes a characteristic length scale ( L Ke ) that is proportional to the kinetic energy per capillary cross-sectional area of the bouncing-back molecules by the capillary walls. The new length scale of the molecular kinetic effects in nano-capillaries is larger than the mean free path of the molecules. The double-slip Klinkenberg equation reduces to the classical equation for slip flow in large capillaries, i.e., h/ L Ke >> 1, and converges to the absolute permeability value at high pressure.

Improving Angiogenesis and Muscle Performance in the Ischemic Limb Model by Physiological Ischemic Training in Rabbits

The aim of this study was to test the effects of physiologic ischemic training on the performance of skeletal muscle in a pathologically ischemic limb models. Twenty-seven New Zealand white rabbits were randomly assigned to three groups: (1) those in the ischemia with cuff inflation training group received right femoral artery ligation and occlusion of blood flow in the left limb by 3 mins of cuff inflation followed by 5 mins of deflation, repeated three times; (2) those in the ischemia with isometric exercise training group received right femoral artery ligation and 4 mins of isometric contraction exercise ischemic training in the left limb followed by 10 mins of rest, repeated twice; (3) those in the sole ischemia group received right femoral artery ligation and no intervention in the left limb. Five weeks later, muscle endurance, resting blood flow, and collateral angiogenesis were examined. Capillary supply, types and cross-sectional areas of muscle fibers and cellular oxidative potential were also evaluated. Gastronomic endurance of rabbits in the cuff inflation training group was the best among the three groups (P < 0.01). Collateral circulation (P < 0.05), distribution of type I fibers (P < 0.01), and cross-sectional area of type IIB fibers (P < 0.05) were also significantly higher in the cuff inflation training group than in the sole ischemia group. Similar differences were recorded between the isometric exercise training and sole ischemia groups. The distribution of type IIA fibers was lower (P < 0.01) in the cuff inflation training group than in the isometric exercise training group. Distribution of type IIB was found to be significantly different between these two groups (P < 0.01). Physiologic ischemic exercise training can promote remote angiogenesis in the pathologic ischemic skeletal muscle and thus improve performance.

Perivascular fatty tissue at the brachial artery is linked to insulin resistance but not to local endothelial dysfunction

Different ectopic fat depots, such as visceral or hepatic fat, are known to affect whole body insulin sensitivity. It has recently been hypothesised that differences in perivascular adipose tissue (PVAT) mass around resistance vessels may also contribute to insulin resistance, possibly via direct vascular effects leading to reduced capillary cross-sectional area in the muscle, which in turn affects muscular blood flow and glucose uptake. Based on this, the aim of the present study was to test whether PVAT around conduit arteries (i.e. the brachial artery) influences NO bioavailability, expressed as flow-mediated dilation (FMD), or insulin sensitivity in humans in vivo. Insulin sensitivity was measured by OGTT in all 95 participants (59 women, 36 men; median age 47 years, range 19-66 years) and by the gold standard, a euglycaemic-hyperinsulinaemic clamp, in a randomly selected subgroup of 33 participants. Quantification of the different fat compartments, including PVAT around the brachial artery, was achieved by high-resolution magnetic resonance imaging (1.5 T). Blood flow and FMD were measured at the brachial artery using high-resolution (13 MHz) ultrasound, after 5 min of forearm occlusion. PVAT was negatively correlated with insulin sensitivity and the post-ischaemic increase in blood flow. The association between PVAT and insulin sensitivity (r = -0.54, beta = -0.37, p = 0.009) was independent of age, sex, visceral adipose tissue, liver fat, BMI and further cardiovascular risk factors. No correlation could be detected between PVAT and local endothelial function. However, we observed an independent association between PVAT and post-ischaemic increase in blood flow (r = -0.241; beta = -1.69; p = 0.02). PVAT seems to play an independent role in the pathogenesis of insulin resistance. This may be due to direct vascular effects influencing muscular blood flow.

Dynamics of the effective capillary cross-sectional area during the alkaline impregnation of eucalyptus wood

Abstract Wood diffusion is strongly affected by the effective capillary cross-sectional area (ECCSA), which is the area of paths available for diffusion. The ECCSA varies dynamically according to the conditions and progress of the alkaline action. The alkali diffusion in natural wood is a complex process in the course of which the local transport properties are modified by chemical reactions and swelling. A method was developed which allows the fast determination of ECCSA as a result of the dynamic process. It is based on measurements of the relative electrical conductivity through thin wood slices. It is assumed that restrictions in diffusion of thin slices can be neglected regardless of alkali action. The evolution of ECCSA was determined in transverse directions of eucalyptus wood. The influence of temperature, alkali concentration and time was established. As demonstrated earlier, alkalinity had a strong effect on the ECCSA at room temperature, which is dramatically increased when the pH is elevated from 12.5 to 13.5. At high temperatures, the steep increase in the ECCSA appears at pH 10.5. It was also demonstrated that the degree of the chemical action – indicated by the deacetylation level – is also very relevant, being even higher than the temperature effect.

The Effects of Pressure and Shear on Capillary Closure in the Microstructure of Skeletal Muscles

Deep tissue injury (DTI) is a severe pressure ulcer, which initiates in muscle tissue under a bony prominence, and progresses outwards. It is associated with mechanical pressure and shear that may cause capillaries to collapse and thus, induce ischemic conditions. Recently, some investigators stipulated that ischemia alone cannot explain the etiology of DTI, and other mechanisms, particularly excessive cellular deformations may be involved. The goal of this study was to evaluate the functioning of capillaries in loaded muscle tissue, using animal and finite element (FE) models. Pressures of 12, 37, and 78 kPa were applied directly to one gracilis muscle of 11 rats for 2 h. Temperatures of the loaded and contralateral muscles were recorded with time using infrared thermography (IRT) as a measure of the ischemic level. In addition, a non-linear large deformation muscle-fascicle-level FE model was developed and subjected to pressures of 12-120 kPa without and with simultaneous shear strain of up to 8%. For each simulation case, the accumulative percentage of open capillary cross-sectional area and the number of completely closed capillaries were determined. After 2 h, temperature of the loaded muscles was 2.4 +/- 0.3 degrees C (mean +/- standard deviation) lower than that of the unloaded contralateral limbs (mean of plateau temperature values across all pressure groups). Temperature of the loaded muscles dropped within 10 min but then remained stable and significantly higher than room temperature for at least 30 additional minutes in all pressure groups, indicating that limbs were not completely ischemic within the first 40 min of the trials. Our FE model showed that in response to pressures of 12-120 kPa and no shear, the accumulative percentage of open capillary cross-sectional area decreased by up to 71%. When shear strains were added, the open capillary cross-sectional area decreased more rapidly, but even for maximal loading, only 46% of the capillaries were completely closed. Taken together, the animal and FE model results suggest that acute ischemia does not develop in skeletal muscles under physiological load levels within a timeframe of 40 min. Since there is evidence that DTI develops within a shorter time, ischemia is unlikely to be the only factor causing DTI.

Placental Growth Throughout the Last Two Thirds of Pregnancy in Sheep: Vascular Development and Angiogenic Factor Expression1

Morphometric methodologies were developed and applied to investigate the patterns of vascular development in maternal (caruncular; CAR) and fetal (cotyledonary; COT) sheep placentas throughout the last two thirds of gestation. We also examined the expression levels of the major angiogenic factors and their receptors in CAR and COT sheep placentas. Although the vascularity of the CAR tissues increased continuously from Day 50 through Day 140 of pregnancy, those of the COT tissues increased at about twice the instantaneous rate (i.e., the proportionate increase/day) of the CAR. For CAR, vascularity increased 2-fold from Day 50 through Day 140 via relatively small increases in capillary number and 2- to 3-fold increases in capillary diameter. For COT, the increased vascularity resulted from a 12-fold increase in capillary number associated with a concomitant 2-fold decrease in capillary diameter. This large increase in fetal placental capillary number, which was due to increased branching, resulted in 6-fold increases in total capillary cross-sectional area and total capillary surface, per unit of COT tissue. Different patterns of expression of the mRNAs for angiogenic factors and their receptors were observed for CAR and COT. The dilation-like angiogenesis of CAR was correlated with the expression of vascular endothelial growth factor receptor-1 (FLT1), angiopoietin-2 (ANGPT2), and soluble guanylate cyclase (GUCY1B3) mRNAs. The branching-like angiogenesis of COT was correlated with the expression of vascular endothelial growth factor (VEGF), FLT1, angiopoietin-1 (ANGPT1), ANGPT2, and FGF2 mRNAs. Monitoring the expression of angiogenic factors and correlating the levels with quantitative measures of vascularity enable one to model angiogenesis in a spatiotemporal fashion.

An electrokinetic cell model for analysis and optimization of electroosmotic microfluidic pumps

A simple bead packed electroosmotic microfluidic pump has been designed and fabricated. Such pumps can generate pressure of over 10 atm and are amenable to integration with other microfluidic components, thus making these pumps highly attractive for lab-on-a chip devices. An analytical theoretical description for such packed beads micropumps is presented. It is based on the cell models for hydrodynamic and electrokinetic transport in complex porous media. The theoretical analysis yields useful relationships between the parameters of the pump (bead size, capillary size, electrokinetic ζ-potential) and its performance (pressure and flow) rate and hence, provides guidelines for optimal design for desired properties. We found that the generated pressure strongly depends on the bead size. It also increases with the bead ζ-potential, volume fraction and capillary length. The flow rate on the other hand is not an explicit function of the bead size, but depends on the overall capillary cross-sectional area. This allows for independently varying of these two essential properties. The theory was tested against model experiments, thus proving its validity, range of applicability and limitations.

A fractal analysis of the radial distribution of bronchial capillaries around large airways

We analyzed published measurements of the bronchial circulation and airway wall (Anderson JC, Bernard SL, Luchtel DL, Babb AL, and Hlastala MP. Respir Physiol Neurobiol 132: 329-339, 2002) and determined that the radial distribution of bronchial capillary cross-sectional area was fractal. We limited our analysis to bronchial capillaries, diameter < or =10 mum, that resided between the epithelial basement membrane and adventitia-alveolar boundary, the airway wall tissue. Thirteen different radial distributions of capillary-to-tissue area were constructed simply by changing the number of annuli (i.e., the annular size) used to form each distribution. For the 13 distributions created, these annuli ranged in size from to of the size of the airway wall area. Radial distributions were excluded from the fractal analysis if the sectioning procedure resulted in an annulus with a radial thickness less than the diameter of a capillary. To determine the fractal dimension for a given airway, the coefficient of variation (CV) for each distribution was calculated, and ln(CV) was plotted against the logarithm of the relative piece area. For airways with diameter >2.4 mm, this relationship was linear, which indicated the radial distribution of bronchial capillary cross-sectional area was fractal with an average fractal dimension of 1.27. The radial distribution of bronchial capillary cross-sectional area was not fractal around airways with diameter <1.5 mm. We speculated on how the fractal nature of this circulation impacts the distribution of bronchial blood flow and the efficiency of mass transport during health and disease. A fractal analysis can be used as a tool to quantify and summarize investigations of the bronchial circulation.

Histomorphometric characterisation of shared and non-shared villus territories in monochorionic (MC) twin placentae

Flow and physiological data suggest there is reduced flow in shared vs. non-shared cotyledons. We hypothesised that there are histomorphometric differences in terminal villus architecture in MC twins. Placentae from uncomplicated MCDA twins and those discordant for IUGR and twin–twin transfusion syndrome (TTTS) were injected immediately after delivery to demonstrate vascular anastomoses and immersion-fixed. Tissue blocks taken from representative areas of shared and non-shared cotyledons were analysed histomorphometrically by image analysis software. Fifty terminal villus cross-sections were examined from each block of co-twin territory and shared cotyledons. Villus diameter, villus cross-sectional area, capillary diameter, capillary cross-sectional area and the percentage of villus cross-sectional area occupied by villus capillaries were calculated and parameters were compared between the groups. In the uncomplicated MCDA twins, the terminal villi in the normal cotyledons of the smaller twins had significantly fewer, smaller capillaries compared to the shared and normal cotyledons of the larger twins. In those complicated by TTTS and discordant for IUGR, the terminal villi in the shared cotyledons had significantly fewer and smaller capillaries compared to the normal cotyledons of the smaller and larger twins. This is consistent with reduced flow rate in the shared cotyledons compared to the normal cotyledons.

Oxidative Stress and Cardiac Microvascular Structure in Ischemia and Reperfusion: The Protective Effect of Antioxidant Vitamins

Reperfusion of the ischemic myocardium results in structural changes in the capillary bed, which may contribute to decreased microcirculatory flow (“no reflow”). This study was designed to correlate the endothelial cell shape changes with both oxidative stress and lipid peroxidation and to evaluate the beneficial potential of Trolox (a hydrophilic analogue of α-tocopherol) and ascorbic acid. Isolated buffer-perfused rat hearts were made ischemic for 45 min and then reperfused with 100 μM Trolox and/or 100 μM ascorbic acid. Morphological changes were quantified by measuring capillary cross-sectional areas. Increased myocardial content of oxidized glutathione and its release into the coronary effluent were used as indices of oxidative stress. Myocardial MDA, an end product of lipid peroxidation, was also measured. Luminal membrane blebs and capillary “constriction” in the ischemic groups occurred when there was no change in either glutathione status or MDA concentrations. Reperfusion altered the redox state of the heart sufficiently to induce lipid peroxidation. It also induced endothelial cell swelling and a reduction in luminal area. Ascorbic acid was a more effective antioxidant than Trolox as it significantly reduced both oxidative stress and ultrastructural injury. The combined antioxidant treatment returned both the stress ratio and the capillary measurements to control values. We conclude that endothelial cell swelling correlates with the degree of oxidative stress and that antioxidant vitamins reduce membrane damage by preventing lipid peroxidation.

Ultrastructural and Morphometric Comparison of Retinal and Myocardial Capillaries Following Acute Ischaemia

The recovery of any tissue following a period of ischaemia is dependent on a patent microvasculature to restore blood flow. In the ischaemic myocardium, a reduction in capillary cross-sectional dimensions occurs, which is likely to contribute to “no-reflow” injury. Clinical and experimental evidence indicates that the retina is able to tolerate moderate periods of ischaemia without significant loss of function. The aim of the present study is to test the hypothesis that, as an end-arterial system, the retina possesses compensatory processes to maintain a functional microcirculation following acute ischaemia. Thirty minutes of no-flow global ischaemia was induced in isolated hearts of Wistar rats without reperfusion. The retina was also made ischaemic for 30 min using two experimental models: microsphere embolization and anoxic superfusion. Changes in capillary dimensions were assessed by ultrastructural morphometry. Following 30 min of myocardial ischaemia capillaries appeared swollen with a significant reduction in total capillary and luminal cross-sectional area. By contrast, ischaemic retinal capillaries showed minimal morphological changes and no significant alteration in dimensions. We have demonstrated notable differences in the response of retinal and myocardial microvessels to acute ischaemia. It is likely that the maintenance of capillary patency following short periods ischaemia in the retina is part of an adaptive mechanism to protect visual function.

Changes in the Actin Cytoskeleton of Cardiac Capillary Endothelial Cells during Ischaemia and Reperfusion: The Effect of Phalloidin on Cell Shape

A reduction in capillary dimensions has been demonstrated in postischaemic reperfusion in the heart. The aim of this study was to demonstrate that in ischaemia and ischaemia followed by reperfusion, the change in shape of the constituent endothelial cells can be inhibited by phalloidin which stabilises the actin microfilament system. Isolated, perfused rat hearts were made globally ischaemic both with and without reperfusion and in the presence or absence of phalloidin. Changes in ischaemic endothelial cell dimensions were quantified by measuring whole capillary and luminal cross-sectional areas, abluminal and luminal membrane lengths. The distribution of β-actin within the endothelial cells was determined by immunocytochemistry. In control hearts, β-actin is distributed throughout the endothelium with a slight increase towards the luminal membrane. In ischaemia, this was more marked and other patterns of actin distribution were also observed. After reperfusion, a ‘double ring’ of actin could be distinguished. With phalloidin, the actin staining was more regular and the ring pattern was not observed. Morphometry showed that phalloidin was more effective in reducing endothelial cell shape change after reperfusion than after ischaemia alone. We conclude that endothelial cell shape change on reperfusion can be modified by agents which target the contractile proteins.