Functional organization of cerebral microvasculature in a marsupial, the northern quoll (Dasyurus hallucatus)

Capillaries within the central nervous system (CNS) of eutherian mammals form meshworks with numerous anastomoses, whereas capillaries in the CNS of marsupials consist entirely of hairpin-like loops, without anastomotic interconnections. Counter-current blood flow in capillary loops may have been important in the evolutionary development of a cerebral vascular supply. However, loops are not found in eutherian mammals, perhaps because of a limited benefit to the diffusive conductance of gases.     

Follicular microvasculature in the porcine ovary

The microvasculature of porcine ovaries, with special regard to the follicles in the interstitial-stromal tissue, was studied by scanning electron microscopy (SEM) of vascular corrosion casts. Porcine ovaries displayed several coiled arteries in the hilus and many branches with small diameters and a tightly spiraling configuration in the cortical areas. However, small arterioles became straight before entering vascular complexes of follicles and finally divided into capillaries. Vascular baskets of various sizes (150-9,900 micro m in diameter) and architecture related to follicles in various developmental stages were observed in the ovarian cortex. Small follicles (150-300 micro m in diameter) began with a polygonal meshwork of a few large capillary meshes and developed to an obvious spherical microvascular network with a thin single layer of capillaries when reaching 500-700 micro m in diameter. The microvascular architecture of follicles 1,000-2,000 micro m in diameter developed further and had a three-layer vascular plexus. With a diameter of more than 2,000 micro m, the microvasculature of antral follicles was arranged as an inner vascular plexus of about 25 micro m, a middle plexus of about 100 micro m, and an outer capillary plexus of about 30 micro m in thickness. The present observations indicate that follicular vascular baskets of diverse sizes and architecture in various developmental stages support the gradual increase of follicular blood flow during follicle growth in the pig.     

Hypophyseal angioarchitecture of common tree shrew (Tupaia glis) revealed by scanning electron microscopy study of vascular corrosion casts.

The vascular corrosion cast technique in conjunction with scanning electron microscopy (SEM) was used for the study of pituitary microvascularization in the common tree shrew (Tupaia glis). The pituitary vascular casts were obtained by infusion of low viscosity methyl methacrylate plastic (Batson's no.17) mixture. It was found that the blood supplies to the pituitary complex were from branches of the circle of Willis and could be divided into two groups. The first group consisted of two to four superior hypophyseal arteries (SHAs) branching off from the internal carotid artery supplying each half of the median eminence (ME), infundibular stalk (IS), and pars distalis (PD). The SHAs supplying the ME branched into internal and external capillary plexi. The internal plexus had a larger capillary size (approximately 15 microns in diameter), was deeper in position, and had denser and more complex capillary loops than those in the external plexus. The capillaries of the external plexus were approximately 10 microns in diameter. The two plexi drained into 15-20 hypophyseal portal veins (HPVs) which were located mainly along the ventral and ventrolateral surfaces of the IS before breaking up into large capillaries (approximately 18 microns in diameter) with an anteroposterior arrangement within the PD. The second group consisted of one inferior hypophyseal artery (IHA) on each side branching off from the internal carotid artery. These arteries gave off branches to pierce the dorsolateral and ventrolateral aspects of infundibular process (IP) before branching off to form a capillary network. They also gave rise to radiating capillaries to supply the pars intermedia (PI) surrounding the cortical area of the IP. The hypophyseal cleft separating the PI from the PD was clearly seen with very few blood vessels. The capillaries in both PD and IP joined to form confluent hypophyseal veins draining the blood into the cavernous sinus.     

ELECTRON MICROSCOPY OF THE AVIAN RENAL GLOMERULUS

Electron microscopy of sections of chicken glomeruli shows them to possess a large central cell mass, occupying the hilum and the centre of the glomerulus, and continuous with the adventitia of the afferent and efferent arterioles. The glomerular capillaries form a much simpler system than in mammals and are spread over the surface of the central cell mass. Between the capillaries the mass is limited externally by the major component of the glomerular capillary basement membrane, which continues over the surface of the mass from one capillary to the next. Projections of the central cell mass characteristically form the support for glomerular capillaries, and smaller knobs of the central mass may project actually into the lumen of the capillaries, but always carry a layer of endothelial cytoplasm before them. They are never in direct contact with blood. The basement membrane of the glomerular capillary loop has a central dense layer and two lateral less dense layers as in mammals. The central dense layer is continuous with similar appearing dense material in the intercellular spaces of the adventitiae of the arterioles, and also with that of the central cell mass. The two less dense layers can also be traced into direct continuity with the less dense regions of this intercellular substance. The endothelial cytoplasm is spread as a thin sheet over the inner surface of the capillary basement membrane, and shows scattered "pores" resembling those described in mammals. Epithelial cells with interlacing pedicels are at least as prominent as those in mammals. Bowman's capsular membrane also possesses three layers similar to but less wide than those of the capillary basement membrane, and all three layers can be traced into continuity with the dark and light regions of the intercellular material of the adventitial cells of the arterioles, and beyond them with that of the central cell mass. At the hilum Bowman's capsular membrane also fuses with the capillary basement membrane.     

Direct observation of epicardial coronary capillary hemodynamics during reactive hyperemia and during adenosine administration by intravital video microscopy

Using high-resolution intravital charge-coupled device video microscopy, we visualized the epicardial capillary network of the beating canine heart in vivo to elucidate its functional role under control conditions, during reactive hyperemia (RH), and during intracoronary adenosine administration. The pencil-lens video-microscope probe was placed over capillaries fed by the left anterior descending artery in atrioventricular-blocked hearts of open-chest, anesthetized dogs paced at 60-90 beats/min (n = 17). In individual capillaries under control conditions, red blood cell flow was predominant during systole or diastole, indicating that the watershed between diastolic arterial and systolic venous flows is located within the capillaries. Capillary flow increased during RH and reached a peak flow velocity (2.1 +/- 0.6 mm/s), twice as high as control (1.2 +/- 0.5 mm/s), with enhancement of intercapillary cross-connection flow and enlargement of diameter (by 17%). With adenosine, capillary flow velocity significantly increased (1.8 +/- 0.7 mm/s). However, the increase in volumetric capillary flow with adenosine estimated from red blood cell velocity and diameter was less than the increase in arterial flow, whereas that during RH was nearly equivalent to the increase in arterial flow. There was a time lag of approximately 1.5 s for refilling of capillaries during RH, indicating their function as capacitance vessels. In conclusion, the coronary capillary network functions as 1) the major watershed between diastolic-dominant arterial and systolic-dominant venous flows, 2) a capacitor, and 3) a significant local flow amplifier and homogenizer of blood supply during RH, but with adenosine the increase in capillary flow velocity was less than the increase in arterial flow.     

Structure of spinal cord capillaries in hypokinesia

Changes in spatial interrelations of the spinal cord capillaries and motoneurons and capillary ultrastructure were studied under hypokinesia. Spatial interrelations between the capillaries and neurons were not demonstrated to change under hypokinesia. They were estimated by the following parameters: area of neuronal profile field, number of capillaries, their length, distance from the nerve cell body, capillary bed area and index of capillary-neuronal interrelations. Quantitative investigation revealed capillary stenosis: their diameter was one and a half times less under hypokinesia. Morphologically, capillary stenosis was accompanied by the basal membrane thickening and endothelial cytoplasm vacuolization. There was a direct relation between endothelial villi and the places of the endothelial cells contacts, dilatation of the contact interstices and solidifying of their borders. Changes in the capillaries were followed by reactions in the pericapillary structures, such as: fibrillae were formed, mitochondrii accumulated in the perivascular glial projections, the membrane next to capillary astrocyte projections underwent desmosome-like condensation. Mitochondrial accumulations were also observed in the nerve cell projections and in their cytoplasm sites contacting with the blood vessels.     

Organization and development of the perivascular space system in the neurohypophysis of the laboratory mouse

Summary The organization of the system of perivascular space around the capillaries in the neurohypophysis was studied in the adult and developing laboratory mouse by the use of histological silver impregnation and electron microscopical techniques.In the median eminence short and long extensions, arising mainly from the shallow space around capillary loops of the primary plexus of the portal system, formed radiations into the adjacent neural tissue of the external zone. The tissue of the neural lobe was separable into non-vascular regions dominated by undilated portions of neurosecretory nerve fibres and pituicytes, and neurovascular regions with perivascular space extensions forming an extensive system of connections between neighbouring capillaries.In the median eminence, the system of extensions of the perivascular space was estimated to increase the neurovascular contact surface area by at least 50%, implying an increased efficiency of the organ without a notable increase of its volume. The possibility that the ramifications of the perivascular space imply an enhanced uptake rate into the bloodstream and a subsequent increased concentration of the neurohormones in the portal blood, was discussed.During development of the median eminence, differentiation of perivascular space extensions of the adult type started in the juvenile of about three weeks of age, when shallow capillary loops had been formed. In the neural lobe, perivascular space ramifications were already present when the internal capillaries were formed and were fairly frequent in ten-day young. At the age of three to four weeks the organization of the system was similar to that of the adult animal.     

The intraorganic lymphatic bed of the mucous membrane of the tongue

The intraorganic lymphatic bed of the canine tongue mucous membrane is presented by the superficial and deep capillary networks and by the plexuses of the intraorganic lymphatic vessels. The capillaries of the superficial network in the thickness of the mucous membrane of the dorsal surface of the lingual tip, body and root form the lymphatic bed of the mechanical and gustatory papillas. The diameter of the capillaries in the both networks and in the intraorganic lymphatic vessels is greater in the mucous membrane of the ventral surface of the tip and of the lateral surfaces of the lingual body, and density of their arrangement is higher in the mucous membrane on the dorsal surface of the lingual tip, body and root. The capillaries of the superficial network in all areas of the lingual mucous membrane are thinner than those of the deep network, and the loops formed by the capillaries of the superficial network are less than the loops of the deep network.     

Quantitative analyses of ultrastructure and vascularization of the slow muscle fibres of the anchovy

A quantitative study has been made of the ultrastructure and vascularization of slow fibres in the lateral muscles of the European anchovy (Engraulis encrasicolus). Mitochondria and myofibrils occupy 45.5 and 44.3% of total fibre volume respectively. More than 95% of all myofibrils are adjacent to mitchondria. A total of 51 % of the sarcolemma is in direct contact with capillaries with a mean of 12.9 capillaries per fibre. In transverse sections anchovy slow fibr es are considerably flattened (long to short axis 12:1) such that the surface to volume ratio is more than twice that of a cylindrical fibre of the same area (1115 μm²). The capillary surface required to supply l μm³ of mitochondria is 0.18 μm² and the maximum distance between any capillary and mitochondrion 8 μm. T-system and sarcoplasmic reticulum occupy 0.43 and 2.7% of fibre volume respectively. Adaptations for increasing the capacity of skeletal muscle for aerobic work are discussed.     

Brain-capillary architecture of the newt,Triturus cristatus carnifex (Caudata: Salamandridae): Scanning electron-microscopical study of vascular corrosion casts

The brain-microvascular architecture of the newt (Triturus cristatus carnifex) was studied by scanning electron-microscopical examination of microvascular corrosion casts. It is characterized at the leptomeningeal level by a superficial network of single vessels that leave the meningeal sheath to form hairpin-shaped capillary loops. These loops penetrate the nervous parenchyma to varying depths and are variously bent, inclined, and twisted. Each hairpin-like loop consists of descending and ascending limbs connected by a distal U-shaped segment. The limbs are of equal diameter and lack physical differentiation. Some loops branch in a secondary loop, but there are no intraparenchymal connections with analogous surrounding structures. On vascular casts we observed detailed imprints of endothelial cell nuclei. This microvascular architecture is present in the whole brain except in leptomeninx and choroidal plexuses. The vascular pattern of T. cristatus carnifex resembles that of apodans. However, it differs from the anuran condition, which is characterized by a three-dimensional parenchymal network and from that of Ambystoma mexicanum which displays an intermediate condition between a single-capillary network and a capillary-loop model. At the level of paired capillaries, a counter-current exchange system may occur between the two limbs of the same loop, an arrangement that could promote uniformity of extracellular fluid composition in parenchyma.     

Red Blood Cells: Centerpiece in the Evolution of the Vertebrate Circulatory System

All vertebrates except cold-water ice fish transport oxygenvia hemoglobin packaged in red blood cells (RBCs). VertebrateRBCs vary in size by thirtyfold. Differences in RBC size havebeen known for over a century, but the functional significanceof RBC size remains unknown. One hypothesis is that large RBCsare a primitive character. Agnathans have larger RBCs than domammals. However, the largest RBCs are found in urodele amphibianswhich is inconsistent with the hypothesis that large RBCs areprimitive. Another possibility is that small RBCs increase bloodoxygen transport capacity. Blood hemoglobin concentration ([Hb])and mean RBC hemoglobin concentration (MCHC) increase from Agnathato birds and mammals. However, the changes in [Hb] and MCHCdo not parallel changes in RBC size. In addition, RBC size doesnot affect blood viscosity. Thus, there is no clear link betweenRBC size and oxygen transport capacity. We hypothesize thatRBC size attends changes in capillary diameter. This hypothesisis based on the following observations. First, RBC width averages25% larger than capillary diameter which insures cell deformationduring capillary flow. Functionally, RBC deformation minimizesdiffusion limitations to gas exchange. Second, smaller capillariesare associated with increased potential for diffusive gas exchange.However, smaller capillaries result in higher resistances toblood flow which requires higher blood pressures. We proposethat the large capillary diameters and large RBCs in urodelesreflect the evolutionary development of a pulmonary vascularsupply. The large capillaries reduced systemic vascular resistancesenabling a single ventricular heart to supply blood to two vascularcircuits, systemic and pulmonary, without developing high pressureson the pulmonary side. The large RBCs preserved diffusive gasexchange efficiency in the large capillaries.     

Three-dimensional reconstruction of the human capillary network and the intramyocardial micronecrosis

Three-dimensional reconstruction of the human heart was performed to define the structure of the intramyocardial microvasculature. A total of 200 consecutive serial sections of 6 μm each were prepared from the left ventricular tissue of an autopsied human heart with normal coronary arteries. The corresponding arteriole, venule, and all capillaries were reconstructed using three-dimensional software. The capillary network extended right and left along the cardiomyocyte with major and minor axes of about 130 and 120 μm, respectively. The capillary length from an arteriole to an adjacent venule was about 350 μm. Two types of sack-like structures, the precapillary sinus and the capillary sinus, were present in the capillary network, and many capillaries diverged from these sinuses. The cardiomyocytes were covered with reticular capillaries. In contrast, the precapillary and capillary sinuses were surrounded by many cardiomyocytes. The arterial and venous capillaries were positioned alternately, forming a lattice pattern. Intramyocardial microcirculatory units forming a capillary network from an arteriole to adjacent venules on both sides were present. The sizes of myocardial micronecroses corresponded to that of the intramyocardial microcirculatory unit. These results show that the capillary network is an ordered and anatomically regulated structure and that the microcirculatory unit and the precapillary and capillary sinuses may play an important role in maintaining the intramyocardial microcirculation during contraction and relaxation.     

Structure of the glomerular capillaries of the domestic chicken and desert quail

The glomerular capillary architecture of nephrons that include a loop of Henle (looped) and those that lack the loop (loopless) nephrons was examined qualitatively and quantitatively by electron microscopy in Gallus gallus and Callipepla gambelii. The glomerular capillaries of looped nephrons form a dichotomously branched network, while those of loopless nephrons are arranged loosely, and the majority are unbranched. There was no significant difference in the diameter of the glomerular capillaries between looped and loopless nephrons; however, in all cases the diameter of the afferent arteriole was significantly larger than that of the efferent arteriole. Based on size alone, the predicted blood flow rate in the efferent arteriole in 20% that of the afferent arteriole in G. gallus and 7% that of the afferent arteriole in C. gambelii. There was no significant difference in the volume density (Vv) of the glomerular capillaries between looped and loopless nephrons. However, the surface area density (Sv) of the glomerular capillaries in loopless nephrons of C. gambelii was significantly larger than for the looped nephrons, and for the loopless nephrons in G. gallus. This suggests that there may be a decrease in blood flow rate along the glomerular capillaries of the loopless nephrons in C. gambelii. Overall, the results indicate that the avian glomerular capillaries are less complex than those of mammals. Reasons may be that either avian blood is more viscous than that of mammals or that avian erythrocytes may be unable to fit physically through a tight intertwining network of capillaries due to the presence of a nucleus, which limits the tank-treading ability of avian erythrocytes. © 1995 Wiley-Liss, Inc.     

Diffusive oxygen shunting between vessels in the preglomerular renal vasculature: anatomic observations and computational modeling

To understand how geometric factors affect arterial-to-venous (AV) oxygen shunting, a mathematical model of diffusive oxygen transport in the renal cortex was developed. Preglomerular vascular geometry was investigated using light microscopy (providing vein shape, AV separation, and capillary density near arteries) and published micro-computed tomography (CT) data (providing vessel size and AV separation; Nordsletten DA, Blackett S, Bentley MD, Ritman EL, Smith NP. IUPS Physiome Project. http://www.physiome.org.nz/publications/nordsletten_blackett_ritman_bentley_smith_2005/folder_contents). A "U-shaped" relationship was observed between the arterial radius and the distance between the arterial and venous lumens. Veins were found to partially wrap around the artery more consistently for larger rather than smaller arteries. Intrarenal arteries were surrounded by an area of fibrous tissue, lacking capillaries, the thickness of which increased from ～5 μm for the smallest arteries (<16-μm diameter) to ～20 μm for the largest arteries (>200-μm diameter). Capillary density was greater near smaller arteries than larger arteries. No capillaries were observed between wrapped AV vessel pairs. The computational model comprised a single AV pair in cross section. Geometric parameters critical in renal oxygen transport were altered according to variations observed by CT and light microscopy. Lumen separation and wrapping of the vein around the artery were found to be the critical geometric factors determining the amount of oxygen shunted between AV pairs. AV oxygen shunting increases both as lumen separation decreases and as the degree of wrapping increases. The model also predicts that capillaries not only deliver oxygen, but can also remove oxygen from the cortical parenchyma close to an AV pair. Thus the presence of oxygen sinks (capillaries or tubules) near arteries would reduce the effectiveness of AV oxygen shunting. Collectively, these data suggest that AV oxygen shunting would be favored in larger vessels common to the cortical and medullary circulations (i.e., arcuate and proximal interlobular arteries) rather than the smaller vessels specific to the cortical circulation (distal interlobular arteries and afferent arterioles).     

A comparison of the cutaneous microvascular properties of the Spontaneously Hypertensive rat and the Wistar-Kyoto rat

The Spontaneously Hypertensive rat (SHR) and its non-hypertensive companion strain, the Wistar-Kyoto (WKY) rat, provide an excellent comparative model to permit study of the differential properties of cutaneous microvascular beds. We explored the possibility that chronically elevated vascular pressures in the SHR rat might affect the microvascular constitution of the skin. We measured skin blood flow at the back and at the paw of a group of 20-week-old WKY rats and a contrast group of SHR rats. We then performed skin biopsies at these two locations and used the NIH Image program to count and measure the size of capillaries, arterioles, and venules. We also determined microvascular density as percentage of total tissue area. At basal temperature, skin blood flow was similar in the two rat strains at both the back and paw. Heat induced vasodilatation resulted in a 50% increase in blood flow at the back, reaching the same level in the two rat groups. However, at the paw site, thermal stimulation resulted in significantly greater flow (39.3 +/- 3.1 ml/100 gm tissue per min) in the SHR rats than the WKY rats (28.6 +/- 1.9 ml/100 gm tissue per min, P < 0.05). The ratio of systemic arterial pressure to skin blood flow was computed as an index of vascular resistance to flow. At basal temperature, this index was 50% greater for the SHR rats at both skin sites. At 44 degrees C, the resistance index decreased at both sites in both rat groups but was still approximately 50% higher at the back of the SHR than the WKY rats. In contrast, the resistance index at 44 degrees C at the paw site fell to the same level in both the SHR and WKY rats. There were twice as many capillaries at the back of the WKY rats than at the back of the SHR rats (9.2 +/- 2.0 per mm2 vs. 4.7 +/- 1.2 per mm2, P < 0.05). Expressed as a percentage of total tissue area, the capillary density at the back in the WKY rats was 0.064 +/- 0.010% as compared to 0.034 +/- 0.008% in the SHR rats (P < 0.05). There were five times more arterioles at the paw compared to the back in both rat groups with no significant difference between the groups. We measured the diameter of the lumen and the thickness of the wall of each arteriole and computed their ratio as an index of possible media hypertrophy. There were minimal differences seen in these parameters between the two rat groups at the back and paw sites. The venular density was significantly higher at the paw than at the back in both rat groups with no significant difference between them. Reduced capillary density at the back of the SHR rats may be a developmental adaptation to high blood pressure. Such a reduction in the pathways of blood flow may help account for increased flow resistance at that site, independent of arteriolar vasoconstriction.     

Perfused transcapillary smooth muscle and endothelial cell co-culture—a novelin vitro model

Summary As mostin vitro endothelial cell (EC)-vascular smooth muscle cell (SMC) co-culture studies have been performed utilizing static culture conditions, none have successfully mimicked the physical environment of these cellsin vivo. EC covering the inner surface of blood vessels are continuously exposed to a hemodynamically imposed mechanical stress resulting from the flow of blood, while SMC are affected by pressure, a flow-related force acting perpendicular to the surface. We have developed a perfused transcapillary co-culture system that permits the chronic exposure of EC and SMC to physiological shear stresses and pressures. SMC and EC co-cultures were successfully established and maintained in long-term culture (7 wk) on an enclosed perfused bundle of semipermeable polypropylene capillaries. By altering flow rate and/or viscosity, shear stresses of 0.07–20 dyn/cm² can be readily achieved in this system. Electron microscopic analysis revealed that SMC formed multilayers around the outside of the capillaries, whereas EC, subjected to 3 dyn/cm² shear stress, formed an intact closely adherent monolayer lining the capillary lumen. EC and SMC exhibited characteristic ultrastructural and gross morphology. EC were separated from SMC by the capillary wall (pore size 0.5 μm, width 150 μM) and while no direct cell-cell contact was evident some cells were seen to migrate into the capillary wall. Both EC and SMC are exposed to the same culture medium, allowing the interaction of substances released in both directions. Yet separate populations of cells are maintained and can be individually harvested for further analysis. This co-culture system that mimics the architecture and physical environment of the vessel wall should have many potential applications in vascular biology.     

Capillary density of skeletal muscle in Andean dogs.

High capillary density and small muscle fiber diameters were found in the sternothyroid muscle of dogs native to 4350 m. The number of capillaries per square millimeter was three times greater while the diameter was less than half of those obtained in the same muscle of normoxic dogs. These findings suggest that tissular adaptative mechanisms are important in the process of acclimatization to hypoxia, contributing to the maintenance of adequate levels of PO2 in the tissue in the presence of hypoxemia.     

A quantitative investigation of microvascular changes in the thyroid gland after infrared (IR) laser radiation.

We present an ultrastructural study of thyroid capillaries in which 50-day-old rats Wistar rats, were irradiated with an infrared (IR) laser, (total dose, 46.80 J/cm2), the tissue quantified 1 day after ending treatment and a quantitative capillary analysis carried out by light and electron microscopy. Light microscopy was used to calculate capillary volume density revealing a significant increase in the irradiated rats. The quantitative measurement of parameters by electron microscopy required a two stage analysis: Level I, Electron Microscopy (Magnification x5,000); and Level II, Electron Microscopy (Magnification x26,000). At Level I, the following parameters were measured in each capillary: capillary area, capillary diameter, luminal area, luminal diameter, endothelial area, nuclear area and mean endothelial thickness. At Level II, pinocytotic vesicle diameter and their numerical density in endothelial cells were evaluated. Electron microscopic analysis revealed an increased luminal area in the capillaries of the irradiated rats. They also presented a decrease in endothelial cell thickness and vesicular diameter and an increase in vesicle numerical density. This latter increase is indicative of presumptive changes in capillary permeability, but the possible functional significance of these morphological changes in the endothelial cells requires further investigation.     

Capillary circular dichroism

Circular dichroism (CD) has become an increasingly important tool in the study of biological molecules as it enables structural information to be obtained nondestructively on solution-phase samples. However, sample requirements for CD are often seen as being too high with protein backbone measurements in standard cuvettes typically requiring ～100-300 μL of 0.1 mg/ml protein. To address this issue, we have designed a new form of CD sample holder, which reduces the sample requirements of the technique by two orders of magnitude, with a sample requirement of less than 3 μl. This sample saving has been achieved through the use of extruded quartz capillaries, the sample being held within the internal diameter of the quartz capillary through capillary action. The extruded quartz capillaries exhibit remarkably little birefringence, although still transmitting high energy UV circularly polarized light. The optics associated with capillaries were investigated. A configuration has been adopted with the light beam of the spectrophotometer being focused in front of the front face of the capillary using a biconvex lens and advantage being taken of the additional focusing effect of the capillary itself. The focusing is vital to the low wavelength performance of the cell, where we have acquired reliable data down to 180 nm using a Jasco J-815 spectrophotometer. The system performance was validated with Na[Co(EDDS)].H(2)O (EDDS = N,N-ethylenediaminedisuccinic acid), concanavalin A, lysozyme, and progesterone.     

Regression of capillary network in atrophied soleus muscle induced by hindlimb unweighting.

Little is known about the mechanisms responsible for the adaptation and changes in the capillary network of hindlimb unweighting (HU)-induced atrophied skeletal muscle, especially the coupling between functional and structural alterations of intercapillary anastomoses and tortuosity of capillaries. We hypothesized that muscle atrophy by HU leads to the apoptotic regression of the capillaries and intercapillary anastomoses with their functional alteration in hemodynamics. To clarify the three-dimensional architecture of the capillary network, contrast medium-injected rat soleus muscles were visualized clearly using a confocal laser scanning microscope, and sections were stained by terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling (TUNEL) and with anti-von Willebrand factor. In vivo, the red blood cell velocity of soleus muscle capillaries were determined with a pencil-lens intravital microscope brought into direct contact with the soleus surface. After HU, the total muscle mass, myofibril protein mass, and slow-type myosin heavy chain content were significantly lower. The number of capillaries paralleling muscle fiber and red blood cells velocity were higher in atrophied soleus. However, the mean capillary volume and capillary luminal diameter were significantly smaller after HU than in the age-matched control group. In addition, we found that the number of anastomoses and the tortuosity were significantly lower and TUNEL-positive endothelial cells were observed in atrophied soleus muscles, especially the anastomoses and/or tortuous capillaries. These results indicate that muscle atrophy by HU generates structural alterations in the capillary network, and apoptosis appears to occur in the endothelial cell of the muscle capillaries.