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There is only one known portal system in the mammalian brain - that of the pituitary gland, first identified in 1933 by Popa and Fielding. Here we describe a second portal pathway in the mouse linking the capillary vessels of the brain’s clock suprachiasmatic nucleus (SCN) to those of the organum vasculosum of the lamina terminalis (OVLT), a circumventricular organ. The localized blood vessels of portal pathways enable small amounts of important secretions to reach their specialized targets in high concentrations without dilution in the general circulatory system. These brain clock portal vessels point to an entirely new route and targets for secreted SCN signals, and potentially restructures our understanding of brain communication pathways., The first known portal system in the mammalian brain was identified in 1933. Here the authors describe a new portal system between the capillary beds of the Suprachiasmatic Nucleus master clock and a circumventricular organ, enabling humoral signals to reach targets without dilution in the systemic circulation.

During metastasis, tumour cells navigating the vascular circulatory system—circulating tumour cells (CTCs)—encounter capillary beds, where they start the process of extravasation. Biomechanical constriction forces exerted by the microcirculation compromise the survival of tumour cells within capillaries, but a proportion of CTCs manage to successfully extravasate and colonise distant sites. Despite the profound importance of this step in the progression of metastatic cancers, the factors about this deadly minority of cells remain elusive. Growing evidence suggests that mechanical forces exerted by the capillaries might induce adaptive mechanisms in CTCs, enhancing their survival and metastatic potency. Advances in microfluidics have enabled a better understanding of the cell-survival capabilities adopted in capillary-mimicking constrictions. In this review, we will highlight adaptations developed by CTCs to endure mechanical constraints in the microvasculature and outline how these mechanical forces might trigger dynamic changes towards a more invasive phenotype. A better understanding of the dynamic mechanisms adopted by CTCs within the microcirculation that ultimately lead to metastasis could open up novel therapeutic avenues.

Erythrocytes have a well-defined role in the gaseous exchange of oxygen and carbon dioxide in the mammalian body. The erythrocytes can contain more than half of the free amino acids present in whole blood. Based on measures showing that venous erythrocyte levels of amino acids are much less than arterial erythrocyte levels, it has previously been proposed that erythrocytes also play a role in the delivery of amino acids to tissues in the body. This role has been dismissed because it has been assumed that to act as an amino acid transport vehicle, the erythrocytes should release their entire amino acid content in the capillary beds at the target tissues with kinetic studies showing that this would take too long to achieve. This investigation set out to investigate whether the equine erythrocytes could rapidly take up and release smaller packages of amino acids when exposed to high or low external concentrations of amino acids, because it seemed very unlikely that cells would be able to release all of their amino acids without serious impacts on osmotic balance. Freshly prepared erythrocytes were placed in alternating solutions of high and low amino acid concentrations in PBS to assess the capacities of these cells to rapidly take up and release amino acids depending on the nature of the external environment. It was found that amino acids were rapidly taken up and released in small quantities in each cycle representing 15% of their total load in equine erythrocytes and 16% in human erythrocytes. The capacity for rapid uptake/release of amino acids by equine and human erythrocytes provided evidence to support the theory that mammalian erythrocytes have a significant role in transport of amino acids from the liver to tissues, muscles and organs. Electronic supplementary material The online version of this article (10.1007/s00726-020-02845-0) contains supplementary material, which is available to authorized users.

Objective— Vascular endothelial dysfunction is a key component of several major human diseases, but the molecular basis of this complex disorder has been difficult to determine in vivo. Previous attempts to identify key mediators of vascular endothelial dysfunction in experimental models have been limited by the lack of suitable methods for system-wide analyses of vascular bed biology. Here, we aimed to develop a novel method for investigating vascular endothelial dysfunction pathogenesis that enables system-wide analyses of molecular interactions between endothelial glycocalyx, endothelial cells, and smooth muscle cells in murine. Approach and Results— We developed a new technique using whole-body differential perfusion with increasing concentrations of detergent buffer to selectively solubilize distinct layers of vascular bed tissue in rodents. When combined with proteomics techniques, our novel approach of differential systemic decellularization in vivo enabled quantitative profiling of vascular beds throughout the body. Initial perfusion with phosphate buffer was used to obtain the endothelial glycocalyx, followed by subsequent extraction of endothelial cell components, and finally by smooth muscle cell constituents with increasing concentrations of detergent. Differential systemic decellularization in vivo has also been successfully applied to characterize molecular events in the vascular bed pathology of lipopolysaccharide-challenged mice. Conclusions— Together, these data indicate that differential systemic decellularization in vivo permits system-wide molecular characterization of vascular bed proteomes in rodent models and can be used to advance our current understanding of vascular endothelial dysfunction pathogenesis and progression in a wide range of disease settings.

The lumped constant is a proportionality factor for converting a tracer analogue's metabolic rate to that of its mother substance. In a uniform system, it is expressed as the ratio of the tracer analogue's extraction fraction (E⁎) to the extraction fraction of its mother substance (E). Here we show that, in capillary beds perfused by unidirectional blood flow, unequal concentration gradients of the tracer analogue and of the mother substance influence extraction fractions both locally and across the organ and that the direct proportionality of E⁎ and E must be replaced by ln(1−E⁎)/ln(1−E) to yield Λ, i.e. the lumped constant derived from first principles of bi-substrate enzyme and membrane kinetics. In other words, at a given capillary blood flow (F), the ratio of systemic clearances (FE⁎/FE), often used in compartmental kinetic analysis, must be replaced by the ratio of the intrinsic clearances, [−F ln(1−E⁎)]/[−F ln(1−E)]. The conclusion is supported by 2-[18F]fluoro-2-deoxy-d-galactose removal kinetics in pig liver in vivo from previous publications by the dependence of E⁎/E and the independence of Λ, on blood galactose concentration. Moreover, our corrections to the results of compartmental kinetics are quantified for comparing extraction fractions in different regions of interest (e.g. by positron emission tomography) and for calculating Λ using whole-organ E⁎ and E measured by arteriovenous concentration differences.

The construction of tissue-engineered devices for medical applications is now possible in vitro using cell culture and bioreactors. Although methods of incorporating them back into the host are available, current constructs depend purely on diffusion which limits their potential. The absence of a vascular network capable of distributing oxygen and other nutrients within the tissue-engineered device is a major limiting factor in creating vascularised artificial tissues. Though bio-hybrid prostheses such as vascular bypass grafts and skin substitutes have already been developed and are being used clinically, the absence of a capillary bed linking the two systems remains the missing link. In this review, the different approaches currently being or that have been applied to vascularise tissues are identified and discussed.

Accurate characterization of capillary geometry is of the utmost importance for physiological tissue studies such as oxygen transport. We show that 3D microscopy can be used to measure tissue capillary geometry both in normal and disease states. We imaged fluorescently labeled gut mucosa capillary beds of three control rats and three rats 4 hours after i.p. injection of 9 mg/kg endotoxin. We used serial optical sectioning microscopy coupled with deconvolution to reconstruct 3D capillary geometry. Theoretical point spread functions accounting for depth into the specimen resulted in better reconstructions than experimentally measured point spread functions. We next derived the distribution of the shortest distances to the nearest capillary from all extravascular tissue voxels. In normal rats the shortest-distance distributions were remarkably constant despite widely varying capillary geometry. Furthermore, the mean of the shortest-distance distributions increased significantly for endotoxemic rats (4.8 ± 0.4 μm) compared to controls (4.3 ± 0.3 μm, P < 0.05). Hence, serial sectioning microscopy provides an accurate venue for measuring physiologically relevant 3D capillary structure. Microsc. Res. Tech. 61:428–437, 2003. © 2003 Wiley-Liss, Inc.

That smooth muscles dilate and contract rhythmically has been known for a long time and the phenomenon has been studied for nearly as long. However, the causes and effects of smooth muscle oscillation (termed vasomotion) are far from clear. It is thought that vasomotion aids the delivery of oxygen to tissues surrounding capillary beds. On the other hand, unregulated vasomotion might participate in the development and maintenance of pathophysiological states. Nilsson and Aalkjaer review what is known about vasomotion and its consequences.

In fixed mouse brain magnetic resonance images, a high prevalence of fixation artifacts have been observed. Of more than 1700 images of fixed brains acquired at our laboratory, fixation artifacts were present in approximately 30%. In this study, two of these artifacts are described and their causes are identified. A hyperintense rim around the brain is observed when using perfusates reconstituted from powder and delivered at a high flow rate. It is proposed that these perfusion conditions cause blockage of the capillary beds and an increase in pressure that ruptures the vessels, resulting in a blister of liquid below the dura mater. Secondly, gray-white matter contrast inversion is observed when too short a fixation time or too low a concentration of fixative is used, resulting in inadequate fixation. The deleterious consequences of these artifacts for quantitative data analysis are discussed, and precautions for their prevention are provided.

Two-dimensional micro-computed tomography (micro-CT) slices can be reconstructed into three-dimensional (3D) models that demonstrate capillary beds. This study focused on the acquisition of data necessary to create scaffolding that directly mimics the unique structural patterns of a microvascular tree system. The Microfil vascular contrasting method was compared to the Baston's methylmethacrylate corrosion casting (BMCC) method to determine which provided the most accurate and high-resolution results for 3D micro-CT reconstruction derived from the two-dimensional micro-CT slices of the capillary beds. It was determined that the BMCC, a method traditionally used in the scanning electron microscopic analysis of the microvasculature, was the best method for representing capillary lumina for micro-CT scanning. The removal of tissues from the BMCC cast resulted in samples that eliminated background material, thus increasing the X-ray contrast levels of the CT images. This provided for a more complete and more distinguishable high-resolution image of the represented capillary lumina. Images created with this BMCC method were reconstructed in a stereolithography file format as 3D mesh structure for later importing into computer-aided design (CAD) software. The resulting Bio-CAD, then, can be used to guide the more accurate fabrication of the microvascular scaffolding and then serve as the framework for tissue engineering of microvascular structures. Results from this study clearly indicated that the BMCC method is superior to the Microfil method for accurate and complete high-resolution imaging of capillary beds.

A study of the microvasculature of the omentum using corrosion casts was undertaken. The object was to supply information regarding the morphology of the three-dimensional structure of the microvasculature information which may be valuable in understanding the functions of the omentum. Corrosion casts of rat omenta were prepared and studied. Characteristic glomerular-like capillary beds were identified. Some of these beds were densely and others loosely arranged. Two types of capillaries made up these beds, tortuous and straight capillaries. These beds also showed a planate surface giving the impression that they lie directly under the mesothelium.

Many bubbles that enter the brain circulation pass through the arterioles and capillary beds and do not obstruct blood flow. Nevertheless, such bubbles could still disrupt brain function. An open-brain model in five anesthetized rabbits used the minimum dose of air (25 microliters) necessary to cause embolism of the exposed vessels, and these bubbles passed through the vessels without any trapping. Despite their rapid transit, the bubbles provoked a marked dilatation of the affected pial arterioles (mean increase after 15 minutes of 27%) that persisted for 90 minutes after the bubbles had disappeared. The changes in vessel diameter were associated with a delayed, but significant and progressive, reduction in both cerebral blood flow measured by hydrogen clearance and neural function measured by cortical somatosensory evoked response. The decrease in blood flow correlated well with the depression of neural function (r = 0.67). Because both cerebral blood flow and neural function temporarily returned to normal after air embolism, the subsequent changes seen in this model cannot be explained simply by the mechanical obstruction of blood flow by bubbles.

Histological and scanning electron microscopy (SEM) characteristics of the microvasculature of muscle fibers in the anterior third of the adult rat tongue are described. For light microscopy, the specimens were embedded in paraffin and frontal sections were stained with Picro-Sirius. Thick sections were obtained from Spurr embedded samples and stained with toluidine blue solution. For SEM, specimens were obtained by the corrosion cast method and fractured specimens in dimethyl sulfoxide were observed with high-resolution SEM (HRSEM). The blood vessels, enveloped with a thin layer of connective tissue, had fibers running parallel to the muscular fibers. Capillary arterioles were noted following the endomysium, but their lateral branches often ran at right angles to the fibers. The capillary beds were clearly revealed in transverse sections where the individual capillaries appeared ring-like or elliptical in shape. The nuclei of endothelial cell cores could be seen on the vessel surfaces. Collagen fibers type I and III were noted in the connective tissue and in the fibrous layer of vessels. (J. Oral Sci, 43, 269-275, 2001)

Particles of known size ranges of carbon fibre-reinforced carbon were presented to in vitro cultures of murine macrophages. Particles of up to 20 μm diameter were phagocytosed. Larger particles were not phagocytosed but became surrounded by aggregations of macrophages, some of which migrated on to the particle surfaces. Mean rates of phagocytosis up to 2.5 particles per hour were observed. Cells presented with a large excess of particles became rounded, detached from the substrate and some underwent lysis. The implications of these findings for the fate of particulates released from implanted medical devices is discussed. It is argued that a mechanism exists where particles in the size range 8–20 μm, released from medical devices, are small enough to be phagocytosed by macrophages and transported to the lymphatics and subsequently to the vascular circulation but large enough to lodge in capillary beds of tissues remote from the implant site.

A modification of the usual microsphere injection method is presented which is appropriate for rat lung blood flow measurement. The injection of microspheres into the abdominal cava vein, together with the sampling of a reference flow from the right ventricle, allowed to calculate pulmonary blood flows in the same range than the cardiac output. The differences between the two figures (about 30%) are attributed to arterio-venous shunts. The tissue distribution of the microspheres bypassing the lung capillary beds agree with this interpretation.

Induction of a spontaneously metastasizing carcinoma in rats was attempted. Four-week-old Sprague-Dawley female rats were thymectomized or/and splenectomized and fed 200 mg (20 mg×10) of 3-methyicholanthrene from 7 weeks of age. In addition to these treatments, the early-appearing tumors were excised in order to select by isoimmunity the late-appearing ones that were less antigenic. The latter were easily transplanted into normal syngeneic female rats with metastasis to remote organs. This metastasizing capacity of the tumor became an inherent character in syngeneic normal rats from generation to generation of transplantation. With one of these tumors (MRMT-1) many cancer cells were histologically detected in circulating blood 3 days after tumor transplantation and arrested in capillary beds of lungs. The spontaneous metastasis to lymph nodes and lungs was macroscopically found within several weeks after tumor transplantation.

Extraction of drugs and other substrates from blood passing through the intact liver (or other capillary beds), inferred from samples taken at the organ inlet and outlet, is influenced by two kinds of heterogeneity of capillaries: transverse and longitudinal with respect to the direction of blood flow. The transverse heterogeneity is exemplified by arteriovenous shunts of the extracting system; the longitudinal one by zones of liver function. These two clinically interesting examples are among transverse and longitudinal distributions of capillary properties that can be inferred from the way the organ transforms the influx of a substance (or of a pair of substances interacting via liver cells) into the outflux over a range of input concentrations or of rates of blood flow. Mathematical and statistical ideas recently developed to implement this program in terms of saturation kinetics of uptake are reviewed and elucidated in relation to key experiments, data analysis, and statistical hypothesis testing.

Morphometric data of the pulmonary veins in the cat right lung are presented. Silicone elastomer casts of the right lungs of five cats were made, measured, counted, and analyzed. The Strahler system is used to describe the branching pattern of the vascular tree. These data are needed for the physicomathematical approach to pulmonary circulation. For all the pulmonary blood vessels lying between the left atrium and the capillary beds, there are a total of 10 orders of vessels in the right upper lobe, 9 orders of vessels in the right middle lobe, and 11 orders of vessels in the right lower lobe. The ratios of the diameters, lengths, and the number of branches in successive orders of vessels are called the diameter, length, and branching ratios, respectively. For the cat pulmonary venous tree, the average branching ratio is 3.521, the average diameter ratio is 1.727, and the average length ratio is 2.402 for vessels of orders 1-3 and 1.532 for vessels of orders 4-10.

Radioactive microspheres have been used for measuring bone blood flow and the extraction ratios of bone-seeking radionuclides, but we have shown that the technique is not completely valid. Bone uptake of 18F and 85Sr was compared with that of microspheres simultaneously injected into the heart or aorta of rats and rabbits under a variety of conditions. In single-passage experiments with quick killing to avoid recirculation, attention was focused on the tibiae and femora which could be dissected quickly to avoid post-mortem migration. For the rest of the skeleton, the effect of the latter was minimized by allowing recirculation for 5 min and comparing blood flow determinations in conjunction wit a cardiac output measurement. The apparent extraction ratio of 18F was variable and always exceeded unity in the single-passage experiments. With recirculation, there were significant differences between the extraction ratios for some bones, and the ratios sometimes exceeded unity. Extraction ratios for 85Sr were similarly variable, but lower. When 85Sr was compared directly with 18F, the relative extraction ratio was 0.8, with little variation between bones or animals. It is concluded that the flux of microspheres entering the vasculature of bone is not representative of blood flow, owing to the removal of some microspheres in pre-osseous capillary beds. Microspheres are therefore not a satisfactory standard for the determination of extraction ratios.

The purpose of the present investigation was to determine the effects of thyroxine (T4), which induces myocardial hypertrophy, on the number per square millimetre and volume per cubic millimetre of both the total and perfused portions of the arteriolar and capillary beds of the heart. Studies were conducted in the subendocardial and subepicardial regions of the left ventricle of anesthetized open-chest rabbits. Fluorescein isothiocyanate–dextran (i.v.) or radioactive microspheres (intra-atrial) were injected to label the perfused microvessels or to determine coronary flow in three groups of rabbits: controls, and rabbits given 0.5 mg/kg T4 for 3 days and for 16 days. Fluorescent photography was used to identify the perfused microvessels. An alkaline phosphatase stain was employed to locate the total microvascular bed. There were 2369 ± 638 (SD) capillaries/mm2 and 4 ± 3 arterioles/mm2 in control hearts. These decreased significantly to 1380 ± 199/mm2 and 1 ± 1/mm2, respectively, after 16 days of T4. In controls, 60 ± 5% of the capillaries and 59 ± 21% of the arterioles were perfused. This increased significantly to 90 ± 5 and 86 ± 18%, respectively, by 16 days of T4 treatment. Similar changes, although smaller, were observed after 3 days of T4. Coronary blood flow increased to 1.7 times control after 3 days and 2.9 times after 16 days of T4. No significant subepicardial versus subendocardial differences were observed in any condition or measurement. Thus, the physiological response to the increased work and increase in anatomic minimum diffusion distance is to increase flow and the proportion of the capillary bed perfused to at least maintain physiological diffusion distances.

Several points concerning the value of PEEP as a treatment for experimental acid aspiration can be underscored. (i) PEEP and mechanical ventilation seem to be of no more benefit in early aspiration pneumonitis than mechanical ventilation alone. (ii) PEEP promoted increased transudation of fluid through injured capillary beds, aggravating the pulmonary edema and the systemic hypovolemia of aspiration pneumonia. (iii) Mechanisms involving changes in microvascular pressures, interstitial pressures, filtration coefficients, and distribution of pulmonary blood flow can only be speculated upon from these data.

Unusually high capillary densities, volumes, and surface areas were revealed by morphometric analysis of the hypothalamic paraventricular nuclei (magnocellular and parvocellular division), supraoptic nuclei, and pituitary neural lobe of Long-Evans and Brattleboro rats. Capillaries of the magnocellular division of the paraventricular nucleus were greater in number, but smaller in diameter, than those in the parvocellular division. Expressed per unit area or volume, capillary dimensions in the hypohalamo-neurohypophysial system of Brattleboro rats were the same as in Long-Evans rats.

The regional blood flow to the rat cochlea has been studied using a method which combines the microsphere method with observation of serially-sectioned, plastic-embedded cochleas. Direct quantitation of the microspheres in a reference blood sample and in the different vascular areas of the cochlea allows the analysis of blood flow patterns with respect to the different capillary beds. inner ear, blood flow, microsphere

It is known that the flow of blood through an extremity is decreased by injection of serotonin (5-hydroxytryptamine [5-HT]) into its arterial blood supply. 10,12,14 This is assumed to be due to narrowing caused by spasm of the vascular conduits. Serotonin also causes marked aggregation of platelets, leukocytes, and erythrocytes both in vitro and in vivo. 17 This has been observed in vivo to be accompanied by a marked slowing of the circulation in the conjunctival blood vessels and, after repeated injections of serotonin, by significant reductions in the hematocrit. These changes could be due to, or contributed to by, microembolism of the smaller blood vessels by aggregated blood cells which remain sequestered in the capillary beds. In the present paper this problem is explored, and the response of the cerebral circulation to intravascular injections of serotonin is reported. Material and Methods Adult mongrel dogs weighing 14.6 ± 3.2 kg were

Intravenous or intraperitoneal administration of Pseudomonas and Salmonella endotoxin resulted in clearance values more rapid than controls. Subcutaneous heparin had no effect on carbon-clearance determinations. When Pseudomonas endotoxin was given in an animal pretreated with heparin, normal clearance values resulted. It is postulated that the administration of endotoxin either by the intraperitoneal or intravenous route alters the coagulability of the blood. Carbon particles coalesce in the fibrin coagulum and are trapped by the capillary beds, especially in the kidneys and lungs. As a result of the large particle size, clearance determinations are no longer an exponential function of time and values are erroneously elevated. Thus, when evaluating the effects of endotoxin on the phagocytic activity of the reticuloendothelial system using the carbon-clearance method, one must be cautious in the interpretation of data. Elevated values may not necessarily reflect an increase in reticuloendothelial activity.

Rapid shifts in the relative frequencies of the white cells of animals may occur following injection e. g. of toxins or other agents, radiation, but even mechanical manipulations (Jacobson 1954, Craddock 1960). The present work demonstrates the complexity of the reactions and the species differences between mice and guinea pigs following X-radiation and the manipulations (sham irradiation). A detailed survey (Table I-III) shows, that in mice eosinophils decrease following sham and X-radiation, that monocytes fall significantly by sham treatment but not furtheron after radiation, that rods increase continuously in number by application of sham treatment and X-rays. In these and other respects guinea pigs show a different behaviour, bearing witness to the multiformity of the reactions. Leucocytes in general are apt to be released into the circulation from myeloid marrow at short notice. The capillary beds of various tissues seems to afford another reservoir (Harris 1959, Osgood 1954). The highly differentiated mode of reaction of the various leucocytes and the species differences is however not easily accounted for on the notion of a simple mechanism regulating the flow to and from the circulating blood. The habitual action of ionizing radiation on the white cell picture of the circulating blood is that of causing a general concentration fall, which becomes manifest some 6–8 hours post-irradiation. The magnitude and duration of this decrease is dose dependant and may serve as an indication of a radiation influence of the organism in practice. Foregoing this stage a period of very rapid concentration changes during the first hours was noticed by many workers, although detailed analyses do not seem to have been performed. On the other hand the white cells are very motile and a flow to and from the circulation is caused by a variety of measures including injections of chemicals, hormones among others. It may well be that the irradiation effects are mediated through release of some such substances. The complexity of the early white cell reactions was realised from our preliminary trials, and particularly the species differences between mice and guinea pigs. This induced us to a general survey of the early radiation reactions, including also the simultaneous stress effects caused by the mechnical manipulations of the animals.

The aim of the present study was the quantification of proteins present in crevicular fluid obtained from individual sulci, and to this effect simplified micromethods for the quantification of individual proteins were developed. Unstimulated, resting crevicular fluid from healthy crevicular spaces (i.e. in the absence of clinically detectable inflammation) of dogs and humans was collected for 3 minutes, either in microcapillary glass tubes or with the aid of filter paper strips. Quantification of proteins was done by radial immunodiffusion without the pooling of samples or by immunoelectrophoresis, without eluting from the papers. The concentrations of albumin and fibrinogen in crevicular fluid so determined proved to be significantly lower than plasma concentrations. These results strengthen the concept that capillary dynamics in healthy gingivae are similar to those in general tissue capillary beds and that gingival fluid is a plasma transudate. However, due to ever present sub-clinical inflammation and other factors, it is improbable that fluid from even healthy sulci is a true transudate.

We have reviewed the distribution of portal circulations throughout the animal body; they are commoner than is generally supposed. Most portal circulations consist of two serial capillary beds connected by one or more larger vessels. We have called these 'convergent' portal circulations: examples are hepatic portal, placental, hypophysial, renal, ovarian and testicular circulations, as are parts of the lymphatic circulation. A second type of portal circulation, which is less common, consists of two serial capillary beds that are not connected by larger vessels. These we have called 'continuous' portal circulations: adrenal and pancreatic circulations are examples of this type. When a countercurrent concentrating mechanism exists in the body it is always part of the primary or secondary bed of a convergent portal circulation, though some convergent portal circulations are not associated with countercurrent mechanisms.

1. The pulmonary vascular anatomy of the toad, Bufo marinus was studied by scanning electron microscopy of vascular corrosion casts and of tissues prepared for light microscopy. 2. The lung is divided by septa into three orders of alveoli. Arterial branches run in the septa and cannot be observed directly through the lung surface. 3. The capillary bed forms a meshwork over the lumenal surface of septa and lung walls. It is divided into longitudinal zones of arterial distribution; it is broken along primary septal margins into primary alveolar units; within alveoli, it is functionally divided by distortion over circum-alveolar smooth muscle bundles. 4. The capillaries form a network of tubes rather than a perforated sheet of vascular space. Capillary beds on either face of septa are interconnected through the septum. 5. There is no evidence of collateral (“bronchial”) vessels or of anatomically definable shunt vessels. 6. Intrinsic pulmonary arterial branches have a muscular coat.

Fenestrated capillaries are provided with two types of regular discontinuities: fenestrae with negatively charged diaphragms, and transendothelial channels fitted with two diaphragms, of which the luminal one is uncharged. These structures are expected to affect macromolecular exchanges on the basis of size and charge. We have detected variations in the surface density of fenestrations and transendothelial channels (normalized to 1 micron of capillary endothelial profiles in sections) in selected areas of different murine organs, i.e., kidney cortex, duodenal mucosa, and exocrine pancreas. The survey was limited to endothelial segments less than or equal to 400 nm thick, and covered a total length of endothelial profiles of 1180 microns, 730 microns, and 1189 microns in the exocrine pancreas, intestinal mucosa, and kidney cortex, respectively. At least 1000 transendothelial openings were recorded by scoring for easily recognizable fenestrations, transendothelial channels, and unknowns, the latter representing either of the above in grazing sections. The linear density of all transendothelial openings taken together was found to vary among the different capillary beds (kidney cortex greater than intestinal mucosa greater than exocrine pancreas). This same sequence was observed for the linear densities of fenestrations, transendothelial channels, and unknowns considered individually. The values obtained were as follows: kidney cortex, 1.35 fenestrations per micron, 0.25 transendothelial channels per micron, 0.52 unknowns per micron; intestinal mucosa, 0.92 fenestrations per micron, 0.10 transendothelial channels per micron, 0.38 unknowns per micron; exocrine pancreas, 0.58 fenestrations per micron, 0.04 transendothelial channels per micron, 0.27 unknowns per micron. The differences in distribution of transendothelial openings among fenestrated capillary beds probably reflect capillary permeability modulations connected with the functions of these various organs.

The regional blood flow in the cochlea has been studied by mapping the distribution of microspheres in 22 μm thick serial sections of plastic embedded rat and rabbit cochleas. Using a computer-assisted reconstruction technique, a graphic display of the microspheres in each cochlea is obtained. From this display, microspheres may be counted and their distribution may be observed both in relation to the different vascular areas and with respect to the length of the cochlea. This technique, coupled with quantitation of the microspheres in a reference blood sample, offers a method for calculating total and regional cochlear blood flow using non-radioactive microspheres. In addition, this technique allows analysis of blood flow patterns with respect to the different capillary beds along the length of the cochlea. Thus it may be possible to determine if regional blood flow displays a longitudinal gradient, as do other functional, morphologic and biochemical characteristics of the cochlea.

The effects of moderate and severe hypoxia on quantitative regional morphometric indexes of the total and perfused arteriolar and capillary network were studied in the rat brain to determine whether diffusion distances were reduced in hypoxia. Fluorescein isothiocyanate (FITC)-labeled dextran was injected into the femoral vein of conscious control and hypoxic rats. After 20 s, the animal was decapitated and the head was frozen in liquid N2. Sections from eight brain regions were photographed to detect the perfused microvessels and then stained for alkaline phosphatase to visualize the total vascular network. There were significant increases in percent perfused arteriolar and capillary morphology between the two groups of hypoxic animals and control animals. In control rats, the percent of capillaries perfused averaged 45.6 +/- 0.6% (mean +/- SE). In moderate hypoxia 63.4 +/- 1.8% of the vessels were perfused and in severe hypoxia 89.4 +/- 0.1% were perfused. The percentage of arterioles perfused changed similarly. There were no significant differences in any index of total or percent perfused arteriolar or capillary morphometry among the regions within any group. During severe hypoxia, a greater percentage of the capillary reserves was utilized. These results demonstrate a uniform response to hypoxia in the capillary and arteriolar network of the conscious rat brain.

Vessel density and the ratio of the tissue area to the vessel surface area were studied by morphometric analysis techniques in normal rats, spontaneously hypertensive rats (SHR), and aged spontaneously hypertensive rats (aged SHR). Horseradish peroxidase was injected intravenously and the animals were killed 10 minutes later. The temporal bones were harvested, fixed in glutaraldehyde, and decalcified in 10% ethylenediamine tetraacetic acid (EDTA). After 7 days of decalcification, the cochleas were dissected and incubated with a diaminobenzidine tetrahydrochloride solution. Sections with stained vessels were projected onto the digitizing plate with the help of the camera lucida. The computer was used to calculate tissue area, vessel length, and vessel surface area. A statistically significant increase (p less than 0.05) in both the tissue area to vessel length ratio and the tissue area to vessel surface area ratio was demonstrated in the SHR and the aged SHR groups when compared to the WKY in the stria vascularis. No statistically significant difference was found between the two SHR groups. These data show a decrease of the vessel density in the capillary beds of the stria vascularis in spontaneously hypertensive rats. No statistically significant difference was found in the diameters of the capillary among the three groups.

This paper reports the results of a scanning electron microscopy (SEM) study of the vessels in the cochlea of the Mongolian gerhil. Using the microcorrosion technique and SEM we were able to obtain an overall picture of the capillary beds in the cochlea of the gerbil. The vasculature of the inner ear of the gerbil was found to differ from Wistar rats. The different vascular anatomy in comparison with the Wistar rat is discussed.

A measure was made of the perfused capillary surface area per gram of tissue (Sf) in postural, anterior latissimus dorsi (ALD), and locomotor, posterior latissimus dorsi (PLD), skeletal muscles in chickens. The animals were anesthetized with L.A. Thesia and the ALD and PLD muscles were prepared for observation using a modification of the method developed by R. E. Klabunde and P. C. Johnson (1977, Amer. J. Physiol.232, H411–417). Sf was determined from the relationship Sf = πdLθf, where d = capillary diameter, L = capillary length, and θf = number of perfused capillaries per gram. Capillary lengths and diameters were measured directly through the microscope. Estimates of θf were measured in two ways: by a flow method (θQf), and by an histochemical method (θHf). It was observed that the average capillary diameter in PLD was the same as in ALD muscles, but the average capillary length in PLD was two times longer than in ALD muscles. Both the flow and histochemical methods yielded values of θf that gave similar values of Sf for PLD muscles (SQf = 24.7 ± 20.0 cm2/g, SHf = 13.7 ± 14.4 cm2/g), but different values for ALD muscles (SQf = 9.8 ± 6.8 cm2/g, SHf = 42.8 ± 19.1 cm2/g). The difference between SQf and SHf for ALD muscles could be explained by the more irregular and longer perfusion path observed in postural versus locomotor muscle. The flow method appears to underestimate Sf in capillary beds with irregular perfusion paths. The results indicate that only a small fraction of the total capillary bed was perfused in resting skeletal muscle and that SHf for ALD was approximately three times larger than SHf for PLD.

Studies on the vascularization of the cochlea with conventional injection methods that use light microscopy have failed in viewing both the overall three-dimensional picture, as well as the detailed construction of the cochlea vascular blood vessels. This basic shortcoming can be omitted by the use of scanning electron microscopy (SEM) on corrosion casts, which only presently has been introduced. The use of a commercial resin (Mercox) as an injected medium, followed by application of macerating fluids, provides clean and completely filled casts of the cochlea vascular system, which can then be inspected by SEM. This method not only confirms the general findings about cochlea vascularization but gives the opportunity to view the overall picture, as well as the detailed pattern of the intricate cochlear capillary beds.

Summary. A detailed study was made of lambs aged 5-7 months naturally infected with Pasteurella haemolytica biotype T. In addition to the well known features of such infections, previously unreported necrotic lesions of the tonsil, oesophagus, pharynx and adjacent areas were consistently seen. Large numbers of P. haemolytica were present in the tonsil, oesophageal lesions, lung, liver and spleen, but few or none in other tissues. The evidence indicated that the disease was not a true septicaemia. It is postulated that P. haemolytica biotype T already present in the tonsils multiplies and invades the adjacent tissues of the upper alimentary tract; groups of organisms from this site enter the blood stream as emboli, most of which lodge in the capillary beds of the lung and liver; rapid multiplication of organisms in these tissues leads to death from the effects of endotoxin.

We examined latex casts of the pulmonary microcirculation with the scanning electron microscope (SEM). Mature rats were anesthetized and ventilated; the pulmonary vasculature was washed out with lactated Ringer solution and then filled with a mixture of Geon latexes. The airways were filled with glutaraldehyde with resulting transmural vascular pressures of 10 cmH2O. After critical-point drying and corrosive removal of the lung tissue, SEM studies of the vascular replicas revealed two distinct patterns of pulmonary microcirculation: 1) sparse, long, tubular capillaries that comprise the thin subpleural layer and appear as “filler” in the peribronchial spaces; and 2) alveolar microcirculation that is composed of tightly matted, intersecting tubules, shorter but of the same diameter as type 1, in spherical array in two layers. The alveolar capillaries at low magnification appear superficially as sheets; however, the detailed morphology is not consistent with the sheet-and-post model. We conclude that the basic component of the pulmonary microcirculation is tubular and not different from other capillary beds except in density.

Horseradish peroxidase was detected in the choroid plexus capillary 5 min after the onset of a 2 1 2 - min injection of 7.5 μl of 40% solution into the cisterna cerebellomedullaris in mice. Venous capillaries in the capillary beds of circumventricular organs including the choroid plexus were indicated as sites of cerebrospinal fluid absorption.

The blood flow rates and ability to remove an added fluid load were studied in the testes of monkeys with surgically induced varicoceles and in sham-operated control monkeys. These studies were conducted to verify a proposed mechanism by which varicocele may cause testicular and spermatogenic damage. Analyses of the data indicated that, at four months after induction, the testes of monkeys with varicocele were less able to remove a perfused fluid load and that, at five months, the blood flow was significantly less in the testes of these animals. The effects were most pronounced in the left testes of the monkeys with varicocele. Blood flow values calculated were: control, right--9.66 ml X 100 g-1 X min-1; control, left--10.42 ml X 100 g-1 X min-1; varicocele, right--7.73 ml X 100 g-1 X min-1; varicocele, left--5.04 ml X 100 g-1 X min-1. These data suggest a new theory, that increased pressure on the venous side of testicular capillary beds in subjects with varicocele may decrease blood flow and cause testicular damage.

Dog hearts were taken without loss of blood under 3 different conditions: (1) normally beating hearts, (2) hearts that were arrested by potassium chloride for varying lengths of time and (3) potassium chloride-arrested hearts that were reperfused with blood after varying lengths of time. In normal hearts counts of open capillaries containing erythrocytes showed a uniform distribution throughout the right myocardium and a gradient decreasing from the epicardium toward the endocardium in the left myocardium. Potassium chloride-arrested hearts showed a reverse gradient in the left myocardium. In normal hearts, erythrocytes are oriented in capillaries so that their flat sides lie against the nearest myocardial cell. In the arrested hearts, one sees few or no erythrocytes with this orientation. The erythrocytes in the arrested hearts are swollen, rounded, or packed in clumps in the capillaries. Arrested hearts exhibit a weakening of the connective tissue elements of the myocardium, evident upon fixation or on perfusion of the myocardium with blood. The weakening increases as the length of myocardial arrest increases.

The validity of current theories concerning the function of the area postrema ultimately rests on the nature of its microcirculation. Therefore a detailed study of the vasculature of the postremal region was undertaken in the rat. The findings indicate a singular arteriolar supply from branches of the posterior inferior cerebellar arteries. These vessels are caudal, intracranial branches of the vertebral arteries. Networks of enlarged capillaries are prominent features of sections taken through the area postrema. These enlarged capillary channels are re-entrant. At the borders of the structure they are joined by short interconnecting vessels to capillaries of smaller caliber typical of the medullary tissue. The bed is considered to be a portal system because two distinctive, serially connected capillary beds are interposed between artery and vein. No arteriovenous shunts or thoroughfare channels are observed in the rat, contrary to reports of this type of vessel in other species. This microcirculatory pattern would seem to be adequate to current theories of postremal function, which attribute neurosecretory or chemosensory functions to this region.

Injections of various opaque materials including latex, India ink, and silicone rubber were used to examine microscopic sections and whole specimens of the rat submaxillary gland. An excretory duct, several large collecting ducts and a complex system of blood vessels occupy the central areas of the gland, surrounded by connective tissue. A major bifurcation of these central structures occurs approximately 1 3 into the gland. Excretory, collecting and striated ducts are well supplied with a thick capillary network which is connected to an extensive secondary network of metarteriole-sized vessels. Thus, a total of three different strata of blood vessels accompany the excretory and central collecting ducts: (1) the intramural extensive network of capillaries of the ducts themselves, (2) an outermost layer of one, two or three large arteries and veins, and (3) a middle area of intermediate sized vessels (intermediate arteriolar plexus). These latter vessels connect the large vessels with the ductal network, and supply capillaries of the connective tissue in the area and vasa vasorum; this intermediate arteriolar plexus also shows connections between larger vessels which may represent an A-V shunt system. The granular ducts and acini appear to be served by the same capillary bed, which is rather sparse compared to that of the more distal striated, collecting and excretory ducts. These acinar capillary beds are composed of end capillaries of the arteries which accompany the collecting ducts as they enter the lobules, the vessels branching together with the ducts to the most proximal parenchymal areas containing the acini. The venous drainage of these areas also parallels the ducts.

THE appearance of tumor cells in peripheral blood drawn from the antecubital vein in patients with various visceral cancers has been frequently reported.1-3Depending upon the location of the primary tumor or its known secondaries, these cells would have traversed one or more organ vascular beds. Tumor cells are generally larger than the normal formed elements of the blood, a factor of possible importance in their arrest and subsequent development into metastases. Certain tissues and organs, including those of the distribution drained by the antecubital veins, are rarely the site of metastatic implant. It could be inferred from the clinical studies on antecubital vein blood that such tumor cells had either passed through or around the capillary beds of hand and forearm unimpeded and, hence, produced no metastases. There is no evidence, however, that other tumor cells had not entered these capillary beds, lodged, and become nonviable. Three possibilities