Overexpression of metalloproteinase inhibitor in B16F10 cells does not affect extravasation but reduces tumor growth

It is widely accepted that a major role of matrix metalloproteinases in the metastatic process is degradation of basement membrane during cancer cell invasion. We tested the hypothesis that the reduction in metastatic potential which has been demonstrated for B16F10 melanoma cells genetically engineered to overexpress tissue inhibitor of metalloproteinase-1 (TIMP-1) is caused by a decrease in their ability to extravasate. Using intravital videomicroscopy of chick embryo chorioallantoic membrane, we studied extravasation of B16F10 cells and B16F10 cells transfected to overexpress TIMP-1. More than 800 cells in 36 chick embryos were analyzed for each cell line during 72 h postinjection. TIMP-1 upregulation had no effect on the time course of extravasation, virtually all cells from both cell lines having extravasated by 36 h. We also studied the morphology of micrometastases at days 3 and 7. Lack of contact between cancer cells within micrometastases at day 3 and reduction in size and number of tumors at day 7 were observed for TIMP-1 overexpressor cells compared to B16F10. Our findings illustrate that the imbalance between TIMP and metalloproteinases created by overexpression of TIMP-1 in B16F10 cells reduces their metastatic ability in vivo by affecting tumor growth postextravasation.

Heterogeneity of red blood cell perfusion in capillary networks supplied by a single arteriole in resting skeletal muscle

Flow heterogeneity within capillary beds may have two sources: (1) unequal distribution of red blood cell (RBC) supply among arterioles and (2) unique properties of RBC flow in branching networks of capillaries. Our aim was to investigate the capillary network as a source of both spatial and temporal heterogeneity of RBC flow. Five networks, each supplied by a single arteriole, were studied in frog sartorius muscle (one network per frog) by intravital video microscopy. Simultaneous data on RBC velocity (millimeters per second), lineal density (RBCs per millimeter), and supply rate (RBCs per second) were measured continuously (10 samples per second) from video recordings in 5 to 10 capillary segments per network for 10 minutes by use of automated computer analysis. To quantify heterogeneity, mean values from successive 10-second intervals were tabulated for each flow parameter in each capillary segment (ie, portion of capillary between successive bifurcations), and percent coefficient of variation (SD/mean.100%) was calculated for (1) spatial heterogeneity among vessels (CVs) every 10 seconds and for the entire 10-minute sample and (2) temporal heterogeneity within vessels for every capillary segment and for the mean flow parameter. Analysis of these data indicates that (1) capillary networks are a significant source of both spatial and temporal flow heterogeneity, and (2) continuous redistributions of flow occur within networks, resulting in substantial temporal changes in CVs, although a persistent spatial heterogeneity of perfusion still exists on a 10-minute basis. In most networks, CVs decreased as supply rate within the network increased, thus indicating that rheology plays a significant role in determining the perfusion heterogeneity.

Reduction of sunburn damage to skin by topical application of vitamin E acetate following exposure to ultraviolet B radiation: effect of delaying application or of reducing concentration of vitamin E acetate applied

The skin of the skh-1 mouse after ultraviolet B (280-320 nm, UVB) irradiation shows the pathological changes typical of sunburn damage: spongiosis (edematous spaces) around some cells, necrosis of keratinocytes, giving rise to sunburn cells, inflammatory infiltration of polymorphonuclear leucocytes, etc. In our previous study, these were accompanied by erythema, increased skin sensitivity, and edematous swelling. The topical application of tocopherol acetate (TA) immediately after the UVB exposure decreased these changes. In this paper, multiple measurements of the skin thickness were made at different locations along the magnetic resonance imaging (MRI) cross-sectional image of the skin. This permits effects to be quantified with (if desired) the contralateral half of the back serving as an internal control, either exposed (positive control) or unexposed (negative control). Topical application of TA resulted in an increase in the concentration of free tocopherol in the skin. No qualitative differences in ultrastructural appearance of the UVB-irradiated, TA-treated skin could be discerned by careful examination. In vivo high resolution video microscopy of blood flow in venules of the irradiated mouse ear revealed a large (tenfold) but not statistically significant decrease in stationary lymphocytes adhering to the venule walls. The delaying of the application of TA up to 8 hours after the termination of UVB irradiation still offered statistically significant protection as did immediate application of 5% TA in diluent Myritol 318 (Delios S, Henkel).

Ischemia-reperfusion induced microvascular dysfunction in skeletal muscle: application of intravital video microscopy

Video microscopy of red cell flow in capillaries at the surface of skeletal muscle provided the opportunity to quantitate ischemia-reperfusion (I-R) induced microcirculatory changes, in vivo. Extensor Digitorum Longus (EDL) muscles of 22 male Wistar rats (300-400 g), anesthetized with sodium pentobarbital (Somnotol, 65 mg kg,-1 IP), were used to measure the number of perfused capillaries (CDper: mm-1) crossing lines drawn perpendicular to the muscle axis, and red blood cell velocity (VRBC: mm/s) within individual capillaries from controls (n = 6), and after 2 hr (n = 4), 3 hr (n = 4), and 4 hr (n = 5) of no-flow ischemia with the muscle temperature maintained at its normal value of 32 degrees C. Ischemia was induced by tightening a tourniquet placed around the limb above the EDL muscle. Measurements were made after 30, 60, and 90 min of reperfusion. To test the usefulness of this skeletal muscle model for evaluating proposed interventions in I-R, the effect of hypothermia (24 degrees C) on the microcirculation following 4 hr ischemia (n = 3) was measured. Edema formation was estimated from the wet/dry weight ratio of the ischemic and contralateral control EDL muscles. Capillary perfusion at the surface of the control muscles was remarkably stable over the 5 hr period studied, while significant changes occurred following the ischemic periods. Significantly lower CDper was measured 30 min following all periods of normothermic ischemia. However, unlike the 2 and 4 hr ischemic periods 3 hr normothermic ischemia resulted in a progressive decline in CDper throughout the reperfusion period. VRBC showed evidence of a hyperemic response following 2 hr normothermic ischemia (control: 0.12 mm/s +/- 0.19 compared to 0.26 mm/s +/- 0.03 following 90 min reperfusion; mean +/- sem). However, no such hyperemia was measured following either 3 or 4 hr normothermic ischemia (i.e., 3 hr control: 0.24 mm/s +/- 0.01 compared to 0.07 mm s +/- 0.003 following 90 min reperfusion). In fact, VRBC was essentially zero 90 min following 4 hr normothermic ischemia (0.01 mm/s +/- 0.01). However, when the muscle was allowed to cool to 24 degrees C during 4 hr ischemia no significant change in either VRBC or CDper was measured compared to pre-ischemic controls. Evidence of edema was found after 3 and 4 hr normothermic ischemia. This study establishes a skeletal muscle model of I-R, which may be useful in testing hypotheses regarding mechanisms of I-R injury, and effectiveness of proposed treatments of I-R.

Scanning and transmission electron microscopy and high resolution intravital video-microscopy of capillaries in the mouse exocrine pancreas, with special emphasis on endothelial cells

Capillaries in the mouse exocrine pancreas were studied by scanning electron microscopy of microvascular corrosion casts, transmission electron microscopy of tissue sections, and high resolution intravital video-microscopy. Two types of capillaries were discerned by corrosion casting. The first type was rather straight, had a constant diameter of 5-6 microns, and its surface showed multiple circumferential furrows. The frequency of such constrictions was less in the second type, which was more undulated and had a diameter of 7-9 microns. In the second type, these constrictions defined bulged areas of the capillary cast. Corresponding tissue sections also showed two types of capillaries, fenestrated and non-fenestrated capillaries. Microtubules were abundant in all capillary endothelial cells, whereas bundles of microfilaments were scarce. Microtubules were arranged along the long axis of endothelial cells as well as parallel to endothelial cell border regions. Endothelial cells were joined by intermediate junctions along cell borders running both circumferentially and longitudinally. Flow reversal in capillaries and spontaneous endothelial contractions were documented in vivo. Endothelial cells bulged into the lumen, either at their nuclear region or distant from it. Spontaneous contraction of pericytes was not observed. These results suggest that contraction of capillaries is carried out by endothelial cells, representing an autonomous flow regulatory device. Capillary contraction in exocrine pancreas may be influenced by blood-borne agents, probably by those released in Langerhans islets.

Early interactions of cancer cells with the microvasculature in mouse liver and muscle during hematogenous metastasis: videomicroscopic analysis

Biomechanical interactions of cancer cells with the microvasculature were studied using high resolution intravital videomicroscopy. We compared initial arrest of murine B16F10 melanoma and D2A1 mammary carcinoma cells fluorescently labelled with calcein-AM, in low pressure (liver) vs high pressure (cremaster muscle) microvascular beds. Cells were arrested due to size restriction at the inflow side of the microcirculation, penetrating further and becoming more deformed in muscle than liver [median length to width ratios of 3.3 vs 1.3 for D2A1 cells, and 2.5 vs 1.2 for B16F10, at 1 min post-injection (p.i.)]. During the next 2 h many cells became stretched, giving maximum length to width ratios of 68 vs 22.1 (D2A1) and 28 vs 5.6 (B16F10) in muscle vs liver. Ethidium bromide exclusion demonstrated that over 97% of the cells maintained membrane integrity for > 2 h p.i. (In contrast, when an acridine orange labelling procedure was used, membrane disruption of B16F10 cells occurred within 15 min p.i.) Our experiments do not indicate the ultimate fate of the cancer cells, but if cell lysis occurs it must be on a time scale of hours rather than minutes. We report a process of 'clasmatosis' in cancer cells arrested in the microcirculation: large membrane-enclosed fragments (> 3 microns in diameter) became 'pinched off' from arrested cells, in both liver and muscle, often within minutes or even seconds of arrest. The significance of this process is not yet understood. In this study intravital videomicroscopy has thus provided a valuable clarification of the interactions of cancer cells with vessel walls during metastasis.

Comparative aspects of splenic microcirculatory pathways in mammals: the region bordering the white pulp

Splenic microcorrosion casts prepared using minimal volumes of material show that most of the flow passes through the region bordering the white pulp. However, the nature of these microcirculatory pathways has received little attention. We have studied these in dog, cat, rat, mouse, and normal versus diseased human spleens. In all 5 species, a marginal sinus (MS) of anastomosing vascular spaces 5-10 microns thick lies between the white pulp and marginal zone (MZ). The morphology differs between species and the MS is absent in immune thrombocytopenia. The MS fills by circumferential flow before blood passes outward to the MZ. Many capillaries supply the MS and MZ, their arrangement and degree of branching differing among species. Capillaries never terminate within the reticulum of the white pulp. In immune thrombocytopenia, marked vascular hyperplasia occurs within white pulp and MZ. The perimarginal cavernous sinus plexus (PMCS), found in human, dog and rat, comprises large flattened spaces up to 300 microns x 1000 microns in area and 30-100 microns thick. It lies between the MZ and red pulp or directly adjacent to white pulp, and receives flow principally via the MZ. In sinusal spleens, the MS, MZ and PMCS are drained by open-ended venous sinuses. In non-sinusal spleens, the MS and MZ are drained by pulp venules. Approximately 90% of the splenic inflow passes through the region bordering the white pulp, bypassing the filtration beds of the red pulp. This suggests that immunologic functions of the spleen take precedence over the filtration of blood cellular elements in the red pulp.

Intravital videomicroscopy of the chorioallantoic microcirculation: a model system for studying metastasis

The chick embryo is a useful model for studying hematogenous metastasis. Cancer cells injected into veins of the chorioallantoic membrane (CAM) circulate briefly through all tissues but form metastases predominantly in the CAM. This respiratory organ is particularly suitable for intravital microscope because of its accessibility without the need for surgery and the density and planar configuration of its vessels (which we confirmed by microcorrosion casting). Using an inverted microscope with oblique transillumination for high-resolution images and epifluorescence to identify labeled B16F1 melanoma cells, we studied successive stages of metastasis formation in the CAM in vivo. By 2 min postinjection (pi) all cancer cells had become arrested within the microvasculature. This initial arrest appeared to be due to size restriction, based on measurements of cell and vessel diameters. At 15-60 min pi, trapped cells were seen in tapering arterioles (27%), orifices from arterioles to the capillary plexus (61%), or in the plexus itself (12%). Some cells had extravasated into the underlying mesenchyme by 3 hr (pi), and at 24 hr all cancer cells had completed this process. The mean rate of migration out of capillary lumens was approximately 1 micron/hr. Micrometastases grew in a planar configuration just beneath the capillary plexus, with a cell doubling time of approximately 24 hr. Our technique is also applicable to other tumor types and host animals and provides a powerful tool to complement studies on the molecular basis of metastasis.

Evidence for Kupffer cell migration along liver sinusoids, from high-resolution in vivo microscopy

Kupffer cells are generally considered fixed tissue macrophages of the liver. However, we have evidence that this opinion is incorrect. High-resolution in vivo video microscopy shows that Kupffer cells have the ability to migrate along sinusoidal walls. Images recorded from anesthetized mice show active locomotion of cells with or against the direction of blood flow or in the absence of flow. The size, changing morphology, and uptake of carbon or microspheres strongly suggest that these are Kupffer cells. Quantitative measurements were made on 29 migrating Kupffer cells. The mean speed of migration was 4.6 +/- 2.6 (SD) microns/min and was not significantly different whether migration occurred with or against the flow. When fluorescent microspheres were given in vivo as a phagocytic challenge, Kupffer cells containing few microspheres migrated more slowly (0.9 +/- 0.9 microns/min, n = 10), whereas those containing many microspheres were never seen to migrate. Individual Kupffer cells were able to move independently, i.e., in directions different from those of neighboring Kupffer cells. These findings may have major implications for the role of Kupffer cells in scavenging foreign particles and as antigen-presenting cells.

Early steps in hematogenous metastasis of B16F1 melanoma cells in chick embryos studied by high-resolution intravital videomicroscopy

BACKGROUND

There are few techniques that permit direct observation of tumor metastasis. The ability to observe steps in this process as they occur in experimental animals would complement studies on molecular mechanisms.

PURPOSE

We have developed a novel procedure using high-resolution intravital videomicroscopy to permit direct observation of cells as they arrest in the microcirculation, extravasate, and form micrometastases. We used this procedure to study early steps in experimental metastasis in immune-deficient chick embryos, permitting us to develop this technique in a relatively accessible respiratory organ and in the absence of host immune responses. Our goals were to develop techniques applicable to this host and to other hosts and to clarify the process of hematogenous tumor spread in this host.

METHODS

We injected fluorescently labeled B16F1 melanoma cells into the circulation of 11- to 13-day chick embryos, and using intravital videomicroscopy, we observed the cells in the chorioallantoic membrane over time.

RESULTS

The majority of injected cells were trapped initially in orifices to the chorioallantoic membrane capillary plexus or in tapering ends of arterioles leading to the plexus. During the first 2 hours, cells were found only in vessel lumina. After 8 hours, 83% of cells had extravasated, and the rest were in the process of extravasation. Cell shape changes and pseudopodial extensions were seen during extravasation and tumor development. Tumor cell division was seen only after extravasation. Tumors tended to develop near microvessels and were often wrapped around them.

CONCLUSIONS

Intravital videomicroscopy can provide new information about steps in metastasis. This procedure is applicable to other hosts and can be used in future studies to test hypotheses about molecular mechanisms of tumor spread.

Muscle capillary-to-fiber perimeter ratio: morphometry

It is known that a substantial amount of capillary tortuosity is found in shortened muscles. However, the increased capillary length and surface area contributed by tortuosity and branching are seldom taken into account when capillarity is estimated and/or blood-tissue exchange is modeled in muscles. In this paper, we sought morphometric estimates of capillarity in transverse sections that incorporated data on capillary geometry. We derived equations to estimate capillary perimeter per fiber perimeter (i.e., capillary-to-fiber perimeter ratio) in transverse sections. We show how capillary-to-fiber perimeter ratio is related to capillary surface per fiber surface, i.e., to the amount of capillary surface available for exchange per muscle fiber surface area, and how it can be obtained by morphometry. Because capillary tortuosity and fiber perimeter are both a function of sarcomere length, the degree of extension or shortening of muscle samples obviously needs to be taken into account when capillary-to-fiber perimeter ratio is compared between muscles and/or samples. Using data currently available on capillary length and diameter with fiber shortening and extension, we show that it is a feature of capillary-to-fiber perimeter ratio to change relatively little with sarcomere length. As sarcomere length decreases from 2.80 to 1.58 microns in perfusion-fixed hindlimb muscles of rats, capillary and fiber perimeters in transverse sections increase substantially, whereas the ratio between the two variables, capillary-to-fiber perimeter ratio, changes only less than or equal to 10-15%.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in splenic microcirculatory pathways in chronic idiopathic thrombocytopenic purpura

The spleen plays a central role in the pathogenesis of chronic idiopathic thrombocytopenic purpura (ITP); it produces massive quantities of antiplatelet antibodies, leading to accelerated phagocytosis of platelets. Lymphoid hyperplasia typically occurs in the spleen, characterized by large numbers of lymphatic nodules with active germinal centers. Whether changes in splenic microcirculatory pathways also occur is not known. We have studied this question by scanning electron microscopy of corrosion casts, comparing spleens removed from patients with ITP with normal spleens obtained from organ transplant donors. The casts demonstrate two major changes in microcirculatory pathways in ITP. Firstly, a striking proliferation of arterioles and capillaries is found in the white pulp and marginal zone (MZ), seen as extensive vascularization in 92.3% of lymphatic nodules (n = 191) versus 0.6% (n = 224) in normal spleens. Secondly, the marginal sinus, a series of flattened, anastomosing vascular spaces between the white pulp and MZ, is absent in 89.4% of lymphatic nodules versus 4.9% in normal spleens. The cause of these microcirculatory changes, which may not be exclusive to ITP, is presently unknown. Absence of the marginal sinus may affect distribution of blood flow through the MZ such that platelets spend increased amounts of time in the proximity of macrophages. In the presence of antiplatelet antibodies found in ITP spleens, this delayed transit would lead to greatly increased platelet destruction.

The high splenic hematocrit: a rheological consequence of red cell flow through the reticular meshwork

The spleen concentrates blood to twice arterial hematocrit, but how it does so is poorly understood. We hypothesize that hemoconcentration results from percolation of blood through the reticular meshwork (RM) between capillary endings and venous channels. The RM has a large flow cross section, producing low shear rates, and an enormous surface area for red blood cell (RBC) adhesion. If these conditions cause slowing of RBCs with respect to plasma, increased hematocrits will occur (inverse Fahraeus effect). Movements of individual RBCs through the RM were studied from intravital microscopic videorecordings of Ringer-perfused mouse spleens. Analysis of three 70-microns paths showed characteristic "stop and go" motion, RBCs spending 0.015 to 9.71 see in any 7-microns segment, despite steady (+/- 15%) perfusate velocity. At some locations RBCs adhered to reticular cells/fibers by point attachment and at others they became caught over fibers. In general, RBCs were detained in the RM by surface interactions rather than by narrow channel. Perfusate ("plasma") velocity was estimated to be at least that of the fastest RBCs in each segment. Ratios of overall mean RBC and plasma velocities for three paths were 0.19, 0.20, and 0.37. Applying these velocity ratios to a feed hematocrit of 40% leads to predicted splenic hematocrits up to 78%. We conclude that this slowing of RBCs within the reticular meshwork provides the primary mechanism for generating the high intrasplenic hematocrit.

Microcirculatory pathways and blood flow in spleen: new insights from washout kinetics, corrosion casts, and quantitative intravital videomicroscopy

The dynamics of splenic microcirculatory blood flow and the role of the spleen with respect to red blood cells (RBCs) have been elucidated by means of several different experimental approaches. First, the organ was treated as a 'black box' and input/output relationships were studied, such as the kinetics of RBC and plasma washout during Ringer perfusion. Second, microcorrosion casts were prepared from minimal amounts of injected material, such that 'fast' pathways for flow were selectively identified. Third, high-resolution video-microscopy was carried out in rat and mouse spleens transilluminated in vivo, with subsequent quantitative analysis of the data. New insights were obtained regarding fast and slow pathways for RBC flow; the origin of the high intrasplenic hematocrit; immature RBCs and the spleen; the pH, O2 tension and glucose concentration within the reticular meshwork; microcirculatory pathways bordering the white pulp; entry of blood into venous sinuses, both by open ends in the marginal sinus/zone and via interendothelial slits in sinus walls; spontaneous cyclic contractions of capillary walls in vivo, impeding RBC flow (i.e. endothelial contractility); and leukocyte interactions with walls of venous vessels. The different experimental approaches have provided complementary information and have clarified a number of important issues about which uncertainty existed in the literature. Exploiting the quantitative analysis of high-resolution intravital videomicroscopic recordings has an exciting potential for gaining new insights into the workings of this complex and neglected organ.

Interactions of leukocytes with vessel walls and with other blood cells, studied by high-resolution intravital videomicroscopy of spleen

Visualization of circulating leukocytes in vivo is difficult because their optical density differs so little from that of plasma. We have obtained intravital microscopic images of leukocytes at high resolution in spleens of rats and mice by means of an inverted microscope with a 100 x oil-immersion lens; oblique lighting gave improved contrast. Photographic evidence and quantitative data describing the behaviour of lymphocytes, polymorphonuclear leukocytes (PMNs), and macrophages within the microvasculature are presented. Mean numbers of marginated lymphocytes in venous vessels ranged from 0.1 to 4.5 per 1000 microns 2 of wall surface, and speeds of rolling from 11 to 20 microns/sec. Adherence times of leukocytes to vessel walls were log normally distributed, median values being 30, 130, and 560 sec, for lymphocytes, PMNs, and macrophages, respectively. Mean speeds of migration along luminal surfaces were similar (7-19 microns/min) for all three types of cells. Lymphocyte migration outward through the venular wall, observed on two occasions, took 1-2 min. Median values for duration of adherence of RBCs and lymphocytes to macrophages were 1 and 42 sec, respectively. Phagocytosis of a lymphocyte was observed and took 3 min. Macrophages often underwent dramatic changes in shape, including formation of a pseudopod up to 155 microns in length. High-resolution intravital videomicroscopy of spleen has great potential for studying leukocyte behaviour, e.g., homing and migration of lymphocytes, and immunologically related macrophage-lymphocyte interactions in vivo.

Effect of sarcomere length on total capillary length in skeletal muscle: in vivo evidence for longitudinal stretching of capillaries

It is generally assumed that when a muscle is shortened or extended the total length of capillaries does not change, implying that capillaries are nondistensible, longitudinally. On the basis of stereological estimates of capillary anisotropy versus sarcomere length, we propose that as long as capillaries are in a tortuous configuration muscle extension will merely decrease the tortuosity, leaving vessel length unaltered. Once capillaries have been pulled into a straight configuration, further extension of the muscle will cause the vessels to stretch. By means of intravital videomicroscopy we have demonstrated that stretching of individual capillaries does indeed occur over a sarcomere length range of 2.1 to 2.9 microns in rat extensor digitorum longus muscle. In vivo measurements of the lengths of six capillaries together with the sarcomere lengths of adjacent fibers were made in muscles positioned at various degrees of extension. Normalized data indicated that four capillaries stretched to the same degree as the muscle, one stretched more and another less. This may reflect differences in distensibility or tortuosity of capillaries in series with one another. The elastic stretching of capillaries during muscle activity may have important consequences in terms of shifts in permeability and increases in capillary surface area.

Temporal distributions of red cell supply rate to individual capillaries of resting skeletal muscle, in frog and rat

Microvascular red cell (RBC) supply in resting skeletal muscle fluctuates with time and varies from capillary to capillary. Our aim was to quantitate this heterogeneity in two species (frog, rat) with very different oxygen requirements. Video recordings were made of RBC flow in capillaries associated with superficial fibers of frog sartorius and rat gracilis muscles, for periods of 2-10 min. RBC supply rate (cell/s) to individual capillaries was computed as the product of RBC 'content' (measured as lineal density, cells/mm, by a video-densitometric method) and RBC velocity (mm/s, measured by a spatial correlation technique). The videotapes were analyzed at rates of 6 to 15 samples per second. Regression analysis of the mean data showed little or no correlation between RBC content and RBC velocity (r2: frog 0.095, rat 0.002), both parameters contributing equally to variations in RBC supply rate. Temporal distributions of the three supply parameters demonstrate (1) the wide range of values present within each capillary, and (2) the symmetry of the distributions at high mean values versus a pronounced skewness as mean values approached zero. The wide range of mean values of each parameter, found in both species, suggests considerable 'spatial' heterogeneity of RBC supply among capillaries in resting muscle. Temporal heterogeneity of RBC supply rate to individual capillaries increased markedly as either velocity or content (or both) approached zero (overall mean coefficient of variation: frog, 62%; rat, 100%). Both species show remarkably similar rates of convective transport of RBCs per capillary in resting muscle (e.g. mean supply rates 3.2 and 6.2 RBCs/s in frog and rat, respectively).

Capillary lengths and anastomoses in rat hindlimb muscles, studied by Aquablak perfusion during rest versus exercise

This investigation shows that provided an adequate perfusion time of the capillary network is allowed following injection of Aquablak, the presence of arterioles and capillaries having zero or near-zero flow rates can be demonstrated in resting muscle. During hyperemia, "flow recruitment" occurs in these vessels, as indicated by their perfusion with Aquablak. Our observations of Aquablak perfusion in hyperemic muscles show that in medial gastrocnemius, gracilis, and soleus the mean arteriolar-to-venular distances, and also the mean capillary pathlengths, were not dramatically different. What was striking, however, was the fact that capillary pathlengths in soleus were divided into twice the number of segments found in gastrocnemius and gracilis. This suggests the possibility that in oxidative muscles the capillary network may exhibit a much higher degree of branching than in glycolytic muscles. This would increase the area for diffusional exchange between blood and tissue in oxidative compared to glycolytic muscle.

Microcirculatory changes in livers of mice infected with murine hepatitis virus. Evidence from microcorrosion casts and measurements of red cell velocity

Hepatitis has been considered, classically, as a diffuse hepatocellular necrosis, and little attention has been paid to the relationship of lesions to the microvasculature. In livers of mice (Balbc/J) infected with murine hepatitis virus (MHV-3), microcorrosion casts showed spherical cavities where casting compound was unable to fill sinusoids. At 48 hr postinfection such "lesions" had a mean diameter of 83 micron +/- 26 (SD) and their number/mm2 (at the surface of casts) was 0.95 +/- 1.3. Blind-ended sinusoids formed a distinct boundary between perfused and nonperfused areas, and concave impressions at their ends indicated cells blocking the lumen. In vivo microscopy of transilluminated livers in infected mice showed localized rounded areas without flow, corresponding to lesions seen in casts. RBC velocity measurements in sinusoids adjacent to lesions demonstrated that velocities fall from normal values to zero over a narrow border zone. Beginning with the most proximal sinusoid with visible flow and moving outward from the lesion to the second and third sinusoids, mean RBC velocities (micron/sec, +/- SD) were 17.4 +/- 6.7, 33.9 +/- 8.7, 66.6 +/- 27.3, respectively; this last value was not significantly different from velocities in normal liver (69.2 +/- 30.6). Transmission electron microscopy of livers of infected mice confirmed the presence of sinusoidal lumens blocked by protruding lining cells, RBCs, platelets, swollen hepatocytes, and cellular debris. This study demonstrates that the lesions are focal in origin, microvascular blockage leading to gradually increasing necrosis in all directions.

Spontaneous cyclic contractions of the capillary wall in vivo, impeding red cell flow: a quantitative analysis. Evidence for endothelial contractility

We have videorecorded spontaneous cyclic contractions of capillary walls which often stopped the flow of blood cells, in spleens of rat and mouse. An inverted microscope and oblique lighting were key elements in obtaining images in which the boundaries of cells composing vessel walls were clearly distinguishable. Using slow motion replay, we measured the widths of endothelial cells (C), pericytes (P, when present) and capillary lumens (L; at the site of constriction; U; 15-20 micron upstream), throughout 11-12 min sequences containing many contraction/relaxation cycles. In roughly 50% of contractions L decreased to 0-1 micron, such luminal "closures" occurring within 2-12 sec and lasting for less than 1 sec to greater than 1 min. Intervals between contractions ranged from 12 sec to 3 min (average 1 min). Documentation of one such cycle by sequential photographs from the video monitor is presented, showing dramatic bulging of an endothelial cell into the lumen. Comparison of records of L and C versus time showed that almost invariably when L decreased C increased, and vice versa; highly significant correlations existed between C and L in every case (P less than 0.0005). Multiple linear regression analysis showed that changes in C were responsible for 18-77% of the total variance in L, whereas P contributed only 0-4%; changes in U, covariance between C, P, and U, and unexplained variance were responsible for 0-20, 11-30, and 11-53%, respectively, of the total variance in L. We conclude that these spontaneous capillary contractions were primarily due to endothelial contractility.

Capillary configuration and fiber shortening in muscles of the rat hindlimb: correlation between corrosion casts and stereological measurements

It has been a matter of discussion whether the dramatic increase in capillary tortuosity visualized in shortened muscles by vascular cast represents in vivo situations. In this study, we combined vascular cast and stereological methods in the same samples, in order to obtain (1) measurements of sarcomere length in the same muscles from which corrosion casts were prepared, and (2) scanning electron micrographs of the three-dimensional arrangement of capillaries in the same muscles where capillary anisotrophy was estimated by morphometry. Various rat skeletal muscles (soleus, gastrocnemius, and gracilis) were examined at lengths ranging from full shortening to full extension. We found a very good correlation between capillary geometry in material prepared for vascular casts and in muscles perfusion-fixed in situ. All muscles, cast and noncast, showed the same progressive curvilinear decrease in capillary anisotropy with decreasing sarcomere length. Capillary tortuosity visualized by corrosion casts in shortened muscles is a consequence of fiber shortening, within physiological sarcomere lengths; it does not represent an artifact related to the casting procedure.

Microcirculatory pathways in normal human spleen, demonstrated by scanning electron microscopy of corrosion casts

Confusion regarding microcirculatory pathways in normal human spleen has arisen due to extrapolation from pathological material and from other mammalian spleens, not to mention difficulties in tracing intricate three-dimensional routes from the study of thin sections or cut surfaces of tissue. We examined microcirculatory pathways in normal human spleens freshly obtained from organ transplant donors. A modified corrosion casting procedure was used to obtain an open view of vessels and their connections. Our results demonstrate: 1) "arteriolar-capillary bundles" within lymphatic nodules and extensive branching of arterioles in the marginal zone (MZ); 2) the marginal sinus around lymphatic nodules; 3) the peri-marginal cavernous sinus (PMCS) outside the MZ or immediately adjacent to the nodule itself; the PMCS receives flow via ellipsoid sheaths and MZ, or directly from arterial capillaries, and drains into venous sinuses; 4) fast pathways for flow into venous sinuses via ellipsoid sheaths; 5) arterial capillary terminations in the reticular meshwork of the red pulp or MZ ("open" circulation); direct connections to venous sinuses also occur ("closed" circulation), although rarely; and 6) numerous open-ended venous sinuses in the MZ, allowing a large proportion of the splenic inflow to bypass the red cell filtration sites in the reticular meshwork and at venous sinus walls.

Kinetics of red blood cell passage through interendothelial slits into venous sinuses in rat spleen, analyzed by in vivo microscopy

Sequential photomicrographs of RBCs passing through interendothelial slits (IES) in walls of venous sinuses in rat spleen were obtained by video recording in vivo microscopic views. Kinetics of RBC passage were analyzed by slow-motion playback of recordings. An inverted microscope and oblique lighting from a water-cooled fiber optic light source were key elements in obtaining images of sufficient quality for analysis. The direction of RBC passage through IES was, invariably, from reticular spaces of the red pulp into venous sinuses. RBC flow through an individual IES occurred as brief discontinuous bursts, separated by periods of zero, or near zero, flow. Mean rates of RBC flow through six IES analyzed in normal relaxed spleen ranged from 1.4 to 9.1 cells/15 sec, the total RBCs studied being 1523 and the total combined period of observation 98 min. The maximum instantaneous rate was 10 RBCs/sec. RBC transit times ranged from 0.02 to 60.5 sec, even for a single IES; the distribution was highly skewed: median 0.23 sec, mean 1.7 sec. Analysis of RBC flow through two closely adjacent IES simultaneously, for 30 min, showed that most bursts were asynchronous. The results indicate that changes in caliber of IES are primarily responsible for the observed pattern of flow. It was estimated that only 19% of the total IES present anatomically actually allowed passage of RBCs during any 5-min period.