Biomedical subjects

I C MacDonald

Publications and source records attributed to I C MacDonald.

At least 37 records · Page 2Linked to original sources

PubMed1993

New aspects of microvascular corrosion casting: a scanning, transmission electron, and high-resolution intravital video microscopic study.

We used intravital microscopy of small intestine and pancreas in order to show dynamic interactions between vascular wall and undiluted Mercox, because previous studies of ours have shown that Mercox diluted with monomeric methylmethacrylate penetrates cells in the vascular wall. Scanning and transmission electron microscopy were used to show three-dimensional pathways and correlating tissue structures, which cannot be identified in vivo. The microvascular diameters were not altered when the vasculature was flushed with saline/dextran solution using perfusion pressures between 70 and 140 mm Hg, but, in circumscribed areas, contraction of vascular wall was observed immediately after Mercox injection. This phenomenon was carried out by endothelial cells; pericytes were never present at the site of constrictions. Extravasation, i.e., leakage of the resin into the surrounding tissue, occurred in circumscribed areas regardless of the applied perfusion pressure. The resin also filled routes, which were not perfused with blood before casting. Scanning microscopy of corresponding specimens showed flattened cast channels, with impressions of valves and endothelial cell nuclear imprints characteristic of lymphatics. These results show that undiluted Mercox is a stimulus for vascular cellular components and that it changes the vascular wall permeability, resulting in extravasation and filling of lymphatics. Transmission electron microscopy showed that large vessels were homogeneously filled with resin and that cellular structures were not infiltrated with Mercox. Cut sections of the gold-coated surface of casts showed grooves up to 20 nm wide, suggestive of minimal deformation, while the abluminal surface of the metal film was almost smooth. Another proof of minimal deformation of undiluted Mercox casts is that the diameter of vessels was not altered during and after polymerization. Obtained casts are not fragile, as are casts of diluted Mercox, and phase separation does not occur, which would result in penetration of the cells in the vascular wall. For these reasons, the use of undiluted Mercox is recommended. Mixing 10 ml Mercox with 1 g catalyst resulted in complete polymerization within 5.5-7 min. This mixture can be used for casting biological specimens.

Animals↗

PubMed1993

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.

Animals↗

PubMed1993

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.

Animals↗

PubMed1993

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.

Animals↗

PubMed1992

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.

Animals↗

PubMed1992

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.

Allantois↗

PubMed1991

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.

Adult↗

PubMed1991

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.

Animals↗

PubMed1991

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)

Animals↗

PubMed1991

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.

Animals↗

PubMed1990

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.

Animals↗

PubMed1990

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.

Animals↗

PubMed1988

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.

Humans↗

PubMed1988

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.

Analysis of Variance↗

PubMed1987

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.

Animals↗

PubMed1983

Circulatory pathways in the sinusal spleen of the dog, studied by scanning electron microscopy of microcorrosion casts.

Scanning electron microscopy of microcorrosion casts was used to visualize circulatory pathways in the sinusal spleen of dog. The examination of contracted versus dilated organs and variations of the volume of material injected gave an indication of flow dynamics. Minimal injections of material into contracted spleens produced filling of mainly the fastest routes for flow, whereas injections into dilated spleens primarily filled slower routes. This procedure yielded a more complete, three-dimensional picture of the arterial, intermediate, and venous pathways as a whole, and of the relative amounts of flow through different arterial routes. Evidence of flow from capillary lumina out into ellipsoid sheaths was plentiful in casts from dilated spleens, but rare in casts from contracted organs. The pattern of flow within and out of the marginal sinus has been elucidated: A circumferential filling occurs first, followed by a flow that radiates outward into the marginal zone and red pulp. Venous sinuses filled via two routes in addition to the generally accepted path from the reticular meshwork via fenestrations in sinus walls. First, many venous sinuses extending out from the marginal sinus and surrounding marginal zone originated as open-ended tubes continuous with the reticular spaces of the marginal sinus or marginal zone. Second, direct connections of arterial capillaries with venous sinuses in the red pulp were found. Evidence indicating that some mechanism is controlling the flow via these routes is discussed. The strikingly different arrangement of venous sinuses in the subcapsular region is demonstrated.

Animals↗

PubMed1983

The intermediate circulation in the nonsinusal spleen of the cat, studied by scanning electron microscopy of microcorrosion casts.

Scanning electron microscopy of microcorrosion casts was used to visualize circulatory pathways of the intermediate circulation in nonsinusal spleen of cat. The marginal sinus (MS) around lymphatic nodules is a distinct vascular space which fills preferentially before the filling of the marginal zone (MZ) and surrounding red pulp occurs. The MS, which has a plentiful vascular supply, does not usually enclose the nodule completely. From the MS, flow occurs radially outwards into the MZ. Corrosion casts and histological sections both showed that a diversity of forms of the MZ exists: The thickness of MZ and the arrangement of its reticulum vary among nodules and between different areas of the same nodule, from a complete absence to a region of up to 50 microns in width. No direct arteriovenous connections were found (in contrast to dog spleen: Schmidt et al., '83b). Aside from capillary endings in the MS and MZ, all arterial capillaries terminate in the reticular spaces of the red pulp, i.e., the circulation appears to be entirely "open." From each capillary termination a great variety of flow pathways through the reticular meshwork to the pulp venules is available; some of these routes are quite long but others may involve distances as short as 15-25 microns. Evidence of flow into ellipsoid sheaths was abundant in casts from dilated spleens, but scarce in contracted spleens. In contrast to the extensive system of interconnected venous sinuses in dog spleen, the pulp venules found in cat spleen are nonanastomosing, shorter, and much smaller in caliber, and all receive flow freely from the reticular meshwork via open ends and fenestrations in their walls.

Animals↗

PubMed1983

Luminal morphology of small arterial vessels in the contracted spleen, studied by scanning electron microscopy of microcorrosion casts.

Unique luminal configurations exhibited by small arterial vessels in contracted spleens of dog and cat were studied by means of vascular corrosion casts examined by scanning electron microscopy. Concertina-like pleating was seen in casts of trabecular arteries/arterioles, whereas within lymphatic nodules arteriolar casts lacked pleating and were smooth and uniformly cylindrical (as were all small arterial vessels in distended spleens). Morphological details of arterial vessels observed in histological sections indicated that pleating is not due to contraction of specially arranged vascular smooth muscle but to overall shortening of trabecular arterial vessels, caused by contraction of longitudinal smooth muscle in trabeculae. Another phenomenon observed in casts from contracted spleens was an almost complete "pinching-off" of many arteriolar lumens; histological evidence indicated that this is due to contraction of vascular smooth muscle, which selectively diverts flow away from certain regions of the organ. Also noted was a markedly convoluted, tortuous configuration of arterioles (penicilli) in the red pulp of contracted spleens.

Animals↗