Macrophage depletion alters vein graft intimal hyperplasia

BACKGROUND

The principal cause of vein graft failure is intimal hyperplasia (IH); however, its etiology remains unclear. In a rat model of vein graft IH we have observed prolonged transmural macrophage infiltration, leading us to hypothesize that these cells regulate IH. To test this, we used liposome-encapsulated dichloromethylene bisphosphonate (L-Cl2MBP) to deplete rat macrophages and observed the effects on IH.

METHODS

Epigastric vein-to-femoral artery grafts were microsurgically placed in male Lewis rats that had been intravenously injected with L-Cl2MBP, phosphate-buffered saline solution liposomes, or phosphate-buffered saline solution alone 2 days before surgery. Several animals in each group received a second equivalent dose at 2 weeks. Grafts, contralateral epigastric veins, spleens, and livers were harvested at 1, 2, and 4 weeks for histologic examination, immunohistochemistry, and transmission electron microscopy.

RESULTS

In the L-Cl2MBP-treated animals splenic and hepatic macrophages were greatly reduced, confirming the efficacy of the agent. At 1 to 2 weeks graft macrophages were significantly decreased, and there was a trend toward decreased IH. At 4 weeks macrophage numbers were normal and IH development had resumed. In contrast, the 4-week grafts treated with 2 doses of L-Cl2MBP had fewer macrophages and displayed severely attenuated IH.

CONCLUSIONS

The results indicate a suppression of IH as macrophages are depleted, with a resumption of the process as macrophages repopulate the graft.

Histologic evaluation of spermatic veins in patients with varicocele

BACKGROUND

Information concerning varicocele is limited in spite of its clinical importance. This study intends to clarify anatomical features of varicocele.

METHODS

Spermatic veins were obtained from varicocele patients at surgery. Areas of two distinct portions (extracellular matrix and smooth muscle) were measured by a micro computer imaging device image analysis system on histologic slides with Masson trichrome stain. In addition, we evaluated the shape and arrangement of the smooth muscle fibers by a scanning electron microscope (SEM).

RESULTS

Masson trichrome stain revealed that grade of varicocele partly correlated with thickness of the wall and with amount of the smooth muscle fibers. In the patients with grade 3 varicocele, SEM examination showed marked hypertrophy of longitudinal smooth muscle fibers, which were discriminated clearly from the inner circular fibers.

CONCLUSIONS

This study indicated that morphological changes occurred in the muscle layers of varicoceles in the worst grade of varicocele. These structural changes which result from abnormal venous blood circulation may cause development of varicocele, resulting in male infertility.

Structural identification and characterization of arteries and veins in the placental stem villi

The vascular wall structure in the human full-term placental villi of normal pregnancy was studied by means of light and electron microscopy with an improved technique of perfusion fixation and tissue preparation. We observed 81 sections of stem villi that showed cross-sectional profiles of paired vessels in their center. Both vascular walls contained a large amount of extracellular matrix and no elastic lamina between smooth muscle cells of the media, making identification of the artery and the vein quite difficult at first sight. We then noted that the density of the smooth muscle cell population was always considerably higher in one than the other, and identified the former as artery and the latter as vein on the basis of their connection with larger arteries and veins running on the chorionic plate. Between the paired vessels, the artery had a smaller caliber than the vein, and the ratio of venous to arterial caliber was distributed from 1.0 to 2.5. The thickness of media was usually thicker in the vein than in the artery. Clusters of elastic fibers were found occasionally in the media of arteries and veins, and basement membrane-like materials were associated frequently with the elastic fibers and were distributed widely in the media as well as in the adventitia. In the veins, the smooth muscle cells of the most superficial part of the media contained well-developed rough endoplasmic reticulum and Golgi apparatus, indicating differentiation to secrete extracellular matrices. The present study revealed the difference of wall structure between arteries and veins in the placental stem villi for the first time at the ultrastructural level, and suggested differentiation of venous smooth muscle cells, possibly by some influence from the luminal side.

Caveolae and vesiculo-vacuolar organelles in bovine capillary endothelial cells cultured with VPF/VEGF on floating Matrigel-collagen gels

In situ vascular endothelium is characterized by many cytoplasmic vesicles (caveolae) and vacuoles. In venules these are organized into prominent clusters called vesiculo-vacuolar organelles or VVOs. VVOs provide an important pathway for plasma protein extravasation in response to vasoactive mediators. In contrast, cultured endothelial cells isolated from many sources lack VVOs and generally have few caveolae. Our goal was to preserve VVOs in cultured endothelium. Bovine adrenal microvascular endothelial cells (BCEs) cultured on floating Matrigel-collagen Type I gels with vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) exhibited typical VVOs by electron microscopy. Both in vivo and in culture VVOs were caveolin-positive by immunoelectron microscopy. On the basis of caveolin immunostaining, VVOs could also be detected by light (confocal) microscopy. When BCEs were cultured without VPF/VEGF, caveolin staining was finely punctate and electron microscopy confirmed the near absence of VVOs. BCE VVOs were sensitive to N-ethylmaleimide. Other types of endothelium cultured on Matrigel-collagen gels with or without VPF/VEGF exhibited few caveolae and no VVOs. Therefore, preservation of VVOs in cultured endothelium required a specific combination of endothelial cells (BCEs), surface matrix (Matrigel-collagen), and growth factor (VPF/VEGF). These endothelial cells should be useful for in vitro studies of trans-endothelial transport.

Immunohistochemical and ultrastructural study of microvessels in diabetic veins

The aim of this study was to examine the localization and features of the intramural microvessels in the wall of inferior limb veins in diabetic patients. The study was conducted in a group of 10 insulin-dependent diabetic patients, who had suffered inferior limb amputation as a consequence of chronic limb ischemia. Sections of long saphenous and posterior tibial veins were investigated by light and transmission electron microscope. The von Willebrand factor and albumin were detected by immunohistochemical techniques. The results show the presence of numerous microvessels in the intima and inner third of the media layer of the venous wall of the sections studied. These microvessels present morphological and functional modifications in relation to those observed in the control veins. They also showed the presence of endothelial cells migrating from the lumen. The authors conclude that the venous wall of inferior limbs in amputated diabetic patients presents a neovascularization process. Some of the endothelial cells of the venous lumen can also have a role in the angiogenesis.

Angioarchitecture of the coeliac sympathetic ganglion complex in the common tree shrew (Tupaia glis)

The angioarchitecture of the coeliac sympathetic ganglion complex (CGC) of the common tree shrew (Tupaia glis) was studied by the vascular corrosion cast technique in conjunction with scanning electron microscopy. The CGC of the tree shrew was found to be a highly vascularised organ. It normally received arterial blood supply from branches of the inferior phrenic, superior suprarenal and inferior suprarenal arteries and of the abdominal aorta. In some animals, its blood supply was also derived from branches of the middle suprarenal arteries, coeliac artery, superior mesenteric artery and lumbar arteries. These arteries penetrated the ganglion at variable points and in slightly different patterns. They gave off peripheral branches to form a subcapsular capillary plexus while their main trunks traversed deeply into the inner part before branching into the densely packed intraganglionic capillary networks. The capillaries merged to form venules before draining into collecting veins at the peripheral region of the ganglion complex. Finally, the veins coursed to the dorsal aspect of the ganglion to drain into the renal and inferior phrenic veins and the inferior vena cava. The capillaries on the coeliac ganglion complex do not possess fenestrations.

Diabetes-induced structural changes of venous and arterial endothelium and smooth muscle cells

The structural alterations of endothelium and smooth muscle cells of the hind limb and heart veins and arteries were investigated in Golden Syrian hamsters subjected to streptozotocin induced diabetes. Animals were examined at 5, 10, and 15 weeks after induction of diabetes. At each time point body weight and plasma glucose concentrations were recorded. Anesthetised animals were washed out of blood, fixed in situ, and the femoral vein and artery, saphenous vein and artery, and heart veins and coronaries were dissected out, and processed for electron microscopical examination. Anionic sites of the endothelial plasmalemma were visualized by in situ perfusion of cationized ferritin. The endothelial localization of von Willebrand factor was carried out by immunocytochemistry. The results showed that induction of experimental diabetes generated morphological changes of the endothelium and smooth muscle cells of both hind limb and heart vessels. The common alterations developed in endothelial cells of venous and arterial origin consisted in: 1) the development of a secretory phenotype, enriched in biosynthetic and degradative organelles; 2) the abundance of cytoskeletal elements, especially intermediary filaments; 3) the increase in number of fused plasmalemmal vesicles and transendothelial channels, and 4) the hyperplasia of the basal lamina. In contradistinction to the arterial endothelium, the peculiarities of the venous endothelium in the diabetic hamsters examined were: 1) the uniform distribution of the anionic sites exposed on the luminal plasma-lemma (as in normal animals), and 2) the increased number of copies of Weibel-Palade bodies (up to 13 copies per endothelial cell in the hind limb). Von Willebrand factor was immunodetected in Weibel-Palade bodies, Golgi cisternae and some vesicles of normal and diabetic hamsters. With time, and especially pronounced at 15 weeks of diabetes, the smooth muscle cells of veins and arteries examined exhibited a characteristic secretory phenotype, and were surrounded by a reticulated basal lamina and a hyperplasic extracellular matrix (especially pronounced in arteries). These data indicate that diabetes affects both heart and hind limb veins and arteries, producing structural changes of the endothelium and smooth muscle cells which may account, at least in part, for the specific vascular complications.

G protein signaling and vein graft intimal hyperplasia: reduction of intimal hyperplasia in vein grafts by a Gbetagamma inhibitor suggests a major role of G protein signaling in lesion development

Vein grafting results in the development of intimal hyperplasia with accompanying changes in guanine nucleotide-binding (G) protein expression and function. Several serum mitogens that act through G protein-coupled receptors, such as lysophosphatidic acid, stimulate proliferative pathways that are dependent on the G protein betagamma subunit (Gbetagamma)-mediated activation of p21ras. This study examines the role of Gbetagamma signaling in intimal hyperplasia by targeting a gene encoding a specific Gbetagamma inhibitor in an experimental rabbit vein graft model. This inhibitor, the carboxyl terminus of the beta-adrenergic receptor kinase (betaARK(CT)), contains a Gbetagamma-binding domain. Vein graft intimal hyperplasia was significantly reduced by 37% (P<0.01), and physiological studies demonstrated that the normal alterations in G protein coupling phenotypically seen in this model were blocked by betaARK(CT) treatment. Thus, it appears that Gbetagamma-mediated pathways play a major role in intimal hyperplasia and that targeting inhibitors of Gbetagamma signaling offers novel intraoperative therapeutic modalities to inhibit the development of vein graft intimal hyperplasia and subsequent vein graft failure.

[Vascular microanastomosis by eversion and stapling using VCS forceps. Presentation of the technique and experimental evaluation of its reliability]

With the objective of further improving the reliability of microvascular anastomoses, several different procedures are now available to microsurgeons, including eversion-stapling by VCS forceps. The authors start by presenting the technique, emphasizing the need for specific instruments and compliance with certain principles determining the success of these anastomoses. In the context of an experimental protocol in the pig, on vessels measuring an average of 2.5 mm in diameter, 80 anastomoses were performed by VCS stapling-eversion and studied clinically, histologically and ultrastructurally, comparing the results to those of conventional anastomoses by approximation-suture with needle and suture. In light of the results, eversion-stapling anastomoses appear to be more reliable due to the absence of intraluminal foreign body, permanent endothelial continuity and effective re-endothelialisation before day 7.

[Intramural blood vessels of the large intestine of the horse (Equus przewalskii f. caballus)]

The vascular system of the large intestine of 12 horses was examined by means of vascular corrosion casts, histology and transmission electron microscopy providing the following results. The Aa. et Vv. breves et longae leave the mesenteric vessels, respectively the subserously on the teniae lying cecal vessels to reach the tela subserosa at the mesenteric margin. The short vessels enter the deeper layers of the wall instantly, whereas the Aa. et Vv. longae move towards the submucosa by penetrating the muscular layers after a variable subserous course. The tela submucosa contains an arterial and a venous vascular plexus. In broader areas of the submucosa a three-dimensional vascular network can be found. This consists of a deep and a superficial vascular plexus, which are closely interconnected. The deep plexus is applied to the inner circular muscles, whereas the superficial plexus is adjacent to the muscularis mucosae. The (deep) arterial plexus receives its afflux from the Aa. breves et longae and supplies parts of the circular muscle layer with recurrent muscle branches. The vascularisation of the mucosa also originates from the submucosal (superficial) plexus. In the basal tunica mucosa, the ascending arteries form a transversal network from which arterioles branch into periglandular capillaries around each Lieberkühn crypt. Close to the lumen, a polygonal subepithelial capillary system is formed. The capillaries turn into postcapillary venules immediately below the epithelium of the mucosal surface. Veins move vertically through the submucosa to enter the submucosal plexus after few inflowing side branches. Branches of the subserous-submucosal connections form an intermuscular plexus between the circular and longitudinal muscular layer. This plexus supplies the capillaries of the tunica muscularis. The subepithelial capillaries are predominantly lined with a fenestrated endothelium, whereas the capillaries of the pericryptal mucosa mainly show a continuous endothelial lining. The latter contain multiple vesicles, which may fuse in order to form transcytoplasmic channels. Sphincter-like muscle bundles at the transition points from capillaries to venules may provide hemodynamic regulatory structures in the submucosa of the horse. Veins with circumferential cushions of smooth muscle fibres, so-called 'throttle veins', are also found.

Endothelin-1 causes luminal constrictions in rat cochlear veins

Serum levels of the vasoconstrictor endothelin-1 (ET-1) increase in ischemia and systemic hypertension. We examined the effects of ET-1 on the cochlear microvasculature. Blood vessels were cast with methacrylate in adult male Wistar Kyoto rats, 10 min after intravenous injection of ET-1 (1.0 microg/kg); control animals received saline. Systemic blood pressure was recorded continuously. ET-1 increased the average systolic pressure by 18% and average diastolic pressure by 22% (P < 0.01). Scanning electron microscopy of cast vessels showed multiple circumscribed luminal constrictions on: (1) postcapillary venules; (2) collecting veins; (3) where collecting veins merged with the spiral modiolar vein; (4) on the spiral modiolar vein itself. Circumscribed constrictions in arteries were not observed. In ET-1 injected animals focal contractions of collecting veins reduced luminal width by 13.4% +/- 2.9 (P < 0.01). In control rats, constrictions on venous casts were minimal and constrictions on arteries were not observed. The present study shows that ET-1 is involved in local control of cochlear blood flow in that it focally contracts cochlear veins. It is suggested that this might be due to the high affinity of ET-1 receptors and/or the large number of ET-1 receptors on contractile cells in venous walls.

An ultrastructural study of progressive intimal hyperplasia in rat vein grafts

PURPOSE

Intimal hyperplasia (IH) poses the greatest challenge for vein graft success. This fibroproliferative disorder causes obliterative stenosis and frequent graft occlusion. Although its causes remain poorly understood, it has been proposed that IH begins as a wound-healing response that cascades into a chronic state of unchecked proliferation. In this ultrastructural study, IH development and concomitant cell changes were evaluated in rat vein grafts.

METHODS

Epigastric vein-to-femoral artery grafts were placed in Lewis rats using standard microsurgical techniques. At various time points, grafts were harvested and processed for transmission electron microscopic, histologic, and immunohistochemical analyses. The proximal region, which displayed the most marked IH, was assessed for ultrastructural changes.

RESULTS

Our findings showed: (1) regeneration of the damaged endothelium by cells displaying an activated appearance; (2) early and complete smooth muscle cell death, with subsequent replacement by myofibroblastic cells; (3) extensive and sustained graft infiltration by monocytes/macrophages; and (4) intramural fibrin deposition.

CONCLUSIONS

The rat vein graft wall was substantially altered after implantation into the arterial circulation. During and after IH development, the cells in the graft did not resemble cells that are present in the nongrafted epigastric vein. Marked cell death, mononuclear cell infiltration, and the presence of myofibroblastic cells suggest a state of aberrant wound healing.

Pancreatic insulo-acinar portal systems in humans, rats, and some other mammals: scanning electron microscopy of vascular casts

Scanning electron microscopy of vascular casts showed that in the mouse, rat, and guinea pig, the pancreatic endocrine islets were frequently interlobular in position and emitted insulo-venous efferent vessels directly draining into veins. In these animals, the intralobular islets, located within the exocrine lobules, issued insulo-acinar portal vessels continuous with the lobular capillaries in addition to the insulo-venous efferent vessels. In humans, monkeys, cows, pigs, dogs, cats, and rabbits, essentially all islets in the pancreas were intralobular in location and emitted the insulo-acinar portal vessels only. In man and animals examined, especially in the murine species, many lobules lacked an islet, therefore the insular control over the exocrine pancreas seemed to be effected in more or less restricted areas of lobules.

Morphologic sites for regulating blood flow in the exocrine pancreas

The exocrine pancreas has a lobular structure and an intricate capillary network supplies the lobules. Casts of these capillaries are either straight and of constant width, provided with many shallow crests, or undulating and of varying diameter, provided with bulges and deeper constrictions. The mean capillary cast diameter is 6.32 microns (SD 0.53) and 3.91 microns (SD 0.84) at constriction sites. The first type corresponds to non-fenestrated capillaries, makes 24% of capillaries and is more frequently provided with pericytes (2.7 +/- 0.9 pericytes per capillary profile). The second type corresponds to fenestrated capillaries, comprises 76% of the capillaries and is less frequently provided with pericytes (1.5 +/- 0.6 pericytes per capillary profile). The endothelial cells of capillaries regularly form intermediate junctions and microvilli and contain microtubuli and cytoplasmic filaments. Intravital observations show that capillaries are capable of contracting and narrowing the capillary lumen. This contractility is accomplished by endothelial cells both at and apart from their nuclear regions while pericytes never contracted spontaneously during our in vivo observations. The capillary diameters estimated by intravital measurements, 3.53 microns (SD 1.05), are similar to cast measurements but differ at constricted segments from cast measurements. Flow reduction shows more variability in smaller capillaries and the flow is more reduced in capillaries of 5 microns diameter to about 40% of open capillaries vs. 68% in capillaries with 7.5 microns diameter. Veins are either provided with smooth muscle sphincters or with valves. These results indicate that corrosion casting accurately shows the geometry of capillaries. However, where the capillaries are drastically constricted, they might not be filled and therefore may be underestimated during measurements. Since none of the intravital luminal constrictions are small enough to reduce flow (smaller than 1 micron luminal diameter) and because many constrictions are effective to reduce flow, we conclude that capillaries of the exocrine pancreas are always capable of maintaining continuous blood flow yet can influence blood perfusion. The presence of venous valves in association with venous sphincters constitutes a new situation concerning blood drainage regulation in the exocrine pancreas.

Angioarchitecture of the human spermatic cord

Human spermatic cords were investigated by means of cast preparations, light-microscopic examination and computer-aided 3-dimensional reconstructions from serial sections of paraffin-embedded material. After leaving the testis, the testicular veins formed two principal groups co-existing side by side. Numerous veno-venous anastomoses could be observed within each individual group, whereas only a few mutual intergroup anastomoses were found. The testicular artery ran within one group but showed no close topographical relationship to the other group. Light microscopy of the serial sections revealed that the group of veins with no close topographical relationship to the testicular artery ran at a distance of several centimeters embedded within fatty tissue. With the help of computer-aided 3-dimensional reconstructions, a spatial picture of the vascular organization was obtained. These results allowed the following classification of the veins of the pampiniform plexus. Group-I veins formed a tight plexus around the testicular artery by means of veno-venous anastomoses. Group-II veins formed veno-venous anastomoses between each other and ran over at a sizeable distance embedded in fatty tissue but showed no close topographical relationship to the testicular artery. Group-III vessels formed veno-venous anastomoses between group-I and group-II. Group IV veins formed arterio-venous anastomoses with the testicular artery. Based on the differences in wall structure and diameter, a subclassification in group-I and group-II was undertaken. This organization of the veins of the human pampiniform plexus should further the understanding of physiological processes, such as the transfer of hormones and other substances from the veins to the testicular artery and vice versa. It should also facilitate the tracing of the veins during antegrade sclerosing.

Antisense oligonucleotide to proto-oncogene c-myb inhibits the formation of intimal hyperplasia in experimental vein grafts

BACKGROUND

The development of intimal hyperplasia is a major cause of early vein graft failure. The study examines the effects of locally delivered antisense oligonucleotides to the proto-oncogene c-myb on the development of vein graft intimal hyperplasia.

METHODS

Common carotid vein bypass grafting procedures were performed on 60 New Zealand White rabbits. Seventeen grafts were controls, 14 had grafts coated with a commercial gel, 17 had grafts coated with gel containing 200 micrograms of an antisense c-myb oligonucleotide, and 6 rabbits each had grafts coated with gel containing one of two control oligonucleotides. Grafts were harvested 28 days after surgery, and sections were taken for dimensional analysis, morphologic evaluation, and vasomotor function. Grafts were also harvested at 1 day for oligonucleotide uptake/localization analysis and at 3 days for c-myb mRNA analysis.

RESULTS

Oligonucleotides were uniformly distributed within the media and adventitia by 1 day. A 38% reduction occurred in mean intimal thickness in the vein grafts coated with antisense to c-myb compared with the other groups. No difference in medial thickness was seen among groups. By scanning and transmission electron microscopy all vein grafts showed a confluent endothelium. In contrast to control vein grafts, which did not relax to acetylcholine, most of the gel and all of the gel/oligonucleotide-coated grafts relaxed by more than 40% of precontracted tension. Responses to a panel of contractile agents were unchanged in the treated groups compared with those in the control group.

CONCLUSIONS

Locally delivered antisense oligonucleotides to proto-oncogene c-myb significantly reduces intimal hyperplasia with preservation of acetylcholine-mediated endothelium-dependent relaxation in experimental vein grafts. These findings suggest that targeting a common regulatory pathway of vascular smooth muscle mitogenesis can be successful in reducing the early development of intimal hyperplasia.

Cardiac-like musculature of the intrapulmonary venous wall of the long-clawed shrew (Sorex unguiculatus), common tree shrew (Tupaia glis) and common marmoset (Callithrix jacchus)

BACKGROUND

The cardiac-like musculature is distributed not only in the heart wall but also in the intrapulmonary venous wall in a few species of insectivores. It has been suggested that the evolutionary origin of venous cardiac-like musculature may be traceable to a basic stock of certain mammalian lines of descent. So, it is important to clarify whether the musculature may be a common structure in lower mammals from insectivores to primates and to examine the functional significance of the structure.

METHODS

The distribution of cardiac-like musculature in the intrapulmonary venous wall of the long-clawed shrew (Sorex unguiculatus), common tree shrew (Tupaia glis), and common marmoset (Callithrix jacchus) was observed by light and electron microscopy. The presence of atrial natriuretic polypeptide (ANP) was examined in the musculature by immunohistochemistry.

RESULTS

All three species contained cardiac-like myocytes in the tunica media of intrapulmonary venous wall. In the common tree shrew and the common marmoset, cardiac-like musculature was found in the small intrapulmonary vein of 150-200 microns in diameter, while, in the long-clawed shrew, it was distributed even in the intrapulmonary vein of 30 microns in diameter. Ultrastructure of myocytes was fundamentally similar to that of atrial myocytes in the long-clawed shrew and the common tree shrew. The presence of atrial natriuretic polypeptide (ANP) was also demonstrated by immunohistochemistry in the intrapulmonary venous walls of common tree shrews.

CONCLUSIONS

The results indicate that the pulmonary venous cardiac-like musculature occurs in the lower eutherian mammals from insectivores to primitive primates. The musculature is thought to act as a regulatory pump in pulmonary circulation and as an endocrine apparatus of ANP.

Short-term preservation of autogenous vein grafts: effectiveness of University of Wisconsin solution

BACKGROUND

Suboptimal preservation of autologous veins in storage solutions causes endothelial cell damage that can contribute to graft failure. The purpose of this study was to compare the effects of short-term storage of veins in autologous whole blood (AWB), 0.9% normal saline solution (NS), and University of Wisconsin solution (UWs) on vein structure and function after grafting.

METHODS

Autogenous jugular and femoral veins were atraumatically harvested from mongrel dogs. One vein segment was immediately implanted to serve as a control, and the other segments were stored for 45 minutes in AWB, NS, or UWs. The veins were implanted as reversed interposition graft in the carotid or femoral arteries. After 6 weeks light and scanning electron microscopy and isometric tension studies were performed on explanted vein grafts.

RESULTS

Morphologic studies revealed an intact endothelium that stained positively for factor VIII. Intimal thickness was similar between controls (48 +/- 12 microns) and veins stored in UWs (53 +/- 8 microns) (p = not significant), but it was significantly increased in veins stored in AWB (151 +/- 29 microns) and NS (149 +/- 18 microns) (p < 0.05). Sensitivity and maximum contraction to norepinephrine were not altered in veins preserved in UWs (6.0 +/- 0.1 mumol/L and 0.19 +/- 0.02 gm/mm2) but were significantly reduced (p < 0.05) in those stored in AWB (7.2 +/- 0.1 mumol/L and 0.08 +/- 0.02 gm/mm2) and NS (7.0 +/- 0.3 mumol/L and 0.09 +/- 0.02 gm/mm2) compared with controls (5.9 +/- 0.2 mumol/L and 0.20 +/- 0.02 gm/mm2). The sensitivity and maximum relaxation to acetylcholine and sodium nitroprusside of veins preserved in AWB, NS, and UWs were similar to controls (p = not significant).

CONCLUSIONS

Vein storage in UWs preserves smooth muscle cell function compared with veins stored in NS or AWB. Therefore UWs is a more suitable medium for short-term preservation of veins in cardiovascular operation.

The microvenous valvular anatomy of the human dorsal thoracic fascia

The use of free scapular fasciocutaneous flaps for reconstruction of recalcitrant grade 6 venous stasis ulcers has shown excellent early success rates. Venous refilling times measured postoperatively over the flaps by photoplethysmography have noted improvements to normal levels. Preliminary anatomic studies have demonstrated valves in the circumflex scapular veins of flaps used in reconstruction. The purpose of this study was to investigate and document the number, morphology, size, and location of valves in the human dorsal thoracic fascia. Ten scapular flaps were obtained from unembalmed cadavers and injected with methyl methacrylate. Each flap cast was divided into four parts: proximal, right and left, and distal, right and left. We reduced the size of specimens (the largest being 24 x 11 mm) and studied them in a scanning electron microscope. We identified all valves, estimated the diameter of the corresponding vein, calculated the depth of the valvular sinus, and related it to the corresponding venous size. Light microscopy and transmission electron microscopy were used as assisting tools applied to glutaraldehyde-fixed specimens. Analysis of injected specimens showed that valves were most abundant in veins with a luminal diameter of 30 to 120 microns (59.3 percent of 905 valves). The depth of valves became larger with increasing venous diameter. The sizes of valve sinuses were not different for individual valves. Except for veins larger than 1000 microns in diameter, there was no significant difference between the number of valves in different parts of an individual flap, nor were there significant differences between the valve numbers in different flaps. Most valves were bicuspid; only in the vein category of 30 to 120 microns were unicuspid valves encountered. Valves sometimes were located in series in a short segment of a vein; occasionally, they were found at the merging site of two veins. Transmission electron microscopy showed that valve leaflets had collagen fibers that ascended toward the tip of the leaflet and occasionally were accompanied by elastic fibers. Myofibroblasts were regularly present in the valve leaflets. These data show that fasciocutaneous flaps from the scapular region have numerous valves (90 valves on average in each flap) in the venous microcirculation. The microvenous valves in the dorsal thoracic fascia appear to be structurally similar to valves in larger veins. These valves may play a role in the improved hemodynamics and promising clinical outcome of patients with chronic venous insufficiency who have undergone free scapular flap reconstruction.

Postnatal development of the blood vasculature in the rat adrenal gland: a scanning electron microscope study of microcorrosion casts

Postnatal development of the blood vasculature in the rat adrenal gland was examined with scanning electron microscopy (SEM), using a microcorrosion casting method. The cortical vascular bed on postnatal day 1 (P1) was incipient, consisting of an outer capillary layer and an inner sinusoidal vascular layer of the juxtamedullary zone. The vascular bed grew continuously with clearer zonal differentiation as the maturation proceeded. By P7 the outer capillary layer had differentiated into the vasculature of the glomerular and fascicular zone, while the juxtamedullary sinusoidal vascular layer had reduced its thickness to differentiate into the vasculature of the reticular zone. The neonatal adrenal vasculature consisted only of the cortico-medullary system. The medullary arteries and the medullary capillary bed were first observed on P14. The adrenomedulla thus came to receive a twofold blood supply by this time. Before the establishment of the medullary arterial system, the medulla appeared to receive its blood supply partly from the cortical capillaries and partly from the radial sinusoidal vessels passing through the cortical vascular bed. The radial sinusoidal vessels were suggested to differentiate into the cortical capillaries. The medullary arteries may originate from the vessels associated with chromaffin bodies incorporated into the adrenal gland or differentiate from the radial sinusoidal vessels. Histological changes, including cortical cell involution and hemorrhage occurring during the neonatal period, would seem to have crucial relevance to the remodeling of the adrenal vasculature.

The roles of the marginal veins in the differentiation of the rat hind limb bud: an immunocytochemical study

Rat hind limb buds, aged between prenatal days 14 and 18, were used for electron microscopy and immunocytochemistry of fibronectin, laminin and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling staining indicative of DNA fragmentation. Fibronectin and laminin were actively synthesized in the rough endoplasmic reticulum of epidermal cells in the apical ectodermal ridge between prenatal days 14 and 15, but most cells underwent apoptosis after prenatal day 15. As the regression of the apical ectodermal ridge progressed, mesenchymal cells associated with the marginal veins were successively incorporated into the endothelium devoid of the basal lamina. No mitotic figures of endothelial cells were recognized either in the marginal vein or in the surrounding growing capillaries. Extracellular matrix components connected the adjacent mesenchymal cells, with the endothelium of such vessels immunoreacting to fibronectin and laminin. In addition, fibronectin-immunoreactive networks among the interstices of the mesenchymal cell cords developed in the avascular zone between the epidermis and the growing capillaries at prenatal day 15, but became inconspicuous at prenatal day 16. These results indicate that the apoptosis of the epidermal cells is the major reason for the regression of the apical ectodermal ridge, and that the capillary ingrowth from the marginal veins to the avascular zone is accelerated by transformation of mesenchymal cells to endothelial ones. Fibronectin and laminin seem to play crucial roles in capillary growth, especially in the adhesion between endothelial cells of the pre-existing vessels and mesenchymal cells.

The blood supply of the human temporalis muscle: a vascular corrosion cast study

Knowledge as to the blood supply of the human temporalis muscle is limited to its extramuscular path and relations, little information existing about the intramuscular vascular architecture. To investigate the 3-dimensional vascular network in the human temporalis muscle, in 5 fresh cadavers an infusion of methylmethacrylate resin was made via the carotid vessels with subsequent removal of the organic tissues by a corrosion process. The vascular corrosion casts of the temporalis muscle were studied by stereomicroscopy and scanning electron microscopy. In 6 well perfused muscle specimens, the temporalis muscle was found to be consistently supplied by 3 arteries: the anterior and posterior deep temporal arteries, and the middle temporal artery. Each primary artery branched into the secondary arterioles and then terminal arterioles. The venous network accompanied the arteries, and double veins pairing a single artery was a common finding. Arteriovenous anastomosis was absent, whereas arterioarterial and venovenous anastomoses were common. The capillaries formed a dense interlacing network with an orientation along the muscle fibres. Understanding of the intramuscular angioarchitecture of the temporalis provides the vascular basis for surgical flap manipulation and splitting design.

Vascular architecture of the human fetal adrenal gland: a SEM study of corrosion casts

The vascular architecture of adrenal glands was investigated in human fetuses aged from 16 to 24 weeks, using microcorrosion casts and scanning electron microscopy. The fetal adrenals showed an arrangement of blood vessels remarkably similar to that described in adult glands. There was a clear centripetal pattern from superficial arteries and their branches, via irregular capillaries of the subcapsular plexus and definitive cortex, and then via the radial sinusoids and venous sinuses of the fetal cortex, to the central vein. Rare medullary arterioles traversed the cortex to break up into small local capillary networks in the central region of the gland. Some superficial capillaries were drained by occasional subcapsular veins. No portal system was observed in the fetal adrenals.

Comparison of the antithrombotic effect of the new recombinant hirudin HBW 023 and heparin in small arteries and veins

The study was composed of two parts, arterial and venous; the 24 rabbits in each arm were divided into three equal groups and treated with either saline (control) or 1 mg/kg body weight (bw) of a new recombinant hirudin HBW 023 given as a single dose or standard heparin 1 mg/kg bw followed by quarter doses of heparin every half hour. Both arms included a control group given equal volumes of saline. The study continued for 2 hours. The following parameters were evaluated: bleeding times from arteriotomy/venotomy, patency rates, and the weights of thrombotic materials. Plasma samples were taken for evaluation of anti-factor lla (anti-Flla), anti-factor Xa (anti-Fxa), and activated partial thromboplastin time (APTT). The bleeding times were significantly prolonged but were still within clinically acceptable levels, following both HBW 023 and heparin treatment. Patency rates were significantly improved in both the arterial and venous arms following HBW 023 and heparin treatment. A corresponding reduction in thrombotic materials was simultaneously registered in the arterial and venous arms following HBW 023 and heparin treatment. Hirudin (HBW 023) significantly improved the reduction compared with the heparin group in the venous study. Heparin treatment caused expected high levels of anti-FXa and prolonged APTT, but hirudin, being at least as effective in antithrombotic potency, changed the pre-treatment levels only slightly. Anti-Flla levels were immediately increased by both heparin and hirudin (the highest levels) but reached low levels after 2 hours of single-dose hirudin treatment, despite a simultaneously excellent antithrombotic effect. We conclude that the new recombinant hirudin HBW 023, like standard heparin, is a highly efficient antithrombotic agent in both small arteries and veins following severe vessel wall trauma. The bleeding times were simultaneously prolonged significantly (still within acceptable limits) following both heparin and HBW 023 treatment in the arterial arm but were only prolonged following heparin treatment in the venous arm. The advantage of r-hirudin HBW 023 was furthermore the single dose administration.

A morphological study of the long-term repair process in experimentally stretched but unruptured arteries and veins

As many avulsion amputations are incomplete and the vessels remain intact, the immediate pathology and long-term repair process (to 3 months post-injury) of experimentally stretched but unruptured rabbit femoral arteries and veins were examined. In stretched arteries, circumferential skip lesions involving endothelium, internal elastic lamina (IEL) and media occurred frequently and often up to 3 cm from the point of stretch. Medial smooth muscle cells (SMC) were significantly damaged or lost at lesions. Macrophages and neutrophils were found in lesions 1-4 days post-injury. Between 2-4 days, lesions were covered by endothelium and synthetic state SMC appeared in the media. At 1 week, a thin neointima (which persisted to 3 months) covered many lesions. The media at lesions gradually filled with SMC but generally remained disorganised even at 3 months post-injury. Stretching caused tears in vein walls, particularly close to the point of injury. There was no evidence of venous damage or repair in specimens examined 3 weeks and 3 months post-injury.

Vein of the vestibular aqueduct in the gerbil

The vein of the vestibular aqueduct in the gerbil runs along the lateral side of the endolymphatic duct, deviates from this course to enter the middle ear cavity, and connects with the lateral sinus. In 20 animals, the vein of the vestibular aqueduct was obliterated by drilling from the middle ear side. Histopathology of these specimens after 2 months' survival revealed consistent sensory cell atrophy in the posterior canal cristae, frequent loss of sensory cells in a small superior portion of the macula sacculi and in the basal end of the cochlea, and fibrosis and osteogenesis in the three semicircular canals. The endolymphatic sacs contained colloidal substances in some specimens which were otherwise normal. Endolymphatic hydrops was absent except in some specimens which showed additional surgical damage to the endolymphatic sac and canals. The blocked vein re-opened occasionally and connected with the vessel formed in new bone from which it attached to the lateral sinus. The sensory cell degeneration and canal fibrosis reflects the pattern of blood drainage by the vein of the vestibular aqueduct. Vascular disorder in the vestibular labyrinth initiates vestibular symptoms; however, it will not produce endolymphatic hydrops unless function of the endolymphatic sac is impaired.

Effects of hypothermic storage on the vascular endothelium: a scanning electron microscope study of morphological change in human vein

OBJECTIVE

The aims of this study were: i) to identify morphological changes occurring in the endothelium of human umbilical veins subjected to the typical storage procedures used in transplantation and ii) to determine the relative efficacy of preservation solutions containing intra and extracellular levels of sodium and potassium.

EXPERIMENTAL DESIGN

Prospective.

PROCEDURE

Scanning electron micrographs were taken pre and post cold hypoxic storage of human umbilical veins for 3 or 16 hours.

RESULTS

Cold preservation resulted in severe cell detachment with subsequent loss of monolayer continuity and exposure of thrombogenic basal membrane components (highly significant after only 3 hours of cold storage, Kruskal-Wallis, p < 0.01). The morphological alterations culminated in EC with spherical shapes. Cytoplasmic membranes presented an increased number of microvilli and intercellular processes, followed by microvillous swelling and surface blebbing as damage increased. Bleb detachment was seen in severely damaged specimens. However, morphological preservation was not significantly affected by the duration of hypoxia or the ionic balance of the solution tested.

CONCLUSIONS

The present results demonstrate that even short periods (3 hours) of cold storage without revascularization cause significant morphological damage to the endothelium. The ionic composition of the preservation solution did not significantly affect the process. The morphological changes seen in this study could explain storage-related problems such as loss of normal vascular permeability and increased thrombogenicity, problems often associated with transplantation procedures.

Venous tone regulatory mechanisms: what's new?

The mechanisms regulating venous tone have an important effect on whether a patient develops the complication on post operative venous thrombosis. In animal studies, venous endothelial damage has been demonstrated in veins remote from the operative wound, and correlated with the amount of operative venodilation. In human studies, operative venodilation has been directly correlated with venographically proven postoperative deep venous thrombosis. Interestingly, operative venodilation and post operative deep venous thrombosis can be avoided with venotonic agents. The mechanisms responsible for the maintenance of venous tone are complex. The venous response is likely a result of a complex interaction of circulating biologically active substances, the endothelium-vascular smooth muscle interaction as well as humoral-endothelial-neurotransmitter balance.

Thymic vascular system of the European common frog, Rana temporaria: a scanning electron-microscopic study of vascular casts

Vascular corrosion casts of the thymus of adult individuals of the European common frog, Rana temporaria, were analysed by scanning electron microscopy. The main arterial vessel, which is derived either from the temporal artery or from the auricular ramus, approaches the central territory of the gland and branches into "twigs" that, on penetrating the parenchyma, give rise to capillaries. Most of these capillaries run vertically towards the surface of the gland; they either join the superficial capillary plexus or follow this plexus for a variable distance and then run back towards the medulla, forming capillary loops. The former capillaries link with the extensive venous plexus composed of irregular meshes, whereas the latter capillaries join the venules at the cortico-medullary boundary and finally escape into collecting veins on the gland surface. The venous twigs, which join together near the gland, form the main thymic vein, which empties into the external jugular vein. The details of the thymic vasculature of the anuran amphibian, R. temporaria, are compared with those described in mammalian species, viz. the mouse, rat and guinea pig.

Alteration of testicular microvascular pressures during venous pressure elevation

We have addressed the hypothesis that varicocele-related infertility is caused in part by a pressure-induced disturbance of testicular convective transport that upsets the testicular hormonal environment and thus impairs spermatogenesis. The left testis of the hamster [pentobarbital sodium (Nembutal), 70 mg/kg ip] was prepared for microcirculatory observations. Testicular venous pressure was acutely elevated by ligating collateral routes of venous outflow and partially occluding, via a snare, the main venous outflow distal to the pampiniform plexus. Simultaneous direct pressure measurements (servo-null method) were made to monitor venous pressure elevation and quantify resulting pressure and diameter changes in the arterial feed to the testis and in postcapillary venules. The data show that over 90% of the venous pressure elevation (VPE) was transmitted to the postcapillary venules. VPE affected intravascular pressures throughout the testis microvasculature; on average, capsular artery pressure increased by 83% of the VPE, although part of this increase was due to a rise in systemic arterial pressure. Vasoconstriction helped to buffer the pressure rise in the capsular artery, probably at the expense of flow amplitude. Yet the vasoconstriction was ineffective in preventing a rise in exchange vessel pressure. These data suggest that microvascular fluid exchange may be dramatically altered in varicocele, upsetting the hormonal and paracrine environment of the testis, and hence, impairing physiological regulation of gametogenesis.

[Intramural blood vessel system of the large intestine of domestic ruminants]

The vascular system of the large intestine of 15 cattle, 10 sheep and 5 goats has been examined by means of corrosion vascular casts, histology and electron microscopy. The results are as follows: The course and ramification of the intestinal vessels are identical in the caecum, colon and rectum. Furthermore, as expected, amongst the species studied no substantial differences in the vascular architecture of the large intestinal wall could be determined. The extramural vessels reach the wall of the intestine at the mesenteric margin. Their branches build arterial or venous networks in the tela subserosa, which then divide into branches in the direction of the antimesenteric region. The connections between the blood vessels of the tela subserosa and the tela submucosa as well as the branches to the muscular layers emerge from these networks. In the tela submucosa an arterial and venous system can be found. The obvious vascular arrangement in the submucosa is arranged not only parallel to the stratum circulare of the tunica muscularis but also along the prevailing direction of the lamina muscularis mucosae. From this arrangement both a deep and a superficial submucosal vascular plexus can be denominated. The recurrent branches for the circular muscle layer as well as the afferent and efferent vessels of the mucosa originate from submucosal arteries and veins. The arterioles of the tunica mucosa branch at the level of the basal crypts into a periglandular capillary system running close to the lumen into a subepithelial capillary system. Here the capillaries drain into venules which advance to the region of the intestinal glands and consequently drain into collecting veins in the submucosa. Capillaries of the subepithelial lamina propria mucosae are furnished with continuous or fenestrated endothelial linings as the morphological equivalent of the secretory or resorption processes, respectively. In the walls of the large intestine of the bovine, sheep and goat there are neither arterio-venous anastomoses nor hemodynamic regulatory structures such as sphincters or so-called throttle veins at the points of transition from capillaries to venules. These results are in accord with the findings in the small intestine of domestic ruminants (Hummel 1980).

Microvascular application of the nonreversed vein graft

To determine the applicability of the nonreversed vein graft technique to 1-mm-diameter vessels, 24 New Zealand White rabbits underwent bilateral replacement of 2-cm defects in the femoral artery with vein graft conduits. On one side a standard reversed vein graft (RVG) was employed, and on the other side a nonreversed vein graft (NRVG) was placed after valve disruption with a Hall valvulotome. Patency rates were not statistically different (RVG 87 percent, NRVG 96 percent, p > 0.1). Electron and light microscopy revealed similar endothelial damage and time to endothelial recovery between the two techniques. There was no difference in flow volume between the two techniques. We conclude that the NRVG technique has acceptable patency rates in 1-mm-diameter vessels within the parameters of this study but that further research is required to determine clinical applicability.

The relationship between density of alpha-adrenoceptor binding sites and contractile responses in several porcine isolated blood vessels

1. The aim of this study was to investigate constrictor alpha-adrenoceptors in three isolated blood vessels of the pig, the thoracic aorta (TA), the splenic artery (SA) and marginal ear vein (MEV) and then compare the functional response with the densities of alpha 1- and alpha 2-adrenoceptor binding sites in these and several other porcine vascular tissues, palmar common digital artery (PCDA), palmar lateral vein (PLV) and ear artery (EA). 2. Noradrenaline (NA), phenylephrine (PE) and UK14304 (all at 0.03-10 microM) elicited concentration-dependent contractions in the TA and MEV, with a rank order of potency of UK14304 > NA > PE. UK14304 produced maximal responses which were 58% (TA) and 65% (MEV) of that of NA. In the SA, UK14304 and PE produced maximal responses which were less than 10% and 50% of the NA-induced maximal response respectively, with an order of potency of NA > PE. In the SA, NA-induced contractions were competitively antagonized by prazosin (pA2 = 8.60 +/- 0.15). Further, rauwolscine (1-10 microM) antagonized NA-induced contractions with an apparent pKB of 6.09 +/- 0.11 (n = 6), indicating an action at alpha 1-adrenoceptors. The combination of the two antagonists at concentrations selective for alpha 1- (0.1 microM) and alpha 2-adrenoceptors (1 microM) had no greater effect than either antagonist alone. This suggests that the SA expresses only post-junctional alpha 1-adrenoceptors. 3. In the TA, prazosin produced non-parallel shifts in the NA-induced CRC and this was also observed with rauwolscine, where reductions in the maximal responses were also observed. In the MEV, prazosin was largely inactive in antagonizing NA-induced contractions. In both these vessels a combination of these two antagonists had a greater effect than either alone, indicating the presence of functional alpha 1- and alpha 2-adrenoceptors. The post-junctional alpha 2-adrenoceptors in all of these vessels were resistant to prazosin, suggesting the alpha 2-adrenoceptor to be of the alpha 2A/2D subtype. The expression of functional alpha 2-adrenoceptors was MEV > TA > PLV > PCDA > SA. 4. In radioligand binding studies using TA P2 pellet membranes, [3H]-prazosin and [3H]-RX821002 ([1,4-[6,7(n)-3H] benzodioxan-2-methoxy-2-yl)-2-imidazole) labelled different high affinity sites, and in competition studies using identical membranes corynanthine displaced [3H]-prazosin with 10 fold higher affinity than rauwolscine, indicating that [3H]-prazosin was selectively binding to alpha 1-adrenoceptor sites. Further, rauwolscine displaced [3H]-RX821002 with approximately 100 fold greater affinity compared to corynanthine, which is indicative of selective alpha2-adrenoceptor binding.5. Separation of the P2 pellet into plasma membrane and mitochondrial fractions was carried out using a differential sucrose density gradient. [3H]-prazosin and [3H]-RX821002 binding sites were found in both the plasma membrane and mitochondrial fractions.6. In saturation studies all tissues produced single site saturation curves with no difference in the Kd(range 0.13-0.20nM) of the alpha1-adrenoceptor sites for [3H]-prazosin. However, there was considerable variation in Bmax of alpha 1-adrenoceptor sites; the highest density was found in the TA (397.9 =/- 52.7 fmol mg-1, n = 4), followed by the PCDA (256.7 +/- 22.7 fmol mg-1, n = 4), the PLV and SA having approximately equal density (143.6 +/- 3.9 and 159.1 +/- 7.0 fmol mg-1 respectively, n = 4 for both), followed bythe EA (91.3 +/- 10.5 fmol mg-1, n = 3) and the MEV had the lowest density (48.9 +/- 11.4 fmol mg-1,n = 3).7. In saturation studies using [3H]-RX821002, all tissues produced single site saturation curves with no differences in the Kd values (range 1.31 +/- 2.16 nM) but the highest densities were found in the TA and MEV (545.3 +/- 36.2 and 531.0 +/- 40.9 fmol mg-1 respectively), followed by the PLV (418.4 +/- 39.4 fmol mg-1), then the EA (266.3 +/- 40.0 fmol mg-1), and low densities of [3H]-RX821002 binding being found in the PCDA and SA (155.9 +/- 18.1 and 117.5 +/- 19.3 fmol mg-1 respectively).8. The pattern of binding site distribution for alpha l- and alpha 2-adrenoceptors is in reasonable agreement with functional studies carried out in these porcine vascular tissues; the TA has the highest densities of alpha 1-and alpha2-adrenoceptors; in the SA and PCDA there is a predominance (although small) of alpha l-adrenoceptor binding sites, the reverse of which is observed both in the PLV and MEV (i.e. greater density of alpha2-adrenoceptor sites). Thus, it would appear that alpha 1- and alpha2-adrenoceptor densities play a role in the expression of functional responses via these receptor subtypes; although it is interesting to note that the SA did have a small density of alpha 2-adrenoceptor binding sites, no functional response was observed after alpha2-adrenoceptor activation.

Histology and ultrastructure of arteries, veins, and peripheral nerves during limb lengthening

The effects of lengthening of the metacarpal bone on peripheral nerves and blood vessels were studied in 8 calves. Specimens for light and electron microscopy were obtained from the palmar neurovascular bundle at 1 cm (8% of the initial length), 2.5 cm (20% of the initial length), and 4 cm (33% of the initial length) of metacarpal lengthening. In 2 calves, specimens were studied 2 months after the end of the lengthening procedure. At 8% of lengthening, myelinated fibers of the palmar nerve showed moderate degenerative changes in the myelin sheath. This became severe at 20% and 33% of lengthening, and affected the axoplasm as well. At 20% of lengthening, the palmar vein started to show fibrous metaplasia of the smooth muscle tissue of the tunica media. This became much thinner than normal. The palmar artery showed moderate alterations of the inner part of the tunica media and the intima. The palmar nerve and blood vessels recovered their normal structure almost completely 2 months after the end of the lengthening procedure. The morphologic alterations of peripheral nerves and vessels may constitute the pathophysiologic basis of the nervous and circulatory disturbance observed in clinical practice.

The vascular system of human fetal long bones: a scanning electron microscope study of corrosion casts

The vascular system of the femur and humerus was investigated in 17-24 wk human fetuses by scanning electron microscopy of corrosion casts. The number of nutrient foramina present in both bones ranged from 1 to 3 and the number of nutrient vessels associated with individual foramina also varied. The medullary arteries supplied both the bone cortex and marrow. There was no arterial supply to the shaft cortex from the periosteal side, where only capillaries were found to enter the bone. The metaphyses were supplied and drained by conspicuous vascular triads composed of an artery and 2 veins. In the marrow cavity, 2 morphologically different areas of the fine vascular network could be distinguished: diaphyseal sinusoids and metaphyseal capillaries forming a 'vascular besom' which was abruptly demarcated by the growth plate cartilage. The cortical microvascular bed was composed of capillaries and more numerous irregular sinusoids. The 2 main vascular systems, nutrient and periosteal, were interconnected not only via the network of cortical capillaries/sinusoids, but also by larger arteries and veins traversing the cortex. The features of the vascular system of human fetal long bones suggest its considerable functional flexibility and its capacity to modify blood flow patterns depending on circumstances.

Cytoarchitecture of periendothelial cells in human cerebral venous vessels as compared with the scalp vein. A scanning electron microscopic study

Three-dimensional cytoarchitectures of the periendothelial cells of human cerebral venous vessels as well as a scalp vein were studied by scanning electron microscopy after removal of extra-cellular connective tissue matrices with a KOH-collagenase digestion method. Postcapillary venules appeared covered with pericytes, while collecting venules had stellate periendothelial cells which formed a basket-like network around the vessel wall. As the size of the venous vessels increased, the stellate periendothelial cells became flat in shape and dense in arrangement. Although they had some characteristics similar to the smooth muscle cells in surface structure, no spindle-shaped smooth muscle cells were recognizable even in the superficial cerebral veins. On the other hand, the scalp vein was densely covered with spindle-shaped smooth muscle cells running circularly. These findings suggest that the cerebral venous vessels cannot constrict strongly as compared with the scalp vein, but probably regulate blood volume by mildly changing the caliber of the vessels.

Cytogenetic studies in venous tissue from patients with varicose veins

Cytogenetic investigation of primary cell cultures from fragments of varicose veins of seven patients with familial varicosity and seven patients with the sporadic type revealed the presence of metaphases with structural abnormalities, clonal trisomies of chromosomes 7, 12, and 18, and monosomy of chromosome 14 only in cases with the familial type, while the sporadic cases had no similar chromosome aberrations. The immunophenotypical results are consistent with fibroblast lineage of the cultured cells. These results suggest that karyotypic variations in familial varicose vein tissue cultures could in some way be associated either with the genotypic constitution responsible for the familial type or a longer duration of disease on average than those with sporadic varicosities.

[The microvascularization of the choroid plexus of the lateral ventricles in the goat (Capra hircus)]

The goat choroid plexus angioarchitecture of the lateral ventricles was studied under the SEM using the method of "microvascular corrosion casts". The whole plexus is semilunar shaped and directed in an antero-posterior, latero-median fashion. In the plexus the lateral extremity is larger than the median one. All the components of the vascular bed (arteries, veins and capillaries) of the choroid plexus have interesting morpho-structural features. In particular, the capillaries are more developed than the other components and they are variously located on both sides of the plexus. The capillary network has a various organization in different zones of each side of the plexus.

In vivo study of the effect of exogenous estradiol on alpha-adrenoceptor responsiveness of human veins

Based on previous experimental and epidemiologic findings, we hypothesized that 17 beta-estradiol (E2) could decrease the alpha-adrenergic responsiveness in venous smooth muscle cells (VSMC), thereby decreasing venous tone and contributing to the pathogenesis of varicose veins. To test this hypothesis, the effect of an acute increase in E2 serum concentrations on venous alpha-adrenergic responsiveness to norepinephrine (NE) was studied in young healthy men. We conducted a double-blind, randomized, placebo-controlled cross-over study in 23 male volunteers; 96 +/- 2 h after a single intramuscular (i.m.) injection of 10 mg estradiol valerate or placebo, we quantified the pharmacologic effects of estradiol on alpha-adrenergic responsiveness of superficial hand veins by venous compliance technique (VCT) and on resting blood pressure (BP). After administration of estradiol, E2 serum levels increased 9.97 +/- 7.54-fold (mean +/- 1 SD, p < 0.001) to within the range of premenopausal preovulatory women. No significant difference was observed in mean dose of NE required for half-maximal venoconstriction (ED50, p = 0.224), however, or in the maximal effect of NE (Emax, p = 0.796) after administration of E2 as compared with placebo. A significant difference in diastolic BP (DBP) (p = 0.039) was observed after E2 administration (64.6 +/- 7.7 mm Hg) as compared with placebo (68.3 +/- 7.6 mm Hg); BP (SBP) was not affected (p = 0.786). Our findings do not support the concept that E2 reduces alpha-adrenoceptor responsiveness of SMC in superficial veins.

Early postnatal growth of skeletal muscle blood vessels of the rat

The development of blood vessels during the first three postnatal weeks was studied in the ventral stripe of the spinotrapezius muscle of the rat by use of India ink-gelatine injections, and electron microscopy. The number of terminal arterioles and collecting venules remained unchanged postnatally in the observed area. A remarkable proximodistal gradient of vascular development was apparent: while the basic structure of the hilar vessels remained unchanged in the time studied, the intramuscular arteries and veins matured gradually. More peripherally, gradual maturation of terminal and precapillary arterioles was observed. The capillary endothelium and the pericytes showed immature features, and remained unchanged during the time studied. An intense rebuilding activity was found in the endothelial cells of the growing venules, expressed by various forms of gaps, covered by an intact basal lamina and pericytes. Numerous mast cells and macrophages were found along all vessels. Intramuscular lymphatics were not present prior to the first postnatal week.

Scanning electron microscope study of the veins at the human esophago-gastric junction

Cast of the mucosal and submucosal veins of the esophago-gastric junction were studied in five necropsy specimens by scanning electron microscopy to analyse some of the characteristics of their shape and surface. Two types of veins were described: 1) veins with circumscript, fusiform and/or ampullar bulges and relatively smooth surfaces; 2) veins with numerous, small bulges and blister-shaped micro-dilatations. The role of these features is considered in the formation of esophageal varices.

Scanning electron microscopic studies of the palatine mucosa and its microvascular architecture in the rat

Detailed observations were made on the structure and microvasculature of the palatine mucosa of the rat by means of microvascular corrosion casts and epithelium-digested specimens using scanning electron microscopy. The rat palate was divided into four regions according to the characteristics of the palatine plicae. In the atrial region, no transverse palatine plicae were present, but there were longitudinal ridges and folds in the median area. These structures contribute to the transportation of rough and grainy foods with the assistance of the hairy buccal part. Capillary loops in the ridge and folds appeared as continuous, sagittally elongated loops. In the palatine fissure or antemolar region, only three typical transverse palatine plicae contribute to the regurgitation of food. Capillary loops appeared in variant forms on the top, and the anterior and posterior slopes of the plicae. Venous palatine plexus was observed only in the palatine fissure region. In the intermolar region, each of the five transverse plicae was composed of many wedges arranged sagittally. These plicae contribute to the transportation of food toward the larynx. Capillary loops in the plica were in the shape of complicated villi. Filiform protrusions or papillae were aggregated immediately posterior to the last plica. The capillary loops appeared as typical hairpins. They contribute to swallowing of food with active assistance from the epithelial eminence of the lingual dorsum. Palatine plicae showed considerable local differences, which may contribute to the prehension, transportation, and mashing of food.

The role of fenestrated vessels for the secretory process in the nasal mucosa: a histological and transmission electron microscopic study in the rabbit

Both nasal glands and nasal vessels are supposed to be responsible for the humidification of inhaled air. After previous studies on the vasculature of the nasal septal mucosa in the rabbit, we examined vessels of the anterior concha in order to find a morphological equivalent to explain the role of endonasal vasculature in the secretory process of this tissue. The main findings of our study include the detection of fenestrated endothelial walls of both capillaries and venous sinuses located underneath and directly adjacent to the basal cell layers of the epithelium. The same phenomenon-fenestrated vessels underneath the epithelium with the fenestrated parts facing the epithelial cells-has been described in other parts of the body and has been called "polar differentiation." In accordance with the interpretations of other authors, we conclude that these features are responsible for the regulation of endonasal fluid exchange.

The reversibility of impaired prostacyclin production of the vein graft

The effects of changes in shear stress (shear stress variation) on production of prostacyclin (PGI2) were examined in canine autologous vein grafts, which were implanted in the poor or normal distal runoff limbs. Four weeks after grafting, the vein grafts were perfused ex vivo and PGI2 was assayed as 6-ketoprostaglandin F1 alpha. The vein grafts were perfused under constant flow for the first 30 min and then under pulsatile flow simulating an abnormal flow with a low shear stress variation or a normal flow with a high shear stress variation for the next 30 min. Basal production rates (30-min cumulative PGI2 production) of vein grafts implanted in the poor runoff and normal runoff limbs were 1.97 +/- 0.71 and 2.19 +/- 0.40 ng/cm2, respectively, with no significant difference. Pulsatile flow effects (increased PGI2 production between 30 and 60 min) of simulated abnormal versus normal flow were 0.50 +/- 0.50 ng/cm2 versus 2.31 +/- 1.87 ng/cm2 in vein grafts implanted in poor runoff limbs (P < 0.05) and 0.48 +/- 0.41 ng/cm2 versus 3.48 +/- 1.08 ng/cm2 in vein grafts implanted in normal runoff limbs (P < 0.01), respectively. There were no significant differences in simulated normal flow effects between poor runoff limbs and normal runoff limbs. The results indicate that the release of PGI2 in vein grafts may decrease in the presence of an abnormal blood flow with a low shear stress variation. In addition, it is suggested that even vein grafts implanted in the poor runoff could increase PGI2 production once the grafts were placed into normal arterial circulation.

Circulatory pattern and structure in the tail and tail fins of Xenopus laevis tadpoles

This investigation was initiated with the intent of study capillary sprouting in the tadpole tail fin microcirculation of the African clawed frog, Xenopus laevis, using a combination of intravital video recordings and electron microscopy. The tadpoles were observed daily for periods up to one hour during one to two weeks. The capillary sprouts originated mostly from postcapillary venules, and within 24-48 h merged with other capillary sprouts, subsequently establishing a capillary loop with blood flow. As the circulatory patterns developed further, capillary regressions also occurred. As the electron microscope analyses of the capillary sprouts progressed, it became obvious that a thorough electron microscope study of the blood vessels of the tadpoles was required in order to explore structural characteristics of arterial and venous blood vessels. Thus, this article deals primarily with the general organization of the tadpole tail circulation, and the ultrastructural characteristics of the vascular walls. A subsequent article will deal with the role of endothelial cells, fibroblasts and pericytes in the process of capillary sprouting and regression, based on intravital recordings and electron microscope analyses.

Impaired endothelial prostacyclin production of the canine vein graft in a poor distal runoff limb

BACKGROUND

Because blood flow modulates endothelial prostacyclin production, the extent of this production in autologous vein grafts implanted in poor distal runoff limbs needed to be examined.

METHODS

Endothelial prostacyclin production in canine autologous vein grafts was measured in poor distal runoff limbs (poor runoff group) and compared with findings in normal runoff limbs (control group). Vein grafts were perfused in a closed circuit at 3 days and 1, 2, 3, and 4 weeks after implantation; after perfusion for the first 30 minutes in a steady flow (basal prostacyclin production), the grafts were exposed to arachidonic acid (stimulated prostacyclin production) for the following 30 minutes. Prostacyclin, as the metabolite 6-keto-PGF1 alpha, was radioimmunoassayed.

RESULTS

Basal and stimulated prostacyclin production increased in both groups during a period of time after implantation. At 2 weeks when endothelialization was complete, prostacyclin production in the poor runoff group was impaired, compared with the findings in the control group, and this difference increased with time. At 4 weeks the stimulated prostacyclin production was 18.91 +/- 4.03 ng/cm2 in the control group and 11.60 +/- 1.67 ng/cm2 in the poor runoff group (p < 0.05).

CONCLUSIONS

We propose that the impaired capacity of the vein graft to produce prostacyclin in a poor distal runoff may lead to loss of graft patency in reconstructed arteries.

Vascular patterns of the saccule of the rat: a microcorrosion cast study

A scanning electron microscope study of corrosion cast preparations of the vessels of the saccule was carried out in adult rats. This method shows the microvasculature of the saccule in the three-dimensional model. As a result of this technique we have been able to demonstrate a particular microvasculature of the saccule in the rat's inner ear. The main blood supply of the saccule consists of the arterioles coming from the vestibulocochlear artery entering the anterior margin of the macula sacculi. A few branches of the anterior vestibular artery enter the macula sacculi from the superior margin. The saccular vein drains the venous blood from a dense capillary area underneath the striola to the posterior vestibular vein which eventually ends in the vein of the cochlear aqueduct.

Ultrastructural alterations of collagen fibrils in blood vessel walls

With increasing concern for elucidation of the role of connective tissues in degenerative diseases of blood vessels, an ultrastructural study was conducted on collagen fibrils of intimal proliferation in experimental autogenous venous pouch aneurysms in rabbits and in atherosclerotic human arteries. The fibrils were compared morphometrically with adventitial collagen as controls. In intimal proliferation from both species intimal collagen fibrils displayed increased variation in shape and size when compared to adventitial collagen fibrils. The abnormal fibrils resembled those of inherited connective tissue diseases, indicating that the changes in collagen fibrils can be acquired and that hemodynamic stress is likely to contribute to their occurrence.

Specialized veins in the submucosa of the equine ileocecal junction

Spirally arranged bundles of sub-endothelial smooth muscle enfold the small to medium-sized submucosal veins in the equine ileocecal junction. The muscle bundles, accompanied by the endothelial lining, bulge into the lumen of the vessels, partly occluding the latter. Transmission electron microscopy of the muscle cells reveals features consistent with vascular smooth muscle ultrastructure. It is proposed that the throttling effect of the muscle bundles causes engorgement of the submucosal venous plexus, which then assists in the closing of the ileocecal orifice.

Pathways of macromolecular tracer transport across venules and small veins. Structural basis for the hyperpermeability of tumor blood vessels

BACKGROUND

Blood vessels supplying tumors are hyperpermeable to macromolecules, but the mechanisms responsible are poorly understood.

EXPERIMENTAL DESIGN

To investigate the structural basis for the leakiness of tumor blood vessels, we performed a transmission electron microscopic study of three syngeneic transplantable carcinomas (mouse ovarian carcinoma and the line 1 and line 10 bile duct guinea pig carcinomas) at early intervals after intravenous injection of several macromolecular tracers. Tracers with widely differing physical properties were studied: horseradish peroxidase, ferritin, 150 kilodalton fluorescein isothiocyanate-dextran and gold-bovine serum albumin.

RESULTS

All tracers leaked primarily from venules and small veins at the tumor-host interface, for the most part vessels lined by a continuous endothelium. The predominant pathway by which all four tracers exited venules in all three tumors was by way of a system of smooth membrane-bound, interconnecting vesicles and vacuoles; these tended to cluster together at irregular intervals in the endothelial cell cytoplasm to form organelle-like structures, vesiculo-vacuolar organelles (VVO). In favorable sections, VVO interfaced with both the luminal and abluminal surfaces of endothelial cells. HRP alone crossed venules and small veins through apposed inter-endothelial cell junctions. Tracers also exited vessels by way of endothelial fenestrae where these occurred (rarely) in mouse ovarian tumor-associated venules. VVO occurred with similar frequency and complexity in the continuous endothelium-lined venules and small veins that supplied the normal subcutis of either tumor-bearing or control animals. As in tumor-associated vessels, VVO provided the predominant pathway by which all four tracers exited normal vessels, but VVO labeling and extravasation were both much greater in tumor than in control vessels (p < 0.001 for ferritin).

CONCLUSIONS

VVO are prominent structures in both tumor-supplying and control vessel endothelial cells and provide the primary pathway for macromolecular extravasation. The large increase in permeability characteristic of tumor vessels is likely attributable to upregulation of VVO function.