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PubMed2001

Perivascular responses after angioplasty which may contribute to postangioplasty restenosis: a role for circulating myofibroblast precursors?

These studies suggest that the adventitia may play a role in vascular lesion formation after balloon overstretch injury of pig coronary arteries by contributing to the cellular mass of the neointima and the synthesis of growth factors. In addition, the adventitia may contribute to vascular remodeling and constriction of the external elastic lamina through accumulation of myofibroblasts containing alpha smooth muscle actin in the adventitia surrounding the injury site. Inhibition of myofibroblast proliferation and/or recruitment by intravascular brachytherapy positively affects vascular remodeling through its action on adventitial cells. Inflammation is a major event associated with balloon angioplasty, resulting in the sequential recruitment of neutrophils (2-24 hours) and monocyte/macrophages (24-72 hours) predominantly into the adventitia surrounding the injury site. It is hypothesized that inflammatory cells release cytokines and/or increase the production of superoxides which stimulate the proliferation and recruitment of adventitial myofibroblasts. Inflammatory and proliferative responses were not confined to the local adventitia but were found extending as far as 1-3 mm away from the injured vessel in the distal perivascular tissues. Studies were performed to examine the expression of genes associated with cell migration at early times after injury in an attempt to determine the source of the adventitial myofibroblasts. Expression of genes involved in cell migration including MMP-2, MMP-9, and tenascin was found as early as 2 hours following angioplasty in the intramyocardial, pericardial, and adipose tissue fibroblasts. While these studies suggest that local tissue was the source of the myofibroblasts recruited to the injury site, we have been unable to confirm this finding by direct fluorescent labeling of adventitial cells. Recent work from our laboratory suggests that myofibroblast precursors may be isolated from buffy coat preparations from peripheral blood. These results lead us to hypothesize that stem cells that differentiate into myofibroblasts may be recruited in early inflammatory infiltrates in the adventitia. Clearly, additional work will have to be directed at a more detailed examination of the response of adventitial and other perivascular cells and tissues to balloon injury to determine their sources and their role in regulating vascular lesion development.

Angioplasty↗
PubMed2005

[Pathway for macrophage invasion into the tunica media and the intima in vein graft].

OBJECTIVE: To test whether the macrophages in vein grafts may invade into the vascular wall from the adventitia apart from the lumen. METHODS: Expression of CD68 (a marker of macrophage) and CD31 (a marker of endothelial cells) in 30 vein grafts were detected by confocal immunofluroscence. Images were processed with Silicon Graphics Octane. RESULTS: In normal veins, there were a few CD68 positive cells in the adventitia, but few CD68 positive cells were found in the media and the intima. In the diseased vein, CD68 positive cells were significantly increased and present in all layers of the vascular wall, the adventitia, media and intima, extending from the adventitia to the media. There was a close relationship between the penetration of CD68 positive cells into the media from the adventitia and the angiogenesis in the media. CONCLUSION: The adventitia may be an important pathway for macrophage invasion.

Antigens, CD↗
PubMed2006

Sequential patterns of chemokine- and chemokine receptor-synthesis following vessel wall injury in porcine coronary arteries.

Inflammation plays a central role in vascular repair, and spreads into perivascular tissue (PVT) following angioplasty. Chemokines (CK) and chemokine receptors (CKR) are key determinants of inflammatory chemotaxis. We sought to assess the arterial and perivascular expression of the CK CCL2 and CXCL2, and the CKR CCR2, CCR5, and CXCR4 in balloon-injured porcine coronary arteries. Vascular cells that express specific CK and CKR mRNA during post-angioplasty time course were detected by in situ hybridization (ISH), and expression was quantified by real time RT-PCR in PVT. CCL2 was maximal in PVT from 2 to 24h post injury, coincident with local macrophage-activation. Expression was upregulated in media and adventitia from 24h to 3 days, and in neointima at 7 days. CXCL2 was detected in media at 2 and 4h, and also in some neointimal cells. CCR2 and CCR5 were maximal in PVT at 24h and 3 days, respectively. Expression shifted to media and adventitia at 2 and 3 days, and to neointima and adventitia at 7 days, and was low at 14 days. CXCR4 was low in PVT, but was upregulated in media and adventitia at 2 and 3 days, as well as in neointima and adventitia at 7 days. In conclusion, PVT is the primary source of inflammatory CK and CKR early post-angioplasty. Specific sequential patterns of CK- and CKR-synthesis are identified that may regulate phase-specific chemotaxis by spatio-temporally differential expression during coronary response to injury.

Angioplasty, Balloon, Coronary↗
PubMed2006

The wrapping method using biodegradable felt strips has a preventive effect on the thinning of the aortic wall: experimental study in the canine aorta.

OBJECTIVES: Wrapping methods have been widely used to reinforce the anastomotic site in vascular surgery; however, postoperative changes in the aortic wall wrapped by nonbiodegradable felt have not been well characterized. The purposes of this investigation are to elucidate the sequelae of wrapping with nonbiodegradable felt on the aortic wall and to modify those changes by using biodegradable felt with or without basic fibroblast growth factor (bFGF). METHODS: The descending thoracic aortas of 15 beagles were wrapped with three different materials: nonbiodegradable polytetrafluoroethylene (PTFE) felt, biodegradable polyglycol acid (PGA) material, and PGA with 100 microg bFGF (n = 5 in each group). The descending thoracic aorta was resected after 3 months. The thickness of the aortic wall, vessel density in the media and the adventitia, and the wall strength were assessed. Untreated native aortic wall served as a normal control. RESULTS: The thickness of the media of the PTFE group was lower than that of the PGA + bFGF group (66% +/- 5% vs 85% +/- 6% of control, P < .05). The adventitia-media ratio in the PTFE group decreased compared with controls (59.1% of normal, P < 0.05), whereas those in the PGA and PGA + bFGF groups increased (172.1% and 189.6% of normal, respectively, P < .01). The collagen-smooth muscle ratio in the media was higher in the PTFE group than in the controls (0.14 +/- 0.02 vs 0.07 +/- 0.01, P < .01). The number of vessels in the adventitia was higher in the PGA + bFGF group than those in PTFE or PGA groups (29.6 +/- 2.5/mm2 vs 6.4 +/- 0.8/mm2, 19.0 +/- 1.1/mm2, P < .01). The PGA + bFGF group demonstrated larger failure force than the PTFE group (4.0 +/- 0.3 kgf vs 1.6 +/- 0.3 kgf, P < .01). The failure stress in the PGA and PGA + bFGF groups was larger than that in PTFE group (PTFE:PGA + bFGF = 5.3 +/- 0.9 x10(2) kPa:11.7 +/- 1.7 x 10(2) kPa, P < .01; PTFE:PGA = 5.3 +/- 0.9 x 10(2) kPa:11.2 +/- 1.2 x 10(2) kPa, P < .05). CONCLUSION: The aortic wall wrapped with nonbiodegradable PTFE felt showed a reduced thickness and diminished vessels in the adventitia. Biodegradable felt (PGA), with or without bFGF, modified these histologic changes. The vessel-rich thickened adventitia, after wrapping by PGA with bFGF, was associated with increased aortic wall strength. CLINICAL RELEVANCE: This investigation was conducted in an attempt to elucidate mechanisms underlying the occurrence of late postoperative false aneurysm after aortic surgery. We hypothesized that sustaining compression of the aorta by the felt strip may cause structural derangement and local ischemia on the aortic wall. We used a simple wrapping of the aorta with a felt strip rather than a felt strip at anastomotic sites to simplify the experimental model and to exclude confounding factors brought by technical inconsistency on the surgical anastomosis. We further attempted to find a clue for preventing adverse effects of wrapping with a conventional felt strip. Practically, we pursued a possible application of a biodegradable felt strip to aortic wrapping in our experimental model before we proceed in a clinical application of the new material.

Aneurysm, False↗
PubMed1998

Limitations of percutaneous transhepatic cholangioscopy for the diagnosis of the intramural extension of bile duct carcinoma.

BACKGROUND AND STUDY AIMS: Vascular dilatation seen on percutaneous transhepatic cholangioscopy (PTCS) is diagnostic of intramural invasive carcinoma of the bile duct, but the limitations of the technique, including biopsy, for the diagnosis of intramural extension of bile duct carcinoma have not to our knowledge been investigated before. The aims of the present study were to estimate the thickness of the specimens of bile duct wall taken by biopsy, to assess the sensitivity of PTCS for detecting intramural invasive carcinoma, and to identify the characteristics of the intramural extension of bile duct carcinoma associated with vascular dilatation. PATIENTS AND METHODS: A total of 135 biopsy, and 16 surgical specimens obtained from 25 bile duct carcinomas were examined for: the thickness of the biopsy specimens and of the mucosa and combined mucosal-fibromuscular layers in the resected common bile ducts and common hepatic ducts; the presence of muscular and neural bundles in the biopsy specimens; the number of invasive carcinomas in the biopsy specimens that had been taken from stenosed regions; and the relation between intramural extension of invasive carcinoma and vascular dilatation. RESULTS: The mean thickness of the biopsy specimens did not differ from the mean thickness of the mucosa in the resected specimens, but was significantly lower than that of the combined mucosa and fibromuscular layer. Muscular bundles were included in only 13 (14%) of the biopsy specimens, and there were no neural bundles. Carcinomas and invasive carcinomas were diagnosed histologically from the biopsy specimen in 96% and 91% of the cases, respectively. The sensitivity of a single biopsy for diagnosis for invasive carcinoma in stenosed regions was 62%, almost the same as the sensitivity in non-stenosed regions with vascular dilatation (68%). On histologic examination of 16 resected specimens, the sensitivity and specificity of vascular dilatation as a marker of the intramural extension of an invasive carcinoma were 39% and 100%, respectively, and this was significantly more common in invasive carcinomas that were invading the mucosa beyond the adventitia than in those limited to the adventitia. CONCLUSION: Histologic examinations of specimens obtained by PTCS-guided biopsy can detect invasive carcinoma in only the superficial layers of the bile duct, such as the mucosa and the shallowest fibromuscular layer. Multiple specimens are needed for the diagnosis of invasive carcinoma because the sensitivity of examination of a single specimen for detecting invasive carcinoma is low. Vascular dilatation is characteristic of carcinoma that is invading the mucosa beyond the adventitia, so the diagnosis of intramural extension of bile duct carcinoma limited to the adventitia, particularly if it has spread to the deeper fibromuscular layer and the adventitia, is difficult to make by PTCS.

Adult↗
PubMed2002

Unconventional vessel wall apposition in off-pump porcine coronary artery bypass grafting: low versus high graft flow.

OBJECTIVE: Facilitated coronary anastomosis techniques may involve unconventional vessel wall apposition in contrast to standard intima-intima apposition. We assessed the patency, anastomotic thrombus formation, and intimal hyperplasia of unconventional intima-adventitia apposition versus conventional suturing techniques in beating heart coronary bypass grafting under low versus high graft flow conditions. METHODS: The intima-adventitia (n = 28) and conventional anastomoses (n = 28) were evaluated intraoperatively (n = 56), at 4 hours (n = 20), and at 5 weeks (n = 36) in a new off-pump low-flow (n = 28) and high-flow (n = 28) porcine bypass model (< or = 15 mL/min and about 60 mL/min, respectively). The anastomoses were assigned to the animals by means of randomized stratification and examined by means of flow measurements, angiography, and histology. RESULTS: Mean graft flows in intima-adventitia and in conventional anastomoses were similar (P =.709). All but 1 of 56 anastomoses (low flow conventional) were fully patent at the time of death. At 4 hours, only small platelet depositions were found at the exposed media and adventitia in the unconventional anastomoses. At 5 weeks, little streamlining intimal hyperplasia was found, which was comparable between the anastomoses (P =.600). CONCLUSIONS: In low-flow conditions (< or = 15 mL/min) unconventional intima-adventitia apposition was not detrimental to the internal thoracic-coronary artery anastomosis in the pig. This finding may expand design strategies of facilitated coronary artery bypass anastomosis techniques.

Angiography↗
PubMed2005

Adventitial remodeling with increased matrix metalloproteinase-2 activity in a porcine arteriovenous polytetrafluoroethylene grafts.

BACKGROUND: We hypothesized the source of early proliferating cells contributing to venous stenosis formation in a porcine hemodialysis grafts is the adventitia and media, and migration of these cells is greatest within the first two weeks following graft placement, resulting in increased matrix metalloproteinase-2 (MMP-2) activity. METHODS: Polytetrafluoroethylene grafts from the iliac artery to the ipsilateral iliac vein were placed in 23 pigs and 5-Bromo-2'-deoxyuridine (BrdU) was given at 24 and 48 hours after surgery to assess cell proliferation and migration. Angiography and magnetic resonance angiography was performed. Animals were euthanized on day three (N= 6), day seven, (N= 5), day 14 (N= 6), and days 19 to 26 (N= 6) after graft placement, and stenotic tissue and unaffected contralateral iliac vein were removed for zymography and immunostaining. RESULTS: Migration of cells derived from the adventitia and media peaked at day 14. Adventitial diameter of the stenotic vein decreased, while the intima to media ratio increased. MMP-2 activity peaks at day seven in the adventitia and days 19 to 26 in the intima. CONCLUSION: These results confirm our hypothesis that the source of cells resulting in venous stenosis formation is derived from the adventitia and media, with cell migration being greatest within the first two weeks after graft placement with translocation of these cells into the intima at four weeks. MMP-2 activity peaks at day seven in the adventitia and again at days 19 to 26 in the intima. A key to limiting venous stenosis formation may lie in inhibiting MMP-2 by adventitial and medial targeting.

Animals↗
PubMed1994

ACE in three tunicae of rat aorta: expression in smooth muscle and effect of renovascular hypertension.

Angiotensin I-converting enzyme (ACE) is known to be present at the surface of endothelial cells and also in the adventitia in large vessels. The presence of ACE in the vascular smooth muscle remains controversial. We microdissected segments of adventitia and media with or without endothelium from a region devoid of collateral arteries. The membrane-bound ACE activity in the media averaged 41% (pmol [glycine-1-14C]hippuryl-L-histidyl-L-leucine hydrolyzed.g tissue-1.min-1) of the values found in the whole aorta, whereas the adventitia contained only 6%. Immunoreactive ACE in media was characterized by Western blotting. ACE mRNAs were detected and characterized after polymerase chain amplification in isolated media. Angiotensin I and angiotensin II were equally able to contract medial rings, and the response to angiotensin I was blocked by enalaprilat. In aortas of two-kidney, one-clip hypertensive rats, there was an increase in ACE mRNA estimated by ribonuclease protection assay (P = 0.02) and in ACE activity at 15 days and 1 and 3 mo after clipping. This corresponded to a 1.5- to 2-fold increase in the ACE activity of both the media and the adventitia compared with sham-operated rats (P < or = 0.02). Thus ACE gene expression occurs in smooth muscle of rat aorta, which contains roughly the same amount of enzyme as the endothelium and readily converts angiotensin I to angiotensin II. ACE in the medial layer and the adventitia is upregulated in renovascular hypertension.

Animals↗
PubMed1994

Blood flow to the trachea and bronchi: the pulmonary contribution.

It is generally assumed that when pulmonary vascular pressures are normal the pulmonary contribution to central airway blood flow (Qp) is negligible compared with systemic blood flow (Qs). However, it has been suggested in recent reports that a substantial portion of central airway blood flow is Qp. We have attempted to confirm whether there is a pulmonary contribution to central airway blood flow and to describe how it is anatomically distributed. Measurements of Qp were made using the radioactive microsphere technique in anesthetized ventilated dogs (n = 7) and sheep (n = 6). Qs to the central airways was also measured in another group of sheep (n = 10). At the end of each study, animals were killed and the lungs and trachea were excised. Qp to the upper and lower trachea, mainstem bronchi, and lobar bronchi was calculated, and the relative distribution of Qp and Qs to mucosa, cartilage, and adventitia was determined. Results showed a progressive increase (P < 0.01) in Qp (in ml.min-1 x 100 g-1) from upper trachea to lobar bronchi in both dogs and sheep. Qp and Qs supplied mainly the airway adventitia and the mucosa, respectively. Expressed as a percentage, 89 +/- 4% (SE) of Qp was to the adventitia and 0.1 +/- 0.07% was to the mucosa (P < 0.01), whereas 60 +/- 3.2% of Qs was to the mucosa and 22 +/- 4.6% was to the adventitia. In conclusion, in dogs and sheep there is a pulmonary contribution to central airway blood flow that increases from upper trachea to lobar bronchi and that supplies mainly the peritracheal adventitia.

Animals↗
PubMed1998

Participation of angiogenesis from rat femoral veins in the neovascularization of adjacent occluded arteries.

The neovascularization of the arterial wall in human and experimental pathology has been demonstrated. The occlusion of the of the rat femoral artery is a suitable model for the study of these angiogenesis processes. Newly formed capillaries growing into the arterial wall have been described in this model. The origin of these ingrowing capillaries has been attribute to the preformed surrounding venules and capillaries. The contribution of the adjacent femoral vein with a supplementary population of vascular sprouts could also be possible. To test this hypothesis in half of the occluded arteries, the adventitia was removed from the side facing the femoral vein. Between 1 and 3 days after surgery several alterations were found both in the endothelial cells and the smooth muscle cells of the tunica media. Between 3 and 6 days, solid or canalized endothelial sprouts were observed arising from the femoral vein. By days 4 and 6, newly formed capillaries grew into the adventitia and tunica media of the femoral artery. Some of them, penetrated the internal elastic lamina. This microvascular penetration from the femoral vein was more prominent in the area of the ostium of the collateral and when the adventitia was removed. Some ingrowing capillaries were in continuity with the endothelial cells of the arterial neointima. At days 7 and 8, regressing capillaries were observed in the neomicrovasculature network between artery and vein, with a selective loss of the smaller vessels. From day 9 onwards, fewer and larger vascular channels were present between the femoral vein and the femoral artery. An arterial neolumen contained what appeared to be circulating "fresh" blood. Quantitatively, the venous neocapillary density increased from days 4 to 6 and then declined significantly by day 8. The arterial neocapillary density increased form days 4 to 8 and declined significantly by day 12. Moreover, both densities were significantly greater when the arterial adventitia was removed. The perfusion with barium solution showed the presence of the contrast material in the newly formed vessels, the lumen of the femoral vein, and the neolumen of the occluded arterial segment. The present findings indicate that putative angiogenic molecules released form the occluded arterial segment may reach the adjacent wall of the vein inducing neovascularization from it. The vein vascular sprouts are connected to the ingrowing capillaries in the occluded arterial wall and to the neocapillaries form the preexisting pericytic microvasculature. When the arterial adventitia were removed up to 2 times greater vein neocapillary's density was observed suggesting an easily access of the putative angiogenic factors to the vein.

Animals↗
PubMed1975

[A new method for the study of flow of material into surviving blood vessel segments].

One of the most important questions arising in experiment on surviving segments of vessels is the question of flow of material into the vessel wall through the intima or adventitia. To make a distinction is important for the interpretation of results of in vitro experiments. By using a "tissuephil" tested already in practical surgery wound-adhesive free of any noxious effect, authors could form segments of vessels, having an only intimal or adventitial surface. Using this technique the flow of blood into the wall through intima or adventitia could be investigated separtely. At in vitro experiments most part of the labelled material flows into the vessel wall through the adventitia. This fact can be explained by the presence of microinjuries of the adventitia caused by the removing of the surrounding fat tissue. It is believed that only the flow through the intima gives an information about the condition of the vessels. Flow through the adventitia is mostly artificial.

Animals↗
PubMed1981

The effects of 6-hydroxydopamine on the disposition of norepinephrine in the rabbit aorta.

Pretreatment of rabbits with 6-hydroxydopamine (6-OHDA; 25 mg/kg i.v. on day 0 plus 50 mg/kg i.v. on day 1, sacrifice on day 4) depleted 95% of the endogenous catecholamines from the rabbit thoracic aorta and heart. A partial recovery of endogenous catecholamines occurred over the next 2 weeks. 6-OHDA pretreatment decreased the cocaine-sensitive accumulation and the binding of l-[3H]norepinephrine (l-[3H]NE) by 85% in the rabbit thoracic aorta. Thus, this pretreatment with 6-OHDA produced an adequate chemical sympathectomy of the rabbit thoracic aorta. The effects of 6-OHDA pretreatment on the accumulation ane metabolism of l-[3H]NE were examined in the isolated adventitia and isolated media of the rabbit aorta to determine the origin of the O-methylated metabolites formed by the isolated adventitia. In the isolated adventitia, 6-OHDA pretreatment decreased the accumulation of l-[3H]NE and the formation of deaminated metabolites by 80%, but the formation of [3H]normetanephrine was increased more than 2-fold. 6-OHDA produced only a slight decrease in the formation of one of the deaminated metabolites of l-[3H]NE by the isolated media. These results are interpreted to mean that in the isolated adventitia most of the accumulation and deamination of l-[3H]NE occurs in the adrenergic nerve terminals whereas most of the O-methylation occurs in the extraneuronal elements of the isolated adventitia.

Animals↗
PubMed1998

Topography of cell replication in human vein graft stenoses.

BACKGROUND: Analysis of the cellular composition of human autogenous vein graft lesions at the time of revision provides an opportunity to identify the cellular processes leading to the development of stenosis in humans after vascular reconstruction. METHODS AND RESULTS: Human vein graft-threatening stenotic lesions were identified by duplex scanning within 3 to 18 months after infrainguinal bypass and surgically removed. They were serially studied by immunocytochemistry for expression of the proliferating cell nuclear antigen (PCNA) in different cell types: alpha-actin-positive smooth muscle cells (SMCs), endothelial cells (ECs), monocytes, and macrophages. Proliferation indexes were separately obtained for each layer of the vessel wall by determining the mean percentage of PCNA-positive nuclei among the total number of nuclei present within the intima, the media, and the adventitia, respectively. The percentage distribution of the replicating cell types was also determined. We report that in autogenous vein graft (n = 14) the intima of the lesion displayed fewer PCNA + nuclei (1.03 +/- 0.88) than the underlying media (3.14 +/- 0.74) or the adventitia (3.01 +/- 0.74). Replicating SMCs were predominantly in the medial layer (68% of PCNA + cells) of stenotic vein grafts. In the adventitia, the proliferation was most intense in the endothelium of microvessels (65% of PCNA + nuclei). CONCLUSIONS: Our findings reveal a 3-fold greater proliferative activity in the media and the adventitia as compared with the intima of autogenous vein graft lesions, in contrast to cellular proliferation identified in recurrent coronary stenotic plaques. Moreover, there are distinctive patterns of distribution of the different cell populations among the 3 layers. The results indicate a proliferative response of the media and the adventitia of autogenous vein grafts transplanted into the arterial circulation, in addition to the cellular proliferation observed in the intima of the lesion.

Actins↗
PubMed1997

Proliferation and differentiation of smooth muscle cell precursors occurs simultaneously during the development of the vessel wall.

Formation of the blood vessel wall depends on the recruitment, proliferation, and differentiation of smooth muscle cell (SMC) precursors. The temporal events associated with the onset of expression of several SMC proteins have been well characterized in mouse and avian species. However, the timing of cell proliferation during this process has not been explored. More importantly, it has not been clear whether commitment to the smooth muscle pathway precludes proliferation during development. In the present study, we have determined the kinetics of replication in developing chick aortae between days 2.5 and 19 and have correlated these data with the expression of various SMC differentiation markers. We found that proliferation of aortic SMC precursors occurs in two waves; an early phase of rapid proliferation (15-17%; between days 4 and 12), and a second phase, when replication was reduced to less than 5% (days 16 to hatching). Proliferation of SMC during the first wave occurred concomitantly with the progressive accumulation of SMC contractile proteins, such as SM alpha-actin, calponin, myosin heavy chain, and the 1E12 antigen. We also found that the relative proliferation capacity within each compartment of the vessel wall, ie., intima, media, and adventitia varies throughout development. Approximately, 55-63% of all replicating cells were found in the tunica adventitia from days 6 to 12, whereas 35% were found in the tunica media (tunica media:adventitia = 1:2). This ratio was inverted after day 12, when most of the replicating cells were located in the tunica media (tunica media:adventitia = 2:1). In addition, we observed a ventral-to-dorsal gradient in the proliferation of SMC precursors between days 2.5 and 5. The ventral-to-dorsal proliferation gradient was similar to the previously described differential expression of two early SMC markers: alpha-actin and the 1E12 antigen. These data support the concept that a polarity exists either in the pool of SMC precursors or, in expression of factors that regulate recruitment of presumptive SMC.

Animals↗
PubMed1988

Development of arteries in embryonic chick bone marrow with special reference to the appearance of periarterial granulopoietic sheaths.

Arterial development was studied in embryonic chick bone marrow starting on day 11 of incubation and continuing until day 18. Arteries first appear on day 11 as vessels with two components to their wall structure, namely a thin, complete endothelium and a nearly complete pericyte layer. With advancing age, three distinct layers--an endothelium, a complete muscularis, and adventitia--appear. Long, narrow endothelial cells form cellular junctions at their basal surfaces. Smooth muscle cells remain relatively undifferentiated and do not consist of more than three layers even in the largest arteries. The adventitia consists of a hypocellular zone containing fibroblasts and a collagenous extracellular matrix. Unmyelinated nerves are located at the peripheral margin of the adventitia. All of the larger arteries are surrounded by a sheath of heterophilic granulopoietic cells. These cells do not intrude into the adventitia, but basophilic or mast cells often do intrude. The stromal cells of the periarterial granulopoietic sheaths remain as either fibroblastic cells or as multilocular preadipocytes. They, unlike those stromal cells beyond the sheath, never become unilocular adipocytes. By day 18, granulopoiesis is restricted to the periarterial sheaths and to the endosteal regions of the marrow. These studies indicate that fibroblastic stromal cells and preadipocytes, but not fully developed adipocytes, support granulopoiesis in the chick marrow. The stromal cells in the periarterial sheaths either represent a subpopulation of cells that do not develop into adipocytes or represent cells whose development into adipocytes is locally inhibited.

Animals↗
PubMed1991

The architecture of adventitial elastin in the canine infrarenal aorta.

Although the artery wall consists of three distinct layers, only the structures of the intima and media have been well characterized. The adventitia has generally been overlooked. Our examination focused on the organization of elastin and collagen which are the major components of this tunic. Canine infrarenal aortas were excised, stretched to their in vivo length, then pressure fixed in formalin. Transverse, longitudinal, and frontal sections were prepared with specific elastin and collagen stains. Areas of adventitia in these sections were examined with LM, and interconnections between collagen and elastin were photographed at various magnifications. Subsequently, the slides were fractured for attachment to SEM stubs, and the coverslips were demounted. The identical areas were then examined with SEM using the LM micrographs as a guide to identify elastin and collagen. Whole mount aortic ring preparations were digested in formic acid for 72 and 96 h at 45 degrees C to confirm adventitial elastin architecture. The adventitia was organized in alternating lamellae of collagen and elastin. The elastin lamellae consisted of continuous sheets of elastin with a longitudinal fibrillar substructure. Finer circumferential elastin fibers were also identified. These attached to both longitudinal elastin and adjacent collagen lamellae. Collagen lamellae were arranged in broad corrugated bands of fibrils. The unique architecture of the adventitia may explain some of the visco-elastic properties of the aorta in both normal and pathologic states.

Animals↗
PubMed1992

Electron microscopic structure and innervation of the carotid baroreceptor region in the rock hyrax (Procavia capensis).

Semi-thin plastic sections reveal that the carotid baroreceptor region in the rock hyrax comprising the origin of the internal carotid artery has a preponderantly elastic structure and a thick tunica adventitia. In contrast, the common carotid artery has a musculoelastic structure, whereas the cranial segment of the internal carotid artery (immediately distal to the baroreceptor areas) shows the features of a muscular artery. Electron microscopy discloses the presence of sensory nerve endings within the parts of the tunica adventitia adjoining the preponderantly elastic zone of the internal carotid artery. These nerve endings are characterized by varicose regions containing a large quantity of mitochondria. Bundles of collagen fibers in the tunica adventitia form convolutions or whorls around the nerve terminals and often terminate on the surface of the elastic fibers or into the basement membranes of the neuronal profiles. The large content of elastic tissue in the tunica media of the baroreceptor region may render the vessel wall highly distensible to intraluminal pressure changes. This, in turn, would facilitate the transmission of the stimulus intensity to the sensory nerve terminals located in the tunica adventitia. It is suggested that the stretching of elastic fibers may form the main mechanical event leading to the distortion of the associated nerve terminals. However, a change in the geometrical configuration of the bundles of collagen under the influence of the elastic fibers may provide a better insight into the mechanisms of distortion of the baroreceptors related to and/or in contact with collagen fibers.

Animals↗
PubMed1989

Action of methylene blue and haemoglobin in rabbit aorta in relation to the surface of drug entry.

The effect of methylene blue and haemoglobin has been evaluated by using a procedure of restricting drug entry to one surface of rabbit aortic rings. In preparations precontracted with noradrenaline, methylene blue and haemoglobin produced, via the intima, an additional rapid and endothelium-dependent contraction. While haemoglobin was without effect via the adventitia, methylene blue produced a slow endothelium-independent contraction that was diminished but not abolished in reserpine-pretreated animals. This augmentation of the noradrenaline-induced contraction produced by methylene blue via the adventitia in reserpine-pretreated rabbits was observed also with phenylephrine but not with methoxamine. Methylene blue, when added to aortic rings incubated with 3H-(-)-noradrenaline, interfered with the neuronal uptake of this amine and enhanced the outflow of 3H. In conclusion, methylene blue and haemoglobin enhanced noradrenaline-induced contraction by an endothelium-dependent mechanism when applied via the intima. Haemoglobin is devoid of effects via the adventitia but methylene blue has indirect sympathomimetic effects. In experiments using intact rings with no restriction to drug entry it was found that the enhancement by haemoglobin of the tyramine-induced response was markedly less than that observed for noradrenaline for the same level of plateau contraction. This finding indicates that the endothelium-derived relaxing factor is more effective on smooth muscle cell layers in the vicinity of intima than on those close to adventitia.

Animals↗