Central splanchnic venous thrombosis. Often unsuspected, usually uncomplicated

Despite the increasingly frequent noninvasive detection of central splanchnic venous thrombosis (CSVT), its pathophysiology and clinical significance remain incompletely understood. We reviewed 50 consecutive cases of partially or totally occlusive thrombosis, primarily of the portal (60%) and splenic (40%) veins. Thirty-eight percent of patients had cancer; 26% had portal hypertension or other conditions associated with splanchnic venous stasis; and in 20%, thrombosis developed postoperatively. Angiography (89%), duplex ultrasonography (46%), CT scan (32%), and MRI (16%) were all useful diagnostic modalities. In 58% of cases, CSVT was clinically unsuspected, and 32% of patients were essentially asymptomatic. Variceal hemorrhage occurred in 30% of cases, and abdominal pain was notable in 26%. Whereas 50% of patients died < or = 6 months of diagnosis, only one of these deaths was directly attributable to CSVT; the remainder were secondary to underlying disease unrelated to the CSVT itself. CSVT, increasingly detected but often unsuspected clinically, is characterized by a self-limited and nonlethal course in the majority of patients. Death from associated disease is, however, common. The treatment and prognosis of CSVT should therefore be dictated by its clinical manifestations and the setting in which it occurs, rather than by the venous thrombosis itself.

Endothelin-stimulated monocyte supernatants enhance neutrophil superoxide production

Endothelin-1 (ET-1) is a vasoconstrictive peptide released by ischemic/injured endothelium which increases intracellular ionized calcium [Ca2+]i in vascular smooth muscle. Previous work from this lab has shown that ET-1 also increases human peripheral blood monocyte [Ca2+]i, and that 24 h incubation of monocytes with 10(-9) M ET-1 causes production of prostaglandin E2 and interleukin-6. In these studies, ET-1-stimulated monocyte supernatants were evaluated for their effect on neutrophil superoxide production. While ET-1 alone had no direct effect, incubation of neutrophils for 20 min in ET-1-stimulated monocyte supernatants resulted in a 10-fold increase in superoxide production over basal levels, 44% as much superoxide production as induced by peptide N-formyl-methionyl-leucyl-phenylalanine (N = 6, p < .001). Monocyte supernatants were analyzed for interleukin-8 (IL-8 or neutrophil activation protein) content by radioimmunoassay. ET-1-stimulation resulted in production of 54% as much IL-8 as lipopolysaccharide controls (N = 6, p < .001). While a number of monokines can activate neutrophils, IL-8 has been shown to be a potent neutrophil activator as well as a superoxide primer. Therefore, ET-1-treated monocytes probably upregulate neutrophil superoxide production via a mechanism which includes IL-8.

Increased ambient pressure stimulates proliferation and morphologic changes in cultured endothelial cells

Very little is known about the effects of pressure within the vascular system on EC phenotype. To study this, bovine aortic EC were seeded on rat type I collagen plates (2,000/cm2) and allowed to attach for 24 hours. The cells were exposed to either atmospheric, 40, 80, or 120 mm Hg pressure by placing them in a plexiglass pressure chamber loaded with 5% CO2/air and maintained at 37 degrees C inside an incubator. Chamber pressure was continuously monitored with an amplified voltage transducer connected to a digital monitor. EC were maintained in DMEM supplemented with 10% calf serum and substrates for up to 9 days. The results indicate that EC proliferation is influenced by their ambient pressure. EC subjected in vitro to pressures comparable to mean systemic blood pressures had a significant increase in cell number compared to EC exposed to atmospheric pressures. EC were elongated and appeared to align randomly. We hypothesize that the systemic pressure which the endothelium is exposed to in vivo may have a significant regulatory influence on the ability of the endothelium to proliferate which may affect the endothelial cell response to injury.

Increased ambient pressure stimulates proliferation and morphologic changes in cultured endothelial cells

Very little is known about the effects of pressure within the vascular system on EC phenotype. To study this, bovine aortic EC were seeded on rat type I collagen plates (2,000/cm2) and allowed to attach for 24 hours. The cells were exposed to either atmospheric, 40, 80, or 120 mm Hg pressure by placing them in a plexiglass pressure chamber loaded with 5% CO2/air and maintained at 37 degrees C inside an incubator. Chamber pressure was continuously monitored with an amplified voltage transducer connected to a digital monitor. EC were maintained in DMEM supplemented with 10% calf serum and substrates for up to 9 days. The results indicate that EC proliferation is influenced by their ambient pressure. EC subjected in vitro to pressures comparable to mean systemic blood pressures had a significant increase in cell number compared to EC exposed to atmospheric pressures. EC were elongated and appeared to align randomly. We hypothesize that the systemic pressure which the endothelium is exposed to in vivo may have a significant regulatory influence on the ability of the endothelium to proliferate which may affect the endothelial cell response to injury.

Chronic cyclic strain reduces adenylate cyclase activity and stimulatory G protein subunit levels in coronary smooth muscle cells

Previous studies from this laboratory have demonstrated that acute cyclic strain causes a reduction in adenylate cyclase activity in cultured coronary vascular smooth muscle cells. The objective of this study was to test the hypothesis that chronic cyclic strain of coronary vascular smooth muscle cells also causes inhibition of adenylate cyclase activity and that this may be related to changes in G protein steady-state levels. Cultured smooth muscle cells obtained from porcine coronary artery were subjected to 24 h of cyclic strain of 20 kPa (24% maximum strain) at 60 cycles/min. Unstretched cells served as controls. Basal, Gpp(NH)p, and forskolin plus Mn(2+)-stimulated adenylate cyclase activities were inhibited significantly in stretched versus unstretched vascular smooth muscle cells. The reduction in adenylate cyclase activity observed after 24 h of cyclic strain was associated with a significant (P < 0.05 vs controls) reduction in steady-state levels of Gs alpha 45, whereas Gi alpha 1,2 and G beta levels remained unchanged. The data support the hypothesis that adenylate cyclase activity and G protein steady-state levels in coronary smooth muscle are sensitive to chronic cyclic strain. It suggests that the G protein adenylate cyclase effector pathway may play an important role in the subacute adaptation of the coronary circulation to changes in intravascular pressure.

Enhanced patency of venous Dacron grafts by endothelial cell sodding

The effect of microvessel endothelial cell (EC) sodding on the patency of Dacron grafts interposed in canine inferior vena cava was studied. EC were harvested enzymatically from canine omentum and isolated by density gradient centrifugation. Preclotted, knitted Dacron grafts were sodded with > 10(6) EC/cm2 surface. The results demonstrate significant improvement in patency of sodded grafts placed in the inferior vena cava as compared with control grafts (p < 0.001 in grafts with a distal arteriovenous fistula and p < 0.05 in grafts without a distal fistula). The neointima of the sodded grafts were thinner and scanning electron microscopy confirmed the presence of a confluent layer of EC. In addition, the production of prostacyclin but not thromboxane A2 was significantly enhanced in the sodded grafts as compared with controls. We conclude that microvessel EC sodding of Dacron grafts significantly improves the patency rate and inhibits neointimal thickening of the prosthesis. The mechanism is unknown but may involve a more rapid endothelialization of the graft surface with the potential of producing more prostacyclin and less thromboxane A2.

Lipoprotein (a): a risk factor for peripheral vascular disease

Lipoprotein (a) [Lp(a)] is a serum protein that has been reported to be predictive of complications from coronary and cerebrovascular atherosclerotic disease. This study was designed to compare plasma levels of Lp(a) in 100 white male patients with and without peripheral vascular disease (PVD) and to determine the role of Lp(a) as a risk factor for PVD independent of known risk factors such as cigarette smoking (CIG), diabetes mellitus (DM), and coronary artery disease (CAD). Patients with PVD (mean age = 67.6 years, n = 50) had a statistically significant (p = 0.04) elevation of Lp(a) (29.8 +/- 3.9 mg/dl) as compared to patients without PVD (20.0 +/- 2.9 mg/dl (mean age = 68.3 years, n = 50). Further analysis revealed that patients with PVD had a significantly higher incidence of CIG (86% vs. 68%, p = 0.03), DM (34% vs. 14%, p = 0.02), and CAD (52% vs. 30%, p = 0.02) than those without PVD. However, there was no statistically significant difference in Lp(a) levels in patients with CIG or CAD compared to those without. Patients with DM had significantly (p = 0.04) lower levels of Lp(a) (17.8 +/- 3.5 mg/dl) than those without DM (27.1 +/- 3.0 mg/dl). Stepwise regression analysis of these various risk factors for PVD revealed that Lp(a) was the strongest significant individual predictor for the presence of PVD (R2 = 0.07) as compared to DM (R2 = 0.05) and CIG (R2 = 0.04). We conclude that there is a significant correlation of Lp(a) levels and the incidence of PVD, which is independent of other major risk factors for PVD.

Defecation syncope secondary to functional inferior vena caval obstruction during a Valsalva maneuver

This report describes a case of defecation syncope secondary to functional inferior vena cava (IVC) obstruction. Preoperative hemodynamic assessment revealed a marked decrease in blood pressure and IVC obstruction when the patient performed a Valsalva maneuver. The intraoperative approach included continuous hemodynamic monitoring as well as transesophageal ultrasonography to assess IVC patency during surgical mobilization of the IVC. Functional obstruction of the IVC at the diaphragmatic hiatus was identified, and this obstruction was relieved with extensive mobilization of the IVC and right crural myotomy. This report describes an effective surgical approach to a rare functional disorder involving the IVC.

Control of smooth muscle cell proliferation by psoralen photochemotherapy

PURPOSE

Restenosis after balloon angioplasty or the intimal hyperplasia occurring at distal anastomoses of bypass grafts severely limits the long-term therapy for peripheral vascular disease. The aim of this study was to evaluate the application of psoralen photochemotherapy with ultraviolet A (UVA)-activated 8-methoxypsoralen (8-MOP) to suppress smooth muscle cell (SMC) proliferation in vitro by the formation of 8-MOP-DNA monoadducts and interstrand cross-links to inhibit DNA synthesis.

METHODS

Bovine aorta SMC (2 x 10(4)/cm2) were treated with 8-MOP (0 to 1000 ng/ml) for 30 minutes, followed by UVA (2 joule/cm2) to determine the dose of 8-MOP and UVA that inhibits SMC proliferation.

RESULTS

The results show that 8-MOP in the range 30 to 1000 ng/ml in combination with 2 joule/cm2 UVA inhibited SMC proliferation by 40% to 60% 3 days after treatment. In time course studies the growth of SMC treated with 100 ng/ml 8-MOP and 2 joule/cm2 UVA were monitored over 5 days, and this regimen was found to be cytostatic. SMC viability was confirmed by trypan blue exclusion.

CONCLUSIONS

Our studies suggest that 8-MOP/UVA photochemotherapy may represent a novel approach to the control of localized SMC proliferation.

The excitation of 8-methoxypsoralen with visible light: reversed phase HPLC quantitation of monoadducts and cross-links

The formation of 8-methoxypsoralen-DNA monoadducts and cross-links is presumed to be responsible for the efficacy of photochemotherapies that employ 8-methoxypsoralen activated with long-wavelength ultraviolet radiation (UVA, 320-400 nm). In this report it is shown that 8-methoxypsoralen can also be activated with visible light (419 nm). Bovine aorta smooth muscle cells were treated with 8-methoxypsoralen (1,000 ng/mL) and 419 nm light (up to 12 J/cm2). Cellular DNA was isolated, hydrolyzed using nucleolytic enzymes and then analyzed by reversed-phase high-performance liquid chromatography. The primary effect of using visible light instead of long-wavelength ultraviolet radiation is a more than 10-fold reduction in the extent of cross-link formation. Because the extent of monoadduct and cross-link formation has not been routinely measured in experiments in which cellular assays have been performed, it is difficult to correlate cell response to the presence of a particular type of 8-methoxypsoralen photoadduct (monoadduct or cross-link). Thus, the use of visible light allows the study of cells containing nearly 100% monoadducts. In addition, the reduction in cross-link formation when visible light is used to activate the compound may also reduce the mutagenicity of 8-methoxypsoralen and hence enhance its therapeutic efficacy.

Endothelin-stimulated human monocytes produce prostaglandin E2 but not leukotriene B4

The activation and proliferation of a prostaglandin E2 (PGE2) producing monocyte/macrophage may play a major role in down-regulating immune function after injury. But the mechanism by which monocyte or macrophage activation occurs in injury is unknown. Endothelin is a 21-amino acid peptide produced by vascular endothelium in response to ischemia, injury, or endotoxin. Prior work from our laboratory has shown that endothelin increases intracellular calcium in monocytes and causes production of interleukins-6 and -8. In the data reported in this paper, 10(-9) M endothelin stimulated human monocytes to produce 1050 +/- 63 pg/ml of PGE2 at 6 hr and 1328 +/- 47 pg/ml at 24 hr. This was nearly as much PGE2 production as that by bacterial lipopolysaccharide (endotoxin) stimulation (1295 +/- 47 pg/ml at 6 hr and 1506 +/- 94 at 24 hr). Endothelin had no effect on production of leukotriene B4. Endothelin may play an important initiating role in post-traumatic immunosuppression.

Phospholipase C: a putative mechanotransducer for endothelial cell response to acute hemodynamic changes

Endothelial cells (EC) in vivo are exposed to a multitude of physical forces with each pulse of the cardiac cycle. Ongoing studies support the concept that EC respond to these forces through specific signal transduction pathways. Previous investigations in our laboratory have shown that EC respond to the initiation of cyclic strain or to an acute increase in cyclic strain frequency with the production of inositol 1,4,5-trisphosphate (IP3). This study demonstrates that EC also respond to an acute decrease in cyclic stretch frequency with a transient increase in IP3 production. Thus, EC detect both increases and decreases in cyclic stretch frequency with phospholipase C (PLC) activation leading to IP3 generation.

Photoinhibition of smooth muscle cell migration: potential therapy for restenosis

Evidence from animal, autopsy, and atherectomy studies demonstrates that migration and proliferation of smooth muscle cells of medial origin result in neointima formation and decreased luminal cross-sectional area. The purpose of this study was to evaluate whether low energy light irradiation can inhibit smooth muscle cell migration and therefore potentially reduce the degree of neointima formation and the incidence of restenosis. The migration kinetics of bovine aortic smooth muscle cell monolayers were examined using a fence assay. The effect on smooth muscle cell migration of irradiation with monochromatic light at wave-lengths ranging from 400 to 700 nm was compared to the migration of cells irradiated with broadband white light or maintained in the dark. Wavelength specific photoinhibition of smooth muscle cell migration was observed; 594-600 nm light reproducibly inhibited migration by 12-29% (P < 0.05). Migration rate was significantly reduced following daily radiant exposures of 1.0 J/cm2 as well as following a single radiant exposure of 0.09 or 0.9 J/cm2. The decrease in migration was not associated with any change in cell proliferation or [3H] thymidine incorporation. We conclude that 594-600 nm light inhibits smooth muscle cell migration in vitro and may potentially be used in vivo to decrease fibrointimal thickening following arterial injury. This application of photoinhibition may be useful in retarding restenosis following angioplasty.

Immunocytochemical expression and localization of protein kinase C in bovine aortic endothelial cells

Total PKC activity in BAEC incubated for 24 hrs in either 10% serum (FBS) or serum-deprived media (SDM) was similar. However, most of the activity (69%) in the FBS group was detected in the particulate fraction, while it was mainly in the cytosolic fraction (66%) in the SDM group. By confocal microscopy, there was diffuse cytoplasmic localization of the antibodies to the alpha and beta PKC isoforms. gamma PKC was not detected. Treatment of FBS or SDM cells with a phorbol ester resulted in an increase in PKC activity with translocation to the particulate fraction. PKC alpha immunofluorescence redistributed to the perinuclear region whereas PKC beta staining remained mostly cytosolic. Calphostin C, a PKC inhibitor, prevented the phorbol ester-induced increase in PKC activity and translocation.

Isolation and characterization of rabbit cardiac endothelial cells: response to cyclic strain and growth factors in vitro

Studies of the cardiac endothelium have been complicated by difficulties in isolating and maintaining cardiac endothelial cells (EC) in culture. We present in this paper a method of obtaining pure EC from rabbit hearts by collagenase digestion and membrane filtration. Pure cultures of EC displaying characteristic EC morphology, uptake of di-I-acetylated LDL, and contact-inhibition of growth were successfully maintained in culture for several weeks in media supplemented with fetal bovine serum, bovine retina-derived growth factor (RDGF), and antibiotics. Since EC in vivo are exposed to a complex pattern of physical forces we also sought to determine the proliferative response of cardiac EC subjected to pulsatile strain in vitro and compared it with the response to the addition of an exogenous growth factor, RDGF. The results demonstrate that a regimen of 60 cycles per minute, 24% cyclic strain induced a significant increase in cardiac EC proliferation and suggests that physical forces may have a trophic effect on EC proliferation.

Protein kinase C is a mediator of the adaptation of vascular endothelial cells to cyclic strain in vitro

BACKGROUND

The mechanism by which hemodynamic forces influence the function of the endothelium lining a blood vessel are unknown. The aim of this study was to determine the effect of in vitro cyclic strain on endothelial cell (EC) activation of protein kinase C (PKC).

METHODS

Confluent bovine aortic ECs grown on flexible-bottomed culture plates were subjected to 24% maximum strain at a frequency of 60 cycles/min for 24 hours. Changes in PKC activity and evidence of translocation from cytosol to membrane fractions were assessed by immunocytochemical staining of ECs with antibodies specific to PKC and direct measurement of PKC activity in cytosol and membrane. To determine whether activation of PKC was responsible for some effects of cyclic stretch on ECs, a specific PKC inhibitor, calphostin C, was added to ECs subjected to cyclic stretch for 5 days and control ECs grown under static conditions.

RESULTS

Immunocytochemical staining of ECs demonstrated translocation of PKC alpha- and beta-antibody fluorescence from the cytosol to the perinuclear and nuclear regions in ECs subjected to cyclic strain. This was confirmed by direct measurements of PKC activity, which demonstrated an early transient translocation of PKC activity from cytosol to membrane fraction at 10 seconds followed by a sustained elevation in PKC activity in the membrane at 100 seconds. Calphostin C abrogated the increase in EC proliferation that occurs in response to stretch.

CONCLUSIONS

We conclude that cyclic stretch of ECs results in activation of PKC, which may be responsible for mediating the effects of cyclic stretch on EC growth.

Intracellular cyclic AMP levels in endothelial cells subjected to cyclic strain in vitro

Human saphenous vein endothelial cells (EC) were grown to confluence in fibronectin-coated culture plates with flexible membrane bottoms and maintained in M-199 supplemented with substrates. One hour prior to experimentation 5 mM IBMX, a phosphodiesterase inhibitor, was added. Vacuum was used to deform the membrane bottoms to 24% strain at 60 cycles/min (0.5 sec elongation alternating with 0.5 sec relaxation). After 10-60 min of cyclic strain, or upon exposure of EC to 100 microM forskolin or 0.1 microM galanin, intracellular cyclic AMP (cAMP) was measured by radioimmunoassay. In parallel experiments, tissue plasminogen activator (tPA) secretion was determined after 24 hr of cyclic strain in the absence or presence of forskolin or galanin. The results demonstrate that exposure of EC to cyclic strain led to no change in cAMP levels and confirmed our previous observation that tPA secretion was enhanced with cyclic strain. Addition of forskolin, which led to an almost 10-fold increase in cAMP levels, or galanin, which led to a 34% decrease in cAMP levels, did not significantly alter the rise in tPA induced by cyclic strain.

Changes in cyclic strain increase inositol trisphosphate and diacylglycerol in endothelial cells

The purpose of this study was to assess the effect of cyclic strain on phosphatidylinositol turnover in cultured bovine aortic endothelial cells (EC). Confluent EC grown on flexible membrane bottoms were deformed by vacuum to 24% maximum strain and subjected to two cyclic strain regimens. In the first set of experiments, EC were subjected to deformation at a frequency of 60 cycles/min for either 0 (stationary control), 1, 5, 10, 25, 50, or 100 cycles of stretch. In the second set of experiments, EC were preconditioned by deforming the membranes at 60 cycles/min for 24 h. The cycling frequency was then acutely increased to 100 cycles/min for 0, 1, 5, 10, 25, or 100 cycles. Inositol phosphate and diacylglycerol concentrations were determined at the end of each regimen. The results demonstrate that either the initiation of pulsatile stretch or an acute change in cyclic stretch frequency stimulates a sequential and transient generation of inositol trisphosphate, its metabolites inositol biphosphate and monophosphate, and diacylglycerol. Thus EC may respond to the initiation and change in cyclic stretch frequency by a signal transduction pathway involving inositol lipid metabolism.

Persistent hypoglossal artery: An anomaly leading to false-positive carotid duplex sonography

Duplex ultrasonography is becoming increasingly popular as the sole diagnostic test in the evaluation of carotid artery bifurcation disease. We present a patient with a persistent hypoglossal artery, a rare primitive internal carotid-basilar anastomosis, masquerading as an internal carotid artery stenosis on ultrasound. The operative management of this anomaly is reviewed.

Tissue plasminogen activator expression in endothelial cells exposed to cyclic strain in vitro

The effects of cyclic strain on the production of tissue plasminogen activator (tPA) and type 1 plasminogen activator inhibitor (PAI-1) by cultured endothelial cells (EC) were examined. Human saphenous vein EC were seeded in selective areas of culture plates with flexible membrane bottoms (corresponding to specific strain regions) and grown to confluence. Membranes were deformed by vacuum (-20 kPa) at 60 cycles/min (0.5 s strain alternating with 0.5 s relaxation in the neutral position) for 5 days. EC grown in the periphery were subjected to 7-24% strain, while cells grown in the center experienced less than 7% strain. The results show a significant increase in immunoreactive tPA production on days 1, 3 and 5 compared to day 0 in EC subjected to more than 7% cyclic strain. There was no significant elevation of tPA in the medium of EC subjected to less than 7% strain. tPA activity could only be detected in the medium of EC subjected to more than 7% cyclic strain. PAI-1 levels in the medium were not significantly different in either group. In addition, immunocytochemical detection of intracellular tPA and messenger ribonucleic acid (mRNA) expression of tPA (assessed by the reverse transcriptase polymerase chain reaction utilizing tPA specific sense and antisense primers) was significantly increased in EC subjected to more than 7% cyclic strain. We conclude that a 60 cycles/min regimen of strain that is greater than 7% can selectively stimulate tPA production by EC in vitro and may contribute to the relative nonthrombogenicity of the endothelium in vivo.

Effect of cyclic stretch on endothelial cells from different vascular beds

Endothelial cells (EC) mediate many of the organ responses to shock. Much of our knowledge of EC are obtained from cell culture studies. However, compared to the dynamic milieu in vivo, the stationary environment for large-vessel EC may be artificial and inappropriate. In this study, the morphology, growth rate, and production of prostacyclin (PGI2) by EC obtained from different vascular beds under stationary and dynamic conditions were examined. EC were harvested from the thoracic aorta (Ao), pulmonary artery (PA), and vena cava (VC) of the same calves and exposed to 0.5 sec 24% deformation alternating with 0.5 sec relaxation (i.e., 60 cycles/min). Our results show that in response to the cyclic regimen, VCEC were elongated perpendicular to the force vector and their actin filaments aligned in the same direction, while AoEC and PAEC did not exhibit any morphological changes. The growth rate of AoEC (but not PAEC or VCEC) was significantly enhanced when stimulated by cyclic stretch. In addition, AoEC demonstrated an increased PGI2 synthetic activity with cyclic stretch, while PAEC and VCEC were unaltered. We conclude that the maintenance of EC phenotype and function is dependent on the hemodynamic milieu in vivo and may be influenced by the vascular origin of the cultured EC.

Morphological response of human endothelial cells subjected to cyclic strain in vitro

Endothelial cells (EC) are subjected to hemodynamic forces in vivo. However, most in vitro studies of EC biology have been performed utilizing stationary culture conditions. To study the morphology and cytoskeletal features of EC under dynamic culture conditions, we utilize a system capable of exerting repetitive strain on cells in culture. Human saphenous vein EC were plated to a subconfluent density in 25-mm wells with a thin flexible bottom and a rat collagen, Type I surface. A -20 kPascals vacuum applied to the bottoms led to a maximum deformation of 24%. EC were exposed to 0.5 sec deformation alternating with 0.5 sec relaxation (60 cycles/min) for 24 hr. EC were fixed with formalin at different time intervals and stained with crystal violet. Actin filaments were stained with rhodamine phalloidin, an F-actin marker, while beta-tubulin and vimentin were visualized by immunofluorescent antibody techniques. Within 15 min after initiation of cyclic strain, actin stress fibers were aligned perpendicular to the force vector. By 12 hr of cyclic strain EC were elongated and oriented in the same direction as the actin filaments. EC elongation and alignment were inhibited by cytochalasin B. Even up to 24 hr of cyclic strain, beta-tubulin and vimentin distributions were unaltered. We propose that cyclic strain of EC in vitro influences cell alignment and elongation by a mechanism dependent on the actin filament system.