Differential regulation of matrix metalloproteinase-9 by monocytes adherent to collagen and platelets.

Circulating monocytes adhere to platelets and matrix proteins at sites of vascular injury, where engagement of specific surface tethering molecules mediates outside-in signaling and synthesis of gene products by the leukocytes. Here we demonstrate that interaction of isolated human monocytes with collagen induces matrix metalloproteinase-9 (MMP-9; gelatinase B) synthesis by monocytes, a process that is greatly enhanced in the presence of platelets. MMP-9 is a potent matrix degrading enzyme implicated in atherosclerotic plaque rupture, aneurysm formation, and other vascular syndromes. Synthesis of MMP-9 by monocytes is tightly regulated and synergistically increased following adhesion to collagen and platelets. Adhesion to control matrix proteins alone did not result in MMP-9 protein production and, similarly, adhesion of monocytes to platelets activated with thrombin in suspension was not sufficient to induce MMP-9 synthesis in the absence of monocyte adhesion to collagen. Interruption of intercellular contact between platelets and monocytes dramatically inhibited MMP-9 synthesis. These observations demonstrate that discrete adhesion-dependent signaling pathways govern MMP-9 synthesis by monocytes. The synthesis of MMP-9 by monocytes may be critical in vascular syndromes and other pathological processes that are dependent on dysregulated cell-cell and cell-matrix interactions.

ELF magnetic fields in a city environment.

Some epidemiological studies indicate an association between extremely low frequency electromagnetic field (ELF-EMF) exposure and cancer risks. These studies have mainly taken residential and occupational exposure into consideration. Outdoor environments are often considered as low level areas, but in this paper we show that this is not true in a city environment. We have mapped the ELF magnetic flux densities along certain stretches of sidewalk in central Göteborg City, Sweden. About 50% of the investigated street length shows flux densities of the same order of magnitude (0.2 microT and above) as those associated with increased risks of cancer in epidemiological studies. We conclude that the outdoor exposures in a city environment also should be considered in exposure assessments and risk evaluations. These elevated flux densities are probably due to stray currents. We also found strong magnetic flux densities (> 1.0 microT) close to ordinary distribution pillars, power substations, shoplifting alarms, and other electrical devices.

An assessment of the current applicability of the EVT endovascular graft for treatment of patients with an infrarenal abdominal aortic aneurysm.

OBJECTIVE: To determine the percentage of elective abdominal aortic aneurysms (AAAs)/aortoiliac aneurysms that currently can be repaired with endovascular grafts (EVGs), the reasons for rejection of EVGs, and the future role of EVG in the treatment of AAA. METHODS: From January 1997 to May 1998, patients at three hospitals (a university hospital, a university-affiliated teaching hospital, and a Veterans Administration hospital with university faculty and residents) were evaluated for EVGs as part of a national clinical trial with grafts manufactured by Endovascular Technologies (EVT, Menlo Park, Calif). All patients at two hospitals and patients treated by the participating surgeons at the third hospital were screened for EVG. Patients with AAAs that were ruptured, symptomatic, or involved renal or mesenteric arteries and patients who declined treatment were excluded from the study. Evaluation included clinical examination, computed tomography scan, and selective arteriography. The decision to proceed with EVG was made by the vascular surgeon, with input and concurrence of medical personnel from a company with extensive experience in endograft repair. The main outcome measures were the determination of the percentage of elective AAAs currently being treated with an EVG and the reasons for exclusion of patients from EVG placement. RESULTS: A total of 162 patients underwent elective treatment of an AAA, 22 (14%) with an EVG (14 bifurcated, eight tube) and 140 (86%) with traditional resection. Indications for not proceeding with an EVG included insufficient proximal cuff in 29 patients (21%), distal common iliac aneurysm or insufficient distal iliac neck in 29 patients (21%), proximal neck too large for an EVG in 24 patients (17%), symptomatic iliac stenosis in 23 patients (16%), iliac stenosis precluding introducer passage in 17 patients (12%), patient preference in 11 patients (8%), and calcification, kink, or extensive thrombus involving the proximal neck precluding safe graft attachment in seven patients (5%). Of the 22 patients treated with an EVG, three were converted to open resection, because of iliac stenosis in two patients and premature stent deployment in one patient (initial technical success rate, 86%). CONCLUSION: Based on currently available technology, 80% of patients were not candidates for an EVG because of proximal calcification, short aortic or distal cuff, coexisting distal iliac aneurysm, and stenotic iliac disease. Even with the use of adjunctive procedures, most patients still require open repair. Significant changes in design will be necessary to apply these devices to most patients with an AAA.

Cytoplasmic Ca2+ oscillations in human leukemia T-cells are reduced by 50 Hz magnetic fields.

The effect of 50 Hz magnetic fields on the cytosolic calcium oscillator in Jurkat E6.1 cells was investigated for field strengths within the range from 0 to 0.40 mT root mean square. The intracellular Ca2+ concentration data were collected for single Jurkat cells that exhibited a sustained spiking for at least 1 h while repeatedly exposing them to an alternating magnetic field in 10-min intervals interposed with nonexposure intervals of the same length. The obtained data were analysed by computing spectral densities of the Ca2+ oscillating patterns for each of these 10-min intervals. For every single-cell experiment the spectra of all exposure as well as nonexposure periods were then averaged separately. A comparison between the resulting averages showed that the total spectral power of the cytosolic Ca2+ oscillator was reduced by exposure of the cells to an alternating magnetic field and that the effect increased in an explicit dose-response manner. The same relationship was observed within the 0-10 mHz (10 x 10(-3) Hz) subinterval of the Ca2+ oscillation spectrum. For subintervals at higher frequencies, the change caused by the exposure to the magnetic field was not significant.

Peripheral aneurysms and arteriomegaly: is there a familial pattern?

PURPOSE: Studies have shown that 11% to 18% of patients with an abdominal aortic aneurysm (AAA) have a first-degree relative with an AAA. A familial pattern among patients with peripheral arterial aneurysms and arteriomegaly has not been reported. The objective of this study was to examine familial patterns among patients with peripheral arterial aneurysm and arteriomegaly and compare them with patterns among patients with AAA. METHODS: Pedigrees were constructed for first-degree relatives of patients who received the diagnosis of peripheral arterial aneurysm, arteriomegaly, or AAA from 1988 through 1996. The presence of aneurysms and risk factors was confirmed for patients and relatives by means of telephone interviews and review of hospital and physician records. RESULTS: Seven hundred three first-degree relatives older than 50 years were contacted for 140 probands with peripheral arterial aneurysm, AAA, or arteriomegaly. There were differences in risk factors for hernia and diabetes mellitus among the probands with peripheral arterial aneurysm, AAA, or arteriomegaly but none for relatives. Patients with peripheral arterial aneurysm (n = 40) had a 10% (4/40) familial incidence rate of an aneurysm, patients with AAA (n = 86) had a 22% (19/86) familial incidence rate, and patients with arteriomegaly (n = 14) had a 36% (5/14) familial incidence rate. AAA (24/28, or 86%) was the aneurysm diagnosed most commonly among first-degree relatives. Most aneurysms (85%) occurred among men. CONCLUSION: There appears to be a gradation of familial patterns from peripheral arterial aneurysm to AAA to arteriomegaly among patients with degenerative aneurysmal disease, and there appears to be a predominance among men. Relatives of patients with any of the 3 lesions-peripheral arterial aneurysm, AAA, arteriomegaly--most frequently have AAA. Relatives of patients with AAA, peripheral arterial aneurysm, or arteriomegaly may be screened by means of a physical examination for peripheral aneurysmal disease. Screening by means of ultrasound examination of the aorta should be limited to first-degree relatives of patients with aortic aneurysms or arteriomegaly.

Revision of reversed infrainguinal bypass grafts without preoperative arteriography.

PURPOSE: To determine whether graft revision on the basis of a duplex scan alone without an arteriogram is effective in identifying graft stenosis and allowing for repair to preserve bypass graft patency. METHODS: From 1994 to 1997, all patients in whom infrainguinal grafts were placed at a University-affiliated teaching hospital were entered into a prospective protocol using duplex scanning to detect stenotic lesions. Studies were performed after the operation, at 1 month, at 3 months, and every 3 months thereafter. All grafts were composed of reversed autogenous vein and were placed subcutaneously to allow for easier monitoring and correction. Patients who had failing grafts underwent operative correction without preoperative arteriography. RESULTS: During this interval, 48 lesions in 31 grafts were repaired. The indication for repair was a velocity ratio greater than 2.5 in all patients and greater than 3.0 for 43 lesions. Forty-four lesions had a peak systolic velocity greater than 250 cm/sec. Twenty-nine lesions reduced the distal graft velocity to less than 45 cm/sec. Sixteen lesions involved the proximal anastomosis, 26 the body of the graft, three the distal anastomosis, two involved inflow arteries, and one affected the outflow vessel. Repair included patch angioplasty for 39 lesions, resection with interposition graft for five, a proximal jump graft for three, and a distal extension graft for one. The severity and location of the stenosis was confirmed at operation in all cases. Twenty-eight of the 31 patients (90%) are currently alive, and follow-up on these patients has ranged from 5 to 36 months (mean, 19 months). Twenty-nine of the 31 grafts (94%) remained patent, with a 92% patency rate by life table analysis at 3 years. Follow-up duplex scans found improvement in the ankle-brachial index (mean increase, 0.33) and distal graft velocity (mean increase, 43 cm/sec) in all patients. After repair, 27 patients had a distal graft velocity greater than 45 cm/sec and no patient had a velocity ratio greater than 1.5. Complications included wound infection in two patients and bleeding that required reoperation in one. All symptomatic patients had clinical improvement, and none required early reexploration for residual stenosis. CONCLUSIONS: Graft repair may be safely performed on the basis of duplex scanning alone with preservation of bypass patency and correction of hemodynamic deterioration. Duplex scanning can detect inflow or outflow disease in addition to intrinsic graft stenoses and can identify sequential lesions, eliminating the need for, expense of, and risk of arteriography.

The influence of 50-Hz magnetic fields on cytoplasmic Ca2+ oscillations in human leukemia T-cells.

We have studied the effects of 50-Hz 100-microT rms magnetic fields on intracellular Ca2+ concentration in the Jurkat T lymphocyte variant E6.1 using fluorescent probes Indo-1 and Fura-2. We found, however, that the pattern of intracellular Ca2+ fluctuations also depended on the agent used for cell attachment, in our case the polypeptide poly-L-lysine. In order to isolate possible effects of magnetic field exposure from those of poly-L-lysine, the action of polypeptide on cytosolic Ca2+ was studied as well. It was found that a 10(-7)% concentration of polypeptide triggered prolonged Ca2+ spiking. Higher (10(-4)%) concentrations induced rapid increases in intracellular Ca2+ followed by high, unstable Ca2+ levels. The response of these cells to the monoclonal antibody anti-CD3 was also inhomogeneous, similar to one caused by poly-L-lysine. The effect of magnetic field exposure was studied on cells initially exhibiting (1) non-oscillating, low Ca2+ concentration and (2) prolonged Ca2+ concentration oscillations. In case (1) the result was negative. In case (2), statistically significant changes were found: the oscillation amplitude was reduced on average by 30%, and the frequency composition was shifted towards higher frequencies.

Simultaneous abdominal aortic aneurysm repair and nephrectomy for neoplasm.

BACKGROUND: Abdominal aortic aneurysm and renal neoplasm are occasionally discovered concurrently. Simultaneous operative therapy may be an effective alternate management strategy to a staged procedure. PATIENTS AND METHODS: The medical records of 10 consecutive patients undergoing abdominal aortic aneurysm repair and nephrectomy for renal neoplasm were reviewed. Data collected included mode of presentation, preoperative evaluation, renal pathology, and in-hospital morbidity and mortality. Long-term follow-up was obtained through office records and telephone contact. RESULTS: In 7 patients, the renal mass was identified during evaluation of abdominal aortic aneurysm. The aneurysm was identified during evaluation of hematuria in 2 patients. One patient was discovered to have both conditions simultaneously. All patients underwent successful aneurysm repair and nephrectomy. Pathology revealed 6 renal cell carcinomas, 2 complex cysts, 1 hemangiopericytoma, and 1 oncocytoma. Four patients have died in the follow-up period: 1 of metastatic cancer and 3 of unrelated causes. There have been no cases of graft infection. CONCLUSION: Simultaneous abdominal aortic aneurysm repair and nephrectomy for neoplasm is an appropriate management strategy for selected patients.

Ca2+ ion transport through patch-clamped cells exposed to magnetic fields.

The total current of Ca2+ ions through patch-clamped cell membranes was measured while exposing clonal insulin-producing beta-cells (RINm5F) to a combination of DC and AC magnetic fields at so-called cyclotron resonance conditions. Previous experimental evidence supports the theory that a resonant interaction between magnetic fields and organisms can exist. This experiment was designed to test one possible site of interaction: channels in the cell membrane. The transport of Ca2+ ions through the protein channels of the plasma membrane did not show any resonant behavior in the frequency range studied.

Effect of microwave radiation on permeability of liposomes. Evidence against non-thermal leakage.

The effect of 2.45 GHz microwave radiation on the permeability of unilamellar phosphatidylcholine liposomes has been studied. Leakage of 5(6)-carboxyfluorescein from the liposomes was measured using spectrofluorimetry after exposure to either microwaves or thermal heating for 5-20 min intervals. The exposure temperature, 37.6 +/- 0.5 degrees C, was well above the phase transition temperature of the lipid membrane. The microwave exposure did not result in any non-thermal increase in permeability above that produced by thermal heating. This study refutes the results reported by Saalman et al. [1] in which an increased liposome permeability due to microwave exposure was reported. The refined analysis in the present study shows that this increased liposome permeability was not a non-thermal microwave effect.

Differential response of arteries and vein grafts to blood flow reduction.

PURPOSE: This study was undertaken to evaluate the effect of blood flow on the dimensions and cellular composition of normal arteries and freshly placed vein grafts (VG). METHODS: Bilateral jugular vein interposition grafts were placed in the common carotid arteries of 12 New Zealand white rabbits, and blood flow was reduced on one side by external carotid artery ligation. Shear stress, tangential stress, vessel dimensions, and smooth muscle cell (SMC) proliferation of reduced-flow arteries and VG were compared with these measures in contralateral controls (CON). RESULTS: A sustained reduction in blood flow was documented at 4 weeks (13 +/- 4 ml/min reduced-flow vs 21 +/- 4 ml/min CON; p < 0.05). Reduced-flow carotid arteries had a smaller lumen radius and greater medial thickness compared with normal-flow arteries, but there was no difference in medial cross-sectional area or medial SMC volume and no differences in any intimal measurements. These changes resulted in normalization of shear stress (15.2 +/- 4.6 dynes/cm2 reduced-flow vs 13.6 +/- 2.5 dynes/cm2 CON; p = NS). All VG underwent a marked postimplantation hyperplasia in intima and media, but the major effect of flow reduction on VG dimensions occurred in the intima. Intimal thickness in reduced-flow VG was 60% greater than that in control VG (57 +/- 12 microns vs 35 +/- 5 microns; p = 0.05), and intimal area was 70% greater than that in controls (0.83 +/- 0.24 microns 2 vs 0.48 +/- 0.08 microns 2; p > 0.05). Smaller differences were found in medial thickness (74 +/- 4 microns reduced-flow vs 63 +/- 4 microns CON; p = 0.02) and medial area (1.03 +/- 0.36 microns 2 reduced-flow vs 0.84 +/- 0.22 microns 2 CON; p = 0.05). Intimal SMC volume in reduced-flow VG was 37% greater than that in control VG (p = 0.07). Tangential stress in VG equaled that in ipsilateral arteries, whereas shear stress in VG remained much lower than that in arteries. CONCLUSIONS: In this model, arteries and VG responded to flow reduction by wall thickening, but the mechanism differed. Arteries underwent medial remodeling, lumen caliber reduction, and shear stress normalization, whereas VG responded by an upward modulation of the proliferative response that follows graft placement. These data support a primary role for tangential stress and a secondary role for shear stress in determination of VG dimensions.

Theoretical study of the resonant behaviour of an ion confined to a potential well in a combination of AC and DC magnetic fields.

Numerical solutions are presented to the equation of motion for an ion confined to a region of space by a restoring force and subject to DC and AC magnetic fields. We have expanded on the theoretical work of Durney et al. [1988] by including a potential well as a confining factor. This additional term in the equation of motion, being nondissipative, could allow for the buildup of stored energy within the system to a level necessary for a macroscopic resonant phenomenon. Resonant behaviour has been studied, including calculation of the trajectory and energy (kinetic and potential) of a confined ion, with emphases on the appearance of both amplitude and frequency windows. The results are discussed in relation to ion transport through transmembrane channels exposed to magnetic fields. When realistic values of the frictional and restoring-force coefficients are considered, all predicted resonant behaviour disappears, except at very high field strengths.

Experimental search for combined AC and DC magnetic field effects on ion channels.

The hypothesis that specific combinations of DC and low frequency AC magnetic fields at so-called cyclotron-resonance conditions could affect the transport of ions through ion channels, or alter the kinetics of ion channels (opening and closing rates), has been tested. As a model system, the ion channels formed by gramicidin A incorporated in lipid bilayer membranes were studied. No significant changes in channel conductance, average lifetime, or formation rate as a function of applied fields could be detected over a wide range of frequencies and field strengths. Experiments were carried out to measure the time-resolved single-channel events and the average conductances of many-channel events in the presence of K+ and H+ ions. The channel blocking effect of Ca++ was also studied.

Flow cytometric assessment of platelet function in patients with peripheral arterial occlusive disease.

This study compared new and traditional measures of platelet function in 16 patients with severe peripheral arterial occlusive disease and 15 age-matched controls. Circulating platelets were characterized by the use of fluorescence flow cytometry to assess platelet aggregate formation and expression of the secretion-dependent alpha granule membrane protein GMP-140, by measurement of plasma beta-thromboglobulin (beta-TG), and by performance of platelet-rich plasma aggregation studies. In addition, blood samples were treated with graded concentrations of adenosine diphosphate (ADP; 0 to 10 mumols/L) to characterize by fluorescence flow cytometry the secretory and aggregatory responses to mild stimulation. No differences were detected between the two groups with regard to platelet function in unstimulated circulating blood by use of these techniques. Values (mean +/- SEM) observed were: GMP-140-positive platelets, 11% +/- 3% versus 13% +/- 2%; platelet aggregates in circulating whole blood, 4% +/- 1% versus 9% +/- 3%; plasma beta-TG, 92 +/- 12 versus 94 +/- 22 ng/ml; and ED50 (concentration of ADP required to produce half maximal aggregation), 3.8 +/- 1.1 versus 3.1 +/- 0.5 mumol/L in the patients with peripheral arterial occlusive disease and controls, respectively. Treatment with ADP caused a dose-related increase in GMP-140 expression in both groups, without significant differences in this parameter between the groups at any given concentration. However, stimulation with ADP concentrations greater than 1 mumol/L resulted in more frequent aggregate formation in the control than in the peripheral arterial occlusive disease group (25% +/- 4% versus 11% +/- 2%, respectively at 5.0 mumols/L, p = 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)

The interaction of vasodilating drugs and sympathetic blockade in normal and ischemic canine hindlimbs.

The purpose of this study was to determine if intraarterial vasodilating drugs could augment the vasodilation produced by sympathetic blockade, such as occurs during epidural anesthesia. Papaverine (2 mg/min), nitroglycerin (1 microgram/kg/min), aand saline were infused into the femoral artery before and after lumbar sympathectomy in six arterially isolated canine hindlimbs. Femoral blood flow was controlled with a perfusion circuit at baseline (80 ml/min), half-baseline (40 ml/min), and low (5 ml/min) flow rates so that hindlimb mean arterial pressure served as an index of peripheral vasodilation. At low flow, hindlimb arteriovenous oxygen content difference increased from 1.4 (baseline) to 6.2 ml O2/dl, consistent with peripheral ischemia. At baseline flow before sympathectomy, papaverine and nitroglycerin caused a decrease in hindlimb mean arterial pressure of 30% and 18%, respectively (p less than 0.01 vs saline control), equivalent to the decreases of 31% and 16% after sympathectomy (p less than 0.01). At half-baseline, papaverine and nitroglycerin reduced hindlimb mean arterial pressure by 22% and 12%, respectively (p less than 0.01), and caused comparable vasodilation after sympathectomy. Neither drug significantly changed hindlimb mean arterial pressure at low flow. Sympathectomy itself reduced hindlimb mean arterial pressure by 23% at baseline flow (p less than 0.01), by 18% at half-baseline flow (p less than 0.01), but had no effect at low flow. We conclude that intraarterial papaverine and nitroglycerin cause peripheral vasodilation that is synergistic with sympathectomy-induced adrenergic blockade, but they cannot augment vasodilation caused by peripheral ischemia.

The effect of ibuprofen on cardiac performance during abdominal aortic cross-clamping.

Decreased cardiac output and increased plasma thromboxane have been observed during aortic cross-clamping under general anesthesia. Amelioration of these changes has been reported by preoperative administration of cyclooxygenase inhibitors, but heterogeneity in patients' intravascular volume status has confounded analysis of the drugs' effects in previous studies. We studied hemodynamic conditions in 24 volume-loaded (pulmonary capillary wedge pressure greater than 10 mm Hg) patients undergoing abdominal aortic aneurysm repair under general plus epidural anesthesia, after preoperative double-blind administration of either ibuprofen 800 mg (n = 12) or placebo (n = 12). The hemodynamic response to aortic cross-clamping was similar in both groups. Pulse and mean arterial pressure remained unchanged; cardiac index decreased after aortic cross-clamping from 2.4 +/- 0.1 (mean +/- standard error of the mean [SEM]) to 2.1 +/- 0.1 1/min/m2 in the ibuprofen group and from 2.5 +/- 0.1 to 2.3 +/- 0.2 1/min/m2 in the placebo group (p less than 0.01 versus preclamp values in both groups, multivariate analysis of variance [MANOVA]), but improved after declamping. Both left and right ventricular stroke work indexes followed a similar pattern. Plasma 6-keto prostaglandin Fl alpha (6-k-PGF1 alpha) increased transiently from a baseline level of 304 +/- 44 to 2083 +/- 698 pg/ml plasma in mixed venous blood 30 minutes after incision in the placebo group (p less than 0.05), but no other significant change in plasma 6-keto prostaglandin Fl alpha or in thromboxane B2 occurred in either group at any other time.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of ATP-regulated K(+)-channels by a photoactivatable ATP-analogue in mouse pancreatic beta-cells.

The effects of a photoactivable (DMNPE-caged) ATP-analogue on ATP-regulated K(+)-channels (KATP-channel) in mouse pancreatic beta-cells were investigated using the inside-out patch configuration of the patch-clamp technique. The caged precursor caused a concentration-dependent reduction of channel activity with a Ki of 17 microM; similar to the 11 microM obtained for standard Mg-ATP. The small difference in the blocking capacity between the precursor and ATP is probably the reason why no change in channel activity was observed upon photolysis of the caged molecule and liberation of ATP. It is suggested that the part of the ATP molecule involved in the blocking reaction of the KATP-channel is not sufficiently protected in DMNPE-caged ATP making this compound unsuitable for studying the rapid kinetics of ATP-induced KATP-channel inhibition.

Male breast cancer.

Male breast cancer is uncommon but important. The diagnosis is easily made by breast biopsy, and patients are presenting earlier in the course of the disease than in the past. Despite this, patients are often first seen with tumors that have metastasized to the axillary nodes, which markedly decreases the survival rate. Therapy of localized disease includes simple excision, modified radical mastectomy, and radical mastectomy, but there is no consensus for which operation is appropriate. Radiation therapy should be strongly considered in patients with metastases to the axillary nodes, but the role of adjuvant hormonal therapy or chemotherapy is unclear. For treatment of disseminated disease, tamoxifen seems to be replacing orchiectomy. The favorable response rate, especially in patients with estrogen-receptor-positive tumors, the lack of side effects, and the high level of patient acceptability make it an attractive therapeutic choice.

Increased platelet deposition on polytetrafluoroethylene grafts after balloon catheter thrombectomy.

Prosthetic graft rethrombosis after thrombectomy may be potentiated by increased thrombogenicity of the restored flow surface. This experiment compared platelet deposition on polytetrafluoroethylene (PTFE) grafts after balloon catheter thrombectomy with deposition on new, nonthrombosed grafts. Three models of graft thrombosis were studied in eight dogs with 4 mm diameter by 7 cm PTFE graft segments: (1) in vitro model: grafts filled with blood, stored in 37 degrees C saline solution; (2) in vivo model: blood-filled grafts stored in subcutaneous tissue; and (3) in situ model: one end of grafts anastomosed to femoral or carotid artery as a blind tube. Duration of thrombosis (1, 2, and 3 weeks) was studied by initiating one graft of each type per week in each dog. After 3 weeks, nine thrombosed grafts per dog were harvested and graft thrombectomy was performed with a 3F balloon catheter. An ex vivo flow-controlled perfusion circuit was then created in each dog and platelet deposition was measured during the initial 20 minutes of graft perfusion after 111In platelet labeling. Thrombectomized grafts were compared with new, control grafts not previously exposed to blood, as well as with grafts exposed for 1 hour to blood or plasma. Compared with control grafts, platelet deposition was significantly increased on in vivo (3.7 times control; p less than 0.01), in situ (2.6 times control; p less than 0.05), and in vitro thrombosed grafts (2.0 times control; p less than 0.05). Age of thrombus was not a significant source of variation. Blood or plasma exposure alone did not significantly increase platelet deposition. These data suggest that antiplatelet therapy may be important at the time of PTFE graft thrombectomy.