Dušan Keber

Increased Plasminogen Activator Inhibitor Activity in Survivors of Myocardial Infarction Is Associated with Metabolic Risk Factors of Atherosclerosis

To assess the relationship between the fibrinolytic system and coronary risk factors, several fibrinolytic parameters were measured in 72 male survivors of myocardial infarction and in 53 age-matched healthy controls. The coronary patients had significantly higher plasminogen activator inhibitor (PAI) activity than the control subjects, while t-PA antigen did not differ between the groups. After stratifying the coronary patients in 14 diabetic and 58 nondiabetic patients, the elevated PAI activity remained limited to the diabetic group. PAI activity correlated significantly with systolic blood pressure, blood glucose, body mass index and LDL cholesterol. In multivariate regression analysis, significant associations persisted between PAI and diabetes, body mass index and LDL cholesterol. Coronary disease had no impact on the regression model. Our results suggest that the increased PAI-1 in selected groups of coronary patients is not a consequence of coronary disease itself, but is rather related to the metabolic risk factors of atherosclerosis, especially diabetes.

Shift work and circadian rhythm of blood fibrinolytic parameters

Abstract The influence of shift work on circadian fluctuation of fibrinolytic parameters was studied in ten men working on alternating 7-day and 7-night shifts. Ten age-matched men working during the day only served as controls. Venous blood was collected on the last day of each shift at 8 a.m., noon, 4 p.m., 8 p.m., midnight and 4 a.m. The well-known diurnal fluctuations were observed in the control subjects t-PA antigen, PAI-1 antigen and PAI-1 activity decreased during the day. A steeper and earlier decrease of PAI-activity explained continuous increase in t-PA activity from the morning hours till late afternoon. In shift workers during both day and night shift t-PA antigen showed much lower fluctuations and an earlier occurrence of the lowest values. This phase advanced shift of several hours was even more evident for PAI-1 activity, which did not lose its amplitude. These results suggest that circadian fluctuation of fibrinolytic activity shows characteristics of disturbed biorhythm: reduction of amplitude and shift of the phase.

Poor fibrinolytic response to venous occlusion by different criteria in patients with deep vein thrombosis.

Five criteria for poor response to a 20 min venous occlusion test were applied to 58 patients 3 months or more after acute deep vein thrombosis (DVT). The criteria were arbitrarily defined as the last 5 percentiles of response distributions in an age- and sex-matched healthy control group of 51 subjects. The criteria were: 1. euglobulin clot lysis time after venous occlusion greater than or equal to 140 min; 2. t-PA activity after venous occlusion less than or equal to 0.04 IU/ml; 3. increase in t-PA antigen above resting value less than or equal to 2-fold; 4. ratio between t-PA antigen increase and resting PAI activity less than or equal to 0.5 ng/IU; 5. PAI activity after venous occlusion greater than or equal to 6 IU/ml. The last criterion of poor response was the only one that was significantly more frequently reached by patients than by controls: 28% (p less than 0.005) of all DVT patients and 35% (p less than 0.005) of the subgroup with idiopathic DVT (N = 34) were found to be poor responders. The percentage of poor responders according to the other four criteria was 7-11% in all patients and 9-15% in the subgroup with idiopathic DVT and thus was not significantly higher than in controls (5% by definition). It was concluded that residual PAI activity after venous occlusion might be a useful criterion for prospective studies on recurrence of DVT.

CAROTID INTIMA-MEDIA THICKNESS OF YOUNG CORONARY PATIENTS

BACKGROUND Although a greater than normal intima-media thickness (IMT) has been found in older coronary patients, the data for younger patients are lacking. OBJECTIVE To determine the carotid IMT in patients with premature myocardial infarction. METHODS We measured IMT (common and internal carotid, carotid bifurcation) in 30 coronary patients, aged 30-50 years (mean 46 years), who had survived myocardial infarctions 1-9 years (mean 6 years) earlier, and in 30 age-matched men without clinically evident coronary heart disease (controls) by B-mode ultrasonography. Blood levels of lipoproteins, glucose, iron and transferrin, fibrinogen, tissue plasminogen activator (t-PA) antigen level and activity and plasminogen activator inhibitor (PAI-1) antigen level and activity were also determined. RESULTS IMT in all segments of carotid arteries in the patients was significantly greater than that in the controls (P < 0.0001). The presence of atherosclerotic plaques was correlated to greater than normal carotid IMT. Other risk factors displaying statistically significant correlations to mean carotid IMT were t-PA antigen level and activity, PAI-1 antigen level and level of high-density lipoprotein cholesterol. CONCLUSIONS The significant association between carotid IMT and coronary heart disease suggests that carotid and coronary atherosclerosis evolve simultaneously. Hence carotid IMT can be used as a predictor of coronary atherosclerosis.

Exhaustion of arm fibrinolytic potential after repeated venous occlusions and local exercise

The effect of repeated venous occlusions of the arm combined with local exercise was assessed in 10 healthy volunteers. The blood was drawn before and after three venous occlusions of 20 minutes. Between occlusions I - II, and II - III, twelve occlusions of 10 minutes were performed on the same arm while a small rubber ball was compressed 30 times per minute. Plasminogen activator (PA) activity was measured on plasminogen rich fibrin plates and by the euglobulin clot lysis time. A high increase in PA activity after venous occlusion (fibrinolytic potential) was present in all three occlusions on the first day, but fell to a very low level on the fourth day. The restitution of potential followed, but was not complete even on fifteenth day. These results indicate that PA continues to be released even after the termination of stimulation and can be temporarily depleted some days afterwards. An increase of fibrin(ogen) degradation products together with a slight decrease of alpha-2-antiplasmin in postocclusion samples, but no change in fibrinogen concentration speak in favour of a small fibrin(ogen)olysis during venous occlusion.

The effect of submaximal exercise on fibrinolysis.

We studied the relationship between sustained submaximal exercise, increased tissue plasminogen activator (t-PA) levels and decreased hepatic clearance of t-PA. Six healthy male volunteers exercised for 35 min while receiving constant rate infusions of either saline or two different doses of recombinant t-PA for 90 min (40 min before, 35 min during and 15 min after exercise). Liver blood flow was estimated simultaneously by constant rate indocyanine green infusion. Since t-PA is cleared rapidly by the liver in direct proportion to liver blood flow, it was expected that a significant decrease in liver blood flow during sustained submaximal exercise would be associated with a proportional increase in plasma t-PA. During submaximal exercise with a saline (placebo) infusion, steady-state t-PA antigen increased from a resting baseline of 6.3 ± 3.1 to 15.1 ± 5.1 ng/ml; with a 20 μg/min t-PA infusion, t-PA antigen increased from 33 ± 12 to 84 ± 25 ng/ml during exercise; and with a 40 μg/min t-PA infusion, t-PA antigen increased from 77 ± 38 to 166 ± 42 ng/ml during exercise. During submaximal exercise, liver blood flow fell on average 71, 68 and 70%, respectively, during the three procedures, while calculated t-PA clearance decreased on average 59, 59 and 53%. t-PA concentration versus time curves, displayed in proportional units, were similar. The comparable relative increases in endogenous and exogenous t-PA with simultaneous proportional decreases in liver blood flow suggests that diminished hepatic t-PA clearance is the major cause of increased t-PA concentration and blood fibrinolytic activity enhancement during sustained submaximal exercise.

Diminished release of tissue plasminogen activator during venous occlusion in manual workers

Abstract The effect of intensive and regular manual work on fibrinolytic response after venous occlusion of the upper arm was studied in 13 male manual workers (masons, foundry workers and grinders) and in 11 male intellectual workers (controls). Fibrinolytic response after 20 min venous occlusion was measured with euglobulin clot lysis, specific assay for tissue plasminogen activator (t-PA) activity, t-PA antigen and t-PA inhibitor (PAI) activity assay. A significant reduction in fibrinolytic potential (difference between post- and preocclusion value) was observed in manual workers. Their fibrinolytic potential measured by t-PA activity assay and by euglobulin clot lysis was 85% and 55% lower, respectively, than in controls. Simultaneously, decrease in PAI activity after venous occlusion was significantly smaller in workers than in controls. t-PA antigen determinations showed that the reduction in fibrinolytic potential was due to decreased t-PA antigen release 40% lower compared to controls) and not the consequence of increased preocclusion PAI activity that could mask fibrinolytic response. It was concluded that chronic muscular work with the arms reduced the amount of t-PA that could be released from the endothelium by venous occlusion. A larger study is required to confirm this observation.

In vivo release of tissue-type plasminogen activator antigen from the human brachial artery

The rate of secretion of t-PA from vascular endothelial cells has been proposed as a good marker of endothelial function. Our aim was to measure the rate of in vivo t-PA antigen release from the human brachial artery and not from the combined vascular pool of the upper extremity. In 10 healthy male volunteers, we have occluded the forearm by a sphygmomanometer cuff for 5-7 min in order to reduce the blood flow in the brachial artery. Arterial blood samples were taken from the cubital artery above the occlusion and from the contralateral artery that served as the control. The arterial t-PA antigen concentrations were significantly higher after forearm occlusion than in the non-occluded contralateral arteries: median 3.3 (range between first and third quartile 2.1-3.6) vs. 2.5 (2.0-3.2) ng/ml, p=0.03. The PAI-1 antigen concentrations did not change significantly: 6.9 (2.3-18.6) ng/ml in the contralateral artery vs. 5.4 (1.8-8.0) ng/ml after occlusion, p=0.09. The average forward blood flow in the distal 15 cm of the brachial artery that was measured by duplex ultrasound decreased from 107 (97-118) ml/min at baseline to 25 ml/min (19-33) ml/min during occlusion. The release rate of circulating t-PA antigen was calculated as the product of the increment in arterial t-PA concentration and the average plasma flow in the arterial segment of interest with a volume of 2 ml. The median release rate of t-PA antigen under conditions of reduced blood flow in the brachial artery was 3.3 (1.1-11.5) ng/min. We conclude that the secretion of t-PA antigen from arterial endothelium of healthy subjects is substantial, whereas the arterial wall is not an important source of PAI-1 in vivo.