Cathepsin G--induced release of PAI-1 in the culture medium of endothelial cells: a new thrombogenic role for polymorphonuclear leukocytes?

Activated polymorphonuclear leukocytes (PMNs) may affect the integrity of blood vessels by endothelial cell injury. We investigated the effects of cathepsin G purified from human neutrophils on the fibrinolytic potential of cultured human umbilical vein endothelial cells (HUVECs). Cathepsin G (5 and 10 micrograms/ml) induced marked intercellular gap formation after 1 hour of treatment, whereas 1 microgram/ml did not, even after 6 hours incubation. In contrast, plasminogen activator inhibitor-1 (PAI-1) antigen levels, measured by a double antibody enzyme-linked immunosorbent assay, were significantly increased in culture media (CM) on cathepsin G (1 microgram/ml) treatment after 15 minutes (5.1 +/- 1.2 ng/ml vs 2.6 +/- 0.6 ng/ml for controls, p < 0.01) and 6 hours of incubation (69.6 +/- 17.5 ng/ml vs 40.0 +/- 9.0 ng/ml for controls, p < 0.01). Likewise, PAI activity, measured by reverse fibrin autography, increased on cell treatment with cathepsin G. Preincubation of cathepsin G with eglin C (10 micrograms/ml) almost completely abolished the increase in both PAI antigen and activity levels induced by cathepsin G. Cycloheximide, a protein synthesis inhibitor, did not block cathepsin G-induced PAI-1 release. PAI-1 mRNA levels were not affected by HUVEC treatment with cathepsin G (1 microgram/ml for 15 minutes), even after 24 hours. In the extracellular matrix (ECM) PAI-1 antigen levels decreased to 77% and 40% of controls, respectively, after 15 minutes and 6 hours of cathepsin G (1 micrograms/ml) treatment. Reverse fibrin autography also demonstrated a dose-dependent reduction of PAI activity in the ECM on 6 hours of cell treatment with 1 or 5 micrograms/ml cathepsin G. Moreover, ECM prepared from confluent HUVECs released PAI-1 in supernatants on 1 micrograms/ml cathepsin G incubation in a cell-free system. Tissue-type plasminogen activator (t-PA) activity was strongly depressed on cathepsin G treatment, both in CM from HUVECs or in a cell-free system. Finally, PAI-1 was also released from cathepsin G-stimulated platelets in a dose-dependent manner. In summary, our results support a potentially thrombogenic role of cathepsin G, which could impair the fibrinolytic potential of the endothelium. These data give a new insight into the mechanisms by which activated PMNs may promote thrombus formation. On the other hand, the decrease of PAI-1 in ECM could favor penetration and migration of inflammatory or tumor cells through the subendothelial layers.

Effect of aspirin on the fibrinolytic response in perfused rat hindquarters

The role of aspirin on tissue plasminogen activator (t-PA) release was studied in rats after experimental venous occlusion. For this purpose, we developed a new experimental model which combines a vascular perfusion system (isolated rat hindquarters) with vascular stimulation, namely the application of venous stasis. Application of venous stasis for 30 min induced the release of t-PA from the vascular endothelium into the perfusate (from 0.19 +/- 0.05 to 0.39 +/- 0.05 UI/ml), reaching a peak 90 s after reperfusion. Aspirin administered to rats 60 min before the experiments (100 mg/kg i.v.), or dissolved in Tyrode solution (100 microM), suppressed 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) synthesis (0.38 +/- 0.09 in control and < 0.01 and 0.15 +/- 0.09 ng/ml, respectively, in aspirin-treated groups) but did not prevent the increase in fibrinolytic activity after venous occlusion (from 0.20 +/- 0.04 to 0.38 +/- 0.06 and from 0.07 +/- 0.03 to 0.27 +/- 0.03 IU/ml, respectively, in the aspirin-treated group). Our results suggest that the increase in fibrinolytic activity after experimental venous occlusion in isolated rat hindlegs is modulated by mechanism(s) other than the cyclooxygenase pathway in the vascular wall.

Modulation of fibrinolytic response to venous occlusion in humans by a combination of low-dose aspirin and n-3 polyunsaturated fatty acids

Aspirin at high but not at low doses reduces the fibrinolytic response to venous occlusion. Inhibition of vascular prostacyclin synthesis could be involved in this effect. Fish oil supplementation may redirect prostanoid metabolism toward an overall "antithrombotic" condition but with controversial effects on prostacyclin formation. In this study we investigated the effect of low-dose aspirin together with n-3 polyunsaturated fatty acid (PUFA) supplementation on the fibrinolytic response to venous occlusion. Following a double-blind, randomized, crossover design, six healthy volunteers (three men and three women, 24-37 years old) were given for 29 days 5.3 g eicosapentaenoic and docosahexaenoic acids or a corresponding dose of n-6 PUFAs as control; aspirin (40 mg/day) was then added for an additional 14 days. A 2-month washout period was allowed before the crossover. Blood was collected before and after venous stasis on days 0, 29, and 43 of each test period. A combination of aspirin with n-3 PUFAs reduced the fibrinolytic response to venous occlusion in all subjects, the mean value of fibrinolytic activity after stasis being 240 +/- 40 mm2, a value significantly lower than at baseline (366 +/- 51 mm2, mean +/- SEM, p < 0.05). Similarly, the tissue-type plasminogen activator (t-PA) antigen level was lower in the aspirin + PUFA-treated group. Plasminogen activator inhibitor activity before stasis was enhanced by n-3 PUFA supplementation (from 7.5 +/- 2 to 14.8 +/- 3 IU/ml, p < 0.05), an effect not affected by aspirin.(ABSTRACT TRUNCATED AT 250 WORDS)

Erythrocyte volume and blood pressure in a cross-sectional population-based study

A reduction in mean erythrocyte volume has been reported in some strains of genetically hypertensive rat, and more recently it has been suggested that a similar alteration might be found in human essential hypertension. The relationship between erythrocyte volume and blood pressure was therefore studied in a random sample of an untreated male working population (n = 317; age 45.1 +/- 6.4 years, mean +/- s.d.). Neither systolic nor diastolic blood pressures were found to be related to erythrocyte volume (r = 0.022 and r = -0.014, respectively); in fact, erythrocyte volume was not different across quintiles of blood pressure. Smokers (n = 171) had lower blood pressure and a greater erythrocyte volume than non-smokers or ex-smokers (n = 144; 91.6 +/- 4.7 versus 88.2 +/- 5.5 fl; P less than 0.001), and heavy drinkers (greater than 110 g ethanol/day) had higher blood pressure and a greater erythrocyte volume compared with the rest of the study population (P less than 0.01). However, after adjustment of erythrocyte volume for these two potentially confounding factors, again no statistical association was found with blood pressure. The present study, therefore, does not support the hypothesis of a negative association between erythrocyte volume and blood pressure, whereas it confirms that the smoking habit and habitual alcohol intake are strong determinants of erythrocyte volume.

Erythrocyte sodium/lithium countertransport and renal lithium clearance in a random sample of untreated middle-aged men

1. It has been proposed that the enhanced erythrocyte Na+/Li+ countertransport observed in many patients with essential hypertension could be a marker of abnormal renal proximal tubular function. We thus investigated the relationship of blood pressure and Na+/Li+ countertransport to an index of proximal tubular function such as renal Li+ clearance. 2. The study was carried out in a sample of 299 untreated male subjects (aged 21-59 years) randomly selected from a population at work. Na+/Li+ countertransport was measured in a representative sub-group of 176 men. 3. We did not detect statistically significant correlation of either blood pressure or Na+/Li+ countertransport (Vmax) with fractional excretion of Li+, while confirming the existence of a significant continuous association of blood pressure and body mass index with Na+/Li+ countertransport (P less than 0.01). 4. A sub-sample of 57 participants belonging to the lowest or the highest quintiles of Na+/Li+ countertransport distribution repeated the Li+ clearance study after moderate Na+ restriction. 5. Although fractional excretions of Na+ and Li+ were reduced on the low Na+ diet (both P less than 0.001), they did not differ significantly between groups. 6. Our results are at variance with the findings of a recent case-control study in a young age group and suggest that further studies are necessary before a conclusion can be drawn as to the suitability of Na+/Li+ countertransport as a marker of Na+ reabsorption in the renal proximal tubule.

Red blood cell sodium-lithium countertransport, blood pressure, and uric acid metabolism in untreated healthy men

The relationship of red blood cell (RBC) Na/Li countertransport to the renal handling of lithium and uric acid was investigated in a sample of 176 untreated men. Subjects in the upper quintile of the Na/Li countertransport distribution (n = 40), compared to those in the two lower quintiles (n = 72), had higher serum uric acid levels (0.34 +/- 0.06 v 0.29 +/- 0.05 mmol/L, P less than 0.001) and systolic blood pressure (131 +/- 19 v 123 +/- 16 mm Hg, P less than 0.02) and slightly lower fractional excretion of uric acid (7.5 +/- 1.5 v 8.4 +/- 2.6%, P less than 0.08). The lithium fractional excretion was not significantly related to either blood pressure or RBC Na/Li countertransport. The altered uric acid metabolism in individuals with high RBC Na/Li countertransport could be the expression of an abnormality of renal tubular function.

Comparison of variability of urinary sodium, potassium, and calcium in free-living men

The variability of 24-hour urinary sodium, potassium, and calcium excretion was studied in a sample of 22 Neapolitan men with mild blood pressure elevation. On 5 days within a 1-month period, 24-hour urine specimens were collected by each subject. The estimated ratio of intraindividual-to-interindividual variance was 1.12 for urinary sodium, 2.46 for urinary potassium, and 0.52 for urinary calcium. Based on these values, five 24-hour urine collections are necessary to reduce to less than 10% the diminution of the correlation coefficient between urinary sodium and another related variable; this number is substantially lower than that found in previous studies in a North American population sample, but similar to the one reported for Chinese population samples. Ten urinary collections are needed for potassium excretion. A different and more favorable situation is observed for 24-hour calcium excretion, as only two collections are necessary for the adequate characterization of individuals in a population.

Use of fractional lithium clearance in clinical and epidemiological investigation: a methodological assessment

1. The fractional clearance of lithium (FCLi) has been validated in the rat under controlled experimental conditions as a reliable indicator of sodium and water handling in the proximal tubule. The purpose of the present study was to evaluate some key methodological aspects related to the use of the FCLi in clinical and epidemiological investigation. 2. FCLi was determined in healthy normotensive, or in some cases, in borderline/mild essential hypertensive subjects, by a morning urine collection obtained between 09.00 and 13.00 hours after a 300 mg oral lithium carbonate load (= 8.1 mmol of elemental lithium). 3. The ratio of intra-individual to inter-individual variance of FCLi, measured in free-living subjects on unrestricted diet, was shown to be low enough (0.33) to allow adequate characterization of individuals in a population with a single measurement, or at most with two (compared with at least four measurements needed to characterize the fractional excretion of sodium). 4. The remarkable influence of dietary sodium intake on FCLi, demonstrated under metabolic ward conditions, might explain a major portion of the observed intra-individual variability. 5. At the dosage employed in the present study, oral lithium administration did not affect the renal handling of sodium, potassium or calcium. Likewise, it did not induce any change in a series of 17 metabolic parameters and indicators of renal and liver function. 6. It is concluded that the FCLi may be a safe and useful tool for the clinical and epidemiological investigation of renal sodium and water handling. The possibility of a confounding effect of dietary sodium intake, however, should be kept in mind.

Controlled trial of long term oral potassium supplements in patients with mild hypertension

A 15 week randomised double blind placebo controlled trial of oral potassium supplements (48 mmol daily) was conducted in 37 patients who had mildly increased blood pressure and a normal dietary intake of sodium. After a two month run in and a one week baseline period the patients were randomly assigned to receive either potassium supplements (n = 18) or placebo (n = 19). By the third week of treatment blood pressure in the actively treated group had decreased significantly compared with that in the placebo group, though the decrease reached its maximum after 15 weeks. Urinary potassium excretion increased significantly in the group who received potassium supplements, but no significant changes were found in plasma sodium and potassium concentrations or in urinary sodium excretion. In a subgroup of 13 patients who underwent a further nine weeks of treatment with oral potassium supplements at half of the previous dose (24 mmol daily) their blood pressure, at the end of this second study period, was still significantly lower compared with their baseline value but not with that of the placebo group. These results show that moderate oral potassium supplements are associated with a long term reduction in blood pressure in patients who have mild hypertension.