Human neutrophils and mononuclear cells inhibit platelet aggregation by releasing a nitric oxide-like factor.

131

Intravenous (i.v.) administration of adenosine diphosphate (ADP), platelet activating factor (PAF) and thrombin induced a dose‐related accumulation of 111indium‐labelled platelets within the thoracic region of anaesthetized rabbits. I.v. administration of the inhibitor of NO biosynthesis, l‐NG‐nitro arginine methyl ester (l‐NAME; 10 mg kg−1) significantly potentiated the peak platelet accumulation induced by ADP, PAF and thrombin. Additionally l‐NAME prolonged the disaggregation of platelets in comparison to d‐NAME (10 mg kg−1). Such changes were reversible by the administration of l‐arginine (900 mg kg−1). I.v. administration of PAF induced a small accumulation of 111indium‐labelled neutrophils within the pulmonary circulation which could be greatly potentiated by pretreatment of the animals with l‐NAME. In contrast, thrombin administration did not cause significant accumulation of 11indium‐labelled erythrocytes in the pulmonary circulation of anaesthetized rabbits. Intracarotid (i.c.) administration of thrombin induced a marked accumulation of radiolabelled platelets within the cranial vasculature which was not potentiated by the prior administration of l‐NAME (at either 10 mg kg−1 or 100 mg kg−1). These results suggest that endogenous NO may regulate platelet and polymorphonuclear leukocyte activation within the pulmonary but not the cerebral circulation of rabbits.

Section: Discussionmentioning

confidence: 66%

The role of nitric oxide as an endogenous regulator of platelet and neutrophil activation within the pulmonary circulation of the rabbit

May

Crook

Moore

et al. 1991

131

“…N0-monomethyl-L-arginine was obtained from Ultrafine Chemicals Ltd (Manchester, U.K.). Oxyhaemoglobin (oxyHb) was prepared by reduction of bovine haemoglobin with sodium hydrosulphite as described previously (Salvemini et al, 1989 (Figure 1). …”

Section: Methodsmentioning

confidence: 99%

“…When required oxyhaemoglobin (oxyHb, 10 fLM) and/or N-acetylcysteine (NAC, 0.5 mM) was added to the platelet mixture for the 3 min incubation period. When using cells or oxyhaemoglobin, the calibrations were performed in the presence of these agents to compensate for possible changes in light transmission (Salvemini et al, 1989). Inhibition of platelet aggregation was calculated as described previously (Salvemini et al, 1989).…”

Section: Platelet Aggregationmentioning

confidence: 99%

Conversion of glyceryl trinitrate to nitric oxide in tolerant and non‐tolerant smooth muscle and endothelial cells

Salvemini

Pistelli

Vane

1993

Exposure of smooth muscle cells (SMC) to glyceryl trinitrate (GTN, 75–600 μm) for 30 min led to a concentration‐dependent increase in nitrite (NO2−), one of the breakdown products of nitric oxide (NO). This was not affected by 30 min pretreatment of the cells with 0.5 mm of sulphobromophthalein (SBP) an inhibitor of glutathione‐S‐transferase (GST), by metyrapone or SKF‐525A inhibitors of cytochrome P450. These experiments were confirmed by organ bath studies using rabbit aortic strips denuded of endothelium and contracted with phenylephrine. Thus, a 30 min incubation of the strips with 0.5 mm SPB, metyrapone or SKF‐525A did not affect the relaxations in response to GTN (10−10−10−6 m). Potentiation of the anti‐platelet effect of GTN (44 μm) by endothelial cells (EC, 40 × 103 cells) was not affected by prior incubation of EC with SBP, metyrapone or SKF‐525A (all at 0.5 mm). Potentiation of the antiplatelet activity of GTN (11–352 μm) by small numbers of SMC (24 × 103 cells) or EC (40 × 103 cells) treated with indomethacin (10 μm) was attenuated when the SMC or EC were treated in culture with a high concentration of GTN (600 μm) for 18 h beforehand (referred to as ‘tolerant’ cells). In addition, tolerant SMC produced far less NO2− than non‐tolerant SMC. Exposure of non‐tolerant SMC or EC (105 cells) to GTN (200 μm) for 3 min increased (3–4 fold) the levels of guanosine 3′:5′‐cyclic monophosphate (cyclic GMP). This increase was much less (≤ 1 fold) in the tolerant SMC or EC (105 cells). The basal levels of cyclic GMP were similar in normal or tolerant SMC or EC. Sodium nitroprusside (80 μm) or atrial natriuretic factor (ANF, 10−7 m) increased the levels of cyclic GMP in normal or tolerant SMC or EC to the same extent. The anti‐platelet effects of GTN (44 μm) were potentiated by the sulphydryl donor N‐acetylcysteine (NAC, 0.5 mm). Incubation of GTN (150–1200 μm) for 30 min with NAC (0.1–1 mm) led to a concentration‐dependent increase in NO2− formation. The reduced ability of tolerant SMC or EC to potentiate the anti‐platelet activity of GTN was restored by NAC (0.5 mm). These anti‐aggregatory effects were abolished by concurrent co‐incubation with oxyhaemoglobin (10 μm) indicating that they were due to NO release. Thus, in SMC or EC, metabolism of GTN to NO does not depend on glutathione‐S‐transferase or the cytochrome P450 system. Furthermore, when compared to normal cells, tolerant SMC or EC metabolize GTN to NO less effectively as assessed by the reduced capacity to potentiate the antiplatelet effects of GTN, to release NO2− and to increase the level of cyclic GMP. This decrease in NO formation shows that tolerance to GTN is mainly due to impaired biotransformation of GTN to NO. NAC, by directly forming NO from GTN, compensates for this failing mechanism.

“…NO can also be formed by an inducible isoenzyme in activated inflammatory cells, particularly macrophages (Marletta et Hibbs et al, 1988;Stuehr et al, 1989) and neutrophils (Rimele et al, 1988;Salvemini et al, 1989;Schmidt et al, 1989;Wright et al, 1989;McCall et al, 1989).…”

Section: Introductionmentioning

confidence: 99%

Time‐dependent enhancement or inhibition of endotoxin‐induced vascular injury in rat intestine by nitric oxide synthase inhibitors

László

Whittle

Moncada

1994

135

1 The effects of the nitric oxide (NO) synthase inhibitors, N0-nitro-L-arginine methyl ester (L-NAME) and NG-monomethyl-L-arginine (L-NMMA), on the vascular damage induced by the endotoxin, E. coli lipopolysaccharide (LPS), in the ileum and colon were investigated in the conscious rat over a 5 h period. 2 Administration of LPS (3 mg kg-', i.v.) increased ileal and colonic vascular injury after a lag period of 2 h, as determined by the leakage of radiolabelled albumin. 3 Administration of L-NAME (1-5 mg kg-', s.c.) concurrently with LPS, produced a dose-dependent increase in vascular albumin leakage in the intestinal tissues, when determined over a 5 h period. Vascular albumin leakage with LPS and L-NAME (5 mg kg-') was substantially increased after 1 h, reached maximal levels 3 h after administration, and then slowly declined. 4 L-NMMA (50 mg kg-1, s.c.), likewise elevated intestinal albumin leakage when administered concurrently with LPS, but this reached maximal levels after 1 h and rapidly declined over the subsequent 2 h. 5 In control rats, in the absence of LPS challenge, neither L-NAME (5 mg kg-', s.c.) nor L-NMMA (50 mg kg-', s.c.) increased intestinal vascular leakage of albumin over a 5 h period. 6 By contrast, when L-NAME (1-5 mg kg-', s.c.) or L-NMMA (12.5-50mg kg-', s.c.) was injected 3 h after LPS, a dose-dependent reduction in the LPS-provoked vascular albumin leakage was observed. 7 Pretreatment with L-arginine (300 mg kg-', s.c.) 15 min prior to the NO synthase inhibitors, reversed either the potentiation or the inhibition by L-NAME (5 mg kg-', s.c.) or L-NMMA (50 mg kg-', s.c.) of the LPS-induced intestinal vascular damage. 8 These findings indicate that initial suppression of the constitutive NO synthase by L-NAME or L-NMMA following challenge with LPS aggravates the acute vascular injury in the ileum and colon, suggesting a defensive role of NO. By contrast, the delayed administration of NO synthase inhibitors, at a time of known expression of the inducible NO synthase, provides protection against the subsequent damage to the intestinal vasculature.