cyclic-gmp and Coronary-Thrombosis

Platelet and endothelial production of bioactive nitric oxide (NO) is known to be impaired in acute coronary syndromes, thus compounds that release NO are useful candidates to restore NO-vascular functions.. We have studied whether donation of NO with a novel platelet-selective S-nitrosothiol compound (LA810) at a systemic level can inhibit thrombosis elicited by damaged vessel wall (eroded and disrupted vessel wall) at hemodynamic conditions typical of patent and stenotic coronary arteries.. Thrombogenicity was measured in the porcine experimental model and assessed as platelet-thrombus formation in the ex vivo Badimon perfusion chamber. After baseline perfusions, female pigs (Large WhitexLandrace) were given intravenous infusion of LA810 or GSNO standard S-nitrosothiol during 2 h. Changes in blood pressure, heart rate and in vitro platelet aggregation were measured.. LA810 significantly decreased thrombus formation at any degree of vascular damage and shear rate (p<0.001) without hypotensive side-effects or heart rate variations. In contrast, inhibition of thrombus formation by GSNO required high doses associated to hypotensive episodes. Platelet aggregation induced by collagen was inhibited after nitrosothiol infusion in whole blood (LA810) and platelet rich plasma (LA810 and GSNO). In addition, there was a drug-dependent rise in platelet guanosine 3',5'-cyclic monophosphate (cGMP) levels.. This new anti-ischemic NO-donor (NOd) LA810 that inhibits platelet function without hypotensive side-effects seems a highly efficacious strategy to reduce acute thrombosis triggered by coronary artery disease.

Topics: Animals; Blood Platelets; Coronary Disease; Coronary Thrombosis; Coronary Vessels; Cyclic GMP; Female; Glycine; Models, Animal; Nitric Oxide Donors; Nitroso Compounds; Platelet Aggregation Inhibitors; S-Nitrosothiols; Stress, Mechanical; Sulfhydryl Compounds; Swine

We sought to determine whether coronary vascular nitric oxide (NO) release in vivo modulates platelet activation.. Nitric oxide modulates vasodilator tone and platelet activity via the cyclic guanosine monophosphate (cGMP) pathway, but whether coronary endothelial dysfunction influences platelet activation in humans is unknown.. In 26 patients, we measured coronary blood flow, epicardial diameter and coronary sinus platelet cGMP content during intracoronary infusions of acetylcholine (ACH), L-NG monomethyl arginine (L-NMMA) and sodium nitroprusside.. Acetylcholine increased platelet cGMP content (p = 0.013), but its magnitude was lower in patients with endothelial dysfunction; thus, patients with epicardial constriction with ACH had a 7 +/- 6%, p = ns change compared with a 32 +/- 13%, p = 0.05 increase in platelet cGMP in those with epicardial dilation. Similarly, patients with atherosclerosis or its risk factors had a smaller increase (9 +/- 6%) compared with those having normal coronary arteries without risk factors (51 +/- 22%, p = 0.019). L-NG monomethyl arginine decreased platelet cGMP content to a greater extent in patients with epicardial dilation with ACH (- 15 +/- 7%, p = 0.06) compared to those with constriction (+5 +/- 6% change, p = 0.5). Sodium nitroprusside produced a similar increase in platelet cGMP content in patients with and without endothelial dysfunction (p = 0.56). The effects of sodium nitroprusside, but not ACH or L-NMMA, were reproduced in vitro.. Platelet cGMP levels can be modulated by basal and stimulated release of NO. The platelet inhibitory effect of NO is reduced in patients with endothelial dysfunction, which may explain their increased risk from thrombotic events and the improved survival associated with strategies designed to improve vascular function.

Topics: Acetylcholine; Adult; Aged; Coronary Circulation; Coronary Disease; Coronary Thrombosis; Cyclic GMP; Endothelium, Vascular; Female; Humans; Male; Middle Aged; Nitric Oxide; Nitroprusside; omega-N-Methylarginine; Platelet Activation

We investigated whether platelet responsiveness to nitroglycerin (NTG) is maintained in long-term smokers and if not, the mechanism. In the absence or presence of NTG, intraplatelet reduced glutathione (GSH) levels and ADP-induced platelet aggregation and intraplatelet cGMP levels were measured in 10 long-term smokers and 10 age-matched nonsmokers. The intraplatelet GSH level was significantly lower in smokers than in nonsmokers (P<0.05). Platelet aggregation was dose-dependently inhibited by NTG in both groups; however, inhibition was significantly weaker in smokers. N-acetylcysteine (1 mmol/L), an exogenous thiol agent, significantly potentiated NTG-induced platelet inhibition in nonsmokers but not in smokers. The ADP-induced intraplatelet cGMP level was significantly greater in the presence of NTG in nonsmokers but not so in smokers. Because the effects of long-term smoking are multifactorial, a rabbit model was made by chronic administration of buthionine sulfoximine (BSO, n=6) to decrease intraplatelet GSH. The intraplatelet GSH level was significantly lower in BSO-treated rabbits than in saline-treated rabbits (P<0.001). The NTG-induced inhibition of platelet aggregation was significantly weaker in BSO rabbits. N-acetylcysteine-induced potentiation was not observed in BSO rabbits, whereas significant potentiation was found in saline rabbits. These findings were similar to those of long-term smokers. In contrast, the intraplatelet GSH-to-oxidized glutathione ratio, which represents the redox state of glutathione, was significantly lower in smokers than in nonsmokers, whereas no difference was found between saline rabbits and BSO rabbits. In conclusion, long-term smoking causes NTG resistance to aggregation in platelets, possibly through the depletion of intraplatelet GSH.

Topics: Animals; Blood Platelets; Buthionine Sulfoximine; Coronary Thrombosis; Cyclic GMP; Female; Glutathione; Humans; Male; Nitric Oxide Donors; Nitroglycerin; Oxidation-Reduction; Platelet Aggregation; Rabbits; Smoking

Platelet-derived nitric oxide inhibits platelet aggregation via constitutive NO synthase (NOS). Tetrahydrobiopterin (BH(4)), a cofactor of NOS, augments NO formation, whereas its deficiency decreases NO bioactivity and increases superoxide generation by NOS. The roles of intraplatelet BH(4) in platelet aggregation and thrombus formation, however, are unknown. Accordingly, we investigated whether intraplatelet BH(4) is involved in regulating cyclic flow variations (CFVs) and platelet aggregation in a canine model with stenosed and endothelium-injured coronary arteries that mimics acute coronary syndromes in humans.. After developing CFVs, dogs received saline or BH(4) (10 or 30 mg/kg) intravenously. Intraplatelet BH(4) and cGMP levels were decreased and intraplatelet nitrotyrosine production was increased during CFVs. ADP- and U46619-induced ex vivo platelet aggregation and platelet P-selectin expression were augmented during CFVs. BH(4) administration restored intraplatelet BH(4) and cGMP levels and decreased intraplatelet nitrotyrosine production, resulting in reduced CFVs and inhibited ex vivo platelet aggregation and platelet P-selectin expression. CFVs again developed after N(G)-monomethyl-L-arginine, an inhibitor of NOS, in BH(4)-treated dogs. Ex vivo platelet NOS activity at baseline, during CFVs, and after BH(4) administration did not differ.. Intraplatelet BH(4) may play an important role in regulating thrombus formation by modulating platelet-derived nitric oxide and superoxide generation by platelet NOS.

Topics: Animals; Biopterins; Blood Platelets; Coronary Thrombosis; Cyclic GMP; Dogs; Enzyme Inhibitors; Hemodynamics; Nitric Oxide; Nitric Oxide Synthase; omega-N-Methylarginine; P-Selectin; Platelet Aggregation; Superoxides; Tyrosine

Sodium nitroprusside (SNP), a nitrosovasodilator, increases platelet cyclic GMP levels and inhibits platelet activity in vitro. The antiplatelet properties of SNP are not well established in vivo, however, and consequently are not appreciated by clinicians. In our established model of mechanically stenosed canine coronary arteries (MSCA) with intimal damage, periodic acute platelet thrombus formation (APTF) occurs, followed by embolization distally, which then causes cyclic flow reductions (CFRs) in coronary blood flow. Aspirin (ASA) abolished platelet-mediated CFRs in our model, but they recur when epinephrine (EPI) is infused (0.2 microgram/kg/min). SNP was given continuously intravenously (i.v.) to 17 dogs with MSCA; CFRs were abolished in all dogs by SNP at 4.4 +/- 2.7 micrograms/kg/min (mean +/- SD). Mean arterial blood pressure (MAP) decreased by 19 +/- 9 mm Hg (p < 0.001) from control, while heart rate (HR) increased 35 +/- 20 beats/min (p < 0.001). Platelet cyclic GMP levels were 2.9 +/- 1.1 pmol/10(8) platelets before SNP infusion, and increased to 4.3 +/- 1.6 pmol/10(8) platelets (p < 0.05) when CFRs were abolished. CFRs were not renewed during the continued SNP infusion when EPI was infused at 0.2 microgram/kg/min for 20 min in 11 dogs, but CFRs returned within 5-25 min after the SNP infusion was terminated. The return of CFRs occurred together with a decrease in platelet cyclic GMP levels to 3.3 +/- 1.4 pmol/10(8) platelets.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Aspirin; Blood Platelets; Blood Pressure; Coronary Circulation; Coronary Thrombosis; Cyclic GMP; Disease Models, Animal; Dogs; Epinephrine; Heart Rate; Injections, Intravenous; Nitroprusside