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An L-arginine/nitric oxide pathway present in human platelets regulates aggregation
M W Radomski1, R M Palmer, S Moncada
1Wellcome Research Laboratories, Beckenham, Kent, United Kingdom.
Summary
Human platelets synthesize nitric oxide (NO) when stimulated by collagen, increasing cyclic GMP levels and modulating platelet aggregation. This NO synthase pathway in platelets has significant physiological and therapeutic implications.
Area of Science:
- Biochemistry
- Physiology
- Pharmacology
Background:
- Platelet aggregation plays a crucial role in hemostasis and thrombosis.
- Cyclic nucleotides, cyclic AMP (cAMP) and cyclic GMP (cGMP), are key regulators of platelet function.
- Nitric oxide (NO) is a signaling molecule involved in various physiological processes, including vascular tone and platelet activity.
Purpose of the Study:
- To investigate the role of nitric oxide (NO) in collagen-induced human platelet aggregation.
- To elucidate the signaling pathways involved in NO production and its effects on cyclic GMP levels in platelets.
- To determine the potential physiological and therapeutic significance of the NO pathway in human platelets.
Main Methods:
- Measurement of cyclic GMP and cyclic AMP levels in human platelets stimulated with collagen.
- Use of NG-Monomethyl-L-arginine (L-MeArg), an inhibitor of NO synthesis, to assess the role of NO.
- Administration of L-arginine, prostacyclin, and phosphodiesterase inhibitors (M&B22948, HL725) to study their effects on platelet aggregation and cyclic GMP.
- Investigation of NO formation and soluble guanylate cyclase stimulation in platelet cytosol.
Main Results:
- Collagen stimulation increased cyclic GMP in human platelets, but not cyclic AMP.
- Inhibition of NO synthesis by L-MeArg reduced cyclic GMP increase and enhanced platelet aggregation.
- L-arginine augmented collagen-induced cyclic GMP increase, inhibited aggregation, and its effects were attenuated by L-MeArg.
- L-arginine stimulated soluble guanylate cyclase, leading to NO formation and increased cyclic GMP in a manner dependent on NADPH, Ca2+, and enantiomer specificity.
Conclusions:
- Human platelets possess an NO synthase that is activated upon stimulation.
- The generated NO modulates platelet reactivity by increasing cyclic GMP levels.
- The NO-cGMP pathway in platelets is a potential target for therapeutic interventions in conditions involving platelet dysfunction.