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Elevation of the cyclic GMP concentration in human platelets by sodium ascorbate and 5-hydroxytryptamine
Journal of Cyclic Nucleotide Research
|October 1, 1977
Summary
Sodium ascorbate significantly increases platelet cyclic GMP (cGMP) levels, independent of extracellular calcium. This effect is blocked by cyclo-oxygenase inhibitors, suggesting a link to endoperoxide formation but not thromboxane pathways.
Area of Science:
- Biochemistry
- Platelet Physiology
- Signal Transduction
Background:
- Platelets play a crucial role in hemostasis and thrombosis.
- Cyclic guanosine monophosphate (cGMP) is a key second messenger in platelet function.
- Ascorbate (Vitamin C) has known antioxidant properties, but its direct effects on platelet signaling are less understood.
Purpose of the Study:
- To investigate the effect of sodium ascorbate on platelet guanosine 3':5'-cyclic monophosphate (cGMP) levels.
- To compare the effects of ascorbate with 5-hydroxytryptamine (5-HT) on platelet cGMP.
- To elucidate the mechanisms and calcium dependency of ascorbate-induced cGMP elevation in platelets.
Main Methods:
- Incubation of human platelets with varying concentrations of sodium L-ascorbate or sodium D-ascorbate.
- Measurement of intracellular cGMP levels using radioimmunoassay.
- Assessment of the role of extracellular calcium by performing experiments with and without calcium.
- Inhibition studies using cyclo-oxygenase inhibitors like aspirin and indomethacin.
- Evaluation of platelet aggregation and [14C]5-hydroxytryptamine release upon stimulation with epinephrine, collagen, or thrombin.
Main Results:
- Sodium ascorbate induced a dose-dependent and significant increase in platelet cGMP, reaching a 25-fold increment at 5 mM.
- The ascorbate-induced cGMP elevation peaked within 1 minute and was sustained for 1 hour.
- 5-hydroxytryptamine also increased platelet cGMP in a dose-dependent manner.
- Ascorbate and 5-HT induced cGMP increases were independent of extracellular calcium and were inhibited by cyclo-oxygenase inhibitors.
- Ascorbate-stimulated cGMP increase did not enhance platelet aggregation or the release of [14C]5-HT induced by other agonists.
Conclusions:
- Sodium ascorbate effectively elevates platelet cGMP levels through a mechanism potentially involving endoperoxide formation.
- The ascorbate-mediated increase in platelet cGMP is independent of extracellular calcium and cyclo-oxygenase activity.
- Despite increasing platelet cGMP, ascorbate does not appear to directly influence platelet aggregation or serotonin release, suggesting a complex relationship with thromboxane pathways.