Effect of retinoic acid on adenosine diphosphate and collagen-induced alterations in enzymes of GSH-linked antioxidant defence system of human blood platelets in vitro.

Collagen stimulation of blood platelets resulted in significant increases in malondialdehyde (MDA) formation and activity of glucose-6-phosphate dehydrogenase (G6PDH) and a decrease in catalase and glutathione peroxidase (GPx). Retinoic acid (RA) pretreatment did not show any appreciable changes except for a decrease in G6PDH activity as compared with collagen alone. RA pretreatment of human blood platelets resulted in an increase in the activities of catalase and GPx, two important radical scavenging enzymes, with significant decrease in MDA formation when compared with ADP alone. It is suggested that RA has a significant effect on the antioxidant defence system in ADP stimulated platelets but not in the collagen stimulated platelets.