Free radicals alter 5 '-nucleotidase activity from rat blood platelets

We have studied the in vitro effects of free radicals on an ecto-5'-nucleot idase activity (EC 3.1.3.5) from rat blood platelets. Treatment of rat plat elets with an oxidant-generating system (H2O2 and Fe2+) resulted in inhibit ion of AMP hydrolysis by 5'-nucleotidase. The enzymatic inhibition was prev ented by catalase, glutathione (GSH) and cysteine but not by trolox as a vi tamin E analogue. These results may indicate that reduced low-molecular-wei ght thiols from plasma are important for the natural defence against the ox idant injury produced by free radicals on the enzyme. Furthermore, since tr olox did not protect AMP hydrolysis activity against inhibition, we suggest that this effect is not related to lipid peroxidation. We have demonstrate d the susceptibility of 5'-nucleotidase activity from rat platelets to free radicals. On the basis of our findings, it is probable that oxygen reactiv e species in the circulation inhibit 5'-nucleotidase activity, leading to a decrease in adenosine generation in the platelet microenvironment. Since a denosine mediates its physiological actions (such as vasodilation and inhib ition of platelet aggregation) by activating its receptors, we are tempted to speculate that the inhibition of 5'-nucleotidase activity from platelets by free radicals leads to a decrease in adenosine generation and thus to v ascular injuries. Med Sci Res 27:63-66 (C) 1999 Lippincott Williams & Wilki ns.