Further studies on the effects of flavine adenine dinucleotide on the platelet functions.

Abstract

Flavine adenine dinucleotide (FAD) may inhibit not only the aggregation but also ATP release of platelets in vitro. FAD did not inhibit the synthesis of thromboxane from 1-14C-arachidonic acid by platelets. FAD was found to be hydrolyzed to FMN and AMP by a plasma enzyme, the activity of which in normal adults being estimated as 32.6+9.1 m,uM/ml plasma/min and AMP, thus produced, and/or FAD might compete for the receptor sites on the platelet surface. This could be the mechanism of the inhibitory effect of FAD upon the platelet functions. The intravenous drip infusion of FAD in a dose of 0.2 mg/kg within 30 min was followed by no marked decrease of platelet aggregation, probably because the plasma concentration of FAD and/or AMP did not reach the levels high enough to suppress the platelet functions.-------FAD; AMP; platelet aggregation; platelet ATP release; FAD hydrolyzing enzyme activity of blood plasma; 1-14C-arachidonic acid metabolism Previously flavine adenine dinucleotide (FAD) has been shown to have an inhibitory effect on the platelet aggregation in vitro (Clayton et al. 1963;Kuzuya 1977;Higashi et al. 1978;Shimada et al. 1980). Such an inhibitory effect of FAD on the platelet function could be demonstrated not only in vitro but also in vivo, when a large dose of FAD was administered intravenously (Shimada et al. 1980).The present investigation was conducted to study the effect of FAD upon the adenosine triphosphate (ATP) release of platelets, the mechanism of action of FAD and the in vivo effect of FAD in an ordinary dose upon the platelet functions. MATERIALS AND METHODSBlood was obtained from normal adult volunteers.Methods were similar to those described in the previous paper (Shimada et al. 1980) unless otherwise indicated.The platelet aggregation and ATP release were measured simultaneously by the use of the Lumi-aggregometer (Chrono-Log Corporation, Havortown, Pa). The citrated platelet-rich plasma (PRP) was preincubated with or without FAD of various concentrations for 20 min, and then the aggregating agent, collagen (HormonChemie, Munchen) or arachidonic acid (Silver et al. 1973) was added.For the study of arachidonic acid-induced platelet aggregation, both PRP and washed platelet suspensions in 0.15 M Tris HCl buffer, pH 7.4 (Okuma 1976) were used.