Effect of heterologous antibody on human platelet prostaglandin synthesis

Rabbit anti-human platelet antiserum (RPA) has been shown to mediate human platelet aggregation and 14C-serotonin release. This effect is not inhibited by aspirin. However, it is not known whether antibody induces platelet prostaglandin synthesis. We, therefore, investigated the effect of RPA on human platelets by measuring malondialdehyde (MDA) production as a reflection of prostaglandin synthesis and comparing it with 14C-serotonin release. Independently, ATP release was also measured as a further measure of platelet secretion. Normal rabbit serum did produce a small amount of MDA (0.54 +/- 0.09 SEM nmole/10(9) platelets). However, RPA produced a much larger amount of MDA (1.43 +/- 0.18 nmole/10(9) platelets) and pre-incubation with aspirin significantly decreased MDA production (0.16 +/- 0.07 nmole/10(9) platelets) (p less than .001). Aspirin did not significantly impair the capacity of RPA to release 14C-serotonin or ATP. These results demonstrate that prostaglandin synthesis occurs when heterologous antibody is added to human platelets. However, prostaglandin formation must be a secondary event in this process since the inhibition of prostaglandin synthesis by aspirin had little effect on the ability of RPA to induce 14C-serotonin release or ATP release.