A defect of platelet release reaction in a patient with SLE: Impaired platelet aggregation induced by phorbol ester with a normal phosphorylation of 40K protein

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Abstract
A 37‐year‐old female who suffered from SLE had a bleeding disorder. At the time of initial evaluation, the main disease demonstrated was a8‐storage pool deficiency. After this improved, a marked decrease of aggregation still remained, when induced by either ADP, epinephrine, collagen, A23187, thrombin, or PAF‐acether. Although arachidonate‐induced aggregation was slightly decreased, thromboxane B2 was produced normally in response to exogenous arachidonate. The patient's endoperox‐ides and/or thromboxane A2 aggregated aspirin‐treated platelets, though her platelets were themselves unresponsive. Impaired aggregability induced by TPA (12‐0‐tetra‐decanoylphorbol‐13‐acetate) or OAG (l‐oleoyl‐2‐acetyl‐glycerol) was also found. However, the phosphorylation of P43 and P20 induced by several stimulators including Ca+ * ionophore was normal, using 32P‐labelled platelets. It is suggested that TPA or OAG‐induced platelet aggregation requires not only the phosphorylation of those proteins, but also another unknown mechanism after the phosphorylation, and that the platelet dysfunction of this patient was due to a defect of some mechanism involving Ca+ + uptake or mobilization of cytoplasmic Ca+ + from intracellular storage sites.