Intracellular Ca2+ stimulates the binding to androgen receptors in platelets.

In this study, we demonstrated that ADP-induced platelet aggregation activates the binding of testosterone (T) to its receptor. It is well known that binding of ADP to its receptors induced the release of Ca2+ ions from dense bodies into the cytosol of platelets. In this work, we compared the binding of testosterone or dihydrotestosterone to their receptors using cytosol obtained from ADP-treated and non-treated platelets. These experiments were repeated using EGTA (a calcium chelator) or U73122 (a phospholipase C enzymatic activity inhibitor) to the ADP-treated platelets. In addition, we also developed a competition analysis for the androgen receptors (AR) using [3H]DHT, non-radioactive T, DHT or cyproterone acetate from ADP-treated platelets cytosol. The results from this study indicate that the cytosol obtained from non-ADP-treated platelets did not show any binding to [3H]T or [3H]DHT, whereas cytosol from ADP-treated platelets binds to the radio-labeled androgens. Furthermore cytosol from ADP plus U73122-treated platelets did not show binding to [3H]T or [3H]DHT. These data suggest that intracellular Ca2+ ions stimulates the binding of androgens to their receptors in platelets cytosol. The competition analysis shows that T and DHT have high affinities for the androgen receptors with similar IC50 values, whereas cyproterone acetate shows a lower affinity. The results from these data clearly indicate the presence of androgen receptors in platelets.