Androstenedione increases thromboxane A 2 receptors in Human Erythroleukemia Cells

Abstract

Previous studies have demonstrated an increased thromboxane A 2 (TXA 2) receptor expression in Human Erythroleukemia (HEL) cells and rat aortic smooth muscle (RASM) cells in response to testosterone treatment. HEL cells have served as a model for megakaryocytes, the progenitor cell for platelets. Platelets have previously been shown to convert androstenedione to testosterone. This study investigated the effects of androstenedione on the TXA 2 receptor density in HEL and cultured RASM cells. Both cell lines were incubated with vehicle, 150 nM testosterone or 250, 500 or 750nM androstenedione for 48 hours. Co-incubation with testosterone or androstenedione significantly (p<0.05) increased the maximum number of TXA 2 binding sites (B max) in HEL cells compared to controls. There was no significant change in K d values. In a separate series of experiments, HEL cells were incubated with the androgen receptor antagonist hydroxyflutamide (2.5μM). Treatment with androstenedione (500nM) significantly (p<0.05) increased the B max value by 35% compared to control and hydroxyflutamide completely antagonized this effect of androstenedione. Incubation with hydroxyflutamide alone had no effect on the B max values compared to control. RASM cells also showed an increase in B max values by 25% and 23% over control (95±6.6, 118±7.2 and 117±5.1 fmoles/mg protein, control, testosterone and androstenedione, n=3). Both cell lines converted androstenedione to testosterone. The results raise the possibility that the adrenal androgen, androstenedione can regulate the expression of TXA 2 receptors either on its own or via conversion to testosterone and through an androgen receptor.