ANDROGEN REGULATION OF THROMBOXANE A(2) PROSTAGLANDIN H-2-RECEPTOR EXPRESSION IN HUMAN ERYTHROLEUKEMIA-CELLS

Thromboxane A2 (TxA2), a platelet aggregator and vasoconstrictor, has been implicated as a potential mediator of cardiovascular diseases. Ab use of androgenic steroids has been associated with thrombotic cardiov ascular diseases. Human erythroleukemia (HEL) cells, a megakaryocyte-l ike cell line, express functional TxA2/prostaglandin H2 (PGH2) recepto rs with characteristics similar to those seen in platelets. This study characterized testosterone regulation of HEL cell TxA2/PGH2 receptors . TxA2/PGH2 receptor affinity (K(d)) and density (B(max)) were determi ned via equilibrium binding experiments using the radiolabeled TxA2 mi metic tenyl]-7-oxabicyclo[2.2.1]heptan-2-yl}-5-heptenoic acid (I-125-l abeled BOP). Testosterone (200 nM) but not estradiol increased B(max) from 108 +/- 9 fmol/mg protein to 157 +/- 9 fmol/mg protein (n = 7 exp eriments; P < 0.01) without any significant change in K(d). Testostero ne had no significant effect on alpha2-adrenergic receptor density. Th e maximum increase in intracellular free calcium induced by the TxA2 a gonists I-BOP or U-46619 was significantly (P < 0.005) greater in test osterone-treated cells compared with controls. Hydroxyflutamide (1 muM ), an androgen-receptor antagonist, completely blocked the effect of t estosterone (P < 0.01). Dihydrotestosterone, the active metabolite of testosterone, also increased B(max) in a concentration-dependent manne r and was more potent than testosterone. The effect of testosterone to increase B(max) was significantly (P < 0.01) inhibited by coincubatio n with cycloheximide (0.1 mug/ml) or actinomycin D (10 ng/ml). These r esults indicate that androgenic steroids regulate the expression of fu nctional TxA2/PGH2 receptors in HEL cells. These findings may have rel evance to cardiovascular disease.