Journal of Steroid Biochemistry & Molecular Biology 96 (2005) 175–178 Androgen action on hepatic vitellogenin synthesis in the eel, Anguilla japonica is suppressed by an androgen receptor antagonist Hyuk Chu Kwon ∗ , Seong Hee Choi, Youn Uck Kim, Sung Ok Son, Joon Yeong Kwon Department of Applied Biological Sciences, Sunmoon University, Chung Nam 336-708, South Korea Received 8 December 2004; accepted 24 February 2005 Abstract Involvement of additional hormones other than estrogen in the control of vitellogenin (Vg) synthesis has been suggested in fish. However, no satisfactory explanation on the mechanism of the action of these hormones has been reported. In this study, we have exploited the possibility of androgen receptor mediation during the androgen action on the pathway of Vg synthesis. Hepatocytes were prepared from sexually immature Japanese eel Anguilla japonica and treated with estradiol-17 (E 2 ), 17-methyltestosterone (MT), growth hormone, tamoxifen or flutamide, or in combination of these. Spent culture media were analysed by SDS-PAGE for Vg detection. Results from the chemical treatments demonstrated the necessity of E 2 as the primary factor for Vg synthesis and requirement of additional hormones for the full expression of Vg. The effects of E 2 and MT were effectively blocked by tamoxifen, an estrogen receptor antagonist and flutamide, an androgen receptor antagonist, respectively, indicating ER-mediated estrogen action and AR-mediated androgen action on Vg synthesis in this species. © 2005 Elsevier Ltd. All rights reserved. Keywords: Vitellogenin; Estrogen; Androgen; Androgen receptor; Flutamide 1. Introduction The synthesis of vitelllogenin (Vg), an important precur- sor of egg yolk protein, is induced mainly in response to circulating estrogen in the liver of sexually maturing female in oviparous animals including fish [1–3]. Various other hor- mones such as androgens and pituitary hormones also play some significant roles in the induction of hepatic Vg synthesis in both in vivo and in vitro experiments in fish and amphibians [4–8]. However, the mechanism of androgen action by which Vg synthesis is influenced has not been well understood in fish. In general, the action of androgen is mediated by specific binding to nuclear androgen receptor (AR) of the target cell [9]. Nonetheless, there have been limited evidences available for the involvement of AR during the androgen action for Vg synthesis; whereas, several studies suggested that androgens bind estrogen receptor (ER) and exert an estrogenic action ∗ Corresponding author. Tel.: +82 41 530 2283; fax: +82 41 530 2917. E-mail address: hckwon@sunmoon.ac.kr (H.C. Kwon). [4,10–12]. To find out the possibility of AR-mediation in the induction of Vg synthesis by androgen, we investigated the effect of flutamide, an androgen receptor antagonist, and ta- moxifen, an anti-estrogen, on the induction of Vg synthesis in the hepatocyte cultures of Japanese eel, Anguilla japon- ica. Flutamide has been shown to inhibit androgen action successfully [13,14]. 2. Materials and methods Immature eels weighing 200–250 g were supplied by a lo- cal fish farm and kept in a recycled freshwater system until use. Hepatocytes were prepared according to the procedure published previously [5]. Cell yield and viability were deter- mined by the Trypan blue exclusion test. Cells were plated into a 60 mm Petri dish at a density of 3 × 10 5 cells/dish. L-15 medium (Sigma) containing 0.2 M bovine insulin (Sigma), streptomycin (100 g/ml), and penicillin (70 g/ml) was used for cell culture. All incubations were carried out in 0960-0760/$ – see front matter © 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jsbmb.2005.02.010