Life Sciences 68 (2001) 1851–1865 0024-3205/01/$ – see front matter © 2001 Elsevier Science Inc. All rights reserved. PII: S0024-3205(01)00983-3 Differential inhibition of progesterone synthesis in bovine luteal cells by estrogens and androgens Ing-Cherng Guo a , Leang-Shin Wu b , Jen-Hsou Lin b , Bon-chu Chung c, * a Department of Veterinary Medicine, National Taiwan University, Taipei, Taiwan, Republic of China b Department of Animal Science, National Taiwan University, Taipei, Taiwan, Republic of China c Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan, Republic of China Received 11 January 2000; accepted 2 May 2000 Abstract We investigated the roles of estrogens and androgens in the progesterone biosynthesis of bovine luteal cells. The responsiveness of primary luteal cells to the stimulation of tropic agents was observed in a dose-dependent manner. Estrogens and androgens significantly inhibited tropic agent-induced progesterone secretions, but glucocorticoids did not, which indicated the inhibitions were specific. The failure of exogenous 8-Br-cAMP to prevent these inhibitions suggested that took place at the post- cAMP steps. The immunoblot showed that testosterone remarkably decreased the amount of induced P450scc protein after 6-hour treatment, yet 17  -estradiol did not. The 3  -HSD activity assays demon- strated that both 17  -estradiol and testosterone efficiently blocked induced 3  -HSD activities. Both inhibitory effects of E2 and T on progesterone synthesis were observed one hour after treatment and accompanied with suppressed 3  -HSD activities. This study presents that estrogens and androgens specifically inhibit bovine luteal function through different mechanisms. © 2001 Elsevier Science Inc. All rights reserved. Keywords: Estrogen; Androgen; Progesterone; Luteal cell; 3-HSD; P450scc Introduction The life span of corpus luteum, which secretes progesterone to prepare the maternal milieu interior for recognizing the conceptus and supporting the pregnancy, is initiated and main- tained by the luteinizing hormone, LH [1]. At the late luteal phase failure of fertilization leads to regression of corpus luteum associated with a sharp decrease of blood progesterone [2]. That falling of progesterone withdraws its negative feedback from the pituitary gland *Corresponding author. Institute of Molecular Biology, Academia Sinica, Nankang, Taipei, Taiwan, Republic of China. Tel.: 886-2-27899215; fax: 886-2-27826085. E-mail address: mbchung@sinica.edu.tw (B.-c. Chung)