Animal Reproduction Science 99 (2007) 244–257 Steroidogenic changes and steady state amount of messenger RNA encoding steroidogenic enzymes, gonadotropin receptors and cell-death signalling in the dominant ovarian follicle during estradiol-induced atresia in cattle  C.R. Burke a,b , H. C´ ardenas a , M.L. Mussard a , C.L. Gasser a , M.L. Day a,∗ a The Ohio State University, Department of Animal Sciences, 2027 Coffey Rd., Columbus, OH 43210, USA b Dexcel Ltd., Private Bag 3221, Hamilton, New Zealand Received 27 September 2005; accepted 23 May 2006 Available online 13 July 2006 Abstract Changes in steroidogenic function and associated gene expression were characterized in dominant ovarian follicles (DF) of cattle where follicles were induced to become atretic by systemic administration of estradiol benzoate (EB). In experiment 1, follicular fluid (FF) steroid concentrations in the DF were measured at 12- hourly time points for 48 h in heifers treated with 1 mg EB i.m./500 kg body weight (EB; n = 20) as compared with untreated controls (C; n = 19). Treatment with EB promoted a transient reduction in circulating FSH, a rapid (12 h) and sustained reduction in FF estradiol, a rapid (12 h) but transient reduction in FF progesterone and a delayed (36 h) increase in FF testosterone concentrations. In experiment 2, whole follicular wall tissue was collected from DF of mature non-lactating cows allocated to a 0 h control group (0HC: n = 7), a 24 h control group (24HC; n = 7) or an EB-treated group where tissue was collected 24 h after administration of 1 mg EB i.m./500 kg body weight (EB; n = 8). As for experiment 1, EB promoted a transient reduction in circulating FSH, a pronounced reduction in FF estradiol and a smaller but significant reduction in FF progesterone concentrations. Semi-quantitative RT-PCR on follicular wall tissue revealed that the loss in estrogen activity at 24 h after EB was associated with two-fold reduction in aromatase mRNA, with an apparent acceleration in loss of 17-hydroxylase mRNA. Expression of genes for gonadotropin receptors (LHR and FSHR) and a cell-death signalling pathway (Fas antigen and Fas ligand) were unchanged during the  Salaries and research support provided by State and Federal funds appropriated to the Ohio Agricultural Resource Development Center (manuscript no. 14-06AS), and through competitive grant funds (no. OHOAO628) provided by the Ohio Agricultural Research and Development Center. ∗ Corresponding author. Tel.: +1 614 292 6583; fax: +1 614 292 7116. E-mail address: day.5@osu.edu (M.L. Day). 0378-4320/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.anireprosci.2006.05.019