title: Effects of synthetic progestagens on the mRNA expression of androgen receptor, progesterone receptor, oestrogen receptor alpha and beta, insulin-like growth factor-1 (IGF-1) and IGF-1 receptor in heifer tissues.
abstract: Synthetic progestagens like melengestrol acetate (MGA) are widely used for oestrus synchronization and for growth promotion in cattle production. The metabolic effects exceed its primary potency as a progestagen. It is speculated that MGA stimulates follicle development and thereby endogenous oestrogen production, but inhibits ovulation. To investigate the dose-dependent effects on mRNA expression levels, six heifers were fed for 8 weeks with different levels of MGA (0.5, 1.5, 5 mg) daily and two heifers served as controls. The expression of steroid receptor mRNA [androgen receptor (AR), progesterone receptor (PR), oestrogen receptor (ER) ERalpha and ERbeta], insulin-like growth factor-1 (IGF-1) and its receptor were quantified in liver, neck (m. splenius) and shoulder muscularity (m. deltoideus). Plasma concentrations of IGF-1 were quantified by radioimmunoassay. In treated animals the MGA plasma levels were elevated over the complete treatment period, corresponding to the MGA treatment concentrations. IGF-1 concentrations of control animals were at constant levels. Plasma levels for oestradiol (E2) and IGF-1 were increased in the low MGA treatment group. Overdosed MGA decreased progesterone (P4) and E2 levels. To quantify the IGF-1 and all receptor mRNA transcripts, sensitive and reliable real-time reverse transcription-polymerase chain reaction (RT-PCR) quantification methods were developed and validated in the LightCycler. A dose-dependent relationship between increasing MGA concentration and mRNA expression was observed in liver for AR and IGF-1 receptor, and in neck muscularity for IGF-1. ERalpha in liver and neck muscle showed a trend of increasing expression.
authors.affiliation: Institute of Physiology, Centre of Life and Food Sciences, Technical University of Munich, Germany. pfaffl@weihenstephan.de
authors.forename: M W
authors.initials: MW
authors.lastname: Pfaffl
authors.forename: A
authors.initials: A
authors.lastname: Daxenberger
authors.forename: M
authors.initials: M
authors.lastname: Hageleit
authors.forename: H H D
authors.initials: HH
authors.lastname: Meyer
mesh_terms: D000818:Animals; D002417:Cattle / Q000378:metabolism*; D017931:DNA Primers; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000097:blood; D005260:Female; D007334:Insulin-Like Growth Factor I / Q000187:drug effects; D008099:Liver / Q000187:drug effects; D008552:Melengestrol Acetate / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D009132:Muscles / Q000187:drug effects; D009334:Neck Muscles / Q000187:drug effects; D045167:Progesterone Congeners / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D012333:RNA, Messenger / Q000187:drug effects* / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000187:drug effects; D011944:Receptors, Androgen / Q000187:drug effects; D011960:Receptors, Estrogen / Q000187:drug effects; D011980:Receptors, Progesterone / Q000187:drug effects; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000662:veterinary; D012782:Shoulder
chemical_list: D017931:DNA Primers; D045167:Progesterone Congeners; D012333:RNA, Messenger; D011944:Receptors, Androgen; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; D004958:Estradiol; D008552:Melengestrol Acetate; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1