title: The somatotropic axis during the physiological estrus cycle in dairy heifers--Effect on hepatic expression of GHR and SOCS2.
abstract: Pituitary growth hormone (GH) release and hepatic insulin-like growth factor-I (IGF-I) production increase after an injection of 17β-estradiol (E2) in ovariectomized dairy cattle. However, whether endogenous sexual steroid hormones also influence the hepatic GH receptor (GHR) signaling pathway during a physiological estrus cycle remains unclear. The aim of this study was to analyze the hepatic GHR signaling pathway during the luteal phase and after a period of increased E2 concentrations (after ovulation) as well as in 7 heifers before ovulation. Ovarian ultrasounds were performed daily during repeated physiological cycles (n = 56) of 30 Holstein Friesian heifers to determine ovulation [before ovulation (n = 7, bOv) and after ovulation 24-60 h after the appearance of estrus signs (n = 49, aOv)] and luteal phase (CLP; d 12 ± 1 after ovulation). Blood samples and liver biopsies were obtained, and blood concentrations of E2, P4, insulin-like growth factor (IGF)-I, IGF-II, and GH were measured. In the liver biopsies, we determined mRNA expression of the estrogen receptor α (ERα), GHR, Janus kinase 2 (JAK2), signal transducer and activator of transcription 5B (STAT5B), suppressor of cytokine signaling (SOCS)2 and 3, IGF-I, and IGF-II by quantitative reverse transcription-PCR. The concentration of E2 was higher bOv than aOv and CLP, as expected. The concentrations of IGF-I and GH were higher bOv and aOv compared with CLP. In contrast, concentrations of IGF-II were lower aOv compared with bOv and CLP. The mRNA expression of GHR was higher in liver biopsies obtained bOv compared with aOv and CLP. Notably, the expression of SOCS2 was higher bOv than aOv and in the CLP. Increased hepatic expression of SOCS2 during estrus was detectable when IGF-I concentrations were high; this result might indicate that SOCS2 expression attenuates the GHR signal transduction pathway during the phase of increased pituitary GH release. In conclusion, hepatic GHR and SOCS2 mRNA expression appeared to be promptly and sensitively regulated by increased E2 levels before ovulation of dairy heifers.
authors.affiliation: Endocrinology Laboratory, Clinic for Cattle, University of Veterinary Medicine, 30173 Hannover, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Mense
authors.affiliation: Endocrinology Laboratory, Clinic for Cattle, University of Veterinary Medicine, 30173 Hannover, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Meyerholz
authors.affiliation: Department of Animal Biology, Faculty of Veterinary Science, University of Zulia, Maracaibo, Zulia 44011, Venezuela.
authors.forename: M
authors.initials: M
authors.lastname: Gil Araujo
authors.affiliation: Clinic for Cattle, University of Veterinary Medicine, 30173 Hannover, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Lietzau
authors.affiliation: Endocrinology Laboratory, Clinic for Cattle, University of Veterinary Medicine, 30173 Hannover, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Knaack
authors.affiliation: Clinic for Obstetrics, Gynecology and Andrology of Large and Small Animals, Faculty of Veterinary Medicine, Justus-Liebig-University, 35392 Giessen, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Wrenzycki
authors.affiliation: Clinic for Cattle, University of Veterinary Medicine, 30173 Hannover, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Hoedemaker
authors.affiliation: Endocrinology Laboratory, Clinic for Cattle, University of Veterinary Medicine, 30173 Hannover, Germany. Electronic address: marion.piechotta@tiho-hannover.de.
authors.forename: M
authors.initials: M
authors.lastname: Piechotta
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D004958:Estradiol / Q000097:blood; D030762:Estrous Cycle / Q000502:physiology*; D005260:Female; D015870:Gene Expression / Q000502:physiology; D013006:Growth Hormone / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000235:genetics; D007335:Insulin-Like Growth Factor II / Q000235:genetics; D008099:Liver / Q000737:chemistry / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D011986:Receptors, Somatotropin / Q000235:genetics*; D050799:STAT5 Transcription Factor / Q000235:genetics; D050826:Suppressor of Cytokine Signaling Proteins / Q000235:genetics*
chemical_list: D012333:RNA, Messenger; D011986:Receptors, Somatotropin; D050799:STAT5 Transcription Factor; D050826:Suppressor of Cytokine Signaling Proteins; D004958:Estradiol; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D013006:Growth Hormone
keywords: estrus cycle; growth hormone; growth hormone receptor; insulin-like growth factor; suppressors of cytokine signaling