title: Seasonal changes of responses to gonadotropin-releasing hormone analog in expression of growth hormone/prolactin/somatolactin genes in the pituitary of masu salmon.
abstract: Gonadotropin-releasing hormone (GnRH) is considered to stimulate secretion of growth hormone (GH), prolactin (PRL), and somatolactin (SL) at particular stages of growth and sexual maturation in teleost fishes. We therefore examined seasonal variation in the pituitary levels of GH/PRL/SL mRNAs, and tried to clarify seasonal changes of responses to GnRH in expression of GH/PRL/SL genes, in the pituitaries of growing and maturing masu salmon (Oncorhynchus masou). Pituitary samples were monthly collected one week after implantation with GnRH analog (GnRHa). The levels of mRNAs encoding GH, PRL, and SL precursors in single pituitaries were determined by a real-time polymerase chain reaction method. The fork lengths and body weights of control and GnRHa-implanted fish of both sexes gradually increased and peaked out in September of 2-year-old (2+) when fish spawned. GnRHa implantation did not stimulate somatic growth, nor elevate gonadosomatic index (GSI) of 1+ and 2+ males, whereas it significantly increased GSI of 2+ females in late August to early September. The GnRHa-implanted 1+ males had higher levels of GH and PRL mRNAs in July, and SL mRNA from June to August than the control males. The levels of GH, PRL, and SL mRNAs in the control and GnRHa-implanted 1+ females, however, did not show any significant changes. Afterward, the PRL mRNA levels elevated in the control 2+ fish of both sexes in spring. GnRHa elevated the GH mRNA levels in both males and females in 2+ winter, and the PRL mRNA levels in females in early spring. Regardless of sex and GnRHa-implantation, the SL mRNA levels increased during sexual maturation. In growing and maturing masu salmon, expression of genes encoding GH, PRL, and SL in the pituitary is thus sensitive to GnRH in particular seasons probably in relation to physiological roles of the hormones.
authors.affiliation: Division of Marine Biological Sciences, Graduate School of Fisheries Science, Hokkaido University, Hakodate, Hokkaido 041-8611, Japan.
authors.forename: Ramji Kumar
authors.initials: RK
authors.lastname: Bhandari
authors.forename: Shinya
authors.initials: S
authors.lastname: Taniyama
authors.forename: Takashi
authors.initials: T
authors.lastname: Kitahashi
authors.forename: Hironori
authors.initials: H
authors.lastname: Ando
authors.forename: Kohei
authors.initials: K
authors.lastname: Yamauchi
authors.forename: Yonathan
authors.initials: Y
authors.lastname: Zohar
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ueda
authors.forename: Akihisa
authors.initials: A
authors.lastname: Urano
mesh_terms: D000818:Animals; D004343:Drug Implants; D005260:Female; D029941:Fish Proteins; D015870:Gene Expression / Q000187:drug effects; D006023:Glycoproteins / Q000235:genetics*; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000494:pharmacology*; D013006:Growth Hormone / Q000235:genetics*; D008297:Male; D017683:Oncorhynchus / Q000254:growth & development* / Q000378:metabolism; D010902:Pituitary Gland / Q000737:chemistry / Q000187:drug effects; D010907:Pituitary Hormones / Q000235:genetics*; D011388:Prolactin / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis; D012621:Seasons; D012727:Sex Characteristics; D012741:Sexual Maturation
chemical_list: D004343:Drug Implants; D029941:Fish Proteins; D006023:Glycoproteins; D010907:Pituitary Hormones; D012333:RNA, Messenger; C064448:somatolactin protein, fish; D007987:Gonadotropin-Releasing Hormone; C010661:surfagon; D011388:Prolactin; D013006:Growth Hormone