title: Evidence that RF-amide related peptide-3 is not a mediator of the inhibitory effects of psychosocial stress on gonadotrophin secretion in ovariectomised ewes.
abstract: It is well known that stress inhibits normal reproductive function, including gonadotrophin secretion; however, the mechanisms and mediators involved are largely unknown. Stress impairs the secretion of luteinising hormone (LH), and it has been suggested that the RF-amide gonadotrophin-inhibitory hormone (GnIH), known as RF-amide related peptide-3 (RFRP-3) in mammalian species, may mediate this inhibitory effect of stress. If this is the case, the GnIH/RFRP system would likely be up-regulated during stress. We tested this hypothesis in ovariectomised ewes using a psychosocial stressor: isolation/restraint. Ewes were randomly allocated to control or stress (n=5 per group). Isolation/restraint stress was imposed for 90 min after control sampling for 4 h, whereas control ewes were sampled continuously for 5.5 h. All ewes were then euthanased and brains were collected. As expected, plasma concentrations of cortisol were increased significantly (P<0.05) by stress and plasma concentrations of LH were significantly (P<0.05) reduced. Immunohistochemistry and in situ hybridisation were conducted for RFRP-3 peptide and RFRP mRNA expression, respectively, in the paraventricular nucleus/dorsal medial hypothalamus region of the hypothalamus. There was no significant effect of stress on RFRP-3 peptide or mRNA levels, with no differences between control or stress ewes. Furthermore, there was no difference in the number of RFRP-3 cells double-labelled for Fos between control and stress ewes and there was no difference in the cellular expression of RFRP mRNA between groups. These results indicate that the GnIH/RFRP system is not activated by psychosocial stress in ewes, suggesting that it is an unlikely mediator of the effects of stress on LH secretion.
authors.affiliation: Department of Physiology, Monash University, Victoria, Australia. melissa.papargiris@monash.edu
authors.forename: M M
authors.initials: MM
authors.lastname: Papargiris
authors.forename: E T A
authors.initials: ET
authors.lastname: Rivalland
authors.forename: I J
authors.initials: IJ
authors.lastname: Clarke
authors.forename: J T
authors.initials: JT
authors.lastname: Smith
authors.forename: A
authors.initials: A
authors.lastname: Pereira
authors.forename: A J
authors.initials: AJ
authors.lastname: Tilbrook
mesh_terms: D000818:Animals; D005260:Female; D006062:Gonadotropins / Q000378:metabolism*; D006854:Hydrocortisone / Q000097:blood; D007031:Hypothalamus / Q000378:metabolism; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D010052:Ovariectomy; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D011897:Random Allocation; D012149:Restraint, Physical / Q000502:physiology / Q000523:psychology; D055571:Secretory Pathway / Q000235:genetics / Q000502:physiology; D012756:Sheep / Q000235:genetics / Q000378:metabolism; D013315:Stress, Psychological / Q000097:blood / Q000150:complications* / Q000235:genetics / Q000378:metabolism*
chemical_list: D006062:Gonadotropins; D009479:Neuropeptides; C416987:RFamide peptide; D012333:RNA, Messenger; D007986:Luteinizing Hormone; D006854:Hydrocortisone