title: Effects of hypothalamic dopamine on growth hormone-releasing hormone-induced growth hormone secretion and thyrotropin-releasing hormone-induced prolactin secretion in goats.
abstract: The aim of the present study was to clarify the effects of hypothalamic dopamine (DA) on the secretion of growth hormone (GH) in goats. The GH-releasing response to an intravenous (i.v.) injection of GH-releasing hormone (GHRH, 0.25 μg/kg body weight (BW)) was examined after treatments to augment central DA using carbidopa (carbi, 1 mg/kg BW) and L-dopa (1 mg/kg BW) in male and female goats under a 16-h photoperiod (16 h light, 8 h dark) condition. GHRH significantly and rapidly stimulated the release of GH after its i.v. administration to goats (P < 0.05). The carbi and L-dopa treatments completely suppressed GH-releasing responses to GHRH in both male and female goats (P < 0.05). The prolactin (PRL)-releasing response to an i.v. injection of thyrotropin-releasing hormone (TRH, 1 μg/kg BW) was additionally examined in male goats in this study to confirm modifications to central DA concentrations. The treatments with carbi and L-dopa significantly reduced TRH-induced PRL release in goats (P < 0.05). These results demonstrated that hypothalamic DA was involved in the regulatory mechanisms of GH, as well as PRL secretion in goats.
authors.affiliation: Faculty of Agriculture, Iwate University, Morioka, Japan.
authors.forename: Jin
authors.initials: J
authors.lastname: Jin
authors.affiliation: Faculty of Agriculture, Iwate University, Morioka, Japan.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Hashizume
mesh_terms: D000818:Animals; D002230:Carbidopa / Q000494:pharmacology; D004298:Dopamine / Q000378:metabolism / Q000502:physiology*; D005260:Female; D006041:Goats / Q000502:physiology*; D013006:Growth Hormone / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D007031:Hypothalamus / Q000378:metabolism / Q000502:physiology*; D007275:Injections, Intravenous; D007980:Levodopa / Q000494:pharmacology; D008297:Male; D011388:Prolactin / Q000378:metabolism*; D013268:Stimulation, Chemical; D013973:Thyrotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D007980:Levodopa; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D002230:Carbidopa; D004298:Dopamine
keywords: GH; GHRH; PRL; dopamine; goat