title: Effects of photoperiod on the secretion of growth hormone in female goats.
abstract: The aim of the present study was to clarify the effect of photoperiod on the secretion of growth hormone (GH) in goats. Adult female goats were kept at 20°C with an 8-h or 16-h photoperiod, and secretory patterns of GH for 4 h (12.00 to 16.00 hours) were compared. In addition, the goats were kept under a 16-h photoperiod and orally administered saline (controls) or melatonin, and the effects of melatonin on the secretion of GH were examined. GH was secreted in a pulsatile manner. There were no significant differences in pulse frequency between the 8- and 16-h photoperiods; however, GH pulse amplitude tended to be greater in the group with the 16-h photoperiod (P = 0.1), and mean GH concentrations were significantly greater in the 16-h photoperiod (P < 0.05). The GH-releasing response to GH-releasing hormone (GHRH) was also significantly greater for the 16-h photoperiod (P < 0.05). There were no significant differences in GH pulse frequency between the saline- and melatonin-treated groups. However, GH pulse amplitude and mean GH concentrations were significantly greater in the saline-treated group (P < 0.05). The present results show that a long photoperiod enhances the secretion of GH, and melatonin modifies GH secretion in female goats.
authors.affiliation: Faculty of Agriculture, Iwate University, Morioka, Japan.
authors.forename: Jin
authors.initials: J
authors.lastname: Jin
authors.forename: Tomoyoshi
authors.initials: T
authors.lastname: Yaegashi
authors.forename: Ken
authors.initials: K
authors.lastname: Sawai
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Hashizume
mesh_terms: D000284:Administration, Oral; D000818:Animals; D005260:Female; D006041:Goats / Q000502:physiology*; D013006:Growth Hormone / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology; D008550:Melatonin / Q000008:administration & dosage / Q000494:pharmacology; D017440:Photoperiod; D011673:Pulsatile Flow / Q000502:physiology; D013268:Stimulation, Chemical; D013997:Time Factors
chemical_list: D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D008550:Melatonin