title: Effects of photoperiod on secretory patterns of growth hormone in adult male goats.
abstract: The aim of the present study was to clarify the effect of photoperiod on secretory patterns of growth hormone (GH) in male goats. Adult male goats were kept at 20°C with an 8-h or 16-h light photoperiod, and secretory patterns of GH secretion were compared. In addition, plasma profiles of prolactin (PRL), insulin-like growth factor-I (IGF-I) and testosterone (T) were also examined to characterize GH secretion. GH was secreted in a pulsatile manner. There was no significant difference in pulse frequency between the 8-h 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 was greater in the 16-h than 8-h photoperiod (P < 0.05). Plasma PRL and IGF-I levels were higher in the 16-h than 8-h photoperiod (P < 0.05). In contrast, plasma T levels were lower in the 16-h photoperiod (P < 0.05). These results show that a long light photoperiod enhances the secretion of GH as well as PRL and IGF-I, but reduces plasma T concentrations in male goats.
authors: Faculty of Agriculture, Iwate University, Morioka, Japan.
authors: Jin
authors: J
authors: Jin
authors: Ken
authors: K
authors: Sawai
authors: Tsutomu
authors: T
authors: Hashizume
mesh_terms: D000375:Aging; D000818:Animals; D006041:Goats / Q000378:metabolism*; D013006:Growth Hormone / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008297:Male; D017440:Photoperiod; D011388:Prolactin / Q000097:blood; D011673:Pulsatile Flow; D013739:Testosterone / Q000378:metabolism; D013997:Time Factors
chemical_list: D013739:Testosterone; D007334:Insulin-Like Growth Factor I; D011388:Prolactin; D013006:Growth Hormone
keywords: GH; IGF-I; PRL; goat; photoperiod