title: Effects of photoperiod on the secretion of growth hormone and prolactin during nighttime in female goats.
abstract: The aim of the present study was to clarify the effect of photoperiod on nighttime secretion of growth hormone (GH) in goats. Adult female goats were kept at 20°C with an 8 h or 16 h dark photoperiod, and secretory patterns of GH for 8 h in the dark period were examined with the profile of prolactin (PRL) secretion. GH was secreted in a pulsatile manner in the dark period. There were no significant differences in pulse frequency between the 8- and 16-h dark photoperiods; however, pulse amplitude tended to be greater in the group with the 16-h dark photoperiod (P = 0.1), and mean GH concentrations were significantly greater in the same photoperiod (P < 0.05). PRL secretion increased quickly after lights off under both photoperiods. The PRL-releasing responses were weaker in the 8-h than 16-h dark photoperiod. The secretory response to photoperiod was more obvious for PRL than GH. The present results show that a long dark photoperiod enhances the nighttime secretion of GH in female goats, although the response is not as obvious as that for PRL.
authors: Faculty of Agriculture, Iwate University, Morioka, Japan.
authors: Jin
authors: J
authors: Jin
authors: Tomoyoshi
authors: T
authors: Yaegashi
authors: Tsutomu
authors: T
authors: Hashizume
mesh_terms: D000818:Animals; D003624:Darkness; D005260:Female; D006041:Goats / Q000502:physiology*; D013006:Growth Hormone / Q000378:metabolism*; D017440:Photoperiod; D011388:Prolactin / Q000378:metabolism*; D011673:Pulsatile Flow; D013997:Time Factors
chemical_list: D011388:Prolactin; D013006:Growth Hormone