Bayarri M J, Rodríguez L, Zanuy S, Madrid J A, Sánchez-Vázquez F J, Kagawa H, Okuzawa K, Carrillo M
Department of Physiology, Faculty of Biology, University of Murcia, Murcia 30100, Spain.
Gen Comp Endocrinol. 2004 Mar;136(1):72-81. doi: 10.1016/j.ygcen.2003.12.004.
Reproduction in fish is cyclical and timed to guarantee the survival of the offspring. Seasonal variations in reproductive hormones of fish have been deeply investigated in fish over the last years. However, there are few studies regarding the daily changes in reproductive hormone profiles in teleosts. The aim of the present research was to investigate the effects of photoperiod manipulation on melatonin and reproductive hormones (pituitary sbGnRH, pituitary LH and plasma LH, testosterone [T], and 11-ketotestosterone [11KT]) daily rhythms in male sea bass, kept in net cages under farming conditions in winter (9L:15D). Fish were distributed in two groups, one under constant long photoperiod (18L:6D) and the other under natural photoperiod. The photoperiod strongly influenced the daily melatonin profile, so that the duration of the nocturnal melatonin rise was longer in the control group than in the group exposed to the artificial photoperiod (18L:6D). A daily rhythm was observed in the pituitary sbGnRH profile in both groups, showing the lowest levels during the dark period. A daily rhythm of pituitary LH was detected in the control group, which was suppressed in the group under long photoperiod. Daily variations in plasma LH were observed, the highest levels being found in the dark phase in both groups, although this profile was significantly altered by artificial light, maintaining a fixed relationship between the first nocturnal rise of melatonin and the nocturnal peaks of plasma LH in both groups. Plasma T levels showed significant fluctuations in their daily cycle following a sinusoidal pattern with an acrophase around sunrise in both groups, without any influence of light regime. No significant daily variations in plasma levels of 11-KT were observed in none of the groups. Our results provide the first evidence of the presence of daily variations in pituitary sbGnRH content, pituitary and plasma LH, and plasma T in sea bass. Artificial lights suppressed the circulating melatonin and significantly affected the daily rhythm of LH storage and release.
鱼类的繁殖具有周期性且时间安排精准，以确保后代的存活。过去几年，人们对鱼类生殖激素的季节性变化进行了深入研究。然而，关于硬骨鱼生殖激素谱的每日变化的研究却很少。本研究的目的是调查光周期调控对雄性海鲈褪黑素和生殖激素（垂体sbGnRH、垂体LH和血浆LH、睾酮[T]以及11-酮睾酮[11KT]）每日节律的影响，这些海鲈在冬季（9小时光照：15小时黑暗）养殖条件下饲养在网箱中。鱼被分为两组，一组处于恒定长光照周期（18小时光照：6小时黑暗），另一组处于自然光照周期。光周期强烈影响每日褪黑素谱，因此对照组夜间褪黑素升高的持续时间比暴露于人工光照周期（18小时光照：6小时黑暗）的组更长。两组垂体sbGnRH谱均呈现每日节律，在黑暗期水平最低。在对照组中检测到垂体LH的每日节律，在长光照周期组中该节律受到抑制。观察到血浆LH的每日变化，两组在黑暗期水平最高，尽管这种谱型因人工光照而显著改变，但两组中褪黑素首次夜间升高与血浆LH夜间峰值之间仍保持固定关系。两组血浆T水平在其每日周期中均呈现显著波动，呈正弦模式，高峰期在日出前后，不受光照制度影响。两组中均未观察到血浆11-KT水平有显著的每日变化。我们的结果首次证明了海鲈垂体sbGnRH含量、垂体和血浆LH以及血浆T存在每日变化。人工光照抑制了循环中的褪黑素，并显著影响了LH储存和释放的每日节律。
