Melatonin influences gonadotropin II secretion in the Atlantic croaker (Micropogonias undulatus)
Melatonin influences gonadotropin II secretion in the Atlantic croaker (Micropogonias undulatus)
复制标题
DOI：
10.1006/gcen.1996.0166
复制
发表时间：
1996-11-01
影响因子：
2.7
通讯作者：
Thomas, P
中科院分区：
文献类型：
--
作者：
Khan, IA;Thomas, P
研究了褪黑素在大西洋花鱼昼夜周期和季节性生殖周期不同阶段对促性腺激素II （GtH II）分泌的调控作用。在昼夜周期的晚光期腹腔注射褪黑激素可引起性腺发育完全的斑马鱼血浆GtH II水平的显著升高。注射后30min观察到GtH II水平升高；该水平在1小时内保持升高，并在2小时的采样时间开始下降。褪黑素的刺激作用在5至500纳克/克体重范围内呈剂量依赖性。在性腺发育完全的鱼体内，循环GtH II水平呈现显著的日变化，在黑暗期水平升高。在LHRH类似物（LHRHa）的刺激下，GtH II的分泌在昼夜周期中也有所变化，在黑暗早期达到最大水平。有趣的是，褪黑激素刺激GtH II在光照后期和黑暗早期和中期的释放。对褪黑激素的促性腺激素反应在（晚光照期）之前或对应于循环GtH II水平升高的时期，以及在黑暗期对LHRHa刺激的反应性增加，这表明褪黑激素可能参与了该物种每日GtH II周期的控制。褪黑素以剂量依赖性的方式抑制lhrha诱导的昼夜周期中暗期GtH II的释放；这种抑制作用的生理意义目前尚不清楚。褪黑素对退化斑马鱼的基础或lhrha诱导的GtH II释放没有显著影响。将褪黑素（1或10 ng/g体重）注射到性腺发育完全的黄花鱼视前下丘脑区（POAH）的第三脑室，可导致血浆GtH II浓度升高。此外，低浓度（0.2 ng/ml）褪黑激素刺激性腺发育完全的鱼垂体片段体外释放GtH II。这些结果表明，褪黑素可以通过作用于POAH水平并直接作用于垂体刺激GtH II释放来影响GtH II的分泌。(C) 1996学术出版社，Inc.
The role of melatonin in the control of gonadotropin II (GtH II) secretion was investigated in Atlantic croaker (Micropogonias undulatus) during different phases of the day-night cycle and seasonal reproductive cycle. Intraperitoneal injection of melatonin during the late-light phase of the day-night cycle elicited a significant elevation in plasma GtH II levels in croaker with fully developed gonads. The increase in GtH II levels was observed 30 min postinjection; the levels remained elevated for 1 hr and started to decline at the 2-hr sampling time. The stimulatory effect of melatonin was dose-dependent over the range 5 to 500 ng/g body weight. Circulating GtH II levels in fish with fully developed gonads showed significant diurnal variation, with elevated levels during the dark phase. The GtH II secretion in response to stimulation by a LHRH analog (LHRHa) also varied during the day-night cycle, with the maximum levels during the early-dark phase. Interestingly, melatonin stimulated GtH II release during the late-light and early- and mid-dark phases. The increased gonadotropic response to melatonin preceded (late-light phase) or corresponded to the period of elevated circulating GtH II levels and increased responsiveness to stimulation by LHRHa during the dark phase, suggesting that melatonin may be involved in the control of daily GtH II cycles in this species. Melatonin inhibited LHRHa-induced GtH II release during the mid-dark phase of the day-night cycle in a dose-dependent manner; the physiological significance of this inhibitory influence is not understood at present. No significant effect of melatonin on basal or LHRHa-induced GtH II release was observed in regressed croaker. Melatonin injection (1 or 10 ng/g body weight) into the third ventricle in the preoptic anterior hypothalamic area (POAH) of croaker with fully developed gonads resulted in an elevation in plasma GtH II concentrations. In addition, a low concentration (0.2 ng/ml) of melatonin stimulated in vitro GtH II release from the pituitary fragments of fish with fully developed gonads. These results suggest that melatonin can influence GtH II secretion by acting at the level of POAH and also directly at the pituitary to stimulate GtH II release. (C) 1996 Academic Press, Inc.