Vanecek J, Klein D C
Institute of Physiology, Czech Academy of Sciences, Prague.
Am J Physiol. 1995 Jul;269(1 Pt 1):E85-90. doi: 10.1152/ajpendo.1995.269.1.E85.
Melatonin inhibits gonadotropin-releasing hormone-induced release of luteinizing hormone (LH) from the neonatal rat gonadotrophs. The second messenger involved is not known, although there are several candidates, including adenosine 3',5'-cyclic monophosphate (cAMP) and intracellular free Ca2+. The present study addresses the question of which second messenger mediates melatonin inhibition of LH release. We found that the effect of melatonin was not prevented by cAMP protagonists, including 8-bromo-cAMP, dibutyryl cAMP, 3-isobutyl-1-methylxanthine, and forskolin. However, treatments that enhanced Ca2+ influx masked the effects of melatonin, and treatments that blocked Ca2+ influx mimicked the effects of melatonin. Moreover, melatonin decreased K(+)-induced LH release, which is dependent on Ca2+ influx but did not block release of LH due to thapsigargin-induced mobilization of Ca2+ from intracellular stores. These findings indicate that melatonin inhibits gonadotropin-releasing hormone-induced LH release, primarily through an action involving inhibition of Ca2+ influx, and that cAMP does not seem to be involved in this effect of melatonin.
褪黑素抑制促性腺激素释放激素诱导的新生大鼠促性腺细胞释放黄体生成素（LH）。尽管有几个候选者，包括3',5'-环磷酸腺苷（cAMP）和细胞内游离Ca2+，但所涉及的第二信使尚不清楚。本研究探讨了哪种第二信使介导褪黑素对LH释放的抑制作用。我们发现，包括8-溴-cAMP、二丁酰cAMP、3-异丁基-1-甲基黄嘌呤和福斯可林在内的cAMP激动剂并不能阻止褪黑素的作用。然而，增强Ca2+内流的处理掩盖了褪黑素的作用，而阻断Ca2+内流的处理则模拟了褪黑素的作用。此外，褪黑素降低了K(+)诱导的LH释放，这依赖于Ca2+内流，但并未阻断因毒胡萝卜素诱导细胞内钙库释放Ca2+而导致的LH释放。这些发现表明，褪黑素主要通过抑制Ca2+内流来抑制促性腺激素释放激素诱导的LH释放，并且cAMP似乎不参与褪黑素的这种作用。
