Löscher W, Mevissen M, Lerchl A
Department of Pharmacology, Toxicology and Pharmacy, School of Veterinary Medicine, Hannover, Germany.
Radiat Res. 1998 Nov;150(5):557-67.
The hypothesis whereby alternating (50 or 60 Hz) magnetic fields such as those produced by electric power reduce the nocturnal production of melatonin in the pineal gland and thereby indirectly enhance development and growth of breast cancer has attracted a great deal of interest. In view of the potential importance of this hypothesis that there is a link between electric power and breast cancer, which is also known as the "melatonin hypothesis", we undertook various experiments in female Sprague-Dawley rats to evaluate whether 100-microT 50 Hz magnetic-field exposure, i.e. a flux density shown recently to exert a tumor (co)promoting effect in the 7,12-dimethylbenz[a]anthracene (DMBA) model of breast cancer in Sprague-Dawley rats, consistently reduces melatonin levels and, if not, which factors may be involved in the inconsistent effects of magnetic-field exposure on production of melatonin. Long-term exposure of female Sprague-Dawley rats to magnetic fields for 13 weeks did not alter the nocturnal levels of melatonin in the pineal gland or serum (determined 5 h after the onset of darkness) significantly, irrespective of whether rats were treated with DMBA or not. In one experiment, when blood was sampled 3, 5 and 6 h after the onset of darkness after 2 weeks of magnetic-field or sham exposure, a significant decrease in melatonin was seen in magnetic-field-exposed rats at 6 h. However, the results could not be reproduced in two subsequent experiments in other groups of rats. Shorter (1 day, 1 week) or longer (4, 8, 13 weeks) exposure periods also did not result in any significant effects of the magnetic field on melatonin levels when blood sampling was performed either 5 or 6 h after onset of the dark phase. Various potential sources of variation in melatonin levels or in magnetic-field effects on melatonin levels were evaluated, but the reason(s) for the inconsistent effect of magnetic-field exposure remains unclear. Thus the present study failed to demonstrate a consistent effect of 100-microT 50 Hz magnetic-field exposure on melatonin levels in Sprague-Dawley rats.
有一种假说认为，诸如电力产生的交变（50或60赫兹）磁场会减少松果体夜间褪黑素的分泌，从而间接促进乳腺癌的发展和生长，这一假说引起了广泛关注。鉴于这一假说（即电力与乳腺癌之间存在联系，也被称为“褪黑素假说”）的潜在重要性，我们在雌性斯普拉格-道利大鼠身上进行了各种实验，以评估100微特斯拉50赫兹的磁场暴露（即最近显示在斯普拉格-道利大鼠的7,12-二甲基苯并[a]蒽（DMBA）乳腺癌模型中具有肿瘤（协同）促进作用的通量密度）是否会持续降低褪黑素水平，如果不会，磁场暴露对褪黑素分泌产生不一致影响可能涉及哪些因素。雌性斯普拉格-道利大鼠长期暴露于磁场13周，无论大鼠是否接受DMBA处理，松果体或血清中褪黑素的夜间水平（在黑暗开始5小时后测定）均未显著改变。在一项实验中，在磁场或假暴露2周后，于黑暗开始后3、5和6小时采集血液样本，发现磁场暴露组大鼠在6小时时褪黑素显著降低。然而，在随后对其他大鼠组进行的两项实验中，该结果无法重现。当在黑暗期开始后5或6小时进行血液采样时，较短（1天、1周）或较长（4、8、13周）的暴露期也未导致磁场对褪黑素水平产生任何显著影响。我们评估了褪黑素水平或磁场对褪黑素水平影响的各种潜在变异来源，但磁场暴露产生不一致影响的原因仍不清楚。因此，本研究未能证明100微特斯拉50赫兹的磁场暴露对斯普拉格-道利大鼠褪黑素水平有一致的影响。
