Baldwin W S, Barrett J C
Laboratory of Molecular Carcinogenesis, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA.
Mol Carcinog. 1998 Mar;21(3):149-55. doi: 10.1002/(sici)1098-2744(199803)21:3<149::aid-mc1>3.0.co;2-h.
Epidemiological studies have suggested a possible link between extremely low frequency electromagnetic fields (EMFs) and increased rates of certain cancers. One cancer that has been postulated to be associated with EMF exposure is breast cancer, for which increased rates have been reported among electricians. These cancer associations are weak, and the link to EMF exposures remains tenuous. Understanding the mechanisms by which EMFs could have biological effects will help in elucidating the risk, if any, from EMFs. One hypothesis that has received considerable attention involves reduction of melatonin levels by EMFs. This hypothesis suggests that loss of melatonin affects a variety of hormonal processes such as estrogen homeostasis and thereby may increase breast cancer rates. Since this theory was first presented, putative melatonin receptors have been cloned, providing new tools with which to examine melatonin's mechanism of action and the melatonin hypothesis. These receptors are found in nuclear and membrane fractions of cells. The nuclear receptors (retinoid Z receptors) are found both in the brain and in non-neural tissues, whereas the membrane-bound receptors are found primarily in neural tissue and have a higher affinity for melatonin. These receptors may control a variety of hormonal and immunological functions, including the release of gonadotropins from the hypothalamus and pituitary and 5-lipoxygenase activity in B lymphocytes. This Working Hypothesis briefly reviews our current knowledge of melatonin receptors and then provides theories on how the inactivation of melatonin receptors may cause cancer and suggests areas of research for addressing this question.
流行病学研究表明，极低频电磁场（EMF）与某些癌症发病率的增加之间可能存在联系。一种被推测与EMF暴露有关的癌症是乳腺癌，据报道，电工群体中乳腺癌的发病率有所上升。这些癌症关联并不显著，与EMF暴露的联系仍然不明确。了解EMF可能产生生物学效应的机制将有助于阐明EMF带来的风险（如果存在的话）。一个受到广泛关注的假说是，EMF会降低褪黑素水平。该假说认为，褪黑素的缺失会影响多种激素过程，如雌激素稳态，从而可能增加乳腺癌发病率。自从这个理论首次提出以来，假定的褪黑素受体已被克隆，这为研究褪黑素的作用机制和褪黑素假说提供了新工具。这些受体存在于细胞的核和膜部分。核受体（类视黄醇Z受体）在大脑和非神经组织中均有发现，而膜结合受体主要存在于神经组织中，对褪黑素具有更高的亲和力。这些受体可能控制多种激素和免疫功能，包括下丘脑和垂体释放促性腺激素以及B淋巴细胞中的5-脂氧合酶活性。本工作假说简要回顾了我们目前对褪黑素受体的认识，然后提出了关于褪黑素受体失活可能导致癌症的理论，并指出了解决这一问题的研究方向。
