Protective effects of melatonin against low- and high-LET irradiation

To investigate the protective effects of melatonin against high-LET ionizing radiation, V79 Chinese hamster cells were irradiated with 100 keV/mu m carbon beam. Parallel experiments were performed with 200 kV X-rays. To avoid the impact from extra solvents, melatonin was dissolved directly in culture medium. Cells were cultured in melatonin medium for 1 hr before irradiation. Cell inactivation was measured with conventional colony forming assay, medium containing 6-thioguanine was used for the selection of mutants at hprt locus, and the cell cycle was monitored by flow cytometry. Both carbon beam and X-rays induced cell inactivation, hprt gene mutation and cell cycle G2 block dose-dependently. But carbon beam showed stronger effects as indicated by all three endpoints and the relative biological effectiveness (RBE) was 3.5 for cell killing (at 10% survival level) and 2.9 for mutation induction (at 5 x 10(-5) mutants/ cell level). Melatonin showed protective effects against ionizing radiation in a dose-dependent manner. In terms of cell killing, melatonin only increased the survival level of those samples exposed to 8Gy or larger of X-rays or 6 Gy or larger of carbon beam. In the induction of hprt mutation and G2 block, melatonin reduced such effects induced by carbon beam but not by X-rays. The results suggest that melatonin reduces the direct interaction of particles with cells rather than an indirect interaction. Further studies are required to disclose the underlying mechanisms.

Melatonin modulates acute testicular damage induced by carbon ions in mice

The present study was performed to obtain evidence of the radioprotective function of melatonin at different administration levels on carbon ion-induced mouse testicular damage. Outbred Kun-Ming strain mice were divided into six groups, each composed of eight animals: control group, melatonin alone group, irradiation group and three melatonin plus irradiation-treated groups. An acute study was carried out to determine alterations in DNA-single strand break, cell apoptosis, and oxidative stress parameters as well as histopathology in mouse testis 24 h after whole-body irradiation with a single dose of 4 Gy Tie results showed that pre-treatment and post-treatment with high-dose melatonin (10 mg/kg) both significantly alleviated carbon ion-induced acute testicular damage, a greater radioprotective effect being observed in the pre-treatment group. On the other hand, low-dose melatonin (1 mg/kg) had a limited radioprotective effect on irradiation-induced degeneration and DNA lesions in mouse testis. Taken together, the data suggest that prophylactic treatment with a higher dose of melatonin is probably advisable to protect against the effects of heavy-ion irradiation.

Melatonin in Chinese medicinal herbs

Melatonin is a highly conserved molecule that not only exists in animals, but also is present in bacteria, unicellular organisms and in plants. Since melatonin is an antioxidant, in plants melatonin was speculated to protect them from intrinsic and environmental oxidative stress. More importantly, melatonin in edible plants inevitably enters animals and human through feed and food. In this study, more than 100 Chinese medicinal herbs were analyzed using the methods of solid phase extraction and HPLC-FD on-line with MS to determine whether melatonin is present in these commonly used herbs. Melatonin was detected in majority of these plants. Sixty-four of them contain melatonin in excess of 10 ng per gram dry mass. Melatonin levels in several herbs are in excess of 1000 ng/g. It is well known that normal average physiological plasma levels of melatonin are only 10-60 pg/mL. These high level-melatonin containing plants are traditionally used to treat diseases which presumably involve free radical damage. The current study provides new information concerning one potentially effective constituent present in a large number of medicinal herbs. The results suggest that these herbs should be reevaluated in reference to their nutritional and medicinal value. (C) 2003 Elsevier Science Inc. All rights reserved.

外源褪黑激素对野芥菜(Brassica juncea)生长的影响

褪黑激素（N-乙酰基-5-甲氧基色胺）是一种广泛存在于生物体内的吲哚类活性分子。本文以野芥菜（Brassica juncea）为例，初步研究了外源褪黑激素对植物生长生殖的影响。我们选取了发芽2天和发芽4天的野芥菜幼苗，用不同浓度的褪黑激素对其处理24小时，然后测量根的伸长量。结果表明，对于发芽2天的野芥菜，0.1 µM的外源褪黑激素能够显著提高野芥菜幼苗根的生长，而100 µM的外源褪黑激素处理则能够显著抑制根的生长;对于发芽4天的野芥菜，低浓度的外源褪黑激素处理对根生长的影响不明显，而高浓度的褪黑激素处理（如100 µM）能够显著抑制根的伸长。结果表明发芽晚期的野芥菜幼苗的根可能对褪黑激素的处理不敏感。由于褪黑激素对植物的生理作用类似于生长素的作用，因此选用了发芽2天的野芥菜幼苗为植物材料，用外源褪黑激素处理其根24小时后，通过间接酶联免疫吸附测定(ci-ELISA)的方法测定了内源吲哚乙酸（IAA）含量的变化。结果表明低浓度的褪黑激素处理时，内源IAA的含量增高，而在高浓度的褪黑激素处理时，内源IAA含量的变化不大。 关于褪黑激素对野芥菜生殖的影响，我们在花蕾期用褪黑激素涂抹野芥菜的花蕾，并在开花授粉后用褪黑激素涂抹柱头，然后在结实时测量果荚长度，种子千粒重，平均每荚种子数，发芽率等指标。结果表明：对于在花蕾期用褪黑激素处理的植株来说，褪黑激素处理对其的果荚长度，千粒重，平均每荚种子数都没有显著的影响。对于开花后用褪黑激素处理授粉后的柱头，1 µM的褪黑激素处理过的主枝具有较长的果荚长度，而褪黑激素处理对千粒重，平均每荚种子数，发芽率，发芽势和发芽指数均没有显著的影响。在花粉萌发实验中，外源褪黑激素的处理浓度和时间均对花粉萌发有一定的影响，表现为随时间的增加，花粉萌发数目增加，在4 h时，低浓度的褪黑激素处理（10 µM）下花粉的萌发较多。

褪黑素对~(12)C~(6+)束辐照损伤小鼠肺的防护作用研究

<正>目的:探讨褪黑素(Melatonin,MLT)对重离子辐照损伤小鼠肺的防护作用,为褪黑素的抗辐射功能[1][2]进一步提供实验依据。方法:预先给小鼠腹腔注射10mg/kg的

褪黑素对重离子辐射损伤小鼠肺的防护作用研究

目的探讨褪黑素(melatonin,MLT)对重离子辐射损伤小鼠肺的防护作用。方法预先给小鼠腹腔注射10mg/kg的MLT,1h后给予0、0.5、1.0、2.0及4.0Gy的全身12C6+束均匀照射,剂量率约1.4Gy/min,辐射后8h,检测辐射损伤小鼠肺组织的SOD活性和MDA、GSH含量,并通过单细胞凝胶电泳技术检测辐射损伤小鼠肺细胞的拖尾长度和尾距。结果和单纯辐射组相比,10mg/kg的MLT腹腔注射能有效抑制重离子辐射引起的小鼠肺组织SOD活性降低、GSH含量下降和MDA含量提高;同时,MLT还能使受损小鼠肺细胞的拖尾长度和尾距显著降低,且都存在剂量效应关系。结论MIT对重离子全身辐射所致小鼠的抗氧化系统有一定的激活效应,对辐射损伤有一定的防护作用,这可能与对抗膜脂质过氧化、清除自由基及其减轻DNA损伤有一定的关系。

低剂量重离子辐射诱导小鼠的适应性反应和褪黑素的辐射保护作用研究

研究目的： 1.研究碳离子辐射对小鼠不同组织抗氧化酶活性及细胞周期进程的影响。 2.研究低剂量碳离子预辐射对离体培养的黑色素瘤B16细胞及正常小鼠诱导的适应性反应。 3. 研究褪黑素（MLT）对碳离子的辐射损伤防护效应。 4. 研究碳离子层叠法辐照对H22荷瘤小鼠的治疗效果。研究方法： 1.采用不同剂量的碳离子辐照小鼠，用黄嘌呤氧化酶法检测外周血、肝脏及脑组织中抗氧化酶活性变化，流式细胞仪检测细胞周期阻滞情况。 2.采用低剂量碳离子预辐射离体培养的黑色素瘤B16细胞及正常小鼠，间隔4h后再以攻击剂量辐照，常规组织切片染色观察各组织器官病理变化，流式细胞仪检测细胞周期阻滞情况，黄嘌呤氧化酶法检测小鼠胸腺、脾脏及B16细胞中抗氧化酶活性，Western-blot法检测胸腺细胞及B16细胞中P53及P21蛋白表达情况，RT-PCR法检测CHK2及CDC25mRNA的表达水平。 3.在碳离子辐照小鼠1h前腹腔注射褪黑素，单细胞电泳方法检测胸腺、脾脏细胞的DNA损伤情况，微核法表征外周血的染色体损伤，黄嘌呤氧化酶法测定胸腺、脾脏细胞的抗氧化酶活性。 4.以碳离子层叠法辐照H22荷瘤小鼠，统计不同剂量照射后的肿瘤体积变化、肿瘤抑制率、肿瘤生长延迟天数及治愈率。结果： 1、小鼠血清和肝脏组织在辐射剂量较低（≤0.75Gy）时SOD活性高于对照组，随着辐射剂量的增高，SOD活性趋于降低；MDA含量在辐射剂量较低（≤0.3Gy）时低于对照，随着辐射剂量的增高其含量趋于升高；脑组织GSH浓度在照射剂量较低（≤0.5Gy）时大于对照组，随着照射剂量的升高其浓度趋于降低；低剂量辐射小鼠引起胸腺G2期细胞比例增加，脾脏G1期细胞比例增加。 2、小鼠肝脏、脾脏、肺脏及脑组织在攻击剂量辐射后，出现明显的病理变化，低剂量预辐射处理后病理变化减轻；低剂量预辐射增加胸腺G2期细胞及脾脏G1期细胞比例；相对于单纯攻击剂量辐射组，低剂量预辐射组胸腺组织P53及P21蛋白表达升高；CHK2 mRNA水平升高，CDC25 mRNA水平降低；脾脏及胸腺组织中SOD活性降低程度减弱，MDA含量升高趋势减弱。B16细胞经低剂量预辐射处理后上述指标均未发生明显变化。 3、与辐照处理组相比，褪黑素处理后小鼠的脾脏胸腺细胞DNA损伤拖尾率及彗尾长度明显降低；SOD活性升高，MDA含量降低，外周血微核率降低。 4、在不同剂量的碳离子辐照处理后观察的12天内，各组肿瘤生长速度减慢，生长延迟，肿瘤抑制率随时间而增加。15Gy照射组肿瘤生长速度最慢，肿瘤抑制率最大，肿瘤生长延迟最为明显，而且肿瘤治愈率达到30%。结论： 1． 低剂量12C6+离子全身辐照小鼠应激激活机体抗氧化系统，随辐射剂量的增加，机体抗氧化能力明显降低，导致脂质过氧化发生；低剂量的碳离子辐射导致小鼠胸腺细胞G2期阻滞，脾脏细胞发生G1期阻滞。 2． 低剂量12C6+离子预辐射引发小鼠正常机体产生适应性反应，减轻随后的大剂量辐射造成的损伤；低剂量12C6+离子预辐射对小鼠黑色素瘤B16细胞未引发适应性反应。 3． 15mg/kg的MLT可以对小鼠的重离子辐射损伤产生明显的防护效果。 4． 12C6+离子适形治疗小鼠移植性肿瘤H22，荷瘤鼠的存活时间、肿瘤体积变化、肿瘤的控制率、治愈率等结果显示，15Gy为最佳治疗剂量

高原鼠兔的季节性繁殖

A nnual changes of the rep roduct ive act ivity in adult male p lateau p ika (Ochotona curzoniae) , a small endemic mammal in Q inghai2T ibet P lateau, w ere invest igated from J anuary to December, 1991. A ll of the animals w ere k illed and decap itated during the nigh t (23:00～ 24:00) and the p lasma, p ineal glands, testes ep ididym is, sem inal vesicles, deferent ducts were co llected and used for biochemical, and histo logical studies. Significant changes associated with seasonal cycles were found. (1) In February～ early April, the restoration phase, the weights of testes, epididym ides and deferent ducts were increased; the process of sperm atogenesis was strengthened and testo sterone level in plasma was increased, but the pineal weight and its melatonin content were decreased. (2) During the middle of April～ late May, the sexually active phase, a significant elevation of gonadal activity was observed. In this period, gonadalw eights were increased, spermatogenesis was completed, pineal weights were decreased and melatonin contents were fluctuated at alow level. These results suggested the increasing in sexual activity as well as in the ability of testo sterone secretion. (3) A striking reduction of test icular activity appears in June～A ugust. In this inhibition phase, gonada lweight, process of sperm atogenesis, plasma testo sterone level were decreased while the pineal weight and pineal melatonin content were increased. (4) During Sep tember～ J anuary, the sexually quiescent phase, declining in weights of testes and epididymides, arrest of spermatogenesis, decreasing of plasma testo sterone concent ration, fluctuating in pineal weights and increasing in pinealmelatonin level were observed. Our findings indicated that the male pikas under natural conditions exhibited an annual rep roductive cycle. A possible relationship between pineal activity and reproductive function was also suggested.