乌司他丁对脂多糖诱导的巨噬细胞炎症反应的影响

目的探讨乌司他丁对LPS诱导的RAW264.7细胞炎症反应的影响。方法采用1.0μg/mL的LPS激活RAW264.7细胞株,与不同浓度组乌司他丁(100～10 000 U/mL)共同孵育,采用ELISA法测定TNF-α和IL-1β的表达;实时荧光定量逆转录聚合酶链反应(RT-PCR)技术分析TNF-αmRNA和IL-1βmRNA表达。结果高浓度乌司他丁(1 000～10 000 U/mL)可抑制LPS诱导的RAW264.7细胞TNF-α和IL-1β表达(P均<0.05),下调LPS诱导的RAW264.7细胞TNF-αmRNA和IL-1βmRNA含量(P均<0.05);低浓度乌司他丁(100 U/mL)对LPS诱导的RAW264.7细胞TNF-α、IL-1β、TNF-αmRNA、IL-1βmRNA表达与LPS单独处理组比较,无显著差异。结论乌司他丁可抑制LPS诱导的巨噬细胞炎症反应;该抑制作用呈浓度依赖性。     

西红花酸对RAW264.7巨噬细胞TLR4/NF-κB信号通路的抑制作用及机制探讨

目的探讨西红花酸对RAW264.7巨噬细胞株TLR4/NF-κB信号通路的抑制作用及其机制。方法常规培养小鼠RAW264.7巨噬细胞,设计合成My D88 siRNA,用LPS刺激RAW264.7巨噬细胞,同时用西红花酸和My D88 siRNA进行干预。RT-PCR法测定RAW264.7巨噬细胞IL-6、TNF-α、i NOS、MCP-1和IFN-β水平,Western blotting法测定NF-κB/p65和p-JNK1/2的水平,ELISA法检测IL-6和TNF-α水平。结果西红花酸可以抑制LPS诱导的RAW264.7细胞IL-6、TNF-α、i NOS、MCP-1 mRNA的表达,下调p-JNK1/2和p65蛋白表达水平,降低IL-6、TNF-α的分泌水平;My D88 siRNA可以阻断西红花酸对LPS刺激RAW264.7巨噬细胞的作用,但西红花酸和My D88 siRNA对LPS刺激IFN-βmRNA表达的阻断作用不明显。结论西红花酸对RAW264.7巨噬细胞的TLR4/NF-κB信号通路的抑制作用可能通过My D88信号通路实现。     

白藜芦醇对db/db小鼠胰岛β细胞功能的影响

目的观察白藜芦醇对db/db小鼠胰岛β细胞的作用并探讨其可能机制。方法取12只db/db小鼠,随机分为糖尿病(DM)组和白藜芦醇干预组,每组各6只,另设对照(Con)组小鼠6只。干预4周后,比较各组OGTT后血糖水平,免疫组织化学分析胰岛中3-磷酸肌醇依赖性蛋白激酶1(PDK-1)蛋白表达量的改变。体外培养小鼠胰岛细胞株MIN6细胞并分为正常葡萄糖(NG)组、高糖(HG)组、高糖+白藜芦醇(HG+Res)组、高糖+白藜芦醇+PI3K特异性抑制剂Wortmannin(HG+Res+Wo)组。Western blot测定4组细胞PDK-1、磷酸化蛋白激酶B(p-AKt)水平,CCK-8法和流式细胞仪检测MIN6细胞增殖、凋亡率;ELISA测定上清液中胰岛素水平。结果与DM组比较,白藜芦醇干预组OGTT血糖曲线下面积下降(P0.05)、胰岛细胞PDK-1蛋白表达增加[阳性率(0.57±0.32)%vs(1.74±0.47)%,P0.01];与HG组比较,白藜芦醇干预后MIN6细胞中PDK-1、p-Akt蛋白增加、上清液中胰岛素水平增加[(124.95±5.37)vs(181.19±30.77)pmol/L]、细胞增殖(D值)增加[(0.71±0.10)vs(1.02±0.09)]、凋亡率下降[(19.3±2.1)%vs(11.2±1.4)%](P0.01);与HG+Res组比较,HG+Res+Wo组MIN6细胞PDK-1表达、Akt磷酸化水平减低,上清液中胰岛素水平及细胞增殖下降、凋亡率增加(P0.05)。结论白藜芦醇可能通过激活胰岛β细胞PDK-1/Akt通路、改善胰岛β细胞功能。     

条件性敲除胰岛β细胞蛋白磷酸酶2Acα对小鼠糖代谢影响机制的探讨

目的探讨条件性敲除胰岛β细胞蛋白磷酸酶2Acα(PP2Acα)对小鼠血糖水平影响的机制。方法选取4月龄条件性敲除胰岛β细胞PP2Acα(KO组)及对照组(Con,与KO组同窝别、性别匹配)各24只。行腹腔葡萄糖耐量实验(IPGTT),测定0、30、60和120min小鼠血糖及胰岛素分泌水平;新鲜分离胰岛,用葡萄糖刺激胰岛素分泌实验(GSIS)评价小鼠胰岛β细胞对葡萄糖反应性。结果IPGTT结果显示,KO组葡萄糖负荷后30min血糖[(23.1±5.1)vs(17.5±5.7)mmol/L]和60min血糖[(20.5±6.8)vs(13.5±5.1)mmol/L]高于Con组(P0.05);KO组葡萄糖负荷后30min血清胰岛素水平较Con组下降[(2.16±0.92)vs(1.07±0.42)μg/L](P0.05);GSIS显示高糖刺激下KO组胰岛素分泌较Con组减少[(0.82±0.15)vs(0.42±0.24)μIU/L](P0.05)。结论条件性失活胰岛β细胞PP2Acα小鼠糖耐量受损可能与胰岛素一相分泌受损相关。     

α-硫辛酸抑制IκB激酶β对胰岛细胞的影响

目的 探讨脂肪细胞对共培养体系中胰岛细胞炎症状态的影响,以及α-硫辛酸对抗胰岛细胞炎症反应的作用.方法 以单纯胰岛细胞培养为对照组、胰岛细胞-脂肪细胞共培养为实验组、胰岛细胞-脂肪细胞共培养加α-硫辛酸为干预组.以胰岛素释放试验比较胰岛细胞的功能,采用实时荧光PCR和Western印迹法检测细胞内IκB激酶(IKK)B的mRNA和蛋白水平.结果 实验组胰岛索释放试验的分泌指数明显低于对照组和干预组(1.0±0.1vs2.6±0.2和2.5±0.5,P<0.01).实时荧光PCR显示,实验组的IKKβ mRNA水平明显高于对照组和干预组(4.62±0.60 vs 1.00±0.46和2.25±O.75,P相似文献   

芪丹通脉片调节TLR4信号通路抑制巨噬细胞泡沫化的研究

目的 观察益气活血中药芪丹通脉片对氧化低密度脂蛋白(ox-LDL)诱导的RAW264.7细胞泡沫化进程、炎症指标及Toll样受体（TLR）4信号通路的影响。 方法 培养RAW264.7细胞，随机分为对照组、ox-LDL组及ox-LDL +芪丹通脉片（QDTM）组，各组细胞干预后进行泡沫化诱导，分析各组细胞油红染色阳性面积，计算各组细胞泡沫化诱导率，收集细胞，ELISA法检测炎性因子肿瘤坏死因子(TNF)-α、白介素（IL）-6、C反应蛋白（CRP）表达水平，Real-time PCR及Western blot分析TLR4、分子核因子（NF）-κB表达水平。 结果 与对照组相比，ox-LDL组细胞泡沫化诱导率、TNF-α、IL-6、CRP水平显著升高（P < 0.05），TLR4、NF-κB表达水平明显上调，QDTM干预后，ox-LDL+QDTM组细胞泡沫化诱导率及TNF-α、IL-6、CRP水平较ox-LDL组显著下调（P < 0.05），同时TLR4、NF-κB表达水平较ox-LDL组明显下降。 结论 QDTM能抑制TLR4信号通路及炎症反应、降低RAW264.7细胞泡沫化诱导率，抑制巨噬细胞泡沫化。     

酰基化Ghrelin对肿瘤坏死因子α诱导的脂肪细胞单核细胞趋化蛋白1及脂联素分泌紊乱的影响

目的探讨酰基化Ghrelin是否可保护3T3-L1小鼠脂肪细胞免受肿瘤坏死因子α(TNF-α)所介导的炎症损伤。方法成熟3T3-L1脂肪细胞分为对照组、TNF-α处理组、酰基化Ghrelin处理组、酰基化Ghrelin+TNF-α处理组。干预完成后,分别检测3T3-L1脂肪细胞上Toll样受体4(TLR-4)mRNA及蛋白水平、核因子κB p65(NF-κB p65)磷酸化蛋白水平以及细胞上清液中脂联素和单核细胞趋化蛋白1(MCP-1)的表达水平。结果 1与对照组比较,TNF-α处理组3T3-L1脂肪细胞TLR-4 mRNA和蛋白水平、NF-κB p65磷酸化蛋白水平均上调,细胞分泌MCP-1增多,脂联素减少(P0.05,n=5)。2与对照组比较,酰基化Ghrelin处理组TLR-4 mRNA和蛋白水平以及NF-κB p65磷酸化蛋白水平下降(P0.05,n=5),脂肪细胞分泌脂联素减少(P0.05,n=5),MCP-1仅有下降趋势(P0.05,n=5)。3与TNF-α(100μg/L)处理组比较,酰基化Ghrelin预孵育4 h可下调TNF-α所致的3T3-L1脂肪细胞TLR-4 mRNA表达增多,其蛋白水平以及NF-κB p65磷酸化蛋白水平亦有所下调(P0.05,n=5),且呈剂量依赖性;而脂肪细胞MCP-1及脂联素的分泌水平差异无显著性(P0.05,n=5)。结论 TNF-α导致3T3-L1细胞TLR-4、NF-κB p65炎症通路活化,脂肪细胞分泌促炎因子(MCP-1)增加,而抗炎因子(脂联素)减少;酰基化Ghrelin可剂量依赖性抑制TNF-α介导的3T3-L1细胞TLR-4、NF-κB p65炎症通路的活化,但不能完全改善脂肪细胞分泌促炎因子和抗炎因子的紊乱。     

呼吸道合胞病毒感染巨噬细胞活化Toll样受体3介导的抗病毒作用研究

目的探讨呼吸道合胞病毒(RSV)感染巨噬细胞(RAW264.7细胞)后,Toll样受体3(TLR3)的水平变化及其介导产生的I型干扰素的抗病毒作用。方法 RSV感染体外培养的小鼠巨噬细胞RAW264.7细胞,并给予TLR3特异性抗体处理,分别于感染的4、8、12、16和24h后收集各组细胞。以未感染病毒的细胞为对照组。用Trizol提取细胞总RNA,半定量RT-PCR法检测TLR3、干扰素α(IFN-α),干扰素β(IFN-β),RSVF蛋白的mRNA表达量变化。结果 (1)RSV感染RAW264.7细胞后,TLR3、IFN-α、IFN-β、RSVF蛋白的mRNA表达量均升高且有时间依赖性,TLR3mRNA24h表达量是基础表达量的6倍多,IFN-α,IFN-βmRNA24h表达量是基础表达量的4倍多,RSVF蛋白mRNA是基础表达量的近1.8倍。(2)预先给予TLR3抗体处理以抑制TLR3受体后,再行RSV感染,IFN-α和IFN-β的mRNA表达量虽有升高,但较感染组相比均有下降,mRNA表达在12h后显著降低,且IFN-β的mRNA表达量下调更明显。但RSVF基因的mRNA表达在12h后升高有统计学差异,24h升高有显著性差异。结论 RSV感染RAW264.7巨噬细胞后可上调TLR3表达,其活化细胞介导产生的I型干扰素起抗病毒作用,在一定程度上可抑制病毒的增殖水平。     

巨噬细胞刺激蛋白对烟熏大鼠肺泡巨噬细胞氧化应激和细胞因子产生的影响

目的 探讨巨噬细胞刺激蛋白(MSP)对烟熏大鼠肺泡巨噬细胞氧化应激和细胞因子产生的影响.方法 培养正常和烟熏不同时间(1个月、2个月、3个月)的大鼠肺泡巨噬细胞,给予不同浓度MSP处理24 h,采用酶联免疫法检测细胞上清液中细胞因子肿瘤坏死因子α(TNF-α)、白介索8(IL-8)和IL-1β的浓度,比色法检测细胞上清液中丙二醛(MDA)和超氧化物歧化酶(SOD)的水平.结果 ①MSP呈浓度依赖性促进正常组和各烟熏组大鼠肺泡巨噬细胞分泌TNF-α、IL-8和IL-1β;经MSP处理后,各烟熏组大鼠肺泡巨噬细胞上清液中TNF-α、IL-8和n-1β浓度均高于正常组(P＜0.05);大鼠肺泡巨噬细胞上清液中TNF-α、IL-8和IL-1β浓度随烟熏时间延长呈时间依赖性增加.②MSP呈浓度依赖性促进正常组和各烟熏组大鼠肺泡巨噬细胞分泌MDA,抑制其产生SOD;烟熏2个月组和烟熏3个月组大鼠肺泡巨噬细胞上清液中MDA水平均高于正常组(P＜0.05),SOD水平均低于正常组(P＜0.05);随着烟熏时间延长,大鼠肺泡巨噬细胞上清液中MDA水平呈时间依赖性增加,SOD水平呈时间依赖性降低.结论 MSP呈浓度依赖性促进正常和烟熏大鼠肺泡巨噬细胞分泌TNF-α、IL-8、IL-1β和MDA,抑制其产生SOD.MSP促烟熏大鼠肺泡巨噬细胞分泌TNF-α、IL-8、IL-1β、MDA及抑制其产生SOD的作用较正常大鼠更显著,且烟熏时间越长此作用越明显.     

瘦素对巨噬细胞白细胞介素1β表达的影响

目的探讨瘦素对鼠源性巨噬细胞系RAW264.7细胞白细胞介素1β表达的影响,以阐明瘦素在动脉粥样硬化发生中的作用。方法不同浓度的瘦素(1.25、2.5、5和10nmol/L)孵育RAW264.7细胞4h后,逆转录聚合酶链反应法检测巨噬细胞白细胞介素1βmRNA的表达。并用该浓度梯度的瘦素分别孵育RAW264.7细胞1、3、6、9h后,采用双抗夹心酶联免疫吸附法检测各组培养上清白细胞介素1β蛋白含量。结果白细胞介素1βmRNA表达水平随瘦素浓度增加逐渐增高(分别为0.107±0.102、0.204±0.019、0.718±0.083、0.642±0.071),5nmol/L瘦素处理组达最高峰。各组培养上清白细胞介素1β蛋白分泌水平随瘦素浓度增加逐渐增高,5nmol/L瘦素处理组白细胞介素1β蛋白分泌量达最高峰;白细胞介素1β蛋白分泌水平随瘦素刺激时间增加逐渐增高,至6h达最高峰(P<0.05)。RAW264.7细胞经不同浓度瘦素处理后,白细胞介素1βmRNA和蛋白表达呈瘦素剂量依赖性增加。结论瘦素可在体外促进RAW264.7细胞白细胞介素1β表达和分泌,这可能是瘦素直接致动脉粥样硬化的机制之一。     

Three layer functional model and energy exchange concept of aging process

Relying on a certain degree of abstraction, we can propose that no particular distinction exists between animate or living matter and inanimate matter. While focusing attention on some specifics, the dividing line between the two can be drawn. The most apparent distinction is in the level of structural and functional organization with the dissimilar streams of ‘energy flow’ between the observed entity and the surrounding environment. In essence, living matter is created from inanimate matter which is organized to contain internal intense energy processes and maintain lower intensity energy exchange processes with the environment. Taking internal and external energy processes into account, we contend in this paper that living matter can be referred to as matter of dissipative structure, with this structure assumed to be a common quality of all living creatures and living matter in general. Interruption of internal energy conversion processes and terminating the controlled energy exchange with the environment leads to degeneration of dissipative structure and reduction of the same to inanimate matter, (gas, liquid and/or solid inanimate substances), and ultimately what can be called ‘death.’ This concept of what we call dissipative nature can be extended from living organisms to social groups of animals, to mankind. An analogy based on the organization of matter provides a basis for a functional model of living entities. The models relies on the parallels among the three central structures of any cell (nucleus, cytoplasm and outer membrane) and the human body (central organs, body fluids along with the connective tissues, and external skin integument). This three-part structural organization may be observed almost universally in nature. It can be observed from the atomic structure to the planetary and intergalactic organizations. This similarity is corroborated by the membrane theory applied to living organisms. According to the energy nature of living matter and the proposed functional model, the decreased integrity of a human body's external envelope membrane is a first cause of the structural degradation and aging of the entire organism. The aging process than progresses externally to internally, as in single cell organisms, suggesting that much of the efforts towards the restoration and maintenance of the mechanisms responsible for structural development should be focused accordingly, on the membrane, i.e., the skin. Numerous reports indicate that all parts of the human body, like: bones, blood with blood vessels, muscles, skin, and so on, have some ability for restoration. Therefore, actual revival of not only aging tissue of the human body's membrane, but the entire human body enclosed within, with all internal organs, might be expected. We assess several aging theories within the context of our model and provide suggestions on how to activate the body's own anti-aging mechanisms and increase longevity. This paper presents some analogies and some distinctions that exist between the living dissipative structure matter and inanimate matter, discusses the aging process and proposes certain aging reversal solutions.     

Unusual responses of nocturnal pineal melatonin synthesis and secretion to swimming: Attempts to define mechanisms

Abstract: The effect of swimming at night on rat pineal melatonin synthesis was compared with that of light exposure at night. Rats were forced to swim at 0030 hr (lights out at 2000 hr) and sacrificed by decapitation 15 and 30 min later, immediately after swimming. Other groups of animals were exposed to white light (650μW/cm²) for 15 and 30 min at same time. Swimming caused a rapid and highly significant drop in the melatonin content in the pineal gland; however, the activity of N-acetyltransferase (NAT), the supposed rate limiting enzyme in the melatonin production, was not changed. Despite the drop in pineal melatonin levels, serum concentrations of the indole remained elevated in the rats that swam. In contrast, melatonin levels in the pineal and serum of light exposed rats fell precipitously, accompanied by a significant suppression of NAT activity. Since we anticipated that the strenuous exercise associated with swimming may induce release of artrial natriuretic peptide (ANP) from the heart, which in turn could cause the release of pineal melatonin, in a second study we injected physiological saline intravenously to stretch the cardiac muscle and release ANP. Three milliliters of normal saline was injected during the day into the jugular vein of anesthetized rats that were pretreated with isoproterenol to stimulate pineal melatonin production. Animals were killed 15 min after the saline injection, and pineal NAT activity and pineal melatonin levels were measured. The saline injections caused no alteration in the elevated levels of either NAT or melatonin. These data suggest that the disparity in pineal NAT activity (which was high) and pineal melatonin (which was low), in animals swum at night, may not be caused by ANP which is released during strenuous exercise such as swimming.     

Melatonin and photoperiodic time measurement: Seasonal breeding in the sheep

Abstract: Well-established circadian physiology supports the view that photoperiodic time measurement utilizes the coincidence between the presence of light and a photosensitive phase of a 'biological clock' to alter reproductive status—the so-called external coincidence model of seasonal breeding. In this review, we examine the mechanism whereby photoperiod interacts with presumed suprachiasmatic nuclei activity to allow endogenous melatonin to normally synchronize reproductive activity to the optimal time of year. The Romney Marsh sheep is particularly explored as an experimental model. It is suggested that the on/off activity of seasonal reproduction may be a robust mechanism able to be predictably manipulated by the judicious use of the light/dark cycle and exogenous melatonin, but firmly based on circadian principles.     

Serological survey of HIV and syphilis in pregnant women in Madagascar

Objectives Peripartal transmission of human immunodeficiency virus (HIV) and Treponema pallidum, the causative agent of syphilis, leads to severe consequences for newborns. Preventive measures require awareness of the maternal infection. Although HIV and syphilis testing in Madagascar could be theoretically carried out within the framework of the national pregnancy follow‐up scheme, the required test kits are rarely available at peripheral health centres. In this study, we screened blood samples of pregnant Madagascan women for HIV and syphilis seroprevalence to estimate the demand for systemic screening in pregnancy. Methods Retrospective anonymous serological analysis for HIV and syphilis was performed in plasma samples from 1232 pregnant women that were taken between May and July 2010 in Ambositra, Ifanadiana, Manakara, Mananjary, Moramanga and Tsiroanomandidy (Madagascar) during pregnancy follow‐up. Screening was based on Treponema pallidum haemagglutination tests for syphilis and rapid tests for HIV, with confirmation of positive screening results on line assays. Results Out of 1232 pregnant women, none were seropositive for HIV and 37 (3%) were seropositive for Treponema pallidum. Conclusions Our findings are in line with previous studies that describe considerable syphilis prevalence in the rural Madagascan population. The results suggest a need for screening to prevent peripartal Treponema pallidum transmission, while HIV is still rare. If they are known, Treponema pallidum infections can be easily, safely and inexpensively treated even in pregnancy to reduce the risk of transmission.     

Variabilité des concentrations plasmatiques de l’angiotensinogène et risque d’hypertension artérielle chez le rat transgénique

Aim

Genetic polymorphisms of the human angiotensinogen gene are frequent and may induce up to 30% increase of plasma angiotensinogen concentrations with a blood pressure increase of up to 5 mmHg. Their role for the pathogenesis of human arterial hypertension remains unclear. High plasma angiotensinogen levels could increase the sensitivity to other blood pressure stressors.

Methods

Male transgenic rats with a 9-fold increase of plasma angiotensinogen concentrations and male non-transgenic rats aged 10 weeks were treated or not with NG-Nitro-L-arginine-methyl ester for 3 weeks in their drinking water (n = 3/group). Systolic blood pressure and body weight were measured at baseline and at the end of the study when left ventricular weight and ventricular expression of angiotensin I-converting enzyme and procollagen Iα1 were determined (polymerase chain reaction).

Results

At baseline, transgenic rats had +18 mmHg higher bood pressure and –8% lower body weight compared to non-transgenic rats (P < 0.05) without significant changes for the vehicle groups throughout the study (P > 0.05). NG-Nitro-L-arginine-methyl ester increased blood pressure, left ventricular weight and left ventricular weight indexed for body weight by +41%, +17.6% and +18.6% (P < 0.05) in transgenic and +25%, +5.3% and +6.7% (P > 0.05) in non-transgenic rats compared to untreated animals, respectively. Cardiac gene expression showed no differences between groups (P > 0.05).

Conclusion

Increased plasma angiotensinogen levels may sensitize to additional blood pressure stressors. Our preliminary results point towards an independent role of angiotensinogen in the pathogenesis of human hypertension and associated end-organ damage.     

Morphological and immunocytochemical heterogeneity of cultured pinealocytes from one-week-and two-month-old rats: Planimetric and densitometric investigations

Abstract: In vitro preparations of rat pinealocytes are widely used for biochemical analyses of signal transduction processes. This paper deals with morphological and immunocytochemical features of such preparations. Special attention was paid to the problems of whether pinealocytes represent a heterogeneous cell population and how such heterogeneity may develop during ontogeny. The investigations were performed with cells which were obtained from the pineal organ of one-week-and two-month-old rats, attached to synthetic peptide-coated coverslips or tissue culture chamber slides, and maintained under in vitro conditions overnight. The attached cells were then fixed with paraformaldehyde. These preparations yielded monolayers of spherical cells of different sizes; most cells were isolated, but some of them were aggregated and formed small clusters. On the average, the cells from the one-week-old animals were smaller than the cells from the two-month-old animals. Immunocytochemical demonstration of S-antigen, a pinealocyte-specific marker, showed that the majority of the cells from two-month-old animals were intensely or moderately labelled. Pinealocytes from one-week-old animals were less S-antigen immunoreactive. Only very few cells (less than 1% displayed glial fibrillary acidic protein (GFAP)-immunoreactivity. Planimetric investigations of the cell size and semiquantitative densitometric investigations of the intensity of the S-antigen immunoreaction revealed that (i) pinealocytes kept in vitro form a heterogeneous cell population, and that (ii) this heterogeneity increases during postnatal development from one-week-old to two-month-old animals. Two groups of pinealocytes can be distinguished based on their developmental fate: pinealocytes of one group grow dramatically, but show only a moderate increase in S-antigen immunoreactivity, and pinealocytes of the other group retain their size, but display a distinct increment in S-antigen immunoreacti vitv.     

A single injection of adrenergic agonists enhances pineal melatonin production in Turkish hamsters

Abstract: The purpose of this study was to determine whether the pineal gland of Turkish hamsters (Mesocricetus brandti) responds to adrenergic agonists with an increase in melatonin production, and, if it does, whether the sensitivity of the pineal gland to agonists would differ throughout the dark phase. Adult Turkish hamsters weighing 110–210 g received a subcutaneous injection of isoproterenol (ISO, 1 mg/kg B.W.) or norepinephrine (NE, 1 mg/kg B.W.) at different times of night. Animals exposed to LD 16:8 responded to ISO or NE with increased pineal melatonin content only when injected at dawn, when endogenous melatonin is at basal or near-basal levels. When the 8 hr scotophase was entirely replaced with light, the responsiveness to ISO injections at dawn disappeared. In animals exposed to light from 30 min prior to injection to the time of sacrifice, ISO injections increased pineal melatonin content (P < 0.005, three-way ANOVA), which varied, depending on the specific time of injection (effect of time of night, P < 0.05, three-way ANOVA). These results demonstrate that (1) adrenergic agonists enhance the production of pineal melatonin in Turkish hamsters, (2) this stimulatory effect takes place late, but not early in the 8 hr scotophase, and (3) the adrenergic induction of pineal melatonin production in Turkish hamsters requires priming by darkness during the appropriate circadian phase.