除草剂西玛津对小鼠的免疫毒性作用

目的 探讨均三氮苯类除草剂西玛津对小鼠的免疫毒性.方法 BALB/c小鼠30只,按体重随机分为5组,每组6只,分别为西玛津90、200、400 mg/k(g染毒剂量组(每日1次,连续21 d灌胃染毒),阴性对照组(予蒸馏水)和阳性对照组(腹腔注射20 mg/kg环磷酰胺).观察小鼠体重变化、脾脏和胸腺的脏器系数、脾脏T细胞转化增殖能力以及血清中白细胞介素(IL)-2、IL-4、IgG和IgM含量.结果 200与400 mg/kg染毒组小鼠体重、脾脏和胸腺脏器系数以及T细胞转化增殖能力均明显低于阴性对照组,差异均有统计学意义(P＜0.05或P＜0.01);200mg/kg染毒组小鼠血清中IL-2、IL-4、IgG和IgM含量分别为(108.50±3.20)pg/ml、(36.54±3.36)pg/ml、(46.25±7.41)μmg/ml、(17.58±2.23)μg/ml;400 mg/kg染毒组小鼠血清中IL-2、IL-4、IgG和IgM含量分别为(85.70±4.00)pg/ml、(35.92±2.29)pg/ml、(40.08±6.80)μg/ml、(11.92±3.23)μg/ml,均明显低于阴性对照组,差异均有统计学意义(P＜0.05或P＜0.01).结论 西玛津对小鼠细胞免疫和体液免疫功能均有抑制作用.     

饮食诱导雄性肥胖大鼠生长激素轴变化

目的　探讨饮食诱导雄性肥胖大鼠生长激素 (GH)轴〔GH/胰岛素样生长因子 -I(IGF -I)〕的轴性变化。方法　建立高脂饮食诱导肥胖的大鼠模型 ,实验 12周末处死大鼠 ,采用放射免疫分析方法检测大鼠血清GH、IGF -I、胰岛素水平 ,用免疫组化方法检测肝脏IGF -I的含量。结果　饮食诱导肥胖后高脂组大鼠血清GH水平下降 (P <0 0 5 ) ;游离IGF -I水平升高 (P <0 0 1) ;血清胰岛素水平升高 (P <0 0 5 ) ;肝脏IGF -I的积分光密度值和阳性面积百分比均显著低于对照组 (P <0 0 1) ,肝脏的IGF -I合成分泌下降。结论　在饮食诱导肥胖的雄性大鼠体内 ,可能并不存在真正意义上的GH/IGF -I轴性变化损伤。     

阿的平对高功率微波损伤小鼠睾丸的保护作用

目的:探讨阿的平对高功率微波辐射小鼠睾丸的保护作用。方法:雄性小鼠随机分为4组,即正常组、辐射对照组、阿的平低剂量组(12.6mg/kg)、阿的平高剂量组(50.4mg/kg)。小鼠分别灌胃给予注射用水和不同剂量阿的平后,使用频率2.856GHz、脉宽500ns的微波源,进行50mW/cm2的微波远场照射30min。于照射后即刻、1d、2d、7d取小鼠睾丸。将小鼠睾丸组织病理切片观察其形态学变化;组织蛋白匀浆法提取睾丸组织蛋白检测热休克蛋白(HSP)70表达变化。结果:微波照射小鼠30min后,辐射对照组的睾丸组织从即刻至7d均有病理改变,曲精小管边缘不整齐,生精细胞水肿,排列紊乱,间质充血。给药组与对照组相比曲精小管排列基本整齐,边缘清晰,生精上皮细胞肿胀较对照组减轻。其中给药低剂量组在照射即刻至2d改善效果与高剂量组相似,但在7d时高剂量组的改善效果明显优于低剂量组。Western blot结果显示,在照后2d阿的平高、低剂量给药组与辐射对照组相比HSP70蛋白表达升高,在7d时只有阿的平高剂量组与辐射对照组相比HSP70蛋白表达升高。结论:阿的平可能是通过上调HSP70蛋白的表达,发挥其抗炎和抗凋亡作用,从而对高功率微波致伤的小鼠睾丸组织产生保护作用。     

功能性消化不良儿童IGF-I水平变化与营养指标关系研究

目的 研究功能性消化不良儿童血清胰岛素样生长因子I(IGF-I)水平变化及其对营养状况影响,探讨功能性消化不良患儿IGF-I与营养关系。方法 选取年龄1~7岁,符合功能性消化不良诊断标准儿童为观察组50例,健康儿童为对照组50例,每例均检测血清IGF-I、前白蛋白(PA)、视黄醇结合蛋白(RBP)、转铁蛋白(TRF)、白蛋白(ALB)及游离脂肪酸(FFA)水平,使用SPSSl8.0统计软件处理数据。结果 功能性消化不良儿童血清IGF-I含量明显低于健康对照组,其营养指标前白蛋白、视黄醇结合蛋白、转铁蛋白同样低于健康对照组,差异有统计学意义(t值分别是7.60、5.00、2.50、2.40,P<0.05),而游离脂肪酸和白蛋白未见明显差异性(t值分别是0.15、1.1,P>0.05)。结论 功能性消化不良儿童消化功能异常,营养吸收障碍,体内合成前白蛋白、视黄醇结合蛋白、转铁蛋白减少,导致血清IGF-I含量下降,低水平IGF-I影响着患儿生长发育。     

Oral administration of BCG encapsulated in alginate microspheres induces strong Th1 response in BALB/c mice

Bacille Calmette-Guerin (BCG) is one of the first vaccines administered to the newborns in developing countries. As an alternative to parenteral administration of vaccines, oral vaccines offer significant logistical advantages. Successful oral immunization, however, requires that vaccine antigens be protected from gastric secretions. In the present study, BALB/c mice were vaccinated orally with BCG encapsulated in alginate microspheres and the immune responses and protective effect were compared with those of mice vaccinated with free BCG by subcutaneous and oral routes. Proliferative and delayed-type hypersensitivity (DTH) responses and IFN-gamma production were significantly higher in mice immunized orally with encapsulated BCG in comparison with results of mice immunized orally with free BCG. Following systemic infection with BCG, mice vaccinated with encapsulated BCG had lower mean bacterial count compared to those vaccinated orally with free BCG. The immune responses induced by oral administration of encapsulated BCG were equal to or better than the responses induced by standard BCG vaccination.     

Hypersensitivity linked to exposure of broad bean protein(s) in allergic patients and BALB/c mice

ObjectiveBroad bean (Vicia faba L.), a common vegetable, belongs to the family Fabaceae and is consumed worldwide. Limited studies have been done on allergenicity of broad beans. The aim of this study was to determine if broad bean proteins have the ability to elicit allergic responses due to the presence of clinically relevant allergenic proteins.MethodsSimulated gastric fluid (SGF) assay and immunoglobulin E (IgE) immunoblotting were carried out to identify pepsin-resistant and IgE-binding proteins. The allergenicity of broad beans was assessed in allergic patients, BALB/c mice, splenocytes, and RBL-2H3 cells.ResultsEight broad bean proteins of approximate molecular weight 70, 60, 48, 32, 23, 19, 15, and 10 kDa that remained undigested in SGF, showed IgE-binding capacity as well. Of 127 allergic patients studied, broad bean allergy was evident in 16 (12%). Mice sensitized with broad bean showed increased levels of histamine, total and specific IgE, and severe signs of systemic anaphylaxis compared with controls. Enhanced levels of histamine, prostaglandin D₂, cysteinyl leukotriene, and β-hexosaminidase release were observed in the primed RBL-2H3 cells following broad bean exposure. The levels of interleukin IL-4, IL-5, IL-13 and regulated on activation, normal T-cell expressed and secreted were found enhanced in broad bean-treated splenocytes culture supernatant compared with controls.ConclusionThis study inferred that broad bean proteins have the ability to elicit allergic responses due to the presence of clinically relevant allergenic proteins.     

Oral administration of live Bifidobacterium substrains isolated from healthy centenarians enhanced immune function in BALB/c mice

Generally, there is an age-related decline in the human gut titer of Bifidobacterium species, but the titer in healthy centenarians was previously reported to be comparable to that found in much younger people. We addressed whether elevated Bifidobacterium titers relate positively to immune function. This study evaluated the immunoactivities of 2 Bifidobacterium strains (B adolescentis BBMN23 and B longum BBMN68) isolated from healthy centenarians in China. Different dosages (2 × 10¹¹, 2 × 10⁹, or 2 × 10⁷ colony-forming units [CFU]/kg body weight) of live bifidobacteria were orally administered once per day to healthy BALB/c mice, and the control group was given sterile skim milk every day. After 4 weeks, the immune parameters including cellular immunity (delayed-type hypersensitivity [DTH], and splenic lymphocyte proliferation), humoral immunity (serum hemolytic activity in immunized animals), and nonspecific immunity (peritoneal macrophages phagocytsis natural killer [NK] cell activity) were measured. We report that both Bifidobacterium strains independently increased the DTH response. Macrophage phagocytosis was also enhanced, while activities of the NK cells and levels of the serum hemolysin also were significantly higher than in the control group. There was a significant increase in splenic lymphocyte proliferation in bifidobacteria treatment animals compared to controls. In conclusion, ingestion of B. adolescentis BBMN23 and B. longum BBMN68 can enhance both innate and acquired immunity in healthy specific pathogen-free (SPF) mice and strains of bifidobacteria from healthy centenarians in Bama longevity villages in China may possess potentially valuable immunomodulatory properties.     

阿特拉津对BALB／c小鼠T淋巴细胞功能的影响

目的探讨阿特拉津对小鼠T淋巴细胞功能的影响。方法健康BALB／c小鼠按体重随机分为阿特拉津高剂量组（400mg／kg）、中剂量组（200mg／kg）、低剂量组（100mg／kg）和阴性对照组（蒸馏水）,经口灌胃,每天1次,连续21d。试验结束后,眼球取血,处死小鼠,观察胸腺组织病理学变化,采用MTY还原法和流式细胞仪分别检测脾脏T淋巴细胞增殖情况和胸腺T淋巴细胞亚群分布,酶联免疫吸附法检测血清中白细胞介素-2（interleu—kin-2,IL-2）和白细胞介素．4（interleukin-4,IL-4）含量。结果阿特拉津暴露使小鼠胸腺皮质细胞减少,各剂量组脾脏T淋巴细胞转化率低于阴性对照组（均有P〈0．05）。阿特拉津中、高剂量组胸腺CD3＋T淋巴细胞亚群比例以及CD4＋T／CD8＋T比值均低于阴性对照组（均有P〈0．05）,各剂量组CD4＋T淋巴细胞亚群比例均明显低于阴性对照组（均有P〈0．05）,CD8＋T淋巴亚群比例随染毒剂量增高有降低趋势,但差异无统计学意义（均有P〉0．05）。阿特拉津高剂量组血清IL-2和IL4含量明显降低（均有P〈0．05）。结论阿特拉津能抑制小鼠T淋巴细胞功能,因而有免疫毒性作用。     

利用白消安致BALB/c小鼠生殖毒性建立NOA疾病模型

目的利用白消安对BALB/c雄性小鼠生殖毒性,建立不同损伤程度的NOA(non-obstructive azoospermia,NOA)动物模型。方法本研究取6~8周龄性成熟的BALB/c雄性小鼠共45只,随机分为3组:0 mg/kg组、30 mg/kg组、40 mg/kg组,每组15只。每2周观察并记录小鼠体重,睾丸和附睾湿重,睾丸体积,及生精细胞损伤程度。通过HE染色,判断生精细胞受损情况;通过免疫组化技术检测受损生精细胞停滞的减数分裂阶段,该法主要借助生精细胞减数分裂过程中的三个标记蛋白:STRA8(Stimulated by Retinoic Acid 8,STRA8)减数分裂启动标记蛋白,SCP3(Synaptonemal Complex Protein 3,SCP3)减数分裂中标记蛋白,TNP1(Transition Protein 1,TNP1)减数分裂后标记蛋白。结果注射白消安后小鼠存活良好,注射白消安2周时,生精细胞开始损伤,30 mg/kg组轻于40 mg/kg组;4周时,40 mg/kg组呈唯支持细胞样变化;6-10周时,生精功能开始恢复,30 mg/kg组恢复明显快于40 mg/kg组;40 mg/kg组STRA8、SCP3、TNP1表达在注射4周最低,第8周开始恢复到正常水平。结论白消安40 mg/kg组单次注射4周时,可建立为唯支持细胞型NOA生精障碍模型;单词注射4-8周期间,可建立损伤程度不同的NOA生精障碍模型,为睾丸组织体外培养提供稳定的研究组织。     

弓形虫感染致BALB/c小鼠生殖毒性作用

目的探讨不同剂量弓形虫感染对BALB/c小鼠的生殖毒性作用。方法将50只受精鼠随机分为5组,每组10只;孕8 d,阴性对照组给予磷酸盐缓冲液,低、中、高剂量组腹腔注射50、100、200个/只纯化RH株弓形虫速殖子,阳性对照组给予环磷酰胺20 mg/kg;孕18 d观察孕鼠主要脏器及胚胎情况。结果阳性对照组吸收胎率(19.6%)、死胎率(23.6%)、流产率(4.6%)、畸胎率(31.4%)与阴性对照组比较明显升高,差异均有统计学意义(P<0.01)。弓形虫100、200个/只剂量组吸收胎率、死胎率、流产率分别为15.7%、8.2%、5.8%和28.9%、12.5%、15.1%,高于阴性对照组(P<0.05);200个/只剂量组活胎畸形率与阴性对照组比较(27.3%,0%)明显升高(P<0.01)。结论 100、200个/只纯化RH株刚地弓形虫速殖子孕中期感染可致BALB/c小鼠生殖毒性。     

Temperature dependence of ethanol depression in C57BL/6 and BALB/c mice

The relationship between environmental temperature, body temperature and brain sensitivity to ethanol was investigated in male C57BL/6S and BALB/cS mice. Age-matched, drug-naive mice of both strains were injected with 3.6 g/kg ethanol (20% w/v) and placed into a chamber kept at one of eight designated temperatures from 12 to 36 degrees C. Chamber temperature significantly affected wake-up rectal temperatures, sleep-times and wake-up brain ethanol concentrations in the intoxicated mice. Wake-up rectal temperatures were significantly, positively correlated with sleep-times and significantly, negatively correlated with wake-up brain ethanol concentrations in both strains. Linear regression analyses indicated that up to 47% of the variability in ethanol sensitivity of C57 mice and up to 31% of the variability in sensitivity of BALB mice could be accounted for by their wake-up rectal temperatures suggesting that the effects of ambient temperature on ethanol sensitivity were mediated, in part, by the resultant body temperatures. These results replicate and extend previous findings and demonstrate that temperature dependence of ethanol depression is not strain specific. The correlational and regression analyses provide additional evidence that brain sensitivity to ethanol depression varies with body temperature in accordance with membrane perturbation theories of anesthesia.     

Preferential induction of mammary tumors in p53 hemizygous BALB/c mice by fractionated irradiation of a sub-lethal dose of X-rays

BALB/c mice are susceptible to radiation-induced mammary tumors as well as lymphomas. We investigated the effects of the p53 deficient allele and of X-irradiation on the tumor spectrum in the BALB/c background. Substantially all p53 -/-animals died of thymic lymphomas before 36 weeks of age, while none of the p53 +/+ animals died during that period. At this age, mortalities of p53 +/- females and males were 5% (1/22) and 11% (1/9), respectively, due to non-thymic lymphoma and sarcoma. When exposed to 4 Gy of X-irradiation, 100% (44/44) and 95% (18/19) of p53 +/- mice died with tumors within 36 weeks. Among these, the predominant cause of death was lymphoma in either sex [26/44 (59%) in females; 13/19 (68%) in males]; mammary adenocarcinoma (15/44, 34%) and sarcoma (3/19, 16%) were semi-dominant in females and males, respectively. The mortalities of similarly treated p53 +/+ mice were 16% (5/31) in females and 17% (3/18) in males: virtually all deaths were due to thymic lymphomas in either sex. When exposed to 4 currency 0.7 Gy of X-irradiation at weekly intervals, 23/23 (100%) of the p53 +/-females died of tumors within 36 weeks. In these animals, mammary adenocarcinoma (15/23, 65%), instead of lymphoma (7/23, 30%), was dominant. None of the similarly treated p53 +/+ females developed malignant tumors during the period. Mammary adenocarcinomas generated in p53 +/- females exposed or non-exposed to radiation showed a frequent loss of the p53 wild-type allele. Hence, we provided a useful experimental system to study radiation-induced mammary tumors in mice.     

Dietary flavones suppresses IgE and Th2 cytokines in OVA-immunized BALB/c mice

Background The flavonoids are a diverse family of chemicals commonly found in fruits and vegetables. Previously, we have shown that the two flavones, chrysin and apigenin could suppress the expression of the high affinity IgE receptor FcεRI in human basophilic KU812 cells. We also demonstrated that dietary apigenin decreased IgE level in C57BL/6N mice sera. Aim of the study To evaluate the anti-allergic effect of the two flavones in vivo, we evaluated the effect of the two flavones, chrysin and apigenin, on the immune system in BALB/c mice sensitized with ovalbumin (OVA). Methods Mice were fed experimental diets containing either of the flavones for 3 weeks and immunized with OVA. After the experimental feeding period, measurement of Igs concentration in the mice sera was performed using a sandwich ELISA. Cytokines expression in mice sera was assessed using a cytokine array. Furthermore, cytokines mRNA levels in spleen lymphocytes from mice sensitized with OVA were measured by RT-PCR. Results The total IgE level in mice fed one of the two flavones were suppressed, whereas levels of IgG, IgM, and IgA were not affected. The production of interleukin (IL)-4, which is known as one of Th2 cytokines and regulates the production of IgE, was down-regulated by the chrysin or the apigenin diet. Moreover, OVA-induced mRNA expression of Th2 cytokines in spleen lymphocytes from mice sensitized with OVA, such as IL-4 and IL-13 were down-regulated by the chrysin or the apigenin diet. Conclusions The results suggest that the diet containing one of the two flavones might suppress the up-regulation of serum IgE induced by OVA-immunization through the suppression of Th2-type immune response.     

Immunogenicity and safety of a novel tetanus toxoid-conjugated anti-gastrin vaccine in BALB/c mice

The objective of this study is to determine the immunogenicity and safety of our novel anti-gastrin vaccine that is composed of the common amino-terminal portions of human carboxy-amidated gastrin-17 (G17) and glycine-extended gastrin-17 (gly-G17) as well as the common carboxy-terminal portion of the gastrin precursor progastrin (in a 50:50 mixture) all covalently linked to tetanus toxoid (TT) via peptide spacers.The vaccine, or immunogen, was injected intramuscularly into the legs of BALB/c mice, which produced high serum titres of specific IgG antibodies and IFN-γ in their spleen cells, identifiable by enzyme-linked immunosorbent assay (ELISA) and enzyme-linked immunospot assay (ELISPOT), respectively. TT as the protein carrier effectively enhanced the antigenic epitopes’ humoural and cellular immune responses, unlike the antigenic epitopes alone or the immunogen’s adjuvant emulsion system (AES), all of which failed to provoke any obvious immune response. Notably, the animals’ body weights increased significantly after immunization (P < .01), while their haematology and serum biochemistry were all generally normal, and the gross anatomy of their main organs (e.g., heart, liver, spleen, lung, kidney) showed no obvious histopathological changes.     

Effect of Shengmai-san on cognitive performance and cerebral oxidative damage in BALB/c mice

The aim of this study was to examine the effect of Shengmai-san (SMS) on learning and memory impairment induced by scopolamine (1?mg/kg, i.p.) in mice. The passive avoidance task (PAT) and Morris water maze (MWM) test served as the behavioral models for testing memory. To elucidate the mechanism of its cognitive-enhancing activity, the effects of SMS (2, 4, or 8?g/kg) on activities of acetylcholinesterase (AChE) and antioxidant enzymes and levels of acetylcholine (ACh) and nitrite were evaluated in brain homogenate. Tacrine (THA) (10?mg/kg, p.o.) was used as a reference drug. SMS (4 or 8?g/kg) significantly prevented scopolamine-induced impairments as measured by the PAT and MWM (probe trial session). SMS (4 or 8?g/kg) also significantly reduced the oxidative-nitrative stress, as evidenced by decreased malondialdehyde and nitrite levels and by its prevention of decreases in glutathione and superoxide dismutase levels. The activity of AChE was decreased in scopolamine-treated mice but was inhibited significantly by SMS treatment (4 or 8?g/kg) in both salt- and detergent-soluble fractions of brain homogenates. Further SMS treatment (4 or 8?g/kg) significantly increased the ACh levels in the brain homogenate to a level similar to that observed in THA treatment. Thus, the significant cognitive enhancement observed after 7 days of administration of SMS is closely related to the strong antioxidant properties of SMS in addition to its inhibition of brain AChE activity. These findings stress the critical impact of SMS on higher brain functions such as learning and memory.     

十溴联苯醚(PBDE-209)暴露对小鼠学习记忆能力的影响

目的 探讨十溴联苯醚(PBDE-209)暴露对小鼠学习记忆能力的影响,为防治PBDE-209危害提供依据.方法 18只雌性BALB/c小鼠随机分成3组,每组6只,分别给予PBDE-209(1500mg·kg~(-1)·d~(-1))+精炼花生油(高剂量组)、PBDE-209(300mg·k~(-1)·d~(-1))+精炼花生油(低剂量组)和0.1 ml/10 g体重花生油(对照组)灌胃.每日1次,连续染毒4周后做Morris水迷宫试验、穿梭箱试验(期间仍然给药),测定小鼠的学习记忆能力,待染毒5周后处死.测定体重、脏器重量、脑组织中乙酰胆碱酯酶活力和丁酰胆碱酯酶活力,观察肝脏细胞组织形态学变化.结果 高剂量组心脏系数明显高于低剂量组,差异有统计学意义(P<0.05).Morris水迷宫试验结果显示,各组动物逃避潜伏期均有不同程度缩短,变化趋势差异有统计学意义(F=3.134,P<0.05);低剂量染毒组在第2象限游泳时间为(15.78±10.92)s,明显短于对照组[(28.80±8.67)s],差异有统计学意义(P<0.05).穿梭箱试验显示,各组主动逃避次数差异无统计学意义(F=3.423,P=0.06).与对照组比较,各染毒组脑组织乙酰胆碱酯酶活力和丁酰胆碱酯酶活力的差异无统计学意义(P>0.05).染毒组肝脏出现脂肪变性和肿胀,高剂量组尤为明显.结论 4周龄BALB/c小鼠暴露于PBDE-209在一定程度上可影响小鼠空间学习记忆能力.     

Evaluation of tandem Chlamydia trachomatis MOMP multi-epitopes vaccine in BALB/c mice model

Chlamydia trachomatis (Ct), an obligate intracellular parasite, is the leading cause of bacterial sexually transmitted diseases worldwide. The best solution to control the spread of Ct is to develop safe and effective vaccines. However, an effective vaccine has not been developed due to some challenges such as selection of appropriate candidate antigens and an effective delivery system. In our previous study, we have developed a Ct vaccine that comprises a multi-epitope peptide of Ct major outer membrane protein (MOMP_370–387) and Hepatitis B virus core antigen (HBcAg). The vaccine was evaluated in a murine model with chlamydial genital infection. The results indicated that Ct MOMP multi-epitope delivered by HBcAg could be an effective vaccine for the prevention of Ct. In this study, another two epitopes were selected from the MOMP protein and tandemly linked with MOMP_370–387 to enhance the immunogenicity and the protective effect of the candidate vaccine. Our results revealed that both the immunogenicity and the protective effect of the tandem Ct MOMP multi-epitopes were much better than that of the single epitope. Therefore, vaccines based on the tandem Ct MOMP multi-epitopes could be more effective immune prophylactics to prevent Ct infection than the single epitope in murine model system.     

Developmental and lactational exposure to environmentally relevant concentrations of dieldrin does not alter pregnancy outcome and mammary gland morphology in BALB/c mice

The objectives of this study were to: (1) determine the dosing range necessary to produce serum levels of dieldrin in mice representative of human body burdens; and (2) define the effect of developmental exposure to environmentally relevant concentrations of dieldrin on mammary gland development. Sexually mature female BALB/c mice (n=140) were randomly assigned to receive vehicle, 0.45, 2.25, 4.5, and 22.5 μg dieldrin/g body weight (BW)/day. Serum levels of dieldrin were quantified by gas chromatography in pooled samples (n=4/treatment group). Target levels of 10-30 ng/ml were achieved in 0.45 and 2.25 μg/g dose groups by the end of 2 weeks of treatment. Vehicle or dieldrin (0.45, 2.25, and 4.5 μg/g BW) was administered weekly to sexually mature female BALB/c mice (n=48) throughout mating, pregnancy, and lactation. Treatments had no effect on fertility parameters in dams or mammary gland morphology at sexual maturity. Developmental exposure to dieldrin has no effect on mammary gland development in aged BALB/c mice.