Maternal exposure to bisphenol a during late pregnancy resulted in an increase of Calbindin-D9k mRNA and protein in maternal and postnatal rat uteri

It has been reported that Calbindin-D9k (CaBP-9k) is rapidly and strongly induced by environmental estrogenic compounds, possibly through estrogen receptors (ERalpha) in the uterus of mammals. CaBP-9k can be evaluated as an early gene marker for assaying estrogenic effects of putative environmental chemicals in the rat uterus. This study was undertaken to investigate CaBP-9k mRNA and protein expression in the postnatal rat uterus following maternal exposure to 17beta-estradiol (E2) and bisphenol A (BPA) during the neonatal period. Treatment with a high dose of BPA (600 mg/kg body weight (BW) per day) resulted in a 3-fold increase in CaBP-9k mRNA expression for 3 days, while a single dose of E2 (40 microg/kg BW per day) induced 2-fold increase of this gene in the maternal uterus. In an agreement with maternal CaBP-9k mRNA, postnatal CaBP-9k mRNA in the uterus increased 4-fold when treated with BPA (600 mg/kg BW per day). In addition, treatment with increasing concentrations of BPA resulted in significant increases in CaBP-9k protein in the maternal rat uterus. It is of interest that increasing doses of BPA induced a significant ERalpha mRNA increase in the postnatal uterus. Furthermore, immunohistochemistry revealed that treatment with BPA induced CaBP-9k protein in the maternal uterus. We demonstrated that maternal exposure to BPA during late pregnancy induced CaBP-9k mRNA and protein in maternal and postnatal rat uteri. These results suggest that rapid absorption and distribution of environmental estrogenic compounds occurs in maternal and neonatal rat uteri and these chemicals can easily pass though the placenta during pregnancy to affect postnatal reproductive functions.     

Potential estrogenic and antiandrogenic effects of permethrin in rats

Many environmental chemicals including pesticides have been reported to possess hormonal activities, and thus are classified as endocrine disruptors. Permethrin, a synthetic pyrethroid insecticide, is used worldwide, which provides potential environmental exposure. However, relatively few studies have reported on hormonal activities, particularly estrogenic and androgenic activities of permethrin, and the results of these studies are in some respects contradictory. Therefore, this study investigated the potential estrogenic and androgenic activities of permethrin in vitro and in vivo. We conducted an uterine Calbindin-D9k (CaBP-9k) gene expression assay and an uterotrophic assay for estrogenic activity, and a Hershberger assay for androgenic activity. The CaBP-9k gene, one of the intracellular calcium binding proteins, is estrogen-responsive in the uterus. The rat uterotrophic and Hershberger assays are generally used as in vivo short-term screening assays for detecting the estrogenic and androgenic activities of chemicals, although these assays are still being validated by the Organization for Economic Cooperation and Development (OECD). Northern blot analysis showed the induction of uterine CaBP-9k mRNA level in response to permethrin as well as co-administration of permethrin with E2. In the uterotrophic assay using 18-day-old female rats, subcutaneous treatments with permethrin (10 to 800 mg/kg) for three days increased relative uterine wet weights, and E2-induced uterine weights. These effects were statistically significant at 800 and 200 mg/kg, respectively. Moreover, permethrin-induced uterine weights were inhibited by the co-administration of ICI 182,780, an antiestrogen. In the Hershberger assay, the administration of permethrin orally to testosterone propionate-treated castrated male rats led to statistically significant reductions in androgen-dependent sex accessory tissue (ventral prostate, seminal vesicles, levator ani and bulbocavernosus muscles, Cowper's gland and glans penis) weights at all doses tested (10, 50 and 100 mg/kg). These results suggest that permethrin might have estrogen-like effects on female rats, but antiandrogen-like effects on males.     

Conflict of estrogenic activity by various phthalates between in vitro and in vivo models related to the expression of Calbindin-D9k

Phthalates are suspected to disrupt the endocrine system, especially through estrogenic effects. In the present study, we investigated the effects of various phthalates and compared them with those of estrogenic compounds that disrupt the female reproductive system. To assess the effects of these phthalates, alteration of the Calbindin-D9k (CaBP-9k) gene was measured as a biomarker because rat CaBP-9k gene carries an estrogen response element (ERE) which is involved in estrogen responsiveness of the gene during the estrous cycle. In this study, phthalates were tested for estrogenic properties in in vitro and in vivo models. First, the E-Screen assay was used to measure the proliferation of MCF-7 cells, a human breast cancer cell line. Treatments with 17beta-estradiol (E2; 9-fold) and 17alpha-estradiol (EE; 9-fold) induced MCF-7 cell proliferation at concentrations of 10(-9) M. Phthalates induced an increase in MCF-7 proliferation at concentration of 10(-6) M up to 10(-4) M. Nbutyl benzyl phthalate (BBP; 6-fold vs. vehicle), dicyclohexyl phthalate (DCHP; 8-fold), 2-ethylhexyl phthalate (DEHP; 6-fold) and di-n-butyl phthalate (DBP; 7-fold) at the concentration of 10(-4) M induced in an increase in MCF-7 proliferation after 6 d of treatment compared to vehicle. However, significant increase in MCF-7 proliferation was induced by diethyl phthalate (DEP). Second, we investigated the expression of CaBP-9k in the uterus of immature rats after oral treatment with BBP, DCHP, DEHP, DBP or DBP (600 mg/kg per day) in this in vivo model, because the immature rat model is highly sensitive to exposure to estrogenic chemicals. None of the phthalates induced the expression of CaBP-9k mRNA and its protein in the neonatal uterus as analysed by Northern and Western blot analyses, respectively. Although phthalates induced an increase in MCF-7 cell proliferation by an estrogenic effect, they could not induce CaBP-9k expression in the in vivo system, suggesting that the assays of estrogenic effects of various phthalates conducted in vitro and in vivo expression of CaBP-9k may produce conflicting results.     

Expression of calbindin-D9k messenger ribonucleic acid in the gastrointestinal tract of dairy cattle

The calcium demands of pregnancy and lactation are known to up-regulate expression of Calbindin-D9k (CaBP-9k) mRNA in the intestines. The gastrointestinal CaBP-9k mRNA expressions has not been studied in dairy cows, which are bound to experience several pregnancies and lactation stages. In this study, the CaBP-9k mRNA expression were examined in the gastrointestinal tract of Holstein dairy cattle by Northern blot analysis. Detectable expression of CaBP-9k mRNA was localized in the proximal portion of the small intestines. These expressions were higher at the most proximal region of the duodenum and gradually decreased distally. The duodenal CaBP-9k mRNA was detected in all dairy cattle from 0.4 to 83.4 months old, but was not detectable in foetuses. There were no significant correlations between the age and the levels of CaBP-9k mRNA expression or between the plasma 1,25-(OH)2D3 concentrations and the levels of CaBP-9k mRNA expression.     

Decreased sperm number and motile activity on the F1 offspring maternally exposed to butyl p-hydroxybenzoic acid (butyl paraben)

Butyl p-hydroxybenzoic acid (butyl paraben, BP) is widely used as a preservative in food and cosmetic products. Routledge et al showed that BP is weakly estrogenic in both in vitro and in vivo (rat uterotrophic) analyses. We investigated whether maternal exposures to BP during gestation and lactation periods affected the development of the reproductive organs of the F1 offspring. Pregnant Sprague-Dawley rats were injected subcutaneously with 100 or 200 mg/kg of BP from gestation day (GD) 6 to postnatal day (PND) 20. In the group exposed to 200 mg/kg of BP, the proportion of pups born alive and the proportion of pups surviving to weaning were decreased. The body weights of female offspring were significantly decreased at PND 49. The weights of testes, seminal vesicles and prostate glands were significantly decreased in rats exposed to 100 mg/kg of BP on PND 49. In contrast, the weights of female reproductive organs were not affected by BP. The sperm count and the sperm motile activity in the epididymis were significantly decreased at doses of 100 and 200 mg/kg of BP. In accordance with the sperm count in the epididymis, the number of round spermatids and elongated spermatids in the seminiferous tubule (stage VII) were significantly decreased by BP. Testicular expression of estrogen receptor (ER)-alpha and ER-beta mRNA was significantly increased in 200 mg/kg of BP treated group at PND 90. Taken together, these results indicated that maternal exposure of BP might have adverse effects on the F1 male offspring.     

Uterine Expression of Epidermal Growth Factor Family During the Course of Pregnancy in Pigs

To stably maintain pregnancy, several genes are expressed in the uterus. In particular, the endometrial expression of genes encoding growth factors appears to play a key role in maternal–foetal communication. The previous studies characterized the endometrial expression kinetics of the genes encoding epidermal growth factor (EGF), its receptor (EGFR), transforming growth factor-alpha (TGF-α), amphiregulin (Areg), heparin-binding (Hb) EGF and calbindin-D9k (CaBP-9k) in pigs during implantation. Here, we further characterized the expression patterns of these molecules during the entire porcine pregnancy. Porcine uteri were collected at pregnancy days (PD) 12, 15, 30, 60, 90 and 110 and subjected to RT-PCR. EGF and EGFR showed similar expression patterns, being highly expressed around implantation and then disappearing. TGF-α and Areg expression levels rose steadily until they peaked at PD30, after which they gradually decreased to PD12 levels. This Areg mRNA expression pattern was confirmed by real-time PCR and similar Areg protein expression patterns were observed. Immunohistochemical analysis of PD60 uteri revealed Areg in the glandular and luminal epithelial cells. Hb EGF was steadily expressed throughout the entire pregnancy, while CaBP-9k was expressed strongly on PD12, and then declined sharply on PD15 before recovering slightly for the remainder of the pregnancy. Thus, the EGF family may play a key role during implantation in pigs. In addition, CaBP-9k may help to maintain uterine quiescence during pregnancy by sequestering cytoplasmic Ca²⁺.     

The biomarker and endocrine disruptors in mammals

The compounds that bind steroid hormone receptors including estrogen receptors (ERs), progesterone receptor (PR) or androgen receptor (AR), and induce or modulate a steroid hormone receptor-mediated response could be defined as endocrine disruptors (EDs). Currently, there are no standard methods to determine whether a chemical is an endocrine disruptor or not. Most results of in vitro and in vivo data are derived from assays that measure estrogenic activity, thus fewer data are available from assays that measure androgenic and progestogenic activities. In this review, we introduce a novel in vivo model to detect EDs using immature rats in the induction of Calbindin-D(9k) (CaBP-9k) mRNA and protein by estrogenic compounds. In addition, we summarize other biomarkers and screening methods for EDs in mammals to describe the usefulness of indicated biomarkers, although mammalian models are very few based on experimental findings.     

牛羊水间充质干细胞对小鼠酒精性肝病的影响

试验旨在分离培养牛羊水间充质干细胞（AF-MSCs），并研究其对酒精性肝病（ALD）小鼠治疗效果以及对肝组织中缺氧诱导因子-1α（HIF-1α）、血管内皮生长因子（VEGF）及Toll样受体4（TLR4）mRNA表达的影响。从4~5月龄雌性胎牛羊水中获取AF-MSCs，进行RT-PCR、免疫荧光及诱导成脂鉴定。将48只ICR小鼠（雄性）随机分为4组：空白对照组（BC组）、模型对照组（MC组）、AF-MSCs组（MC+AF-MSCs组）和水飞蓟宾胶囊（SC）组（MC+SC组），每组12只。除BC组灌胃0.2 mL生理盐水，其余各组均灌胃56度红星二锅头（5 g· kg ^-1，2次· d ^-1），连续4周；第29天MC+AF-MSCs组进行肝外注射Dil标记的AF-MSCs（5×10⁶个·mL ^-1），MC+SC组分2次灌胃SC 2.4 mg（溶于56度红星二锅头）；试验结束后，测定小鼠血清谷丙转氨酶（ALT）、谷草转氨酶（AST）和甘油三酯（TG）活性。HE染色、免疫组化法观察造模情况，Dil示踪AF-MSCs在肝内定植分布；qRT-PCR法检测HIF-1α、VEGF及TLR4基因表达情况。RT-PCR、免疫荧光结果表明，分离得到牛AF-MSCs，且有诱导成脂分化能力。血清学结果显示，MC组ALT、AST和TG活性极显著高于BC组（P<0.01）。组织病理切片显示，MC组肝组织中出现脂肪性变、炎性细胞浸润及肝血窦充血等病理性变化，说明56度红星二锅头成功复制ALD小鼠模型；与MC+SC组相比，MC+AF-MSCs组ALT、AST活性显著降低（P<0.01），肝组织中脂肪性变减轻，肝血窦未见充血，说明AF-MSCs对肝功能的改善比SC效果显著；qRT-PCR结果显示，MC+AF-MSCs组下调HIF-1α、VEGF、TLR4基因的表达量较MC+SC组显著（P<0.01），说明AF-MSCs参与HIF-1α/VEGF信号通路的调控，抑制TLR4表达的效果优于SC；细胞示踪术证明，AF-MSCs定植在病变部位并趋化更多AF-MSCs向炎症部位迁移参与肝组织的修复。综上，本研究成功分离得到牛AF-MSCs，其能够参与调节氧化应激、血管生成及抑制炎性因子的释放，且改善ALD的效果优于SC。     

黄芩苷对大鼠口服非索非那定的药动学影响

为了研究黄芩苷在大鼠体内对非索非那定药动学及P-gp表达的影响,将SD大鼠36只随机分为A、B、C三组,连续灌胃7天,A组给予黄芩苷200mg/kg,B组蒸馏水空白对照,C组维拉帕米药物对照(10mg/kg),第8天灌胃后2小时,各组随机取6只大鼠处死,解剖并迅速取出肝脏、空肠,荧光定量PCR测定各组织P-gp的mRNA表达水平。各组另外6只大鼠灌胃后同时给予非索非那定（30mg/kg）,按时间点连续采集血样,采用高效液相色谱法测定非索非那定血药浓度。结果表明,黄芩苷对非索非那定的吸收有明显促进作用,主要表现在黄芩苷组非索非那定峰浓度(Cmax)比空白对照组增加17.04%（P<0.05）,曲线下面积AUC(0-12)增加19.23%（P<0.05）,黄芩苷减少了大鼠空肠和肝脏P-gp蛋白的表达（P<0.05）。结论：黄芩苷能下调大鼠P-gp表达,增加P-gp底物非索非那定在大鼠体内的生物利用度,是一种P-gp抑制剂。     

Estrogenic effects of genistein on reproductive tissues of ovariectomized gilts

The soybean phytoestrogen genistein has a range of estrogenic actions demonstrated in various species; however, only limited research has been done to investigate its effects in swine. The objective of this study was to characterize the effects of a graded dose of genistein on estrogen-sensitive uterine and cervical tissues in ovariectomized gilts. Thirty-four postpubertal gilts were ovariectomized and assigned randomly to 1 of 6 treatment groups 15 d postovariectomy. Treatment groups received vehicle, estradiol benzoate (2 mg/d), or genistein (50, 100, 200, or 400 mg/d) via intramuscular injection at 12-h intervals for 10 d. Following the treatment period, gilts were euthanized, and uterine and cervical tissues were collected and processed for chemical or histological analysis. Uterine and cervical tissue mass, as indicated by wet, dry, and protein weights and total DNA content (expressed per 100 kg of BW), increased as the dosage of genistein increased (P < 0.001 for each regression). Uterine and cervical wet weights were increased by a dosage of 200 mg of genistein/d (P < 0.001 and P < 0.01, respectively) but not by 100 mg of genistein/d (P = 0.38 and P = 0.14, respectively) compared with those of control gilts. Height of epithelial cells lining the uterine glands and the lumen of uterus and cervix increased when gilts were treated with estradiol benzoate or 400 mg of genistein/d (P < 0.01). When the gilts were treated with estradiol benzoate or 400 mg of genistein/d, immunohistochemical staining demonstrated an increase in the percentage of cells that stained positive for progesterone receptor in the uterine glands and in the cells lining the vaginal cervix (P < 0.05). In gilts treated with 400 mg of genistein/d, the percentage of cells stained positive for proliferating cell nuclear antigen increased in the epithelium of the uterine glands, uterine lumen, and vaginal cervix (P < 0.05). Tissue growth was stimulated by genistein in a dosage-dependent manner, although no dosage of genistein induced a response as great as that of estradiol benzoate. Estrogen-sensitive tissues of the ovariectomized gilt, such as the cervix and uterus, are affected by injection of large dosages of the phytoestrogen genistein. The sensitivity of the uterus of the gilt to estrogenic substances makes it a potential model to examine the impact of environmental endocrine modulators on reproductive tissues.     

Reproductive disorders in pubertal and adult phase of the male rats exposed to vinclozolin during puberty

Vinclozolin (VCZ) is a systemic dicarboximide fungicide with antiandrogenic activity. Reproductive toxicity of VCZ was investigated in male rats exposed to VCZ during puberty. Sprague-Dawley male rats aged with 35 days were assigned to six different groups; negative control, positive control receiving flutamide (100 mg/kg), VCZ (100, 200 and 400 mg/kg), and a combination of VCZ (200 mg/kg) + methyltestosterone (100 mg/kg). The animals were treated with test compounds by oral gavage daily during 35 to 44 days of age. In pubertal rats sacrificed on the next day after final treatment, VCZ or flutamide-treated group showed a decrease in weights of prostate, epididymis, and seminal vesicle, hypertrophy of Leydig cells in the testis, detached debris and sloughed cells in the tubules of the caput epididymis, and an increase in serum testosterone levels. On the other hand, combined treatment of VCZ + methyltestosterone decreased testicular weight, increased seminal vesicle weight, and induced degeneration of spermatocytes. In adult rats sacrificed at five weeks after final treatment, flutamide decreased testicular sperm counts, and VCZ, flutamide and VCZ + methyltestosterone also decreased epididymal sperm counts. In addition, treatment of VCZ (400 mg) or VCZ + methyltestosterone decreased some motion kinematic parameters of sperms including curvilinear velocity, mean angular displacement and lateral head displacement. Flutamide treatment also decreased lateral head displacement. These results indicate that VCZ exposure during pubertal period in male rats causes reproductive disorders in puberty and adulthood.     

葛根素对镉致大鼠血脑屏障损伤的保护效应

为探究葛根素在镉暴露引起大鼠血脑屏障损伤中的保护效应,24只雄性SD大鼠随机分为4组,分别为对照组、葛根素组、镉组、镉与葛根素共处理组.试验期间,每天按200 mg/kg剂量的葛根素(溶解于5 g/L羧甲基纤维素钠)对葛根素组、镉与葛根素共处理组大鼠进行灌胃,同时以相同剂量的5 g/L羧甲基纤维素钠将对照组、镉组大鼠进...     

酵母多糖对环磷酰胺所致免疫损伤大鼠的拮抗作用

为研究酵母多糖(YP)对环磷酰胺(CTX)所致免疫损伤大鼠的拮抗作用,本实验将80只雄性SD大鼠随机分为YP(50 mg/kg)+CTX组、YP(100 mg/kg)+CTX组、YP(200 mg/kg)+CTX组、CTX对照组和正常对照组。YP+CTX组按剂量灌胃并称重,CTX和正常对照组则灌胃给予等量生理盐水,连续给药10 d;在第8 d、9 d,除正常对照组外,其余4组腹腔注射CTX 100 mg/kg。第11 d采血及对相关的免疫器官组织进行检测。结果显示,YP(100 mg/kg)组平均日增重和饲料报酬比正常对照组显著增加(p<0.05);胸腺指数,血清中IgA、IgG、表皮生长因子(EGF)、碱性磷酸酶(AKP)含量及空肠SIgA水平显著(p<0.05)或极显著(p<0.01)高于CTX对照组;结肠壁中前列腺素E2(PGE2)含量与CTX对照组相比显著降低(p<0.05)。以上结果表明,YP能提高大鼠的生长性能;YP对CTX所致免疫损伤具有一定的拮抗保护作用,其中100 mg/kg剂量的YP效果最为显著。     

麦麸阿魏酰低聚糖对敌草快致氧化应激大鼠血浆和组织抗氧化能力的影响

本试验以酿酒酵母和枯草芽孢杆菌作为混合菌种发酵小麦麸皮,通过Amberlite XAD-2柱分离纯化制备麦麸阿魏酰低聚糖(feruloyl oligosaccharides,FOs),探讨麦麸FOs对敌草快(diquat)诱导的大鼠氧化应激是否有缓解作用。试验选用体重相近的断奶雄性大鼠48只,随机分为未攻毒组、攻毒组、攻毒+100 mg/kg BW麦麸FOs组、攻毒+200 mg/kg BW麦麸FOs组、攻毒+300 mg/kg BW麦麸FOs组和攻毒+100 mg/kg BW维生素C组,每组8个重复,每个重复1只鼠,各组大鼠均饲喂相同的商业饲料。麦麸FOs和维生素C配制成水溶液,采用灌胃的方式给予,未攻毒组、攻毒组用生理盐水替代,灌胃体积0.2 mL,连续灌胃15 d。灌胃结束当天,未攻毒组大鼠注射0.3 mL生理盐水,其他5组按0.1 mmol/kg BW的剂量腹腔注射0.3 mL敌草快。敌草快攻毒12 h后取样,分析各组大鼠血浆以及肝脏、肾脏和回肠中总抗氧化能力(T-AOC),过氧化氢酶(CAT)、超氧化物歧化酶(SOD)和谷胱甘肽过氧化物酶(GSH-Px)活性以及谷胱甘肽(GSH)和8-羟基脱氧鸟苷(8-OHd G)的含量。结果显示:1)通过混菌发酵小麦麸皮制备麦麸FOs,利用Amberlite XAD-2柱进行分离纯化,获得的麦麸FOs浓度为0.059 mmol/g。2)腹腔注射敌草快显著降低大鼠血浆中SOD活性和GSH含量(P0.05),显著降低大鼠肝脏中T-AOC,CAT、GSH-Px活性及GSH含量(P0.05),显著降低大鼠肾脏中T-AOC及CAT、SOD活性(P0.05),显著降低大鼠回肠中T-AOC,CAT、GSH-Px活性及GSH含量(P0.05),并显著提高大鼠血浆和各组织中8-OHd G含量(P0.05)。3)在敌草快引起的氧化应激状态下,灌胃一定剂量的麦麸FOs可以显著提高大鼠血浆中SOD(400 mg/kg BW)、GSH-Px活性(100和200 mg/kg BW)以及GSH含量(100和200 mg/kg BW)(P0.05),显著提高大鼠肝脏中T-AOC(100、200和400 mg/kg BW),CAT(200和400 mg/kg BW)、SOD(100、200和400 mg/kg BW)和GSH-Px活性(100、200和400 mg/kg BW)以及GSH含量(100、200和400 mg/kg BW)(P0.05),显著提高大鼠肾脏中T-AOC(400 mg/kg BW),CAT(200 mg/kg BW)和GSH-Px活性(200和400 mg/kg BW)以及GSH含量(400 mg/kg BW)(P0.05),显著提高大鼠回肠中T-AOC(200 mg/kg BW),SOD(400 mg/kg BW)和GSH-Px活性(100、200和400 mg/kg BW)以及GSH含量(100、200和400 mg/kg BW)(P0.05),显著降低血浆和各组织中8-OHd G含量(血浆、肾脏、回肠:100、200和400 mg/kg BW;肝脏:100 mg/kg BW)(P0.05);且灌胃200、400 mg/kg BW麦麸FOs后,大鼠血浆和组织中部分抗氧化相关指标可恢复到正常生理状态水平。综上所述,本试验制备的麦麸FOs可以通过有效提高大鼠血浆和组织中抗氧酶活性和GSH含量,降低DNA氧化应激代谢产物8-OHd G的含量,有效缓解由敌草快诱导产生的氧化应激。     

Effects of the β2 -agonist clenbuterol on testicular steroidogenic acute regulatory protein mRNA expression in adult rats

Ma, J.‐K., Zhu, W.‐J. Effects of the β₂‐agonist clenbuterol on testicular steroidogenic acute regulatory protein mRNA expression in adult rats. J. vet. Pharmacol. Therap. 33 , 558–563. This study was carried out to investigate the effects of clenbuterol (CLB) on the testicular (steroidogenic acute regulatory, StAR) protein mRNA expression in rats. Thirty adult male rats were administered CLB by gavage daily at the doses of 0.4, 2.0 and 18.5 mg/kg bw for 14 days in the subacute experiment, whereas 20 rats received a single treatment with CLB at the doses of 20 and 40 mg/kg bw in the acute experiment and 20 rats were treated with 0.9% NaCl solution as vehicle groups. Testicular tissues were collected and snap‐frozen in liquid nitrogen and stored at ?70 °C until use. The levels of StAR mRNA were detected by RT–PCR. The levels of StAR mRNA were markedly increased (P < 0.05) at both dosages of 20 and 40 mg/kg bw but the effects were not dose‐dependent and the mRNA levels of StAR were returned to near normal level after 7 days of CLB withdrawal, compared with the control animals. In the subacute experiment, CLB induced a dose‐dependent but no statistical significant reduction (P > 0.05) in the expression levels of StAR mRNA, and the mRNA levels were recovered to near normal level in the groups treated with CLB at dosages of 0.4 and 2.0 mg/kg bw/day following a 7‐day withdrawal period, compared with the control animals. The mRNA levels of StAR showed a significant decrease in the groups treated with CLB at the dosage of 18.5 mg/kg bw/day (P < 0.05) after a 1‐ or 7‐day withdrawal period with respect to the control animals. These results demonstrated transient stimulative effects of CLB on testicular StAR mRNA levels and inhibitory effects after treatment with CLB for 14 consecutive days.