Time‐course analysis of pulmonary inflammation induced by intratracheal instillation of nanosized crystalline silica particles in F344 rats

Crystalline silica is an important cause of serious pulmonary diseases, and its toxic potential is known to be associated with its surface electrical properties. However, in vivo data clarifying the relevance of silica's toxic potential, especially its long-term effects, remain insufficient. To investigate the contribution of physico-chemical property including surface potential on the hazard of nanocrystalline silica, we performed single intratracheal instillation testing using five different crystalline silicas in a rat model and assessed time-course changes in pulmonary inflammation, lung burden, and thoracic lymph node loads. Silica-nanoparticles were prepared from two commercial products (Min-U-Sil5 [MS5] and SIO07PB [SPB]) using three different pretreatments: centrifugation (C), grinding (G), and surface dissolving (D). The five types of silica particles-MS5, MS5_C, SPB_C, SPB_G, and SPB_D-were intratracheally instilled into male F344 rats at doses of 0 mg/kg (purified water), 0.22 mg/kg (SPB), and 0.67, 2, or 6 mg/kg (MS5). Bronchoalveolar lavage, a lung burden analysis, and histopathological examination were performed at 3, 28, and 91 days after instillation. Granuloma formation was present in MS5 group at 91 days after instillation, although granuloma formation was suppressed in MS5_C group, which had a smaller particle size. SPB_C induced severe and progressive inflammation and kinetic lung overload, whereas SPB_G and SPB_D induced only slight and transient acute inflammation. Our results support that in vivo toxic potential of nanosilica by intratracheal instillation may involve with surface electrical properties leading to prolonged effect and may not be dependent not only on surface properties but also on other physico-chemical properties.

Time-course comparison of pulmonary inflammation induced by intratracheal instillation of four different nickel oxide nanoparticles in male Fischer rats

Occupational exposure to nickel oxide (NiO) is an important cause of respiratory tract cancer. Toxicity is known to be associated with the dissociated component, i.e. nickel (II) ions. To address the relationship between physicochemical properties, including solubility in artificial lysosomal fluid, of NiO and time-course changes in the pulmonary response, we conducted an intratracheal instillation study in male Fischer rats using four different well-characterized NiO products, US3352 (NiO A), NovaWireNi01 (NiO B), I small particle (NiO C), and 637130 (NiO D). The NiOs were suspended in purified water and instilled once intratracheally into male F344 rats (12 weeks old) at 0 (vehicle control), 0.67, 2, and 6 mg/kg body weight. The animals were euthanized on days 3, 28, or 91 after instillation, and blood analysis, bronchoalveolar lavage fluid (BALF) testing, and histopathological examination were performed. The most soluble product, NiO B, caused the most severe systemic toxicity, leading to a high mortality rate, but the response was transient and surviving animals recovered. The second-most-soluble material, NiO D, and the third, NiO A, caused evident pulmonary inflammation, and the responses persisted for at least 91 days with collagen proliferation. In contrast, NiO C induced barely detectable inflammation in the BALF examination, and no marked changes were noted on histopathology. These results indicate that the early phase toxic potential of NiO products, but not the persistence of pulmonary inflammation, is associated with their solubility.

Kinetics and dissolution of intratracheally administered nickel oxide nanomaterials in rats

BACKGROUND

The toxicokinetics of nanomaterials are an important factor in toxicity, which may be affected by slow clearance and/or distribution in the body.

METHODS

Four types of nickel oxide (NiO) nanoparticles were single-administered intratracheally to male F344 rats at three doses of 0.67-6.0 mg/kg body weight. The rats were sacrificed under anesthesia and the lung, thoracic lymph nodes, bronchoalveolar lavage fluid, liver, and other organs were sampled for Ni burden measurement 3, 28, and 91 days post-administration; Ni excretion was measured 6 and 24 h after administration. Solubility of NiO nanoparticles was determined using artificial lysosomal fluid, artificial interstitial fluid, hydrogen peroxide solution, pure water, and saline. In addition, macrophage migration to trachea and phagosome-lysosome-fusion rate constants were estimated using pulmonary clearance and dissolution rate constants.

RESULTS

The wire-like NiO nanoparticles were 100% dissolved by 24 h when mixed with artificial lysosomal fluid (dissolution rate coefficient: 0.18/h); spherical NiO nanoparticles were 12% and 35% dissolved after 216 h when mixed with artificial lysosomal fluid (1.4 × 10^-3 and 4.9 × 10^-3/h). The largest irregular-shaped NiO nanoparticles hardly dissolved in any solution, including artificial lysosomal fluid (7.8 × 10^-5/h). Pulmonary clearance rate constants, estimated using a one-compartment model, were much higher for the NiO nanoparticles with a wire-shape (0.069-0.078/day) than for the spherical and irregular-shaped NiO nanoparticles (0-0.012/day). Pulmonary clearance rate constants of the largest irregular-shaped NiO nanoparticles showed an inverse correlation with dose. Translocation of NiO from the lungs to the thoracic lymph nodes increased in a time- and dose-dependent manner for three spherical and irregular-shaped NiO nanoparticles, but not for the wire-like NiO nanoparticles. Thirty-five percent of the wire-like NiO nanoparticles were excreted in the first 24 h after administration; excretion was 0.33-3.6% in that time frame for the spherical and irregular-shaped NiO nanoparticles.

CONCLUSION

These findings suggest that nanomaterial solubility differences can result in variations in their pulmonary clearance. Nanoparticles with moderate lysosomal solubility may induce persistent pulmonary inflammation.

Effects of pentobarbital, isoflurane, or medetomidine-midazolam-butorphanol anesthesia on bronchoalveolar lavage fluid and blood chemistry in rats

Bronchoalveolar lavage fluid (BALF) is commonly examined for pulmonary toxicity in animal studies. Two common means of anesthesia before euthanasia and bronchoalveolar lavage in rats are intraperitoneal injection of pentobarbital and inhalation of isoflurane. Medetomidine-midazolam-butorphanol is an alternative anesthesia to pentobarbital for animal welfare; however, the effect of this combination on BALF and blood chemistry is unknown. Here, we compared the effects of anesthesia by intraperitoneal injection of pentobarbital or one of two combinations of medetomidine-midazolam-butorphanol (dose, 0.375-2.0-2.5 or 0.15-2.0-2.5 mg/kg) or by inhalation of isoflurane on BALF and blood chemistry in rats with or without pulmonary inflammation. In BALF, we determined total protein, albumin, lactate dehydrogenase, total cell count and neutrophil count. In serum, we conducted a general chemistry screen. After anesthesia with pentobarbital or isoflurane, there were no significant differences between any of the BALF or blood chemistry parameters with or without inflammation. After anesthesia with either of the combinations of medetomidine-midazolam-butorphanol, lactate dehydrogenase, total cell count, neutrophil count, and almost all of the blood chemistry parameters were comparable with those observed after pentobarbital or isoflurane; however, BALF albumin and serum glucose were significantly increased in rats without inflammation. After the combination of low-dose medetomidine in rats with inflammation, BALF parameters were comparable with those observed after pentobarbital or isoflurane. Our results show that, of the anesthetics examined, inhalation of isoflurane is the most appropriate means of anesthesia when examining BALF or serum for toxicity studies in rats.

Comparison of the local pulmonary distribution of nanoparticles administered intratracheally to rats via gavage needle or microsprayer delivery devices

Intratracheal administration methods are used to conduct toxicological assessments of inhaled nanoparticles (NPs), and gavage needles or microsprayers are common intratracheal delivery devices. The NP suspension is delivered in a liquid state via gavage needle and as a liquid aerosol via microsprayer. The differences in local pulmonary NP distribution (called the microdistribution) arising from the different states of the NP suspension cause differential pulmonary responses; however, this has yet to be investigated. Herein, using microbeam X-ray fluorescence microscopy, we quantitatively evaluated the TiO₂ pulmonary microdistribution (per mesh: 100 μm × 100 μm) in lung sections from rats administered an intratracheal dose of TiO₂ NPs (6 mg kg^-1 ) via gavage needle or microsprayer. The results revealed that: (i) using a microsprayer appears to reduce the variations in TiO₂ content (ng mesh^-1 ) among rats (e.g., coefficients of variation, n = 3, microsprayer vs gavage needle: 13% vs 30%, for the entire lungs); (ii) TiO₂ appears to be deposited less in the right middle lobes than in the rest of the lung lobes, irrespective of the chosen intratracheal delivery device; and (iii) similar TiO₂ contents (ng mesh^-1 ) and frequencies are deposited in the lung lobes of rats administered TiO₂ NPs via gavage needle or microsprayer. This suggests that the physical state of the administered NP suspension does not markedly alter TiO₂ pulmonary microdistribution. The results of this investigation are important for the standardization of intratracheal administration methods. Copyright © 2016 John Wiley & Sons, Ltd.

Effects of dose volume and delivery device on bronchoalveolar lavage parameters of intratracheally administered nano-sized TiO2 in rats

The intratracheal (IT) test is useful for screening the pulmonary toxicity of inhaled materials, including nanomaterials. However, a standard procedure has not yet been authorized internationally, and the effects of different test parameters are unknown. To determine appropriate experimental conditions for the IT test, we intratracheally administered nano-sized TiO₂ to male F344 rats at 3.0 mg/kg body weight by using two delivery devices (gavage needle or microaerosolizer) and dose volumes of 0.5-3.0 mL/kg (gavage needle) or 0.5-2.0 mL/kg (microaerosolizer). We evaluated the pulmonary deposition and interlobar distribution of TiO₂ at both 30 min and 3 days after administration. In addition, the inflammatory components in bronchoalveolar lavage (BAL) fluid were measured 3 days after administration of TiO₂. At dose volumes of 0.5-2.0 mL/kg, the BAL values were comparable regardless of the device used. In addition, pulmonary TiO₂ burden and lobar concentration patterns were equivalent at all combinations of dose volume and delivery device. In conclusion, the acute pulmonary toxicity of nanomaterials can be assessed effectively by using an IT test in which the test agent is provided to rats at a dose volume of 0.5-2.0 mL/kg with either a gavage needle or microaerosolizer.

Categorization of nano-structured titanium dioxide according to physicochemical characteristics and pulmonary toxicity

A potentially useful means of predicting the pulmonary risk posed by new forms of nano-structured titanium dioxide (nano-TiO₂) is to use the associations between the physicochemical properties and pulmonary toxicity of characterized forms of TiO₂. In the present study, we conducted intratracheal administration studies in rats to clarify the associations between the physicochemical characteristics of seven characterized forms of TiO₂ and their acute or subacute pulmonary inflammatory toxicity. Examination of the associations between the physicochemical characteristics of the TiO₂ and the pulmonary inflammatory responses they induced revealed (1) that differences in the crystallinity or shape of the TiO₂ particles were not associated with the acute pulmonary inflammatory response; (2) that particle size was associated with the acute pulmonary inflammatory response; and (3) that TiO₂ particles coated with Al(OH)₃ induced a greater pulmonary inflammatory response than did non-coated particles. We separated the seven TiO₂ into two groups: a group containing the six TiO₂ with no surface coating and a group containing the one TiO₂ with a surface coating. Intratracheal administration to rats of TiO₂ from the first group (i.e., non-coated TiO₂) induced only acute pulmonary inflammatory responses, and within this group, the acute pulmonary inflammatory response was equivalent when the particle size was the same, regardless of crystallinity or shape. In contrast, intratracheal administration to rats of the TiO₂ from the second group (i.e., the coated TiO₂) induced a more severe, subacute pulmonary inflammatory response compared with that produced by the non-coated TiO₂. Since alteration of the pulmonary inflammatory response by surface treatment may depend on the coating material used, the pulmonary toxicities of coated TiO₂ need to be further evaluated. Overall, the present results demonstrate that physicochemical properties may be useful for predicting the pulmonary risk posed by new nano-TiO₂ materials.

Dose-dependent clearance kinetics of intratracheally administered titanium dioxide nanoparticles in rat lung

AEROSIL(®) P25 titanium dioxide (TiO2) nanoparticles dispersed in 0.2% disodium phosphate solution were intratracheally administered to male F344 rats at doses of 0 (control), 0.375, 0.75, 1.5, 3.0, and 6.0 mg/kg. The rats were sacrificed under anesthesia at 1 day, 3 days, 7 days, 4 weeks, 13 weeks, and 26 weeks after administration. Ti levels in various pulmonary and extrapulmonary organs were determined using sensitive inductively coupled plasma sector field mass spectrometry. One day after administration, the lungs contained 62-83% of TiO2 administered dose. Twenty-six weeks after administration, the lungs retained 6.6-8.9% of the TiO2 administered at the 0.375, 0.75, and 1.5 mg/kg doses, and 13% and 31% of the TiO2 administered at the 3.0 and 6.0 mg/kg doses, respectively. The pulmonary clearance rate constants from compartment 1, k1, were estimated using a 2-compartment model and were found to be higher for the 0.375 and 0.75 mg/kg doses of TiO2 (0.030/day for both) than for TiO2 doses of 1.5-6.0 mg/kg (0.014-0.022/day). The translocation rate constants from compartment 1 to 2, k12, were estimated to be 0.015 and 0.018/day for the 0.375 and 0.75 mg/kg doses, and 0.0025-0.0092/day for doses of 1.5-6.0mg/kg. The pulmonary clearance rate constants from compartment 2, k2, were estimated to be 0.0086 and 0.0093/day for doses of 0.375 and 0.75 mg/kg, and 0-0.00082/day for 1.5-6.0 mg/kg doses. Translocation of TiO2 from the lungs to the thoracic lymph nodes increased in a time- and dose-dependent manner, accounting for 0.10-3.4% of the administered dose at 26 weeks. The measured thoracic lymph node burdens were a much better fit to the thoracic lymph node burdens estimated assuming translocation from compartment 1 to the thoracic lymph nodes, rather than those estimated assuming translocation from compartment 2 to the thoracic lymph nodes. The translocation rate constants from the lungs to the thoracic lymph nodes, kLung→Lym, were 0.000037-0.00081/day, and these also increased with increasing doses of TiO2. Although a small amount of TiO2 had translocated to the liver by 3 days after the administration (0.0023-0.012% of the highest dose administered, 6.0 mg/kg), translocation to the other extrapulmonary organs was not detected.

Expression alterations of genes on both neuronal and glial development in rats after developmental exposure to 6-propyl-2-thiouracil

The present study was performed to determine target gene profiles associated with pathological mechanisms of developmental neurotoxicity. For this purpose, we selected a rat developmental hypothyroidism model because thyroid hormones play an essential role in both neuronal and glial development. Region-specific global gene expression analysis was performed at postnatal day (PND) 21 on four brain regions representing different structures and functions, i.e., the cerebral cortex, corpus callosum, dentate gyrus and cerebellar vermis of rats exposed to 6-propyl-2-thiouracil in the drinking water at 3 and 10ppm from gestational day 6 to PND 21. Expression changes of gene clusters of neuron differentiation and development, cell migration, synaptic function, and axonogenesis were detected in all four regions. Characteristically, gene expression profiles suggestive of affection of ephrin signaling and glutamate transmission were obtained in multiple brain regions. Gene clusters suggestive of suppression of myelination and glial development were specifically detected in the corpus callosum and cerebral cortex. Immunohistochemically, immature astrocytes immunoreactive for vimentin and glial fibrillary acidic protein were increased, and oligodendrocytes immunoreactive for oligodendrocyte lineage transcription factor 2 were decreased in the corpus callosum. Immunoreactive intensity of myelin basic protein was also decreased in the corpus callosum and cerebral cortex. The hippocampal dentate gyrus showed downregulation of Ptgs2, which is related to synaptic activity and neurogenesis, as well as a decrease of cyclooxygenase-2-immunoreactive granule cells, suggesting an impaired synaptic function related to neurogenesis. These results suggest that multifocal brain region-specific microarray analysis can determine the affection of neuronal or glial development.

Methacarn as a whole brain fixative for gene and protein expression analyses of specific brain regions in rats

For molecular analysis in anatomically-specific brain regions for rodent studies, it is necessary to establish a fast and accurate procedure for tissue sampling to achieve high integrity and expression fidelity of extracted molecules. The present study was performed to examine suitability of whole brain fixation with methacarn and subsequent tissue sampling using punch-biopsy devices for gene expression analysis in rats. After fixation, each specific region, i.e., hippocampal dentate gyrus, corpus callosum, cingulate cortex or cerebellar vermis was collected, and the integrity and variability of expression data of extracted total RNAs and polypeptides were examined. Methacarn fixation, acetone fixation, and unfixed tissues were compared. Methacarn fixation resulted in high integrity of total RNAs sufficient for conducting global expression analysis and superior in terms of uniformity in the integrity among brain regions to that of acetone fixation. Extracted polypeptide after methacarn fixation revealed similar integrity to that without fixation or with acetone fixation. Methacarn fixation resulted in lower mRNA expression variability between samples than acetone fixation in microarray analysis. The fidelity of polypeptide expression was mostly equivalent between methacarn and acetone fixation in 2-dimensional differential in-gel electrophoresis, although the expression levels of a small number of polypeptides from acetone-fixed tissues were affected. These results suggest that whole brain fixation with methacarn retains advantages for global analyses of mRNAs and polypeptides in rodent studies.

Subacute oral toxicity study of di(2-ethylhexyl)adipate based on the draft protocol for the "Enhanced OECD Test Guideline no. 407"

We performed a 28-day repeated-dose toxicity study of di(2-ethylhexyl)adipate (DEHA) based on the draft protocol of the "Enhanced OECD Test Guideline 407" to investigate whether it has endocrine-mediated properties according to this assay. DEHA was orally administered to SD rats at doses of 0, 40, 200 and 1,000 mg/kg/day for at least 28 days, and disturbance of the estrous cycle and increased ovarian follicle atresia were detected in the 1,000 mg/kg group.

Subacute oral toxicity study of diethylphthalate based on the draft protocol for “Enhanced OECD Test Guideline no. 407”

We performed a 28-day repeated-dose toxicity study of diethylphthalate based on the draft protocol of the "Enhanced OECD Test Guideline 407" to investigate whether it has endocrine-mediated properties according to this assay. Diethylphthalate was orally administered to SD rats at doses of 0, 40, 200, and 1,000 mg/kg/day for at least 28 days, but no endocrine-mediated effects were detected based on any of the parameters examined, suggesting that diethylphthalate does not possess endocrine properties according to this assay.

Comparative study of the uterotrophic potency of 14 chemicals in a uterotrophic assay and their receptor-binding affinity

We performed an immature rat uterotrophic assay of 14 chemicals having various receptor-binding affinities in order to assess the relationship between their uterotrophic potency and receptor-binding affinity. The chemicals tested were phthalic acid di-n-hexyl ester, phthalic acid di-n-amyl ester, phthalic acid di-n-propyl ester, 2-ethylhexyl-p-hydroxybenzoate, 4,4'-biphenol, 4,4'-sulfonyldiphenol, 4,4'-dihydroxydiphenylmethane, 2,4-dihydroxybenzophenone, 4,4'-cyclohexylidenebisphenol, 4-t-butylpyrocatechol, clomiphene citrate, 4,4'-(1,3-phenylenediisopropylidene)bisphenol, p-t-butylphenol, and diallylterephthlate. Two of the 14 chemicals, phthalic acid di-n-propyl ester and diallylterephthlate, exhibited no receptor-binding affinity, and the receptor-binding affinity of phthalic acid di-n-hexyl ester and phthalic acid di-n-amyl ester was lower than that of the other chemicals. Ten of the chemicals showed uterotrophic potency, the exceptions being phthalic acid di-n-propyl ester, diallylterephthlate, phthalic acid di-n-hexyl ester, and phthalic acid di-n-amyl ester. The results of the present study demonstrate that the affinity of the chemicals in the receptor-binding assay correlated well with their potency in the uterotrophic assay except for a few chemicals with very low receptor-binding affinity.

Immature rat uterotrophic assay of 18 chemicals and Hershberger assay of 30 chemicals

We performed an immature rat uterotrophic assay of 18 chemicals and Hershberger assay of 30 chemicals to assess the relationship between the results of two assays. The chemicals tested by the uterotopic assay were 4-n-amylphenol, p-dodecyl-phenol, p-(tert-pentyl)phenol, 4-cyclohexylphenol, 4-(1-adamantyl)phenol, 4,4'-thiobis-phenol, diphenyl-p-phenylenediamine, 4-hydroxyazobenzene, 4-(phenylmethyl)phenol, 4,4'-(hexafluoroisopropylidene)diphenol, 2,2-bis(4-hydroxyphenyl)-4-methyl-n-pentane, 4,4'-(octahydro-4,7-methano-5H-inden-5-ylidene)bisphenol, 4,4'-dihydroxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 4-hydroxybenzophenone, 2,4,4'-trihydroxybenzophenone, testosterone enanthate, and methyltestosterone. The chemicals tested by the Hershberger assay were the 18 chemicals tested in the uterotrophic assay plus the following: 17 alpha estradiol, estrone, equilin, norethindrone, norgestrel, ethynyl estradiol, bisphenol A, bisphenol B, bisphenol F, 4-tert-octylphenol, p-cumyl phenol, and nonylphenol. All chemicals examined in this study were positive in a reporter gene assay for ER-alpha. In the immature rat uterotrophic assay, all chemicals induced uterotrophy and p-(tert-pentyl)phenol, 4,4'-thiobis-phenol, 4-(phenylmethyl)phenol, 4,4'-(hexafluoroisopropylidene)diphenol, 2,2-bis(4-hydroxyphenyl)-4-methyl-n-pentane, 4,4'-(octahydro-4,7-methano-5H-inden-5-ylidene)bisphenol, 4,4'-dihydroxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 4-hydroxybenzophenone, and 2,4,4'-trihydroxybenzophenone exerted both estrogen agonistic effect and reduced the estrogenic effect of ethynylestradiol. In the Hershberger assay, a clear androgen agonistic effect was detected in the androgen derivatives testosterone enanthate and methyltestosterone.

Subacute oral toxicity study of ethynylestradiol and bisphenol A, based on the draft protocol for the "Enhanced OECD Test Guideline no. 407"

We performed a 28-day repeated-dose toxicity study of ethynylestradiol (EE) and bisphenol A (BPA) based on the draft protocol of the "Enhanced OECD Test Guideline no. 407", and assessed the sensitivity of a list of parameters for detecting endocrine-related effects of endocrine disruption. Doses of EE at 0, 10, 50 or 200 microg/kg per day, or BPA at 0, 40, 200 or 1000 mg/kg per day were orally administered to Sprague-Dawley rats. The highest dose of BPA was decreased to 600 mg/kg per day from the second week of administration because a male rat given 1000 mg/kg BPA had died within 1 week with toxic clinical signs. In the assay using EE, the decrease of prostate, seminal vesicle and pituitary weights, increase of the testis weight, atrophic changes of the prostate, seminal vesicle and mammary gland, and degenerative changes in the testes were detected in male rats in the 50 and/or 200 microg/kg groups. In females of the 200 microg/kg group, decrease of the ovary weight, increase of the uterine weight, atrophy of the ovary, hypertrophy or squamous metaplasia of the uterine epithelial cells and mucification in the vagina were observed. Furthermore, diestrous, estrous or the unknown stage was prolonged in the 50 and 200 microg/kg groups of rats. Endocrine-mediated effects of EE were not detected in general observations, hematology, serum biochemistry, or hormonal or spermatological examinations. In the assay using BPA, the diestrous stages were prolonged at the highest dose, but changes related to endocrine effects were not detected in other examinations. Thus, among the parameters tested, the weight of endocrine-linked organs and their histopathological assessment and estrous cycle stage allowed the detection of the endocrine-related effect of EE, whereas the estrous cycle stage was only a useful parameter to detect the effect of BPA.

Comparison of reporter gene assay and immature rat uterotrophic assay of twenty-three chemicals

We performed a reporter gene assay for ERalpha-mediated transcriptional activation and an immature rat uterotrophic assay of 23 chemicals, to study the relationship between these two assays and to examine the usefulness of the reporter gene assay. The chemicals analyzed in the study were as follows: benzophenone, bisphenol A, bisphenol B, bisphenol F, p-cumyl phenol, dibutyl phthalate, dicyclohexylphthalate, dihydrotestosterone, equilin, 17alpha-estradiol, estrone, ethynyl estradiol, genistein, hematoxylin, nonylphenol mixture, 4-n-nonylphenol, norethindrone, norgestrel, octachlorostyrene, 4-n-octylphenol, 4-tert-octylphenol, tributyltin-chloride and zearalenone. To perform the reporter gene assay, HeLa cells were transfected with a rat ERalpha expression construct and an estrogen-regulated luciferase reporter construct. The transcriptional activities of each chemical were tested over concentrations ranging from 10 pM to 10 microM and the EC50, PC50 and PC10 values were calculated. In the immature rat uterotrophic assay, the doses of 21 chemicals, with the exception of dibutyl phthalate and ethynyl estradiol, were 0, 2, 20 and 200 mg/kg; each group consisted of six rats. The doses of dibutyl phthalate and ethynyl estradiol were 0, 40, 200 and 1000 mg/kg per day and 0, 0.2, 2 and 20 microg/kg per day, respectively. In the reporter gene assay, the PC10 values were calculated for 15 chemicals: bisphenol A, bisphenol B, bisphenol F, p-cumyl phenol, dihydrotestosterone, equilin, 17alpha-estradiol, estrone, ethynyl estradiol, genistein, nonylphenol mixture, norethindrone, norgestrel, 4-tert-octylphenol and zearalenone. These chemicals corresponded to the chemicals that tested positive in the uterotrophic assay. The other chemicals were negative in the reporter and uterotrophic assays. Although the EC50 and PC50 values could only be calculated for five and six chemicals, respectively, the PC10 values were shown to be well correlated with the EC50 values by a correlation analysis (R(2)=0.9202). These findings demonstrate that PC10 values are preferable to EC50 and PC50 values for predicting the estrogenic activities of chemicals.