No androgenic/anti-androgenic effects of bisphenol-A in Hershberger assay using immature castrated rats

Several studies have demonstrated that bisphenol A (BPA) exhibited weak estrogenic activity in the 3-day uterotrophic assay using ovariectomized (OVX) and immature rats (Toxicol. Lett. 115 (2000) 231; Regul. Toxicol. Pharmacol. 32 (2000) 118; J. Toxicol. Sci. 26 (2001) 111) and BPA also possessed anti-androgenic activity in in vitro yeast based assays (J. Endocrinol. 158 (1998) 327). To investigate anti-androgenic effects of BPA. a rodent Hershberger assay was carried out using immature Sprague-Dawley male rats. An androgen agonist, testosterone (0.4 mg/kg per day), was administered for 7 consecutive days by subcutaneous (s.c.) injection as a positive control. Additionally, a pure androgen antagonist, flutamide (1, 5. 10 mg/kg per day. oral) was co-administered with testosterone (0.4 mg/kg per day s.c.). BPA was also administered orally with or without testosterone (0.4 mg/kg per day, s.c.) for 7 consecutive days. In the testosterone treated groups, glans penis, seminal vesicles, ventral prostate, and levator ani plus bulbocavernosus muscles (LABC) weights were significantly increased compared with control. However. flulamide dose-dependently inhibited the testosterone-induced re-growth of seminal vesicles, ventral prostate, and LABC, with a significant decrease at flutamide 1.0 mg/kg and above (P<0.05). Serum LH levels were also significantly increased (5 mg/kg and above, P<0.05), but no changes in serum testosterone levels. In contrast, BPA had no effects on the re-growth of seminal vesicles, ventral prostate and LABC induced by testosterone, and no significant differences were observed in serum LH and testosterone levels. In summary, the Hershberger assay could be a sensitive method for detecting androgenic or anti-androgenic chemicals, but BPA did not exhibit any androgenic or anti-androgenic activities in Hershberger assay.     

Androgen receptor antagonism by the organophosphate insecticide fenitrothion.

Organophosphate insecticides represent one of the most widely used classes of pesticides with high potential for human exposure in both rural and residential environments. We investigated the interaction of the organophosphothioate pesticide fenitrothion (O,O-dimethyl O-(4-nitro-m-tolyl) phosphorothioate) with the human androgen receptor (AR). Fenitrothion blocked dihydrotestosterone-dependent AR activity in a concentration-dependent and competitive manner in HepG2 human hepatoma liver cells transiently transfected with human AR and an AR-dependent luciferase reporter gene. Schild regression analysis yielded an equilibrium dissociation constant value of 2.18 x 10(-8) M. To determine the antiandrogenic potential of fenitrothion in vivo, 7-week-old castrated Sprague-Dawley rats were dosed once a day for 7 days with testosterone propionate (50 microg/day, sc) plus gavage doses of either corn oil vehicle or fenitrothion (15 or 30 mg/kg/day). An additional group of rats was given testosterone propionate and flutamide (50 mg/kg/day). Motor activity and acetylcholinesterase activity in whole blood and brain were also assessed. Both fenitrothion and the reference antiandrogen flutamide caused significant decreases in the ventral prostate, seminal vesicle, and levator ani plus bulbocavernosus muscles tissue weights. In contrast, blood acetylcholinesterase activity, a standard biomarker of organophosphate poisoning, was only inhibited at the higher dose of fenitrothion (30 mg/kg). Our results demonstrate that fenitrothion is a competitive AR antagonist, comparable in potency to the pharmaceutical antiandrogen flutamide and more potent, based on in vitro assays, than the known environmental antiandrogens linuron and p,p'-, 2,2-bis(p-hydroxyphenyl)-1,1-dichloroethylene ( p,p'-DDE).     

Development of a stickleback kidney cell culture assay for the screening of androgenic and anti-androgenic endocrine disrupters

Issues raised by the presence in the environment of chemicals able to mimic or antagonize the action of androgenic hormones are of growing concern. Here we report the development of a novel in vitro test for the screening of (anti-)androgenic chemicals, based on primary cultures of stickleback kidney cells that produce a protein, the spiggin, in response to androgenic stimulation. Cell spiggin content was measured by ELISA. Comparison between cell cultures from quiescent males, photoperiodically stimulated males, control females and dihydrotestosterone (DHT)-primed females led to the selection of cell cultures from DHT-primed females for the development of a standardized protocol. 48h of treatment with androgens proved to be sufficient to induce concentration-dependent increase in spiggin cell content with a high sensitivity. DHT induced a significant spiggin increase at 10(-12)M, while testosterone (T) and the teleost specific androgen 11-ketotestosterone (11-KT) had a significant effect at 10(-10)M. Maximal responses were obtained with 10(-8)M DHT and 10(-6)M T and 11-KT. This indicates a higher sensitivity to DHT than to T and 11-KT, in agreement with previous data on stickleback kidney androgen receptor affinity. No effect was observed with other steroids or thyroid hormone, indicating the androgen specificity of the test. The anabolic steroid 17beta-Trenbolone (TB) was able to stimulate spiggin synthesis in a concentration-dependent manner with a significant effect at a concentration as low as 10(-10)M, and a maximal effect at 10(-6)M. The synthetic human androgen receptor antagonist, flutamide had no effect alone, but concentration-dependently inhibited the stimulatory effect of 10(-8)M 11-KT with a complete inhibition at 10(-6)M flutamide. This cell culture system provides an innovative tool for the rapid and sensitive screening of androgenic and anti-androgenic properties of environmental contaminants.     

Chlropyrifos-methyl shows anti-androgenic activity without estrogenic activity in rats

Chlorpyrifos-methyl (CPM), an organophosphate insecticide, widely used for grain storage and agriculture, has been suspected as endocrine disrupter by a few in vitro studies. This study was performed to investigate the (anti-) estrogenicity and (anti-) androgenicity of CPM in vivo using immature rat uterotrophic assay and rat Hershberger assay. CPM with or without 17beta-estradiol were administered to 20 days old female rats to investigate its (anti-) estrogenic activity. Uterine and vaginal weight, uterine epithelial cell height were not affected by the treatment of CPM (2, 10, 50, 250 mg/kg). CPM 250 mg/kg potentiated relative vagina weight in 17beta-estradiol treated immature female rats without any changing of uterine weight. Relative liver weight was increased with decrease of body weight by CPM 250 mg/kg treatment. Uterine cell proliferation tested with bromodeoxyuridine labeling index was not observed in CPM treated rats. CPM with or without testosterone propionate were administered to castrated rat of 51 days old for 10 days to investigate the (anti-)androgenic activity,. The weight of relative and absolute androgen-dependent accessory sex organs; seminal vesicle with coagulating glands (SV/CG), ventral prostate gland (VP), glans penis (GP), levator ani plus bulbocarvernosus muscle (LABC) and Cowper's gland (CG,) were unchanged by the treatment of CPM alone. While CPM induced the increase of relative adrenal gland weight, CPM 50mg/kg decreased the weights of CV/CG, VP, CG and LABC without change of GP without changing of GP when it was treated with TP. In conclusion, CPM dose not show estrogenic and anti-estrogenic activity in immature female rats, but it represents anti-androgenic activity by inhibition of the TP-stimulated increase of the weight of accessory sex organs.     

Pulmonary toxicity of the insecticide fenitrothion in the rat following a single field exposure

The pulmonary toxicity of the organophosphorus insecticide fenitrothion was evaluated following a single exposure of rats to the field formulation, at the site of an aerial spraying. Four groups of 40 Sprague-Dawley rats (including a control), set in wood enclosures, were placed under the aerial lines of the spraying aircraft. The degree of exposure was monitored at the ground level by air sampling and visual evidence of droplet activity deposition. Plasma pseudocholinesterase activity and pulmonary alveoli ultrastructure were used as indices to the fenitrothion exposure. Rat lungs were examined under light and electron microscopy at days 3, 7, 21, 60 and 180 after the exposure. Although a few signs of toxic lung injury were observed at days 3 and 7 there was no cholinergic crisis nor an effect on the pseudocholinesterase activity within 12 h in the exposed animals, when compared with controls. The alveolar toxic reaction was limited to small and discrete foci, and was entirely reversible within a period of 2 months. On a morphological basis it is thus concluded that a single field exposure to fenitrothion did not induce any permanent change in the alveolar area of the rat lung.     

Effects of the organophosphorus insecticide fenitrothion on growth in five freshwater species of phytoplankton

The acute toxicity of the insecticide fenitrothion was measured using four freshwater algae (Chlorella saccharophila, Chlorella vulgaris, Scenedesmus acutus, and Scenedesmus subspicatus) and one cyanobacteria (Pseudanabaena galeata). Insecticide concentrations eliciting 50% growth reduction over 96 hr (EC50) ranged from 0.84 to 11.9 mg/L. Fenitrothion was more toxic than other pesticides studied with the same algal species such as chlorsulfuron, molinate, and pyridaphenthion. The transformation of effective concentrations of fenitrothion and other pesticides obtained from toxicity measurements into percent of the saturation level in water is used as a first evaluation of potential hazard to aquatic systems. The insecticides fenitrothion and pyridaphenthion were less hazardous than the herbicides atrazine, benthiocarb, cinosulfuron, chlorsulfuron, methyl-bensulfuron, and molinate. The two species of Chlorella and the cyanobacterium Pseudanabaena were more tolerant to fenitrothion than the two species of Scenedesmus.     

The uptake and in vivo metabolism of the organophosphate insecticide fenitrothion by the blue crab, Callinectes sapidus

Callinectes were exposed to [14C]fenitrothion at a level of 5.2 micrograms/liter in either 22 degrees C, 34 ppt; 22 degrees C, 17 ppt; or 17 degrees C, 34 ppt seawater. Uptake from the water, as measured by a decrease in fenitrothion, and the distribution of radioactivity throughout the Callinectes were determined. The nature of radiolabeled metabolites in the water and hepatopancreas was also determined. Fenitrothion was absorbed more rapidly from the water at the higher salinity and temperature. Radioactivity was detected in all the organs assayed by 24 hr postexposure, though the levels increased in most tissues throughout the experiment. The highest concentrations of radioactivity were found in the hepatopancreas and stomach. The metabolites which were detected in the water and liver indicate that Callinectes metabolize fenitrothion by oxidation of the phosphorothioate to a phosphate to yield fenitrooxon. The presence of aminofenitrothion and 3-methyl-4-aminophenol shows that reduction of the nitro group to an amino group also occurs. The isolation of desmethyl forms of fenitrooxon and fenitrothion as well as 3-methyl-4-nitrophenol indicates that hydrolysis of both the P-O-aryl and P-O-alkyl bonds occurred. Glycoside and sulfate conjugates of both phenols were inferred in the hepatopancreas. Higher levels of fenitrooxon and lower levels of desmethyl fenitrothion were detected in the 34 ppt seawater than in the 17 ppt seawater. The 5 degrees C differential had no significant effect on the nature and concentrations of metabolites detected in the seawater.     

Possible oestrogenic and anti-androgenic effects in rats treated with the oral hypoglycaemic agents tolbutamide and acetohexamide

Tolbutamide has an oestrogenic activity; when administered in four oral daily doses of 125, 250 and 500 mg/kg to ovariectomized young rats, it significantly increased their uterine weight. Tolbutamide, when administered in five oral daily doses to castrated young male rats, decreased the weight of the prostatic tissue; the effect was significant with a dose of 250 mg/kg. Acetohexamide in oral doses of 125, 250 and 500 mg/kg, had no significant effect either on the prostatic or the uterine weight.     

Morphological abnormalities during early-life development of the estuarine mummichog, Fundulus heteroclitus, as an indicator of androgenic and anti-androgenic endocrine disruption

We tested the hypothesis that gross morphological abnormalities are a sensitive indicator of exposure to waterborne androgenic and anti-androgenic compounds during embryonic, larval and juvenile stages of development in the common estuarine killifish, the mummichog (Fundulus heteroclitus; Pisces: Cyprinodontidae). Static exposures with daily renewal were carried out with 10-100,000 ng/L of the androgen agonist, 17alpha-methyltestosterone (MT), or the androgen antagonist, cyproterone acetate (CA), for 60 days post-fertilization (PF) in duplicate exposures. Measured concentrations were 78.4-155.8% of nominal concentrations for MT and 13.5-168.1% for CA. No dose-related or consistent effects of MT or CA were observed before hatch. In 60 days PF juveniles, incidence of skeletal abnormalities (scoliosis, lordosis, head, facial and fin), soft tissue abnormality (anal swelling) and hemorrhaging were significantly increased by MT but only at high concentrations (> or =1000 ng/L). The 10,000 and 100,000 ng/L concentrations of MT produced a wider range of abnormalities than 1000ng/L. Over 90% of fish exposed to 10,000 or 100,000 ng/L were abnormal with an average of over 3.5 abnormalities per fish. CA did not increase the incidence of any type of abnormality. Survival of juveniles to the end of the exposure was reduced by MT at concentrations of 1000 ng/L and greater in the first experiment and at concentrations of 10,000 ng/L and greater in the second experiment. Juvenile length was reduced by high concentrations of MT (> or =10,000 ng/L) in the first experiment and by most concentrations in the second experiment. We conclude that morphological abnormalities in early-life stages of mummichogs are not a sensitive indicator of exposure to androgenic or anti-androgenic waterborne EDSs at environmentally relevant concentrations.     

Evaluation of anti-androgenic activity of di-(2-ethylhexyl)phthalate

DEHP is a widely used platiciser in the manufacture of PVC-based materials. It is known to disrupt the reproductive tract development in male rats. We have performed the Hershberger assay with DEHP on an immature castrated rat model to check if DEHP antagonise the testosterone propionate androgenic effect on the accessory sex organs development. DEHP significantly decreased the BC/LA muscles, the prostate, and the seminal vesicles relative weights from 100, 200, and 400 mg/kg bw/day, respectively. DEHP increased the liver relative weight from 100 mg/kg bw/day. A study was also performed on MDA-MB453 cell line stably transfected with pMMTVneo-Luc with DEHP and its major metabolites (MEHP and metabolites VI and IX) to identify anti-androgenic activity. Neither DEHP nor MEHP antagonised DHT activity in the MDA-MB453 transfected cells. In contrast, metabolites VI and IX were anti-androgenic in vitro. DEHP appeared not to be a 5alpha-reductase inhibitor and acted in an independent mechanism from the testicular production in the young rat.     

Minoxidil does not possess androgenic activity

Minoxidil is a potent antihypertensive vasodilator. One of the side effects of minoxidil is hirsutism. Therefore the hypothesis was tested whether minoxidil has androgenic effects. The weights of seminal mice vesicles, organs with a high sensitivity to androgens, are widely used as a sensitive bioassay for testing androgenic activity. Our results demonstrated that minoxidil in relatively high doses did not produce any significant changes in the weight of seminal vesicles of castrated mice. We conclude that minoxidil in this experimental model does not have any androgenic properties.     

Estrogenic and anti-androgenic activity of nitrophenols in diesel exhaust particles (DEP)

We recently isolated 4-nitrophenol, 2-methyl-4-nitrophenol, 3-methyl-4-nitrophenol, and 4-nitro-3-phenylphenol from diesel exhaust particles (DEP) and identified them as vasodilators. Because these compounds are alkylphenolic derivatives that might mimic hormones, we evaluated their estrogenic activity by human estrogen receptor (hER)-yeast screen assay. All of these nitrophenol derivatives except 2-methyl-4-nitrophenol exhibited estrogenic activity. Some estrogenic compounds are also anti-androgenic, so we measured the anti-androgenic activity of the same compounds by human androgen receptor (hAR)-yeast screen assay. We found anti-androgenicity in all four nitrophenols. Nitrophenols in DEP possess not only vasodilatory activity but also estrogenic and anti-androgenic activity.     

Evaluation of a 5-day Hershberger assay using young mature male rats: methyltestosterone and p,p'-DDE, but not fenitrothion, exhibited androgenic or antiandrogenic activity in vivo

A 5-day Hershberger assay using young mature male rats to detect compounds interfering with androgen receptor (AR)-mediated mechanisms was evaluated for ability to identify p,p'-DDE (a weak AR antagonist) and methyltestosterone (MT, an AR agonist). Fenitrothion, an organophosphate pesticide, was also evaluated in this validated assay. Castrated male Crj:CD(SD)IGS rats (1 week after castration, 11 weeks of age) were subjected to experiments. To determine a suitable value of testosterone propionate (TP) as a reference androgen for detection of antiandrogenic chemicals, castrated male rats were treated daily with TP (0, 0.06, 0.25, 1, 4, or 16 mg/kg/day, s.c.). TP produced increases in weights of ventral prostate, seminal vesicles and levator ani plus bulbocavernosus muscles. Serum androgen level measured by RIA kit (mostly TP) were elevated in a dose-related manner, while the weights of organs with 1 mg/kg/day of TP were nearly equivalent to the maximum responses (i.e., sub-maximal). One hundred mg/kg/day of p,p'-DDE significantly attenuated TP 0.1 mg/kg-induced increases in weights of seminal vesicles and muscles, and TP 1 mg/kg-induced increases in weights of ventral prostate, seminal vesicles and muscles, but did not affect the weight of these organs in either TP 16 mg/kg-treated or intact rats, demonstrating that the dose range of 0.1-1 mg/kg TP is suitable for reference androgen. Oral treatment with 100 mg/kg of MT increased the weights of ventral prostate, seminal vesicles and muscles as strongly as did subcutaneous injection of 1 mg/kg of TP. These findings demonstrate that the 5-day Hershberger assay using young mature as well as immature male rats is a sensitive and valid short-term screening method for the detection of chemicals interfering with AR-mediated mechanisms. To determine whether fenitrothion interferes with AR-mediated mechanisms in vivo, fenitrothion (0, 0.75, 1.5 or 3 mg/kg/day) was administered by gavage for 5 days to castrated rats for androgenicity, or to castrated rats treated with 1 mg/kg TP for antiandrogenicity. Treatment with fenitrothion had no adverse effects on clinical signs, body weight, or liver or kidney weights, but cholinesterase activities in the brain and erythrocytes were significantly suppressed by fenitrothion to, respectively, 77-81% and 66-67% of control levels. In the antiandrogenicity experiment, serum androgen levels of TP-treated, castrated rats did not differ among groups. Treatment with 100 mg/kg of p,p'-DDE as a positive control again significantly attenuated TP-induced increases in weights of the ventral prostate and seminal vesicles, while fenitrothion had no effect on the weights of any organs. In the androgenicity experiment, treatment with 100 mg/kg of MT significantly increased weights of ventral prostate, seminal vesicles and muscles, but fenitrothion had no effects on the weights of any of these organs. These findings yield no evidence that fenitrothion interferes with AR-mediated mechanisms in vivo, consistent with the result of several toxicological bioassays.     

Oestrogenic and androgenic activity of triclosan in breast cancer cells

As a consequence of its widespread use as an antimicrobial agent in consumer goods, triclosan has become distributed ubiquitously across the ecosystem, and recent reports that it can cause endocrine disruption in aquatic species has increased concern. It is reported here that triclosan possesses intrinsic oestrogenic and androgenic activity in a range of assays in vitro which could provide some explanation for the endocrine disrupting properties described in aquatic populations. In terms of oestrogenic activity, triclosan displaced [(3)H]oestradiol from oestrogen receptors (ER) of MCF7 human breast cancer cells and from recombinant human ER alpha/ER beta. Triclosan at 10(-5) m completely inhibited the induction of the oestrogen-responsive ERE-CAT reporter gene in MCF7 cells by 10(-10) m 17beta-oestradiol and the stimulation of growth of MCF7 human breast cancer cells by 10(-10) m 17beta-oestradiol. On its own, 1 microm triclosan increased the growth of MCF7 cells over 21 days. Triclosan also had androgenic activity. It displaced [(3)H]testosterone from binding to the ligand binding domain of the rat androgen receptor (AR). Triclosan was able to inhibit the induction of the androgen-responsive LTR-CAT reporter gene in S115 mouse mammary tumour cells by 10(-9) m testosterone and in T47D human breast cancer cells by 10(-8) m testosterone at concentrations of 10(-7) m and 10(-6) m, respectively. Triclosan at 2 x 10(-5) m antagonized the stimulation of the growth of S115+A mouse mammary tumour cells by 10(-9) m testosterone. The finding that triclosan has oestrogenic and androgenic activity warrants further investigation in relation to both endocrine disruption of aquatic wildlife and any possible impact on human health.     

Serotonin-1A receptor activity and expression modulate adolescent anabolic/androgenic steroid-induced aggression in hamsters

Repeated high dose (5.0 mg/kg) anabolic/androgenic steroid exposure during adolescence stimulates offensive aggression in male Syrian hamsters. These studies examined whether anabolic/androgenic steroid-induced aggression was regulated by the activity and expression of serotonin (5HT) type-1A receptors. In a first experiment, adolescent male hamsters were treated with a mixture of anabolic/androgenic steroids and then scored for offensive aggression in the absence or presence of the selective 5HT1A receptor agonist R(+)-8-OH-DPAT (0.1-0.6 mg/kg). Adolescent anabolic/androgenic steroid-treated hamsters displayed high levels of offensive aggression that could be reversed by enhancing the activity of 5HT1A receptors. The agonist R(+)-8-OH-DPAT dose-dependently reduced the steroid-induced aggressive response, with significant reductions in aggression observed at 0.1-0.3 mg/kg. In a second set of experiments, adolescent hamsters were administered anabolic/androgenic steroids or vehicle and then examined for 5HT1A receptor localization and expression in regions of the brain important for aggression control. Hamsters treated with anabolic/androgenic steroids showed significant decreases in 5HT1A receptor-immunoreactive staining and protein levels in the anterior hypothalamus (i.e., a brain region central to the control of offensive aggression in hamsters) with no concomitant decrease in the number of 5HT1A receptor-expressing neurons. Together, these data support a role for site-specific down-regulation of 5HT1A receptor activity in adolescent anabolic/androgenic steroid-induced aggression.     

Effects of in utero exposure to the organophosphate insecticide fenitrothion on androgen-dependent reproductive development in the Crl:CD(SD)BR rat.

Fenitrothion [0,0-dimethyl-O-(4-nitro-m-tolyl) phosphorothioate] is an organophosphate insecticide that has been shown to have antiandrogenic activity using in vitro and in vivo screening assays. Studies were performed to evaluate the ability of fenitrothion to disrupt androgen-dependent sexual differentiation in the male rat. Pregnant Crl:CD(SD)BR rats were administered fenitrothion by gavage at 0, 5, 10, 15, 20, or 25 mg/kg/day ( n = 6-11/group) from gestation day (GD) 12 to 21. Maternal toxicity was observed in the dams treated with 20 and 25 mg fenitrothion/kg/day based on muscle tremors and decreases in body weight gain from GD 12 to 21. Fetal death was increased in the 20 and 25 mg/kg/day exposure groups, as evidenced by a decrease in the proportion of pups born alive. Androgen-mediated development of the reproductive tract was altered in male offspring exposed in utero to maternally toxic levels of fenitrothion (25 mg/kg/day), as evidenced by reduction in anogenital distance on postnatal day (PND) 1 and retention of areolae on PND 13. However, these effects were only transient, and there were no indications of abnormal phenotypes or development of androgen-dependent tissues on PND 100. At the dose levels evaluated in this study, fenitrothion was only weakly antiandrogenic in vivo compared with other androgen receptor antagonists such as flutamide, linuron, and vinclozolin. Based on observed fetotoxicity at 20 mg/kg/day, the lowest observed adverse effect level (LOAEL) for developmental effects can be lowered from 25 to 20 mg/kg/day.     

Application of protein expression profiling to screen chemicals for androgenic activity

Protein expression changes can be used for detection of biomarkers that can be applied diagnostically to screen chemicals for endocrine modifying activity. In this study, surface enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF-MS) coupled with a short term fish assay was used to investigate changes in plasma protein expression as a means to screen chemicals for androgenic activity. Adult gravid female sheepshead minnows (Cyprinodon variegatus) were placed into separate aquaria for seawater control, ethanol solvent control, and the following androgen agonist treatments at 5.0μg/L: dihydrotestosterone (DHT), methyldihydrotestosterone (MDHT), testosterone (T), methyltestosterone (MT) and trenbolone (TB). Treatments of 0.6μg/L endosulfan and 40μg/L chlorpyrifos (CP) served as non-androgenic negative stressor controls. Test concentrations were maintained using an intermittent flow-through dosing apparatus supplying exposure water at 20L/h. Fish were sampled at 7 days, the plasma diluted, processed on weak cation exchange CM10 ProteinChip arrays and analyzed. Spectral processing resulted in 249 individual m/z peak clusters for the androgen exposed fish. Partial least squares-discriminant analysis was used to develop an androgen-responsive model using sample spectra from exposures with DHT and unexposed solvent control fish as the training set. The androgen classification model performed with ≥79% specificity (% true negative) and ≥70% sensitivity (% true positive) for non-aromatizable androgens. The aromatizable androgens T and MT were classified as androgenic with specificities of 42 and 79%, respectively. The reduction in sensitivity observed with T is thought to be caused by its metabolic conversion to an estrogen by aromatase. The results of these studies show diagnostic plasma protein expression models can correctly classify chemicals by their androgenic activity using a combination of high throughput mass spectrometry and multivariate approaches.     

Effects of fenitrothion and carbaryl on Xenopus laevis development

When Xenopus laevis embryos were treated with fenitrothion, a substantial proportion failed to survive to hatching only when the concentration approached saturation. However, after exposure to 10 ppm of fenitrothion, most were abnormal and did not survive past feeding stage. Different embryonic stages were not equally sensitive to fenitrothion and the greatest sensitivity was observed at gastrulation. The most common visible abnormalities were altered body shape, including microcephaly, and edema. Internally, abnormalities of the heart, spinal cord and notochord were common. Though carbaryl was toxic at somewhat lower concentrations, carbanyl-induced abnormalities were less severe. In particular, cardiac malformation were less extreme. Recently hatched tadpoles were less sensitive to carbaryl than the embryos, but were more sensitive to fenitrothion. However, with both compounds, the effects were seen only at concentrations higher than would normally be expected in the environment after spraying.     

Mutagenicity of the C-nitroso analog of fenitrothion

The chemicals fenitrothion, nitroso fenitrothion, amino fenitrothion and 3-methyl-4-nitrophenol were tested for mutagenicity to Salmonella typhimurium strains TA98 and TA100, both in the presence and absence of rat liver S-9 mix. The strong mutagenicity of nitroso fenitrothion to both strains either in the presence or absence of S-9 mix contrasted with the observation that fenitrothion displayed no mutagenicity in these tester strains. The results suggest that the normal nitroreductases present in TA98 and TA100 cannot metabolize fenitrothion to a mutagenic metabolite. This inability of the tester strains to effect partial nitroreduction results in the failure of this screening system to predict the potential genotoxicity of this pesticide.