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D M Sheehan

Publications and source records attributed to D M Sheehan.

85 records · Page 5Linked to original sources
PubMed1979

Diethylstilbestrol and estradiol binding to serum albumin and pregnancy plasma of rat and human.

The equilibrium binding of diethylstilbestrol (DES) and 17 beta-estradiol (E2) to plasma proteins has been characterized. DES exhibits a 10- to 20-fold greater binding affinity index for bovine serum albumin and rat plasma than E2. As expected, E2 gave high values for binding to plasma from pregnant mice or rats, reflecting the presence of alpha-fetoprotein. DES bound to these samples as it did to bovine albumin and rat plasma. These results suggested that DES ineracts weakly with alpha-fetoprotein. This was verified by Scatchard plots of DES and E2 binding to rat and human pregnancy plasma. High affinity, low capacity binding was demonstrated with E2 but not with DES. The significantly lower binding of DES suggests that increased delivery of DES to the fetus may be at least partially responsible for the transplacental toxicity and carcinogenicity of DES.

Animals↗
PubMed1979

Failure of rotenone to interfere with 17 beta-estradiol action in the rat uterus.

The involvement of rotenone in rat mammary carcinogenesis has been suggested to occur through estrogenic effects. This hypothesis was tested by determining the extent of rotenone inhibition of 17 beta-estradiol binding to the estrogen receptor and of the 17 beta-estradiol-induced uterotrophic response in ovariectomized Sprague-Dawley rats. Estradiol binding to the uterine estrogen receptor in the presence of rotenone was determined by charcoal assay and Scatchard analysis. Additionally, 17 beta-estradiol-receptor interactions were assessed on sucrose density gradients. No inhibition of binding was observed in either assay with ratios of rotenone/17 beta-estradiol in excess of 10,000. Finally, an in vivo approach was used to extend the in vitro data. Silastic capsules containing rotenone or 17 beta-estradiol were implanted in various combinations into eight groups of ovariectomized Sprague-Dawley rats (four rats/group). After five days, uteri were removed and weighed. An analysis of variance revealed that rotenone neither interfered with 17 beta-estradiol-induced uterine weight gain nor displayed any uterotrophic properties by itself. Results from these three procedures demonstrate that rotenone does not act as an estrogen or as an estrogen antagonist. Additionally, there were no other effects attributable to rotenone.

Animals↗
PubMed1976

Effects of estrogen on gene expression in the chick oviduct. Isolation and fractionation of chromatin non-histone proteins.

Non-histones isolated from hen oviduct chromatin have been fractionated by a variety of methods. Chromatin was dissociated in 2 M NaC1, 5 M Urea, 0.1% beta-mercaptoethanol and 0.01 M Tris - HC1, pH 8.3, and the DNA removed by ultracentrifugation. After desalting by gel filtration the chromatin proteins were separated into three distinct fractions by stepwise elution with 0.10 M NaC1, 0.25 M Na C1 and 15% guanidine - HC1 from Bio-Rex 70 columns. Fractions I and II contain only non-histones and Fraction III contains histones plus a small amount of non-histones. Further fractionation of the non-histones was achieved by ammonium sulfate precipitation and DEAE-cellulose chromatography for Fraction I and phosphocellulose chromatography and gel filtration on Bio-Gel A-15 m for Fraction II. The histone and non-histones present in Fraction III were separated by gel filtration on Bio-Gel A-0.5 m. All fractionation methods have been used preparatively with reasonable recoveries of protein (greater than or equal to 60%). The fractions have been characterized by acrylamide gel electrophoresis. The integrity of the histones was maintained during the fractionation procedure indicating that proteolytic degradation was unlikely to have occurred. There was no selective loss of chromatin proteins during the ultracentrifugation and desalting steps and the non-histones were separated into distinct fractions with enrichment of some species not apparent prior to fractionation of the chromatin proteins.

Animals↗
PubMedDate not supplied

Prenatal dexamethasone or stress but not ACTH or corticosterone alter sexual behavior in male rats.

Prenatal maternal stress in rats and mice can demasculinize and feminize the sexual behavior of adult male offspring. Causal mechanisms are unknown, but one attractive hypothesis is that stress activation of maternal adrenal glucocorticoid secretion is the responsible agent. To test this hypothesis, pregnant rats were exposed to a variety of substances which enhance glucocorticoid actions. These included ACTH (20 IU of a gel preparation, SC once daily), corticosterone (CORT; 7 mg/kg SC in oil, three times daily), or dexamethasone (DEX; 0.1 mg/kg, SC once daily). Controls included noninjected dams and a positive stress control group (restraint under bright lights three times daily). All treatments reduced maternal weight gain, DEX most potently. No treatment altered litter size, stillbirths, or sex ratio, but DEX reduced weight at birth, an effect still seen at postnatal day 85. DEX, CORT, and stress reduced male adrenal weight at birth, while DEX and CORT altered sexual differentiation as measured by anogenital distance. Stress impaired adult male sexual performance but not the lordosis quotient following exposure of animals to stud males. DEX affected both measures. No other treatment had any significant effect on sexual behavior. No treatment altered plasma LH levels, either basal or in response to an estrogen challenge in adult gonadectomized males. In adulthood there was no treatment effect on stress reactivity, measured behaviorally or by plasma glucocorticoids. Correlational analysis revealed that weight gain during pregnancy was the single best predictor of subsequent sexual performance. It is concluded that prenatal dexamethasone exposure demasculinizes and feminizes male offspring.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗
PubMedDate not supplied

QSAR models using a large diverse set of estrogens.

Endocrine disruptors (EDs) have a variety of adverse effects in humans and animals. About 58,000 chemicals, most having little safety data, must be tested in a group of tiered assays. As assays will take years, it is important to develop rapid methods to help in priority setting. For application to large data sets, we have developed an integrated system that contains sequential four phases to predict the ability of chemicals to bind to the estrogen receptor (ER), a prevalent mechanism for estrogenic EDs. Here we report the results of evaluating two types of QSAR models for inclusion in phase III to quantitatively predict chemical binding to the ER. Our data set for the relative binding affinities (RBAs) to the ER consists of 130 chemicals covering a wide range of structural diversity and a 6 orders of magnitude spread of RBAs. CoMFA and HQSAR models were constructed and compared for performance. The CoMFA model had a r2 = 0.91 and a q2LOO = 0.66. HQSAR showed reduced performance compared to CoMFA with r2 = 0.76 and q2LOO = 0.59. A number of parameters were examined to improve the CoMFA model. Of these, a phenol indicator increased the q2LOO to 0.71. When up to 50% of the chemicals were left out in the leave-N-out cross-validation, the q2 remained significant. Finally, the models were tested by using two test sets; the q2pred for these were 0.71 and 0.62, a significant result which demonstrates the utility of the CoMFA model for predicting the RBAs of chemicals not included in the training set. If used in conjunction with phases I and II, which reduced the size of the data set dramatically by eliminating most inactive chemicals, the current CoMFA model (phase III) can be used to predict the RBA of chemicals with sufficient accuracy and to provide quantitative information for priority setting.

Animals↗
PubMedDate not supplied

Evaluation of quantitative structure-activity relationship methods for large-scale prediction of chemicals binding to the estrogen receptor.

Three different QSAR methods, Comparative Molecular Field Analysis (CoMFA), classical QSAR (utilizing the CODESSA program), and Hologram QSAR (HQSAR), are compared in terms of their potential for screening large data sets of chemicals as endocrine disrupting compounds (EDCs). While CoMFA and CODESSA (Comprehensive Descriptors for Structural and Statistical Analysis) have been commercially available for some time, HQSAR is a novel QSAR technique. HQSAR attempts to correlate molecular structure with biological activity for a series of compounds using molecular holograms constructed from counts of sub-structural molecular fragments. In addition to using r2 and q2 (cross-validated r2) in assessing the statistical quality of QSAR models, another statistical parameter was defined to be the ratio of the standard error to the activity range. The statistical quality of the QSAR models constructed using CoMFA and HQSAR techniques were comparable and were generally better than those produced with CODESSA. It is notable that only 2D-connectivity, bond and elemental atom-type information were considered in building HQSAR models. Since HQSAR requires no conformational analysis or structural alignment, it is straightforward to use and lends itself readily to the rapid screening of large numbers of compounds. Among the QSAR methods considered, HQSAR appears to offer many attractive features, such as speed, reproducibility and ease of use, which portend its utility for prioritizing large numbers of potential EDCs for subsequent toxicological testing and risk assessment.

Animals↗
PubMedDate not supplied

Hazard assessment of lead.

Exposure to lead (Pb) continues to be a source of concern for the US Food and Drug Administration and other United States federal regulatory agencies. Blood lead levels as low as 10 micrograms/dl have been associated with impaired neurobehavioural and cognitive development and electrophysiological deficits in children and reduced gestational age and birth weight in infants. Blood lead levels of 10 micrograms Pb/dl are also of concern in pregnant women because of exposure to the fetus. Blood lead levels of 30 micrograms Pb/dl have been associated with elevated blood pressure and other adverse effects in adults. Thus, the values of 10 and 30 micrograms Pb/dl represent lowest-observed-effects levels for developing and adult populations, respectively. The ingestion levels that result in these blood levels of concern were estimated to be 60 micrograms Pb/day for children ages 6 years or younger, 150 micrograms Pb/day for children aged 7 years or older, 250 micrograms Pb/day for pregnant women and 750 micrograms Pb/day for adults. Provisional total tolerable intake levels for lead were derived from these blood lead levels for each group by applying the Renwick approach to obtain a tolerable exposure level.

Adult↗
PubMedDate not supplied

Comparative molecular field analysis (CoMFA) model using a large diverse set of natural, synthetic and environmental chemicals for binding to the androgen receptor.

A large number of natural, synthetic and environmental chemicals are capable of disrupting the endocrine systems of experimental animals, wildlife and humans. These so-called endocrine disrupting chemicals (EDCs), some mimic the functions of the endogenous androgens, have become a concern to the public health. Androgens play an important role in many physiological processes, including the development and maintenance of male sexual characteristics. A common mechanism for androgen to produce both normal and adverse effects is binding to the androgen receptor (AR). In this study, we used Comparative Molecular Field Analysis (CoMFA), a three-dimensional quantitative structure-activity relationship (3D-QSAR) technique, to examine AR-ligand binding affinities. A CoMFA model with r2 = 0.902 and q2 = 0.571 was developed using a large training data set containing 146 structurally diverse natural, synthetic, and environmental chemicals with a 10(6)-fold range of relative binding affinity (RBA). By comparing the binding characteristics derived from the CoMFA contour map with these observed in a human AR crystal structure, we found that the steric and electrostatic properties encoded in this training data set are necessary and sufficient to describe the RBA of AR ligands. Finally, the CoMFA model was challenged with an external test data set; the predicted results were close to the actual values with average difference of 0.637 logRBA. This study demonstrates the utility of this CoMFA model for real-world use in predicting the AR binding affinities of structurally diverse chemicals over a wide RBA range.

Androgens↗
PubMedDate not supplied

The effect of teratogens on maternal corticosterone levels and cleft incidence in A/J mice.

It is unknown whether orofacial clefting, one consequence of teratogenic exposure, results from a direct interaction between the teratogen and the embryonic palate, or indirectly from maternal alterations caused by the teratogen. In the current study pregnant A/J mice were exposed to one of three cleft-inducing agents in order to examine the relationship between drug-induced clefting and the response of maternal plasma corticosterone to drug administration. The agents used, haloperidol (HAL), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), or phenytoin (PHT), were administered in teratogenic doses between 0800 and 0930 on gestational day 10 (GD 10). For corticosterone determinations, mice were dosed on GD 10, and blood was collected at 1, 4, 24, or 48 hr after dosing. For fetal evaluation of cleft lip and/or cleft palate, mice were dosed on GD 10 and killed on GD 18. Phenytoin was the most potent inducer of cleft lip and palate and induced a sustained elevation of plasma corticosterone in maternal animals. The other treatments, in order of decreasing potency to induce clefting and/or cause an elevation of corticosterone in plasma were 2,4,5-T > HAL > controls. Correlations between maternal corticosterone levels and clefting incidence were very high at all time points examined; total exposure (area under the curve) was also highly correlated. A linear relationship between drug-induced increases in maternal corticosterone levels and the incidence of clefting in A/J mice was evident. Based on these findings, we believe that increased maternal corticosterone levels may play a role in orofacial clefting in A/J mice.

2,4,5-Trichlorophenoxyacetic Acid↗