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Biomedical subjects

V L Davis

Publications and source records attributed to V L Davis.

16 recordsLinked to original sources
PubMed1997

Accelerated onset of uterine tumors in transgenic mice with aberrant expression of the estrogen receptor after neonatal exposure to diethylstilbestrol.

The role of estrogen and the estrogen receptor (ER) in the induction and promotion of tumors was investigated by using transgenic MT-mER mice, which overexpress the ER. It was hypothesized that because of this abnormal expression of the ER, the reproductive-tract tissues of the MT-mER mice may be more susceptible to tumors after neonatal exposure to the potent synthetic estrogen diethylstilbestrol (DES). Normally non-estrogen responsive tissues that may have expressed ER as a result of the transgene were also studied for DES-induced tumors. Wild-type and MT-mER littermates were treated with 2 micrograms/pup/d DES 1-5 d after birth and then killed at 4, 8, 12, and 18 mo of age. The DES-treated MT-mER mice demonstrated a significantly higher incidence of uterine adenocarcinoma at 8 mo (73%) than the DES-treated wild-type mice (46%). The tumors of the MT-mER mice were often more aggressive than those in the wild-type animals. These tumors were also preceeded at 4 mo by a significantly higher incidence of the preneoplastic lesion atypical hyperplasia in the MT-mER mice (26% compared with 0% in the wild-type mice). Other DES-induced abnormalities were observed at equal rates in the wild-type and MT-mER mice. Although no tumors were observed in untreated wild-type females, a single untreated MT-mER female had uterine adenocarcinoma at 18 mo. These data indicate that the level of ER present in a tissue may also be a determining factor in development of estrogen-responsive tumors.

Adenocarcinoma↗
PubMed1996

Assessing environmental chemicals for estrogenicity using a combination of in vitro and in vivo assays.

Because of rampant concern that estrogenic chemicals in the environment may be adversely affecting the health of humans and wildlife, reliable methods for detecting and characterizing estrogenic chemicals are needed. It is important that general agreement be reached on which tests to use and that these tests then be applied to the testing of both man-made and naturally occurring chemicals. As a step toward developing a comprehensive approach to screening chemicals for estrogenic activity, three assays for detecting estrogenicity were conducted on 10 chemicals with known or suspected estrogenic activity. The assays were 1) competitive binding with the mouse uterine estrogen receptor, 2) transcriptional activation in HeLa cells transfected with plasmids containing an estrogen receptor and a response element, and 3) the uterotropic assay in mice. The chemicals studied were 17 beta-estradiol, diethylstilbestrol, tamoxifen, 4-hydroxytamoxifen, methoxychlor, the methoxychlor metabolite 2,2-bis(p-hydroxyphenyl)-1,1,1-trichloroethane (HPTE), endosulfan, nonylphenol, o,p'-DDT, and kepone. These studies were conducted to assess the utility of this three-assay combination in the routine screening of chemicals, or combinations of chemicals, for estrogenic activity. Results were consistent among the three assays with respect to what is known about the estrogenic activities of the chemicals tested and their requirements for metabolic activation. By providing information on three levels of hormonal activity (receptor binding, transcriptional activation, and an in vivo effect in an estrogen-responsive tissue), an informative profile of estrogenic activity is obtained with a reasonable investment of resources.

Animals↗
PubMed1996

Functional outcome measures for knee dysfunction assessment.

Maximizing the functional abilities of the individual is the primary objective of any therapeutic intervention. Functional outcome data are valuable to those involved in the care of the athlete because such data provides information that helps facilitate the clinical decision-making process and, therefore, helps insure a safe and efficient return to athletics. Functional outcome measures also provide useful data for assessing therapeutic intervention efficacy. The clinician/researcher must consider various factors when selecting an appropriate outcome measure, such as: the patient population, pathology, specific test parameters, psychometric properties, and practicality of the measure. The primary purpose of this paper is to provide the reader with guidelines for either assessing existing measures or developing new measures of functional outcomes for use in clinical practice and research.

Journal Article↗
PubMed1995

Interrater reliability of isokinetic measures of knee flexion and extension.

The purpose of this investigation was to determine the interrater reliability of peak torque and total work values obtained with isokinetic measures of knee flexion and extension. Eight male and eight female students were evaluated on four occasions by four different examiners (range of isokinetic test experience: 0 to 10 yrs) using a standardized isokinetic measurement protocol. Subjects were randomly assigned to participate in a test sequence determined by a 4 x 4 balanced Latin square. Peak torque and total work values at 60 degrees /sec and 180 degrees /sec were obtained for the concentric measures of knee extension and flexion. The measures of peak torque and total work were corrected for the effects of gravity. Intraclass correlation coefficients and standard error of measurement estimates were used to estimate the interrater reliability for each test condition (test speed x muscle group). Intraclass correlation coefficient values ranged from .90 to .96 for peak torque and .90 to .95 for total work. Standard error of measurement estimates ranged from 8.9 to 13.3 Nm for peak torque and 11.3 to 16.8 Nm for total work. The results of this investigation demonstrate that reliable measures of isokinetic muscle performance of knee extension and flexion may be obtained by four clinicians with varied experience when following a standardized measurement protocol.

Journal Article↗
PubMed1994

Correlation between low levels of estrogen receptors and estrogen responsiveness in two rat osteoblast-like cell lines.

With the knowledge that estrogen replacement therapy can circumvent postmenopausal osteoporosis and with the discovery of estrogen receptors (ER) in cultures of normal osteoblast-like cells, extensive investigations have been directed toward understanding the role of the ER in normal bone homeostasis. ROS 17/2.8 and UMR-106-01, two established osteoblast-like cell lines derived from rat osteosarcomas, have been shown to have estrogen-regulated biologic responses. Only the ROS 17/2.8 cell line has been reported to contain ER. In this study, high-affinity, saturable binding sites characteristic of the ER were detected in UMR-106-01 cells by binding assays with the high-affinity ligand, [125I]17 beta-estradiol. An initial immunoconcentration step before western blot analysis also allowed detection of the full-length ER protein. In addition, northern blot analysis indicated that the entire ER transcript was expressed and that the half-life of the ER message was increased following cycloheximide treatment. Message levels were also regulated by removal of serum and treatment with estradiol. An estrogen-regulated reporter vector, ERET81CAT, was transfected into the UMR-106-01 cells to determine whether the detected level of ER was transcriptionally functional. Using this assay, estrogen responsiveness was evident; however, the response was inconsistent. Multiple factors, such as serum, estradiol, and cell density, influence the ER levels in these cells and probably cause fluctuations in the abundance of receptors available to induce the CAT response. When the cells are responsive, the ICI 164,384 antagonist could block the estrogen-induced activation of CAT.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Aberrant reproductive phenotypes evident in transgenic mice expressing the wild-type mouse estrogen receptor.

The estrogen receptor (ER) acts as a transcription factor to regulate multiple cellular functions involved in normal physiology, differentiation, and reproduction. To date, there is no known animal model for studying aberrant ER expression. Therefore, we created transgenic mice expressing the wild-type mouse ER under the control of the mouse metallothionein-I (MT) promoter to determine whether overexpression of the ER would disrupt normal reproductive processes. Five male and one female founder mice were produced, and all were fertile. The progeny from these mice were screened for MT-mER expression by the ribonuclease protection assay. Mice in all six lines were found to express the transgene in a variety of tissues, although generally at low levels. The highest level of expression was observed in the female reproductive tract of line E. Females in all six lines demonstrated aberrant reproductive phenotypes involving processes at parturition and, with some of the lines, a tendency toward reduced fertility. Gestational length was prolonged up to 4 days beyond the normal gestation of 19 days, providing evidence of delayed parturition. In addition, prolonged labor (up to 3 days in length to deliver all pups) and labors requiring cesarean sections for maternal survival demonstrated the occurrence of dystocia in the MT-mER females. As maternal age increased, the incidence of stillborn litters, delayed parturition, and dystocia approached 100% in the transgenic dams. Difficulties at parturition were not observed in nontransgenic control females. These phenotypes suggest that the mechanisms regulating parturition may be perturbed by improper expression of the ER. The MT-mER transgenic mice may provide a novel approach for studying the estrogen-regulated signals involved in parturition and fertility as well as a unique animal model for the human reproductive phenotypes of delayed parturition and dystocia.

Animals↗
PubMed1992

Estrogens modulate the responsiveness of osteoblast-like cells (ROS 17/2.8) stably transfected with estrogen receptor.

Recent studies have demonstrated the presence of estrogen receptor (ER) in both normal human osteoblast-like and osteoblast-like osteosarcoma cells. The number of ER in cultured osteoblastic cells is very low (200-500 sites/cell). This has complicated characterization of the biological role of estrogens in bone cells. To study the responsiveness of bone cells to estrogens, we established osteoblast-like cell lines expressing higher ER levels. ROS 17/2.8, an osteoblastic cell line, was stably transfected with the cDNA encoding for the mouse ER. After a selection period, positive clones were isolated and evaluated for the presence of ER by both Northern blot analysis and ligand binding assays. Using these techniques, we detected a significant increase in the level of both ER transcript and binding compared to that in wild-type cells. The levels of expressed ER protein were similar to those reported in normal human osteoblast-like cells in primary culture (approximately 2000 sites/cell). To test whether the exogenously inserted ER was responsive, both wild-type and ER stably transfected cells were transiently transfected with a reporter construct containing an estrogen-responsive element linked to a truncated thymidine kinase promoter and a chloramphenicol acetyltransferase (CAT) reporter gene. Exposure of the cells to increased concentrations of estradiol induced a slight increase in CAT activity in wild-type cells (approximately 1.5-fold) at maximal stimulation; however, it provoked a clear concentration-dependent increase in CAT activity in the ER stably transfected cells, with a maximal stimulation of approximately 10-fold. This event was receptor mediated, since ICI 164,384, an ER antagonist, blocked the enhancement of estradiol-induced CAT activity, and it was specific, since other steroid hormones did not stimulate CAT activity. Finally, we evaluated the ability of ER to modulate an endogenous estrogen-responsive gene by measuring the activity of the enzyme alkaline phosphatase. In addition, diethylstilbestrol, a synthetic estrogen agonist, increased the activity of both the CAT reporter gene and the endogenous alkaline phosphatase enzyme. In summary, we have established osteoblast-like cells expressing high levels of an exogenously inserted ER, which has characteristics similar to those of the endogenous ER in terms of its Kd. Finally, the exogenous ER regulates both exogenously inserted construct (VITERECAT) and endogenous properties of the cells (enzymatic activity and proliferation).

Alkaline Phosphatase↗
PubMed1991

The mechanism of ICI 164,384 antiestrogenicity involves rapid loss of estrogen receptor in uterine tissue.

The antiestrogen ICI 164,384 (ICI) binds the estrogen receptor (ER) with approximately 20% the affinity of estradiol, but without the partial agonistic effects caused by tamoxifen. Investigations into the mechanism of ICI action have used ER molecules expressed in vitro to examine the binding of ER to ICI and the capacity of ICI-ER complexes to dimerize and bind to the estrogen response element (ERE). Our objectives were to study the biological effects, cellular distribution, and ERE-binding capacity of native uterine ICI-ER complexes after ip injection of 1 mg/kg ICI into 10-day castrate adult female mice. Synthesis of DNA and progesterone receptor were measured as end points of agonistic activity. ICI failed to stimulate either DNA or progesterone receptor synthesis above control levels, and pretreatment with ICI for 0.5 h reduced the stimulatory effect of estradiol by 75%. Measurement of uterine nuclear ER and cytosolic levels by exchange binding assay indicated a reduction in total ER levels within 0.5 h after ICI treatment, which remained below 20% for 24 h. Cycloheximide treatment did not block the ICI effect. Western blot analysis, immunohistochemistry, and steroid autoradiography confirmed the loss of ER protein. The ICI effect on ER was also demonstrable in vitro in the mouse TM4 estrogen-responsive cell line. ICI dramatically reduced ER levels to 5% of the control value by 4 h. Northern analysis indicated that ICI did not affect ER message levels, suggesting that the observed reduction in ER did not occur at the level of transcription. Gel shift assays indicated a low, but detectable, amount of ICI-ER binding to the vitellogenin A2 (VitA2) ERE. These results suggest that, although the ICI-ER complex binds weakly to DNA, ICI may cause its antagonistic effect by producing a rapid disappearance of the ER from the target tissue, resulting in an insufficient amount of ER to bind the native ligand and elicit agonist responses.

Animals↗
PubMed1991

New perspectives on the relationship of hormone changes to affective disorders in the perimenopause.

Menopause and the preceding climacteric years are normal aspects of the reproductive life cycle in women. However, the fluctuations and declines in hormone levels are physiologic changes that may have a significant impact on perimenopausal mood changes. These observations are based on both clinical experience with perimenopausal women and recent neuroendocrine research that describes hormone effects on central nervous system neurotransmitters regulating mood, sleep, and behavior. In particular, both estrogen and progesterone have profound effects on the serotonin, norepinephrine, dopamine, and endorphin receptor systems that are involved in mood regulation. This chapter discusses these correlations, describes pharmacologic and nonpharmacologic treatment approaches, and recommends directions for needed research.

Female↗
PubMed1984

Interferon inhibits agonist-induced cyclic AMP accumulation in human lymphocytes.

Wheezing episodes often accompany viral respiratory infections. Viral pathogens are also known to induce interferon production. Cyclic AMP (cAMP) levels affect bronchial reactivity; therefore, we analyzed cAMP accumulation in human lymphocytes as a model to determine if interferon might influence the accumulation of this important intracellular mediator. After an overnight exposure to interferon in whole blood, a reduction in agonist-stimulated cAMP accumulation was demonstrated. Basal cAMP concentrations were equivalent in control and interferon-exposed lymphocytes from the same donor, but the response to isoproterenol and prostaglandin E1 was significantly reduced by 61 and 30%, respectively. The decreased responsiveness persisted in the presence of RO 20-1724, a phosphodiesterase inhibitor, indicating that the effect was in part due to a decrease in cAMP synthesis in intact cells. These results suggest that interferon may play a role in inducing or potentiating bronchospasm.

Cyclic AMP↗
PubMed1981

Seasonal variations of serum IgE levels in normal children.

The importance of season as a variable in total IgE production in normal children is demonstrated. Recent history of allergen exposure as well as respiratory infection, both of which are seasonally determined, should be considered in evaluating serum IgE values.

Adenoviruses, Human↗
PubMedDate not supplied

Six high-priority organochlorine pesticides, either singly or in combination, are nonestrogenic in transfected HeLa cells.

There have been increasing concerns that environmental chemicals may adversely affect the health of humans and wildlife by acting as endocrine modulators. These concerns have been augmented by the realization that human exposure occurs not just to single chemical agents, but typically to mixtures of chemicals that could exhibit estrogenic activity qualitatively and/or quantitatively different from that of individual components. To address these concerns, we have evaluated the ability of six organochlorine pesticides (4, 4'-DDT, 4,4'-DDD, 4,4'-DDE, aldrin, dieldrin, or endrin, all classified high priority by ATSDR) to modulate transcriptional activation of an estrogen-responsive reporter gene in transfected HeLa cells. In these assays, HeLa cells cotransfected with an expression vector encoding estrogen receptor and an estrogen-responsive chloramphenicol acetyltransferase (CAT) reporter plasmid were exposed to these pesticides individually and in defined combinations. While estradiol consistently elicited 10- to 23-fold dose-dependent inductions in these assays, the six organochlorine pesticides showed no detectable dose-related response when tested individually. When tested in binary combinations, the pesticide mixtures showed no additional estrogenicity. Thus, the pesticides tested, singly or as mixtures, showed virtually no evidence of estrogenicity.

Aldrin↗
PubMedDate not supplied

Large-area contrast of a fiber-optic coupled x-ray image intensifier.

Large-area contrast measurements have been made upon a fiber-optic x-ray image intensifier with an external input phosphor. Both photometric and photographic techniques were used. For a shadowed area of 10% of the input window area, a contrast ratio in excess of 150 was determined. This is a factor of 5 higher than previously reported for any x-ray image intensifier. The improved contrast in the device is attributed to (1) reduced effect of x-ray Compton scattering in the input window; (2) less cross-chord light at the photocathode; and (3) greatly reduced light scattering and reflecting in output phosphor and window.

Fiber Optic Technology↗