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Biomedical subjects

R D Thomas

Publications and source records attributed to R D Thomas.

At least 19 recordsLinked to original sources
PubMed1992

Metastatic malignant struma ovarii. Two case reports.

Struma ovarii is an ovarian germ cell tumor consisting mainly of thyroid tissue. Five percent of struma ovarii are malignant, and of these only five percent metastasize. The rarity of this disease has resulted in difficulty in agreeing on treatment regimes and in limited imaging experience. The authors report two cases and highlight the imaging and monitoring difficulties encountered in their management. The authors conclude that I-131 has a role to play both therapeutically and in monitoring these patients, but that biochemical testing is a more reliable indicator of disease status.

Adolescent↗
PubMed1992

Carcinogenic mixtures.

Human populations are generally exposed simultaneously to a number of toxicants present in the environment, including complex mixtures of unknown and variable origin. While scientific methods for evaluating the potential carcinogenic risks of pure compounds are relatively well established, methods for assessing the risks of complex mixtures are somewhat less developed. This article provides a report of a recent workshop on carcinogenic mixtures sponsored by the Committee on Toxicology of the U.S. National Research Council, in which toxicological, epidemiological, and statistical approaches to carcinogenic risk assessment for mixtures were discussed. Complex mixtures, such as diesel emissions and tobacco smoke, have been shown to have carcinogenic potential. Bioassay-directed fractionation based on short-term screening test for genotoxicity has also been used in identifying carcinogenic components of mixtures. Both toxicological and epidemiological studies have identified clear interactions between chemical carcinogens, including synergistic effects at moderate to high doses. To date, laboratory studies have demonstrated over 900 interactions involving nearly 200 chemical carcinogens. At lower doses, theoretical arguments suggest that risks may be near additive. Thus, additivity at low doses has been invoked as as a working hypothesis by regulatory authorities in the absence of evidence to the contrary. Future studies of the joint effects of carcinogenic agents may serve to elucidate the mechanisms by which interactions occur at higher doses.

Animals↗
PubMed1992

Helping those in need.

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Dental Care for Persons with Disabilities↗
PubMed1992

Echocardiography and genetic counselling in tuberous sclerosis.

OBJECTIVE: To assess echocardiography as an investigation for the detection of occult gene carriers in tuberous sclerosis. PATIENTS: Sixty parents of children with tuberous sclerosis who had been extensively investigated for signs of the disease and 60 age and sex matched controls. PROCEDURE: Blind study by two experienced echocardiographers and blind interpretation of video recordings by an adult cardiologist. SETTING: Cardiology department of a district general hospital. RESULTS: Two parents and three controls had bright echodense areas interpreted as possible rhabdomyomas. CONCLUSIONS: In our hands echocardiography of adults is not an investigation with a high specificity for gene detection in tuberous sclerosis.

Adult↗
PubMed1991

Stereoselective formation of bis(alpha-aminoacyl) esters of 5'-AMP suggests a primitive peptide synthesizing system with a preference for L-amino acids.

In the biosynthesis of proteins, each amino acid passes from the aminoacyl adenylate to become an amino acid ester and finally a 2' (3') peptidyl ester of the AMP residue at the end of a tRNA. Consequently, the chemistry of protein synthesis is the chemistry of aminoacyl and peptidyl AMP. Our data has revealed properties of 5'-AMP and its esters which should allow the preferential catalytic synthesis of L-amino acid peptides via a bis(2', 3'-aminoacyl) ester intermediate. Results in this paper concern one step in the proposed process and show that preexisting Ac-L-Phe monoester reacts about 2.5-times faster to form diester than preexisting Ac-D-Phe monoester.

Adenosine Monophosphate↗
PubMed1991

Double duty.

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Career Choice↗
PubMed1990

Ribonucleic acids may be catalysts for the preferential synthesis of L-amino acid peptides: a minireview.

This minireview is a summary of the basic concepts and pieces of experimental evidence supporting a hypothesis that suggests a mechanism whereby purine monoribonucleotides having D-ribose may be able to preferentially catalyze the synthesis of L-amino acid peptides. The proposed mechanism involves a 2'-3' diaminoacyl intermediate and the preference accrues from several factors that favor the L-isomer, principally for hydrophobic amino acids. Although the hypothesis has not been fully tested, some crucial evidence has been published. Other pieces of evidence are now being submitted or are in press for publication and still other experiments, principally on the step of peptide bond formation, are in the process of being carried out. The purpose of a review at this point is to present the hypothesis to the scientific community in hopes of generating discussion, suggestions, and evaluation by other workers. Should the hypothesis prove correct, it may represent the most primitive and fundamental relationship between the nucleic acid and protein systems. In addition, it would represent another important example of the catalytic ability of RNA.

Amino Acids↗
PubMed1990

11 beta-methoxy-, 11 beta-ethyl- and 17 alpha-ethynyl-substituted 16 alpha-fluoroestradiols: receptor-based imaging agents with enhanced uptake efficiency and selectivity.

We have prepared three analogues of 16 alpha-fluoroestradiol (FES) substituted either with an 11 beta-methoxy group (1, 11 beta-MeO-FES), an 11 beta-ethyl group (2, 11 beta-Et-FES), or a 17 alpha-ethynyl group (3, 17 alpha-ethynyl-FES). These substituents all lower the binding of FES to the serum proteins alphafetoprotein and sex steroid binding protein, but their effect on estrogen receptor binding varies: Receptor binding is increased by the 11 beta-ethyl and 17 alpha-ethynyl groups, but decreased by the 11 beta-methoxy group. These substituents also have a parallel effect on the lipophilicity, and hence the nonspecific binding estimated for these compounds. All three compounds were prepared in fluorine-18 labeled form, at effective specific activities of 90-1600 Ci/mmol, by fluoride ion displacement reactions as done previously with FES. Tissue distribution studies in immature rats show high uptake selectivity by target tissue (uterus) and effective competition by an excess of unlabeled estradiol. Percent injected dose per gram values (% ID/g) at 1 h are 6% for 11 beta-MeO-FES and 11-13% for 11 beta-Et-FES and 17 alpha-ethynyl-FES (FES itself has a % ID/g of 9%). Uptake selectivity in terms of uterus to blood or muscle ratios at 1 h is highest for 11 beta-MeO-FES and 17 alpha-ethynyl-FES (43-149). Metabolic consumption studies show that most activity in uterus is unmetabolized and in blood is rapidly and nearly completely metabolized. In muscle, FES and the substituted estrogens show intermediate levels of metabolic consumption; in some cases activity in muscle extracts is nearly unmetabolized. Thus, the substituents on FES cause major alterations in receptor and nonreceptor binding affinity, uptake efficiency and selectivity, and extent of metabolism. It is not readily clear, however, whether the alterations in uptake efficiency and selectivity are the result of differences in receptor or nonreceptor binding or lipophilicity, or altered patterns of metabolism. Nevertheless, these compounds should be useful in providing a spectrum of uptake properties that could be used for imaging different estrogen-receptor-containing structures.

Animals↗
PubMed1979

Potassium depletion and tissue loss in chronic heart-disease.

Weight-loss, total body-potassium, and total body-nitrogen were measured in 12 men and 15 women with severe chronic heart-disease. Compared with age-matched healthy controls, the men had lost an average of 13 kg in weight, 915 mmol of potassium, and 354 g of nitrogen, whereas the women had lost 5.6 kg of weight, 327 mmol of potassium, and 66 g of nitrogen. Although the potassium/nitrogen ratio in the lost tissue is not precisely known, the loss of nitrogen indicates that most of the potassium loss in men is due to tissue loss and that there is little fall in the intracellular concentration of potassium in either the men or the women.

Body Weight↗
PubMed1979

Echocardiographic pattern of posterior mitral valve leaflet movement after mitral valve repair.

The pattern of movement of the posterior leaflet at the time of opening of the stenosed mitral valve has been described as either anterior or posterior in direction. In 32 patients who underwent mitral annuloplasty, the anatomical features of the mitral apparatus were correlated with the postoperative echocardiographic pattern of movements of the posterior leaflet. Anterior movement of the posterior leaflet was associated with extensive disease of this leaflet, and posterior movement with minimal disease. No relation was found between valve orifice or anterior leaflet mobility and the pattern of movement of the posterior leaflet.

Adult↗
PubMed1979

The cause of the raised plasma urea of acute heart failure.

The concentrations of urea, urate, phosphate and creatinine were measured in the plasma of 30 consecutive patients admitted acutely with heart failure. On admission, 20 had a raised plasma urea, 21 had a raised plasma urate, but only 6 had a raised plasma phosphate and only 6 had a raised plasma creatinine. A further 9 of the patients developed a raised plasma urea after admission. The increase in plasma urea present on admission was greater than expected for the fall in GFR (as indicated by the increase in plasma creatinine). The results for plasma and urine taken together suggest that a major cause of the raised plasma urea was an increased urea production rather than a reduced glomerular filtration rate. There was no obvious relationship between plasma urea and clinical features, or diuretic therapy.

Acute Disease↗