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Biomedical subjects

D D Brown

Publications and source records attributed to D D Brown.

At least 73 records · Page 4Linked to original sources
PubMed1990

Xenopus laevis alpha and beta thyroid hormone receptors.

The Xenopus laevis genome encodes two genes for the alpha (TR alpha) and two genes for the beta (TR beta) thyroid hormone receptors. The two TR alpha genes closely resemble their rat, human, and chicken counterparts. No alternatively spliced TR alpha cDNA clones were found in the 5' untranslated region (5' UTR). In contrast, complex alternative splicing of TR beta mRNA occurs within the 5' UTR as well as possible alternative transcriptional start sites. As many as eight exons encoding mainly the 5' UTR are alternatively spliced, giving rise to at least two amino termini for each of the two TR beta proteins. The 5' UTR of transcripts from both TR alpha and TR beta genes contain multiple AUG sequences with short open reading frames suggesting translational control mechanisms might play a role in expression of TR genes.

Amino Acid Sequence↗
PubMed1990

A correlation of thyroid hormone receptor gene expression with amphibian metamorphosis.

The expression of the thyroid hormone (TH) receptor genes alpha (TR alpha) and beta (TR beta) in Xenopus laevis begins after the embryo hatches. The TR alpha mRNA increases throughout the premetamorphosis stage of tadpole development, is maximal by prometamorphosis, and falls after climax of metamorphosis to a lower level in frogs. The TR beta mRNA is barely detectable during premetamorphosis. In synchrony with the onset of endogenous TH synthesis by the thyroid gland (prometamorphosis), the level of TR beta mRNA rises in parallel with endogenous TH, reaching a peak at the climax of metamorphosis (stage 61) and drops to approximately 10% of its peak level after metamorphosis. As suggested by this correlation, exogenous TH up-regulates TR beta mRNA as much as 20-fold during premetamorphosis, whereas TH up-regulates TR alpha mRNA by approximately 2-fold during the same period. Up-regulation of TR beta mRNA is the earliest response to exogenous TH by competent tadpoles yet detected.

Animals↗
PubMed1990

Developmental and thyroid hormone-dependent regulation of pancreatic genes in Xenopus laevis.

We have isolated and sequenced a cDNA encoding Xenopus laevis pancreatic trypsin, which has approximately 70% amino acid sequence identity to mammalian trypsinogen. Northern blotting analysis shows that the trypsin gene is activated just before the tadpole starts to feed, reaches peak activity in the swimming tadpole (premetamorphosis), and is then repressed during prometamorphosis, attaining its lowest activity at the climax of metamorphosis. The same gene is then activated again in frogs but to a much lower level. The pattern of the changes in trypsin gene expression is followed by at least two other pancreas-specific genes and marks the remodeling of the pancreas of the animal at metamorphosis. Thyroid hormone, which is the causative agent of metamorphosis, can down-regulate trypsin gene expression prematurely.

Amino Acid Sequence↗
PubMed1990

The characterization of the TFIIIA synthesized in somatic cells of Xenopus laevis.

In somatic cells of Xenopus, transcription of the TFIIIA gene initiates greater than 200 bp upstream from the start site used in oocytes. The resultant mRNA encodes a protein, S-TFIIIA, that is 22 amino acids longer at its amino terminus than the abundant form of TFIIIA in oocytes (O-TFIIIA). S-TFIIIA binds the 5S RNA gene and 5S RNA, and both O- and S-TFIIIA promote the formation of stable transcription complexes on oocyte-type 5S RNA genes in an oocyte nuclear extract. We have not found any functional difference between the two forms of TFIIIA. Different transcription start sites suggest differential promoter usage--one in oocytes that permits high levels of gene activity and another that is used in somatic cells for low-level TFIIIA mRNA synthesis.

Amino Acid Sequence↗
PubMed1990

Effect of paraxanthine on FFA mobilization after intravenous caffeine administration in humans.

Because it has previously been shown that it takes much more caffeine to cause fat mobilization in vitro than in vivo, it has been suggested that there may be an active metabolite working with caffeine causing an increase in lipolysis in vivo. To determine the relationship between the appearance of paraxanthine (caffeine's major dimethylxanthine metabolite) and free fatty acid (FFA) mobilization after intravenous caffeine administration, 10 men were studied at rest after receiving a dose of 4 mg/kg lean body mass. Venous blood samples were obtained before dosing and at minutes 5, 10, 15, 30, 45, 60, 90, 120, 150, and 180. Serum levels of FFA, glycerol, caffeine, and paraxanthine were determined in duplicate. Concentrations of FFA and glycerol were corrected for plasma volume changes. A high negative correlation was seen between decreases in caffeine and increases in FFA (r = -0.90) and a high positive correlation was seen between the appearance of paraxanthine and FFA (r = 0.93). It was concluded that paraxanthine may play a role in increased lipolysis after caffeine administration in humans.

Adult↗
PubMed1990

Venous and fingertip blood to calculate plasma volume shift following exercise.

This study determined whether fingertip blood samples used to calculate percentage change in calculated plasma volume following exercise were in agreement with values obtained from venous blood samples. Twenty-five subjects engaged in two cycle ergometer exercises at 100 and 200 W, with percentage plasma volume shift (% PVS) determined after each from venous (VB) and fingertip (FT) blood. Values for % PVS were FT -6.25% compared with VB -8.04% (P less than 0.05), with the correlation between the two methods at r = 0.88. The following equation was established: corrected FT % PVS = (0.8662 * FT) - 2.625; SEE = 2.60%. In order to cross-validate this equation, fifteen additional subjects submitted to VB and FT. Corrected FT % PVS using the established equation resulted in a mean value of 9.53 compared with 10.53% for actual VB % PVS. Although these means were not significantly different, there was approximately a 25% chance that the corrected FT % PVS would be more than one standard error of estimate from the regression line. It was concluded that FT underestimates VB % PVS. However, when limited to group data, FT can be corrected to favorably represent VB % PVS following moderate to heavy cycle ergometer exercise.

Adult↗
PubMed1989

The effect of voluntary ventilation on acid-base responses to a Moo Duk Tkow form.

Voluntary control of breathing is taught in Moo Duk Tkow in order to maximize force during striking, kicking, and blocking. Form, a formalized practice routine which incorporates these techniques, is a short predetermined sequence of arm and leg movements performed at high intensity which includes a number of pauses. The purpose of this study was to investigate the acid-base and lactate responses to a beginning level form, Ki Cho I. Nine subjects, five black belts and four brown belts, were asked to perform Ki Cho I at competitive intensity. Arterialized finger capillary blood was drawn prior to and immediately after the form for the determination of pH, bicarbonate, base excess, and PCO2 by use of the Siggaard-Anderson Nomogram. Heart rate was obtained by ECG, and lactate was measured by enzymatic assay. Statistically significant differences (p less than .05) were found for all variables. Mean pre and post values (+/- standard deviations) were: pH 7.39 +/- .04 to 7.34 +/- .03; base excess -.3 +/- 1.2 to -2.8 +/- 1.7 mEq/L; bicarbonate 23.7 +/- 1.0 to 21.8 +/- 1.4 mEq/L; PCO2 39.9 +/- 3.9 to 45.1 +/- 5.4 mmHg; lactate 1.51 +/- .71 to 3.23 +/- 1.56 mM; and heart rate 74.9 +/- 12.6 to 132.1 +/- 17.0 bpm. The mean form time was 17.2 +/- 1.8 s. It was concluded that respiratory compensation does not occur and that respiratory acidosis may contribute to the metabolic acidosis.

Acid-Base Equilibrium↗
PubMed1989

Cardiovascular and ventilatory responses during formalized T'ai Chi Chuan exercise.

T'ai Chi Chuan (TCC) is a widely practiced Chinese martial art said to physically develop balance and coordination as well as enhance emotional and mental health. TCC consists of a series of postures combined into a sequential movement providing a smooth, continuous, low-intensity activity. The purpose of this study was to examine the ventilatory and cardiovascular responses to the Long Form of Yang's style TCC. In addition, the subjects' TCC responses were compared to their ventilatory and cardiovascular responses during cycle ergometry at an oxygen consumption (VO2) equivalent to the mean TCC VO2. Six experienced (M = 8.3 yrs) male TCC practitioners served as subjects with data collected during the Cloud H and movement of the TCC exercise. Significantly (p less than .05) lower responses for ventilatory frequency (Vf) (11.3 and 15.7 breaths.min-1), ventilatory equivalent (VE/VO2) (23.47 and 27.41), and the ratio of dead space ventilation to tidal volume (VD/VT) (20 and 27%) were found in TCC in comparison to cycle ergometry. The percentage of minute ventilation used for alveolar ventilation was significantly higher during TCC (p less than .03) than cycle ergometry, with mean values of 81.1% and 73.1%, respectively. Cardiac output, stroke volume, and heart rate were not significantly different between TCC exercise and cycle ergometry at the same oxygen consumption. We concluded that, during TCC, expert practitioners show significantly different ventilatory responses leading to more efficient use of the ventilatory volume than would be expected from comparable levels of exertion on a cycle ergometer.

Adult↗
PubMed1989

Monitoring of intraoperative auditory brainstem responses.

Intraoperative ABR monitoring provides a measure of reassurance when a surgical procedure places the cochlear nerve or its blood supply in jeopardy. ABR monitoring has demonstrated its place in the operating room during retrolabyrinthine vestibular nerve section for vertigo, and in acoustic neuroma operations, when hearing preservation is a high priority in surgical outcome.

Brain Stem↗
PubMed1988

Developmental regulation of two 5S ribosomal RNA genes.

The developmental regulation of two kinds of Xenopus 5S RNA genes (oocyte and somatic types) can be explained by differences in the stability of protein-protein and protein-DNA interactions in a transcription complex that directs transcription initiation by RNA polymerase III. Dissociation of transcription factors from oocyte 5S RNA genes during development allows them to be repressed by chromatin assembly. In the same cells, somatic 5S RNA genes remain active because their transcription complexes are stable.

Animals↗
PubMed1988

A new rhythm library for testing automatic external defibrillators: performance of three devices.

A library of arrhythmias obtained from patients with cardiac arrest was developed. Such a data base will permit both in vitro testing of the rhythm analysis system of automatic external defibrillators before clinical field trials are conducted and comparison of devices. Defibrillators equipped with voice/electrocardiographic tape recorders and used in the prehospital defibrillation programs in Iowa and King County, Washington provided the rhythm source. From these recordings, segments of ventricular fibrillation with minimal artifact and a duration of greater than or equal to 6 s were selected. Segments of ventricular fibrillation (n = 102) were categorized by average peak amplitude as fine (1 to less than 3 mm), medium (3 to less than 7 mm), coarse (7 to less than 12 mm) and extra coarse (greater than or equal to 12 mm), and transcribed onto high fidelity videocassette tapes. Nonventricular fibrillation cardiac arrest rhythms (n = 144), which included wide complex idioventricular rhythms, ventricular and supraventricular tachycardias, asystole and artifact, were also transcribed. Automatic external defibrillators developed by three manufacturers reached a treat (shock) decision on 88 to 93% of the ventricular fibrillation rhythms and on 5 to 10% of the nonventricular fibrillation rhythms. The latter decisions were defined as false positive, though for many rapid nonventricular fibrillation rhythms, countershock may be the appropriate treatment response. There were no statistically significant differences among the three devices in the shock/no shock decisions. A variety of ventricular fibrillation arrhythmias and terminology to express the preclinical performance of automatic external defibrillators are defined. Three commercially available automatic external defibrillators appear to successfully identify ventricular fibrillation and nonventricular fibrillation rhythms.(ABSTRACT TRUNCATED AT 250 WORDS)

Arrhythmias, Cardiac↗
PubMed1988

Internal sclerectomy with an automated trephine for advanced glaucoma.

An automated trephine (trabecuphine) was used to perform an internal sclerectomy in seven glaucoma patients who were aphakic or had undergone previous filtering surgery that had failed or both. A patent fistula was achieved intraoperatively in all seven eyes. Postoperatively, six patients received subconjunctival injection of 5-fluorouracil (5-FI) once daily for an average of 8 days. Five of seven patients have retained a functional bleb and a controlled intraocular pressure (IOP) after surgery (follow-up, 4-24 months). The only intraoperative complication was hemorrhage from the sclerectomy site in a patient with aniridia that resulted in a 20% hyphema. The hyphema cleared quickly, and the bleb has remained functional with a pressure of 12 mmHg for 9 months. The trabecuphine makes it possible to perform a glaucoma filtering operation safely from within the anterior chamber. This technique minimizes conjunctival trauma in the filtration area. The absence of a conjunctival incision overlying the fistula simplifies the adjunctive use of antimetabolites such as 5-FU.

Choroid↗
PubMed1988

Transcription complexes that program Xenopus 5S RNA genes are stable in vivo.

The long-term stability of transcription complexes on 5S RNA genes has been demonstrated in vivo. Complexes on oocyte and somatic-type 5S RNA genes injected into Xenopus laevis oocyte nuclei are stable for at least 4 days. Tissue culture cells and mature erythrocytes have equivalent numbers of somatic 5S RNA genes programmed into transcription complexes, yet the former cell type has a greater than 50-fold higher cellular content of transcription factor IIIA (TFIIIA). Functional transcription complexes on somatic 5S RNA genes in nucleated erythrocytes of Xenopus are stable for weeks, perhaps months, even though a mature erythrocyte has less than two molecules of TFIIIA for each somatic 5S RNA gene. These findings strengthen our proposal that stable transcription complexes are a means of maintaining the differentiated state.

Animals↗
PubMed1988

Mapping functional regions of transcription factor TFIIIA.

Functional deletion mutants of the trans-acting factor TFIIIA, truncated at both ends of the molecule, have been expressed by in vitro transcription of a cDNA clone and subsequent cell-free translation of the synthetic mRNAs. A region of TFIIIA 19 amino acids or less, near the carboxyl terminus, is critical for maximal transcription and lies outside the DNA-binding domain. The elongated protein can be aligned over the internal control region (ICR) of the Xenopus 5S RNA gene with its carboxyl terminus oriented toward the 5' end of the gene and its amino terminus oriented toward the 3' end of the gene. The nine "zinc fingers" and the linkers that separate them comprise 80% of the protein mass and correspond to the DNA-binding domain of TFIIIA. The zinc fingers near the amino terminus of the protein contribute more to the overall binding energy of the protein to the ICR than do the zinc fingers near the carboxyl end. The most striking feature of TFIIIA is its modular structure. This is demonstrated by the fact that each zinc finger binds to just one of three short nucleotide sequences within the ICR.

Animals↗
PubMed1987

Differential 5S RNA gene expression in vitro.

In extracts derived from activated eggs of Xenopus, oocyte 5S RNA gene transcription complexes are destabilized under conditions where somatic 5S RNA gene transcription complexes are stable. Trans-acting factors in destabilized complexes are in equilibrium with free factors in the extract, and thus transcription becomes dependent upon the concentration of the limiting factor in the extract. By reducing TFIIIA, a limiting factor in the egg extract, a cloned somatic 5S RNA gene is transcribed as much as 400-fold more efficiently than a cloned oocyte 5S RNA gene.

Animals↗
PubMed1987

Transient activation of oocyte 5S RNA genes in Xenopus embryos by raising the level of the trans-acting factor TFIIIA.

The concentration of the trans-acting factor, TFIIIA, required for the activation of 5S RNA genes in Xenopus can be elevated in developing embryos by injecting a synthetic full-length mRNA into fertilized eggs. 5S RNA genes are activated by the increased factor concentration at the mid-blastula transition through mid-gastrulation. The activated oocyte 5S RNA genes are then inactivated, leaving the TFIIIA-enhanced embryos with the same profile of differential 5S RNA gene activity as control embryos, i.e., synthesizing mainly somatic 5S RNA. Inactivation of the oocyte 5S RNA genes is complete by neurulation and can occur in the absence of DNA replication. We propose that this loss of gene activity is due at least in part to destabilization of transcription complexes that are associated with oocyte 5S RNA genes.

Animals↗
PubMed1987

A bacteriophage RNA polymerase transcribes in vitro through a nucleosome core without displacing it.

Small linear DNA molecules containing histone octamers (nucleosome cores) are transcribed by SP6 RNA polymerase with only slightly lower efficiency than naked DNA templates. The position of the histone octamer on the DNA remains unchanged even after multiple passages by the polymerase. The histone octamer is not released even transiently from the DNA by polymerase transit. We conclude that histone octamers do not impede transcription elongation.

Animals↗