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Biomedical subjects

J Moon

Publications and source records attributed to J Moon.

At least 55 records · Page 3Linked to original sources
PubMed1996

Is respiratory sinus arrhythmia a good index of cardiac vagal tone in exercise?

To assess the relative roles of neural and nonneural mechanisms in respiratory sinus arrhythmia (RSA) at rest and during exercise (steady-state supine cycle ergometry at 25% of peak oxygen uptake), we studied 10 healthy men (mean age 21 +/- 1 yr) before (control) and during ganglion blockade (GB) with trimetaphan camsylate (3-5 mg/min i.v.). GB was confirmed by the abolition of the reflex bradycardia in response to intravenous phenylephrine and of the blood pressure rise with the cold pressor test. RSA was calculated from the power of the spectral component of the R-R interval variability centered at the breathing frequency. GB decreased but did not abolish RSA. At rest, this nonneural component of RSA was negligible, accounting for < 1% of the control RSA. During GB, exercise did not affect RSA significantly. However, because control RSA was decreased by exercise, the proportion of nonneural RSA increased by 32% (range from 17 to 75%). These results indicate that as the vagal tone decreases with exercise, an increasing proportion of RSA is due to nonneural mechanisms.

Adolescent↗
PubMed1996

A comparison of test-retest variability of caloric induced nystagmus in a normal population using an air stimulus presented via a standard and modified irrigating probe.

The caloric test has traditionally been carried out using water. Air caloric techniques have been available for some time but one of the reported disadvantages is the high variability of response (Coats et al., 1976). The aim of this study was to compare the test-retest variability of the air caloric response using a normal irrigation probe and a modified probe. The modified probe allowed observation of the placement of the probe tip within the ear canal and could be used to observe the direction of air flow during the irrigation. It was found that the variability with the modified probe is smaller than with the normal probe.

Adolescent↗
PubMed1995

The efficiency of translation termination is determined by a synergistic interplay between upstream and downstream sequences in Saccharomyces cerevisiae.

In a recent study we found that the efficiency of translation termination could be decreased several hundred fold by altering the local sequence context surrounding stop codons in the yeast Saccharomyces cerevisiae. Suppression of termination was shown to be mediated by near-cognate tRNA mispairing with the termination codon. We have now examined in greater detail how the local sequence context affects the efficiency of translation termination in this organism. Our results indicate that the sequence immediately upstream of the termination codon plays a significant role in determining the efficiency of translation termination. An extended termination sequence (containing the stop codon and the following three nucleotides) was also found to be a major determinant of termination efficiency, with effects attributable to the fourth nucleotide being largely independent of the termination codon. For the UGA and UAA stop codons, the influence of the fourth position on termination efficiency (from most efficient to least efficient termination) was found to be G > U,A > C, while for the UAG codon it was U,A > C > G. These sequence-specific effects on the efficiency of translation termination suggest that polypeptide chain release factor (or another molecule that may play a role in translation termination, such as rRNA) recognizes an extended termination sequence in yeast. A previous study found a statistically significant bias toward certain tetranucleotide sequences (containing the stop codon and the first distal nucleotide) in several organisms. We found that tetranucleotide sequences most frequently used in yeast are among the most efficient at mediating translation termination, while rare tetranucleotide sequences mediate much less efficient termination. Taken together, our results indicate that upstream and downstream components of an extended sequence context act synergistically to determine the overall efficiency of translation termination in yeast.

Amino Acid Sequence↗
PubMed1995

Cloning and sequencing of the catechol 2,3-dioxygenase gene of Alcaligenes sp. KF711.

The catechol 2,3-dioxygenase is an aromatic ring-fission enzyme catalyzing the conversion of catechol to 2-hydroxymuconic semialdehyde. A catechol 2,3-dioxygenase gene has been cloned from chromosomal DNA of Alcaligenes sp. KF711, and its sequence was determined. The catechol 2,3-dioxygenase gene was consisted of 927 nucleotides with ATG initiation codon and TGA termination codon, which can encode a polypeptide of molecular weight 35 kDa containing 308 amino acid residues. G+C content of the gene was 58 mol%, and a putative ribosome-binding sequence was identified at about 10 nucleotides upstream from the ATG initiation codon. The sequence of catechol 2,3-dioxygenase from Alcaligenes sp. KF711 exhibited 81-92% homology at nucleotide level and 84-92% homology at amino acid level with those of corresponding enzymes encoded in xylE of TOL plasmid, nahH of NAH7 plasmid, and dmpB of Pseudomonas CF600.

Alcaligenes↗
PubMed1994

The role of vitamin D in toxic metal absorption: a review.

Vitamin D increases intestinal calcium and phosphate absorption. Not so well known, however, is that vitamin D stimulates the co-absorption of other essential minerals like magnesium, iron, and zinc; toxic metals including lead, cadmium, aluminum, and cobalt; and radioactive isotopes such as strontium and cesium. Vitamin D may contribute to the pathologies induced by toxic metals by increasing their absorption and retention. Reciprocally, lead, cadmium, aluminum, and strontium interfere with normal vitamin D metabolism by blocking renal synthesis of 1,25-dihydroxyvitamin D. This is the first review of the role of the vitamin D endocrine system in metal toxicology.

Aluminum↗
PubMed1993

Laparoscopically assisted vaginal hysterectomy as definitive therapy for stage III and IV endometriosis.

Operative laparoscopy combined with vaginal hysterectomy and salpingo-oophorectomy was used to treat advanced endometriosis in 40 of 46 patients. This treatment plan was abandoned in favor of laparotomy in six patients. Of the 40 patients successfully treated by laparoscopically assisted vaginal hysterectomy, 39 are completely free of symptoms. Major complications, including blood loss requiring transfusion and injury to the ureter or bowel, were sustained at acceptable rates. No serious infections occurred. The mean operating time was 191 minutes. Laparoscopically assisted vaginal hysterectomy and removal of all ovarian tissue combined with excision of all endometriosis may be used as definitive therapy for advanced endometriosis. The major complications associated with surgical therapy for high-stage endometriosis are encountered; therefore, laparoscopic treatment requires advanced laparoscopic surgical skills.

Adult↗
PubMed1992

Effects of ligands on reduction of oxygen by vanadium(IV) and vanadium(III).

V(IV) and V(III) reduce molecular oxygen with increasing rates as the pH is raised from 6.0 to 7.4. Under all conditions tested, V(IV) is the more efficient reductant. EDTA and ATP generally inhibit the reduction of oxygen by V(III) and V(IV). In contrast, desferrioxamine accelerates the reduction of oxygen by V(IV) but with decreasing effectiveness at pH 7.4 compared to pH 6.0, while desferrioxamine accelerates the reduction of oxygen by V(III) only at pH 6.0. Histidine enhances the reduction of oxygen by V(IV) at pH 7.0 and 7.4. The observed rates of oxygen reduction by V(III) and V(IV) imply that the intracellular distribution of vanadium among its redox states reflects not an equilibrium but a steady state.

Adenosine Triphosphate↗
PubMed1992

Desferrioxamine enhances the reactivity of vanadium (IV) and vanadium (V) toward ferri- and ferrocytochrome c.

Ligands, especially desferrioxamine, affect the rate at which vanadium reduces or oxidizes cytochrome c. Whether reduction or oxidation occurs, and how fast, depends on the nature of the ligand, the state of reduction of the vanadium, the pH (6.0, 7.0, or 7.4), and the availability of oxygen. In general, oxidation of ferrocytochrome c was favored by (1) low pH, (2) an oxidized state of the vanadium, (3) the presence of oxygen, and (4) more strongly binding ligands (desferrioxamine much greater than histidine = ATP greater than EDTA greater than albumin greater than aquo). Thus, at pH 6.0, desferrioxamine accelerated the V(V)-catalyzed ferrocytochrome c oxidation 160-fold aerobically, and 3500-fold anaerobically. In general, strongly binding ligands slowed oxidations, especially at higher pH. Desferrioxamine was unique among the five ligands in that it not only accelerated oxidation of ferrocytochrome c at pH 6.0, but at pH 7.4 the redox balance shifted to the point where it paradoxically reduced ferricytochrome c. V(V) is an improbable electron donor, but desferrioxamine will reduce cytochrome c, and V(V) accelerates this process. Oxidation of cytochrome c by V(V):desferrioxamine was faster anaerobically, and reduction by V(IV):desferrioxamine was faster aerobically. Although V(V) did not oxidize ferrocytochrome c at pH 7.4, V(IV) did, provided oxygen and desferrioxamine were both present. V(IV):desferrioxamine almost completely reduced ferricytochrome c, and this reduction was followed by a slow, progressive oxidation. This latter oxidation of cytochrome c is mediated by active species generated in the reaction between V(IV):desferrioxamine and oxygen, because none of these reagents alone can induce oxidation at a comparable rate. The mediating species were transient, and generated in reactions with oxygen.(ABSTRACT TRUNCATED AT 250 WORDS)

Catalase↗
PubMed1992

Treatment of postcataract fibrinous membranes with tissue plasminogen activator.

PURPOSE: The purpose of this study is to investigate the efficacy and toxicity of tissue plasminogen activator (tPA) in treatment of postcataract fibrinous membranes. METHODS: The authors injected 25 micrograms of tPA into the anterior chamber of 52 pseudophakic eyes with moderate to severe fibrinous membranes that developed after cataract surgery. RESULTS: Intraocular tPA injection resulted in complete fibrinolysis in 47 of 52 eyes (90%) and partial fibrinolysis in 5 of 52 eyes (10%). In cases of complete fibrinolysis, resolution of the fibrinous membrane occurred within 30 minutes in 22 of 47 eyes (47%) and within 1 hour in 25 of 47 eyes (53%). No evidence of toxicity was observed as measured by slit-lamp biomicroscopy, intraocular pressure, and corneal endothelial cell density, size, and morphology. Complications of tPA administration included periorbital pain (4 eyes), anterior chamber hemorrhage (4 eyes), and anterior chamber turbidity (3 eyes). CONCLUSION: The authors believe that intraocular tPA is effective and safe in the treatment of postcataract fibrinous membranes.

Adult↗
PubMed1992

Hypothesis: etiology of atherosclerosis and osteoporosis: are imbalances in the calciferol endocrine system implicated?

Atherosclerosis and osteoporosis are currently considered unrelated diseases. Osteoporosis involves bone calcium (Ca) loss and predominantly affects females after menopause. Atherosclerosis is an illness predominantly affecting males, and is primarily characterized by abnormal lipid metabolism. However, pathological calcification of the arterial wall is an underlying feature of atherosclerosis. Ca homeostasis is thus important in atherosclerosis as well as in osteoporosis. Men also develop osteoporosis although at a later age than women, and, as osteoporosis progresses in women, there is an accompanying calcification of arteries leading to increased incidence of atherosclerosis in aging women. Thus, during old age, both atherosclerosis and osteoporosis are prevalent in both males and females. The dramatic increase in atherosclerosis among women as they develop osteoporosis suggests that the two illnesses may be more closely related than previously realized. The use of vitamin D as a food supplement coincides with epidemic onsets of atherosclerosis and osteoporosis, and excess vitamin D induces both conditions in humans and laboratory animals. These observations suggest a role for chronic vitamin D excess in the etiology of the two illnesses. Magnesium (Mg) deficiency, nicotine, and high dietary cholesterol are contributing factors that accentuate adverse effects of vitamin D.

Animals↗
PubMed1990

Multiple actions of superoxide dismutase: why can it both inhibit and stimulate reduction of oxygen by hydroquinones?

Superoxide dismutase can either inhibit or stimulate autoxidation of different hydroquinones, suggesting multiple roles for O2.-. Inhibitory actions of superoxide dismutase include termination of O2.(-)-propagated reaction chains and metal chelation by the apoprotein. Together, chelation of metals and termination of O2.(-)-propagated chains can effectively prevent reduction of oxygen. Chain termination by superoxide dismutase can thus account for negligible accumulation of H2O2 without invoking a superoxide:semiquinone oxidoreductase activity for this enzyme. One stimulatory action of superoxide dismutase is to decrease thermodynamic limitations to reduction of oxygen. Whether superoxide dismutase inhibits or accelerates an autoxidation depends on the reduction potentials of the quinone and the availability of metal coordination for inner sphere electron transfers.

Animals↗
PubMed1990

The influence of nasal patency on accelerometric transduction of nasal bone vibration.

The transmission characteristics of nasal tract energy to a nasal accelerometer were evaluated in relation to nasal tract airway resistance. Ten adult speakers repeated three utterances while recordings of nasal bone vibration, as detected by miniature accelerometers, were obtained simultaneously from both sides of the nose and referenced to a common throat signal. Average nasal-to-oral accelerometry ratios recorded from the more resistant side of the nose were significantly larger in magnitude than those recorded simultaneously from the less resistant side of the nose. While accelerometer ratio waveforms from each side of the nose essentially overlapped for some subjects, others displayed unilateral variations in accelerometer output as a function of time. The anatomic and physiologic condition of the nasal passage appears to be an important variable in the detection of nasal tract acoustic energy using the accelerometric technique.

Adult↗
PubMed1990

[An x-ray computed tomography study with radiographic splints in implant evaluation].

CT-Scan provide a powerful diagnostic tool in the presurgical evaluation for endosseous implants. This article overviews a computer assisted system combined with a "marked radiographic stent" and a "surgical stent". The technique evaluates the ideal number, location and direction of the implants for a successful treatment.

Dental Implantation, Endosseous↗