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Biomedical subjects

M Potts

Publications and source records attributed to M Potts.

At least 73 records · Page 4Linked to original sources
PubMed1994

Lea's Shield, a new barrier contraceptive preliminary clinical evaluations three-day tolerance study.

In this study the Lea's Shield was evaluated for its tolerance by women who wore the device for three consecutive days. Ten women who wore the Lea's Shield for 72 hours completed the tolerance study without adverse effects. Examination of the cervix and vagina revealed that the device did not provoke any significant cellular or microbial changes among the wearers. No major changes in the appearance or prevalence of vaginal flora occurred in the women after three days of wearing the device. A gradient in the pH could be detected between the contents of the vagina, which was more acidic than the contents of the bowl of the device. The range of cervical shapes and vaginal morphology among the study participants has had no influence upon the ability of the device to remain in its proper position. The device "settles in place" as it is pushed in, thereby obviating any special maneuvers for proper positioning. No vaginal nor cervical trauma occurred. We have concluded from these basic clinical evaluations that Lea's Shield is well tolerated during three days of use. Efficacy trials in women at risk recently completed have confirmed the high degree of acceptability and that the device can function adequately as one size fits all.

Cervix Uteri↗
PubMed1994

Desiccation tolerance of prokaryotes.

The removal of cell-bound water through air drying and the addition of water to air-dried cells are forces that have played a pivotal role in the evolution of the prokaryotes. In bacterial cells that have been subjected to air drying, the evaporation of free cytoplasmic water (Vf) can be instantaneous, and an equilibrium between cell-bound water (Vb) and the environmental water (vapor) potential (psi wv) may be achieved rapidly. In the air-dried state some bacteria survive only for seconds whereas others can tolerate desiccation for thousands, perhaps millions, of years. The desiccated (anhydrobiotic) cell is characterized by its singular lack of water--with contents as low as 0.02 g of H2O g (dry weight)-1. At these levels the monolayer coverage by water of macromolecules, including DNA and proteins, is disturbed. As a consequence the mechanisms that confer desiccation tolerance upon air-dried bacteria are markedly different from those, such as the mechanism of preferential exclusion of compatible solutes, that preserve the integrity of salt-, osmotically, and freeze-thaw-stressed cells. Desiccation tolerance reflects a complex array of interactions at the structural, physiological, and molecular levels. Many of the mechanisms remain cryptic, but it is clear that they involve interactions, such as those between proteins and co-solvents, that derive from the unique properties of the water molecule. A water replacement hypothesis accounts for how the nonreducing disaccharides trehalose and sucrose preserve the integrity of membranes and proteins. Nevertheless, we have virtually no insight into the state of the cytoplasm of an air-dried cell. There is no evidence for any obvious adaptations of proteins that can counter the effects of air drying or for the occurrence of any proteins that provide a direct and a tangible contribution to cell stability. Among the prokaryotes that can exist as anhydrobiotic cells, the cyanobacteria have a marked capacity to do so. One form, Nostoc commune, encompasses a number of the features that appear to be critical to the withstanding of a long-term water deficit, including the elaboration of a conspicuous extracellular glycan, synthesis of abundant UV-absorbing pigments, and maintenance of protein stability and structural integrity. There are indications of a growing technology for air-dried cells and enzymes. Paradoxically, desiccation tolerance of bacteria has virtually been ignored for the past quarter century. The present review considers what is known, and what is not known, about desiccation, a phenomenon that impinges upon every facet of the distributions and activities of prokaryotic cells.

Adaptation, Physiological↗
PubMed1994

The value of the short tau inversion recovery sequence in magnetic resonance imaging of thyroid eye disease.

22 patients with thyroid eye disease were examined with magnetic resonance imaging (MRI) and the results compared with 10 controls. Imaging was performed on a 1.0 T scanner using a head coil. All patients were examined using both T1W and short tau inversion recovery (STIR) sequences. The relative signal intensity (SI) of individual extraocular muscles were quantified by comparison with SI from the adjacent temporalis muscle to give a signal intensity ratio (SIR). The results were compared with clinical disease activity assessed by the Werner grading system. Visual evaluation of muscle size and calculated SIRs showed an increase when compared to normals in 15 of the 22 patients. This difference was significant in patients with high grade (4-6) clinical disease. The known histological changes in this disease suggest that this increase in signal is caused by oedema secondary to acute inflammation. STIR sequences suppress the retro-orbital fat and thus enhance these changes both in the muscles and in the fat itself. The MR findings suggest that the STIR sequence can be used to predict those patients that will respond to anti-inflammatory treatment.

Adult↗
PubMed1994

Pediatric clerkship performance in diverse community clinical settings.

OBJECTIVE: To determine whether multiple and diverse clinical settings and resources in a pediatric clerkship result in satisfactory performance by medical students and affect their choice of a pediatric residency after graduation. DESIGN: Retrospective study 1985 through 1990. SETTING: Medical students in a pediatric clerkship in a medical school that is part of a land grant university where the clinical curriculum is conducted in six geographically distinct communities. MAIN OUTCOME MEASURE: (1) Three performance criteria including: multiple choice final examination score, clinical performance evaluations by preceptors, and formal evaluation of patient written records. (2) Students matching with a pediatric or combined internal medicine/pediatric residency. RESULTS: Of 499 students 92.8% successfully passed all three criteria with no statistically significant differences between communities. A smaller percentage of students (15.2%) (community range, 6 to 18.5%) entered straight or combined pediatric residencies, whether or not a pediatric residency was present in the community. CONCLUSIONS: Medical students can achieve satisfactory competency in pediatric clerkships offered in diverse clinical settings, and choose pediatric residency training whether or not they are exposed to a pediatric residency during their clerkship. A problem-based learning curriculum does not hinder selecting pediatrics as a career choice.

Career Choice↗
PubMed1993

Rehydration induces rapid onset of lipid biosynthesis in desiccated Nostoc commune (Cyanobacteria).

Water, which contained [1,3-3H]glycerol, [35S]sodium sulfate, or [32P]sodium orthophosphate, was used to rehydrate air-dried cells of the desiccation-tolerant filamentous cyanobacterium Nostoc commune. The cells retained their capacities for the uptake and transport of all three compounds and, in response to rewetting, they mobilized the radiolabels into lipid precursors and initiated complex lipid biosynthesis. The onset of these events, measured in short-term, long-term and pulse-chase labeling experiments, was judged to be very rapid. The radiolabeled pool sizes of the major membrane species phosphatidylglycerol (PG) and sulfoquinovosyl diacylglycerol (SQDG) reached steady-state within several minutes, while those of the two abundant membrane glycolipids, mono- and di-glycosyldiacylglycerol (MGDG, DGDG), achieved uniform labeling within 2 h. The pattern of sulfolipid synthesis was generally more complex than the other lipid species. Analysis of the maturation of SQDG through differential labeling provided the only example of a lag in lipid maturation during the early stages (minutes) of cell rehydration. In this instance, the lag appeared to be associated specifically with the incorporation of 35SO3- by the sulfoquinovose. During the initial 2 h of rewetting there was complete turnover of 3H-label in the pools of the principal lipid precursors 1,2-sn-diacylglycerol and 1,3-diacylglycerol. In contrast, the accumulation of label by the major lipid of the heterocyst cell-wall, a non-saponifiable glycolipid, became detectable only after 24 h of rewetting. The present data are discussed in relation to the basis for desiccation tolerance in N. Commune.

Chromatography, Thin Layer↗
PubMed1993

A protein-tyrosine/serine phosphatase encoded by the genome of the cyanobacterium Nostoc commune UTEX 584.

Protein-tyrosine phosphorylation has long been regarded as an exclusively eukaryotic phenomenon. Although some non-eukaryotes, mainly viruses, possess genes encoding protein-tyrosine kinases or protein-tyrosine phosphatases, these were probably appropriated from the eukaryotic hosts that constitute the sites of action of these enzymes. Herein we identify a gene, iphP, from the chromosome of the cyanobacterium Nostoc commune UTEX 584 that contains the His-Cys-Xaa-Ala-Gly-Xaa-Xaa-Arg sequence characteristic of known protein-tyrosine phosphatases. The expressed gene product, IphP, displayed protein-tyrosine phosphatase activity toward phosphotyrosine residues on reduced, carboxyamidomethylated, and maleylated lysozyme with optimum activity at pH 5.0. In addition, IphP dephosphorylated the phosphoseryl groups on casein that had been phosphorylated by the cAMP-dependent protein kinase. Cell lysates of N. commune probed with antibodies to phosphotyrosine indicated the presence of a tyrosine-phosphorylated protein of M(r) approximately 85 kDa. This tyrosine-phosphorylated protein was detected in cells grown in the presence of combined nitrogen but not in nitrogen-deficient media that induces the formation of differentiated N2-fixing cells (heterocysts). Together, these data suggest a role for protein-tyrosine phosphorylation in regulating cellular functions in this cyanobacterium. IphP is the first protein-tyrosine phosphatase to be discovered that is encoded by the chromosomal DNA of any prokaryote. Given the free-living nature of N. commune and the phylogenetic antiquity of the cyanobacteria, these findings suggest for the first time the existence of a protein-tyrosine phosphatase of genuine, unambiguous prokaryotic ancestry, thus raising fundamental questions as to the origin and role of tyrosine phosphorylation.

Amino Acid Sequence↗
PubMed1993

Better barriers.

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Condoms↗
PubMed1993

Should oral contraceptives be available without prescription?

In this paper, it is argued that oral contraceptives should be available without prescription. Prescription status entails heavy costs, including the dollar, time, and psychological costs of visiting a physician to obtain a prescription, the financial and human costs of unintended pregnancies that result from the obstacle to access caused by medicalization of oral contraceptives, and administrative costs to the health care system. After a review and evaluation of the reasons for strict medical control of oral contraceptives in the United States, safety concerns anticipated in response to the proposal discussed here are addressed. Also, concerns that prescription status is necessary for efficacious use are evaluated. It is concluded that neither safety nor efficacy considerations justify prescription status for oral contraceptives. Revised package design and patient labeling could allow women to screen themselves for contraindications, to educate themselves about danger signs, and to use oral contraceptives safely and successfully. Several alternatives to providing oral contraceptives by prescription with current package design and labeling and selling them over the counter are suggested; the proposals discussed would make these safe and effective contraceptives easier to obtain and to use.

Contraceptives, Oral↗
PubMed1992

Myoglobin in a cyanobacterium.

Myoglobin was found in the nitrogen-fixing cyanobacterium Nostoc commune. This cyanobacterial myoglobin, referred to as cyanoglobin, was shown to be a soluble hemoprotein of 12.5 kilodaltons with an amino acid sequence that is related to that of myoglobins from two lower eukaryotes, the ciliated protozoa Paramecium caudatum and Tetrahymena pyriformis. Cyanoglobin is encoded by the glbN gene, which is positioned between nifU and nifH-two genes essential for nitrogen fixation-in the genome of Nostoc. Cyanoglobin was detected in Nostoc cells only when they were starved for nitrogen and incubated microaerobically.

Amino Acid Sequence↗
PubMed1992

AIDS in Africa.

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Acquired Immunodeficiency Syndrome↗