Search PubMed⌕ Search

Biomedical subjects

M C Williams

Publications and source records attributed to M C Williams.

At least 19 recordsLinked to original sources
PubMed1992

A longitudinal study of the effects on the oral mucosa of treatment for acute childhood leukaemia.

A longitudinal study was undertaken of the effect of therapy on the oral mucosa of 12 children with acute leukaemia. The major oral problem was ulceration, which was associated with neutrophil counts of less than 1.0 x 10(9)/l. Candida carriage rates were consistently high in patients with or without oral candidosis. Salivary flow was not significantly different between leukaemic children and the control group.

Antineoplastic Agents↗
PubMed1992

Effects of surfactant apolipoproteins on liposome structure: implications for tubular myelin formation.

Tubular myelin is one of several forms of lung surfactant and may play an important role in its surface activity. To determine possible mechanisms of tubular myelin formation, we studied the effects of purified surfactant proteins (SP-A, SP-B, and SP-C) on large unilamellar dipalmitoylphosphatidylcholine-egg phosphatidylglycerol (7/3; wt/wt) liposomes. We studied different types of membrane interaction induced by the apolipoproteins and correlated these with the observed changes in ultrastructure. Aggregation was assessed by measurement of light absorbance, lysis, and fusion by measurement of the fluorescence emitted by water-soluble and lipid-soluble probes, respectively. Mixtures of the apolipoproteins and liposomes were examined in ultrastructural studies by negative staining and by thin sectioning. We found that each protein had a pronounced and distinct effect on liposome structure. SP-A caused aggregation, whereas SP-B and SP-C also caused extensive leakage of liposome contents (lysis) and some degree of lipid mixing (fusion). The disruptive effects of SP-B and to a lesser extent those of SP-C were correlated by negative staining with the appearance of bilayer disks, which tended to aggregate into large sheets. There was a marked synergy between SP-A and SP-B in the process of membrane fusion in the presence of calcium, which correlated with an early (10 min) and extensive rearrangement of the structures seen by electron microscopy followed by a delayed (24 h) appearance of small amounts of tubular myelin.

Animals↗
PubMed1992

Effective interventions for reading disability.

A simple, readily accessible, and inexpensive intervention which produces immediate improvements in the reading comprehension abilities of reading-disabled children has been found. The intervention consists of colored overlays, or overlays which reduce the contrast of printed materials. This intervention produces reading comprehension gains in approximately 80 percent of the reading-disabled children tested.

Analysis of Variance↗
PubMed1992

Anaplastic tracheal squamous cell carcinoma in a cat.

A cat with primary intratracheal squamous cell carcinoma presented with severe dyspnoea and a dry cough. Radiographic changes included pulmonary hyperinflation and tracheal thickening at the thoracic inlet. On post mortem examination, proliferative, white, granular nodules in the trachea were confirmed to be an anaplastic squamous cell carcinoma.

Animals↗
PubMed1991

Metacontrast with masks varying in spatial frequency and wavelength.

In a metacontrast masking paradigm, adult subjects were required to detect briefly presented target lines followed at various delays by a flanking mask varying in spatial frequency and wavelength. Detection accuracy, the dependent measure, was recorded as a function of the delay of the mask. The results showed that long wavelength masks produced maximum masking at a relatively short delay, while short wavelength masks produced maximum masking at a relatively long delay. Results are discussed within the framework of transient/sustained (magnocellular/parvocellular) theory of visual processing, and suggest that low spatial frequency channels respond with shorter latency and/or faster rise time to short wavelength stimuli, and high spatial frequency channels respond with greater sensitivity to long wavelength stimuli.

Adult↗
PubMed1991

Regulation of ATP-dependent surfactant secretion and activation of second-messenger systems in alveolar type II cells.

Several different classes of agonists are known to stimulate exocytosis in type II cells. These agonists cause increases in second messengers, such as adenosine 3',5'-cyclic monophosphate (cAMP) or cytosolic Ca2+, and/or stimulate protein kinase C. We studied generation of cAMP and phosphoinositide (PI) turnover in monolayer cultures of type II cells and measured [Ca2+]i in single cultured cells. ATP [10(-4) M], which stimulates secretion of phosphatidylcholine (PC) and increases cellular cAMP, also stimulated PI turnover and increased [Ca2+]i. 12-O-tetradecanoylphorbol-13-acetate (TPA), which stimulates PC secretion and activates protein kinase C, did not increase [Ca2+]i. Pretreatment of type II cells with the calmodulin antagonist N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) inhibited the PC secretion induced by ATP and TPA and blocked the increase in PI turnover caused by ATP. ATP-dependent surfactant secretion and stimulation of PI turnover could also be inhibited by pretreatment of the cells with pertussis toxin. We used the fluorescent probe indo-1 to measure [Ca2+]i in single cultured type II cells. ATP produced rapid transient increases in [Ca2+]i, which could be prevented by pretreatment of the cells with either TPA or W-7. Our data suggest that pertussis toxin-sensitive G protein(s) are involved in ATP-dependent activation of PI turnover and in secretion of surfactant in type II cells. Activation of protein kinase C blocks the ATP-stimulated increase in [Ca2+]i. Finally, calmodulin may be involved in the regulation of ATP-dependent increase in [Ca2+]i, the activation of PI turnover, and the secretion of surfactant in type II cells.

Adenosine Triphosphate↗
PubMed1991

Changes in lipid structure produced by surfactant proteins SP-A, SP-B, and SP-C.

Pulmonary surfactant phospholipids may assume several different structures including tubular myelin, unilamellar and multilamellar vesicles, and others. These populations of materials appear to have similar phospholipid compositions but may differ in their association with surfactant proteins SP-A, SP-B, or SP-C. We have used electron microscopy to determine the changes in structure of simple lipid mixtures (phosphatidylglycerol, dipalmitoylphosphatidylcholine) produced by adding one or combinations of the three proteins. Adding SP-A to lipids generated multilamellar structures composed of membranes with fuzzy or particulate surfaces. In contrast, SP-B or SP-C generated discoidal particles and structures that appeared to be sheets of membrane formed by associated particles. Used together, SP-A and SP-B reorganized some of the lipid into tubular myelin, a structure that was not observed in SP-A, SP-C recombinants. These observations confirm the in vitro formation of tubular myelin reported by others and support the possibility that surfactant materials with defined structure can be produced in vitro for analyses of their molecular organizations.

Animals↗
PubMed1991

Differentiation of type II cells during explant culture of human fetal lung is accelerated by endogenous prostanoids and adenosine 3',5'-monophosphate.

Explant culture of the fetal lung, in the absence of serum or hormones, results in precocious biochemical and morphological differentiation of alveolar epithelial cells. In this study we tested the hypothesis that these maturational events are induced by endogenous cAMP. During culture of human fetal lung the content of tissue cAMP increased 140% from days 3-6. Treatment with isobutylmethylxanthine caused a further doubling of cAMP content, and indomethacin blocked most of the increase in cAMP. Isobutylmethylxanthine accelerated and indomethacin inhibited the increases during culture in surfactant protein-A (SP-A), SP-A mRNA, SP-B mRNA, phosphatidylcholine content, and activity of fatty acid synthetase. There was no effect of these treatments on the content of SP-C mRNA, which did not increase during culture. Increasing concentrations of prostaglandins E1 and E2 in the presence of indomethacin produced a parallel stimulation of cAMP content, SP-A, and fatty acid synthetase activity. The temporal increase in SP-A was also blocked by inhibitors of protein kinase-A. In morphological studies, indomethacin-treated explants appeared less mature, with decreased intralumenal volume and more columnar epithelial cells. We conclude that increased tissue cAMP levels, stimulated by endogenous prostaglandins, accelerate differentiation of alveolar epithelial cells during explant culture.

1-Methyl-3-isobutylxanthine↗
PubMed1991

Childhood leukemia and dental considerations.

Leukemia is the major form of cancer in children in Britain and mirrors the percentage of children affected in the USA. This report outlines some of the medical aspects of leukemia and its treatment and gives a guide to the dentist, who may have the responsibility of dealing with leukemic children and their families.

Child↗
PubMed1991

A randomized comparison of assisted vaginal delivery by obstetric forceps and polyethylene vacuum cup.

The assisted vaginal delivery methods of rigid obstetric forceps and polyethylene vacuum cup extraction were compared in a prospective, randomized study. The 99 women studied had all completed 35 full weeks' gestation, required attempted assisted vaginal delivery, and were randomly assigned to either attempted forceps or vacuum-assisted delivery. All presentations were cephalic, with stations ranging from +1 to +4. Neonates were evaluated at 24 hours by neonatal staff. The infants underwent intracranial ultrasound screening during the first 24 hours of life and ophthalmologic examination within 48 hours. Vaginal delivery was successful with the intended method in 83% of vacuum-assisted deliveries and in 78% of forceps deliveries (not statistically significant). Neonatal retinal hemorrhage was found in 17 and 38% (P less than .043) of the randomized forceps and vacuum deliveries, respectively. No intraventricular hemorrhage was found. Apart from associations between vacuum-assisted delivery and mild hyperbilirubinemia and neonatal retinal hemorrhage (of uncertain clinical significance), and between assisted forceps delivery and an increased potential for facial injury, neonatal outcomes did not differ significantly. Maternal outcomes also did not differ significantly. No significant differences in safety or efficacy were found between polyethylene cup vacuum extraction and rigid obstetric forceps-assisted vaginal delivery in this population of predominantly low-pelvic assisted deliveries. Patients delivered by sequential use of forceps after vacuum or by vacuum after failed forceps application did not suffer significantly increased morbidity relative to those delivered by forceps or vacuum alone. Use of alternate or sequential methods allowed an overall cesarean rate of 3% in this population.

Acid-Base Equilibrium↗
PubMed1991

Sequential outpatient application of intravaginal prostaglandin E2 gel in the management of postdates pregnancies.

A randomized blinded investigation was undertaken to determine the efficacy and safety of sequentially applied intravaginal prostaglandin E2 (PGE2) gel for accelerating cervical ripening in an outpatient setting in low-risk prolonged pregnancies. Fifty women with uncomplicated pregnancies at or beyond 41 weeks' gestation and Bishop scores below 9 received twice-weekly outpatient administration of gel containing 2.0 mg of PGE2 or placebo. Thirty nulliparas and 20 multiparas were enrolled. The PGE2 gel failed to improve cervical ripening over placebo, as judged by Bishop scores. There was no difference between the groups in gestational age on admission to the labor and delivery suite, number of gel applications, requirement for oxytocin, incidence of cesarean delivery, or neonatal outcome. Only two patients (4%) experienced regular uterine contractions after gel insertion; these subsided spontaneously in both. None of the subjects experienced labor, tetanic contractions, evidence of fetal distress, or any other side effects related to gel insertion. We conclude that PGE2 gel in this dosage may be used safely in an outpatient setting, but more frequent application or earlier initiation may be required to produce a clinical effect.

Administration, Intravaginal↗
PubMed1990

Lamellar bodies of cultured human fetal lung: content of surfactant protein A (SP-A), surface film formation and structural transformation in vitro.

Lamellar bodies were isolated from dexamethasone and T3-treated explant cultures of human fetal lung, using sucrose density-gradient centrifugation. We examined their content of surfactant apoprotein A (SP-A), and their ability to form surface films and to undergo structural transformation in vitro. SP-A measured by ELISA composed less than 2% of total protein within lamellar bodies; this represented, as a minimum estimate, a 2-12-fold enrichment over homogenate. One- and two-dimensional gel electrophoresis also suggested that SP-A was a minor protein component of lamellar bodies. Adsorption of lamellar bodies to an air/water interface was moderately rapid, but accelerated dramatically upon addition of exogenous SP-A in ratios of 1:2-16 (SP-A:phospholipid, w/w). Similar adsorption patterns were seen for lamellar bodies from fresh adult rat and rabbit lung. Lamellar bodies incubated under conditions that promote formation of tubular myelin underwent structural rearrangement only in the presence of exogenous SP-A, with extensive formation of multilamellate whorls of lipid bilayers (but no classical tubular myelin lattices). We conclude that lamellar bodies are enriched in SP-A, but have insufficient content of SP-A for structural transformation to tubular myelin and rapid surface film formation in vitro.

Cell Fractionation↗
PubMed1990

Eye movement indices of mental workload.

Four investigations were carried out to assess the feasibility of using eye movement measures as indices of mental workload. In the first experiment, saccadic extent was measured during free viewing while subjects performed low, moderate and high complexity, auditory tone counting as the workload tasks. The range of saccadic extent decreased significantly as tone counting complexity (workload) was increased. In the second experiment the range of spontaneous saccades was measured under three levels of counting complexity with a visual task that did not require fixation or tracking. The results indicated that the extent of saccadic eye movements was significantly restricted as counting complexity increased. In the third experiment, the effects of practice were examined and decreased saccadic range under high tone counting complexity was observed even when significant increases in performance occurred with practice. Finally, in experiment 4, the first experiment was repeated with additional optokinetic stimulation and the saccadic range was again observed to decrease with tone counting complexity. The results indicated that the extent of spontaneous and elicited eye movements was significantly restricted as counting complexity increased. We conclude that this measure may provide a valuable index of mental workload.

Adult↗
PubMed1990

Effects of isoluminant-background color on metacontrast and stroboscopic motion: interactions between sustained (P) and transient (M) channels.

The magnitudes of metacontrast masking and of stroboscopic motion were investigated as a function of the color of isoluminant backgrounds on which the stimuli consisting of rectangular-shaped luminance decrements appeared. White, green, and red backgrounds were employed. Background isoluminance was obtained by minimal flicker settings with heterochromatic flicker of uniform fields. Both metacontrast and stroboscopic motion were decreased when red as compared to white or green backgrounds were used. Within the context of current sustained-transient channel approaches to visual masking and motion, these results indicate that the activity of transient channels is attenuated by red relative to white or green backgrounds. Moreover, these psychophysical findings may correspond to the suppressive effects of diffuse red light on neural activity in the transient M pathway of monkey.

Adult↗
PubMed1990

The effect of magnesium sulfate infusion on systemic and renal prostacyclin production.

Recent in vitro studies have suggested that magnesium sulfate (MgSO4) infusions may increase prostacyclin production. We studied the effect of MgSO4 infusion on prostacyclin (PGI2) metabolite excretion in women with either pregnancy induced hypertension or preterm labor. Excretion of renal and systemic metabolites of PGI2 was measured prior to and following the start of MgSO4 infusion in the two groups. An increased in renal PGI2 metabolite preterm labor excretion was noted in the hypertension group but no change was noted in systemic PGI2 excretion in either group. These data fail to support a generalized, short term increase in endothelial cell PGI2 production as the basis for the beneficial effect of MgSO4.

Adult↗
PubMed1990

Optimizing radiation worker protection: the practical application of risk analysis.

This paper presents the concepts of equivalent risk and risk minimization in optimizing radiation worker protection. When prescribing worker protection requirements and identifying work restrictions, all significant contributions to worker risk should be considered, not just the risk associated with radiation dose. This approach requires a practical application of risk analysis that allows comparison of a variety of risks. Examples of the types of worker risks that must be evaluated are given, and the author proposes that the scientific community develops a methodology for risk comparison that can be implemented via an expert system to facilitate risk analysis and decision making.

Humans↗