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Biomedical subjects

J P Williams

Publications and source records attributed to J P Williams.

At least 19 recordsLinked to original sources
PubMed1992

Low temperature-induced fatty acid desaturation in Brassica napus: thermal deactivation and reactivation of the process.

When Brassica napus plants are grown at low temperatures (e.g., 5 degrees C) the rate of desaturation in leaves of newly formed fatty acids in both chloroplastic (MGDG) and cytosolic (PC) diacylglycerols is higher or more rapid than in plants grown at higher temperatures (e.g., 30 degrees C). This low temperature-induced increase in the rate of desaturation is lost within hours if plants are transferred to higher temperatures. However, if plants are then returned to low temperatures they regain the ability to rapidly desaturate fatty acids. This process is restored relatively slowly (over days) in contrast to the more rapid loss at high temperatures. This has important physiological consequences on the level of unsaturated fatty acids in plant membranes and the process of temperature control of the fatty acid composition of membrane lipids.

Brassica↗
PubMed1992

Low temperature-induced fatty acid desaturation in Brassica napus: thermal lability of the process.

The leaves of Brassica napus plants grown at 5 degrees C have a higher rate of fatty acid desaturation in both the cytosolic and chloroplastic pathways of diacylglycerol biosynthesis than plants grown at higher (up to 30 degrees C) temperatures. This physiological response to low growth temperature results in higher levels of unsaturated fatty acids in the leaf membrane lipids. These data suggest that this low temperature-induced desaturation process is thermolabile and can be inactivated by placing the leaves at temperatures of 30 degrees C for 4-8 h. Our evidence suggests that it is an additional rapid process to the normal 'basal' desaturation which occurs at a relatively slower rate. The data also show that the C16 and C18 fatty acids in the cytosol are desaturated at different rates and react differently to the high temperature treatment, suggesting that they are separate processes and are controlled independently.

Brassica↗
PubMed1992

Phosphorylation by casein kinase II alters the biological activity of calmodulin.

Calmodulin is the major intracellular Ca(2+)-binding protein, providing Ca(2+)-dependent regulation of numerous intracellular enzymes. The phosphorylation of calmodulin may provide an additional mechanism for modulating its function as a signal transducer. Phosphocalmodulin has been identified in tissues and cells, and calmodulin is phosphorylated both in vitro and in intact cells by various enzymes. Phosphorylation of calmodulin on serine/threonine residues by casein kinase II decreases its ability to activate both myosin-light-chain kinase and cyclic nucleotide phosphodiesterase. For myosin-light-chain kinase the primary effect is an inhibition of the Vmax. of the reaction, with no apparent change in the concentration at which half-maximal velocity is attained (K0.5) for either Ca2+ or calmodulin. In contrast, for phosphodiesterase, phosphorylation of calmodulin significantly increases the K0.5 for calmodulin without noticeably altering the Vmax. or the K0.5 for Ca2+. The higher the stoichiometry of phosphorylation of calmodulin, the greater the inhibition of calmodulin-stimulated activity for both enzymes. Therefore the phosphorylation of calmodulin by casein kinase II appears to provide a Ca(2+)-independent mechanism whereby calmodulin regulates at least two important target enzymes, myosin-light-chain kinase and cyclic nucleotide phosphodiesterase.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1991

Selective liquid chromatographic assay for propylthiouracil in plasma.

A liquid chromatographic assay was developed to quantitate propylthiouracil in plasma using an internal standard, 5-propyl-2-thiouracil, of similar structure and physical properties. Caffeine, which coelutes with propylthiouracil, was removed by extraction from serum treated with base. No other compounds were found to interfere in the assay. The drug was extracted from plasma with chloroform with a recovery of 59.4% and the intra- and inter-assay coefficients of variation were 5.7 and 3.3%, respectively. The assay was linear to 3 micrograms/ml with a lower detection limit of 40 ng/ml for a sample volume of 1 ml.

Caffeine↗
PubMed1991

Comprehension by learning-disabled and nondisabled adolescents of personal/social problems presented in text.

Four groups of 14-year-olds, differing in reading level, learning disability status, and socioeconomic status, read and retold short problem narratives and answered questions. The pattern of reporting components of the problem schema (goal/obstacles/choices) differed for problems presented with or without a statement of the character's priority for action, suggesting that including priorities adds another level of information to the problem text and changes its macrostructure. Even the poorest readers showed this sensitivity to text structure. Three of the four measures of problem representation (idea units recalled, problem-schema components reported, and error rate) reflected overall reading ability. However, the degree to which extraneous information was incorporated into problem representations did not. Learning-disabled students made more importations, and more implausible importations, than did non-disabled students. Moreover, this pattern was associated with poor problem solving. Only proficient readers showed awareness of the source of the information (text or extratext) on which their predictions were based.

Adolescent↗
PubMed1990

Magnetic resonance imaging of bone marrow in sickle cell disease: clinical, hematologic, and pathologic correlations.

A longitudinal, prospective, controlled evaluation of magnetic resonance images (MRI) of long bones in sickle cell patients was undertaken simultaneously with assessment of clinical status and hematologic parameters, including dense erythrocytes. MRI of bone marrow in sickle cell patients during steady states appeared patchy and were markedly different from those in matched controls (P approximately 0). Patients with severe patchiness were older than those with mild or moderate patchiness (P less than .03). Sixty-nine MRI were performed during 28 painful episodes occurring in 14 subjects with sickle cell disease (SCD). Increased signals on intermediate and T2-weighted images were detected in 35.7% of painful episodes. These abnormalities were distinct and not observed to occur spontaneously during the steady-state examinations (P approximately 0). Bone marrow infarcts were confirmed by biopsy in two instances and autopsy in one instance. Dense red cells decreased by 40.81% of baseline during pain crises (P = .00005), more remarkably in those who had pain in the lower extremities (P = .0145). Patients with change in MRI during pain crises had a greater percentage change in the dense cells than those without the change in MRI (69.7% v 31.3%, P = .0120).

Anemia, Sickle Cell↗
PubMed1990

Depressive self-presentation: beyond self-handicapping.

An experiment was conducted to examine the notion that depressives' responses would reflect a protective self-presentation style (Hill, Weary, & Williams, 1986), the underlying goal of which would be the avoidance of future performance demands and potential losses in self-esteem. In this study, depressed and nondepressed Ss were asked to perform a relatively simple visual-motor task. Half of the depressed and half of the nondepressed Ss were told that if they were successful at the task, they would be asked to perform a 2nd, similar task. The remaining Ss were given no such expectation of future performance. We predicted and found that depressed compared with nondepressed Ss strategically failed at the task when presented with the possibility of future performance and further losses in esteem. Moreover, this strategic failure was associated with some costs; depressed-future performance expectancy Ss experienced more discomfort or negative affect as a result of their performance. The relationship between this depressive self-presentation and self-handicapping strategies is discussed.

Achievement↗
PubMed1990

Experimental studies of radiation carcinogenesis in the skin: a review.

Skin has been widely used in radiation carcinogenesis studies because of the accessibility and visibility of its tumours. Both rat and mouse models have proved to be sensitive, reproducible systems to study the dose and time response of cancer induction following different modes and qualities of radiation exposure. This paper discusses the variation in the shape of the low-LET dose responses from purely linear with no threshold to the highly quadratic curves with significant thresholds, although a linear response is more consistently reported following high-LET radiations. Some dose-response curves show no tendency to turnover at high doses, others show a declining incidence of skin cancer at the highest doses. Protraction or fractionation of the dose reduces the carcinogenic effect in rat skin, whilst the reported dose rate studies in mice are equivocal regarding any sparing effect. Mouse skin cancer studies, in particular, have empirically refuted the 'hot particle hypothesis'. The extensive studies of Albert and Burns highlight hair follicle damage at 300 microns depth as critical in the development of the majority of rat skin tumours. In contrast, mouse studies report a wide variety of cell types as the putative 'cells at risk' in the skin from the spectrum of epidermal and dermal tumours which are induced, and which have been found to be amenable to classification using human pathological categories. Despite these interspecies differences, it is shown that all of the experimental data for radiogenic skin cancer, when expressed per unit area of skin, fall on a relatively narrow and well defined response curve, which is approximately two orders of magnitude more sensitive than the human skin cancer dose response.

Animals↗
PubMed1990

Computerized tomography in the diagnosis of the congenital fibrosis syndrome.

A patient with congenital ptosis and inferior rectus fibrosis is described. Marked atrophy of the left inferior rectus muscle was demonstrated by orbital computerized tomography (CT). Computerized tomographic findings in this patient and a series of 20 patients with no ocular disease and normal motility indicate that CT is a valuable tool for the evaluation of extraocular muscle size when qualitative comparison is made between corresponding muscles in the same patient.

Amblyopia↗
PubMed1979

Computed tomography changes in neurosarcoidosis clearing with steroid treatment.

Contrast enhancement computed tomography (CT) in a patient with central nervous system (CNS) sarcoidosis revealed increased densities particularly in the frontal and temporal areas. Treatment with prednisone improved the condition, and the CT abnormality disappeared. These previously undescribed findings can be of help in establishing the diagnosis and in following the patient's response to treatment.

Adult↗
PubMed1979

Growth of the skull in the mutant dwarf mouse.

By following the development of individual mice from birth to 200 days of age, it was found that the skull of the homozygous mutant (dwdw) was 5% shorter than that of the normal phenotype at birth and some 30% shorter at 200 days of age. During post-natal growth of the skull, the cranium was least altered but the facial skeleton was greatly affected. The differences seen in different parts of the skull are attributed to the peak growth velocities of the various parts occurring at different times.

Animals↗
PubMed1978

Interhemispheric subdural empyema: neuroradiological diagnosis.

A case of subdural empyema situated in the interhemispheric subdural space is described. CT scan is useful in the diagnosis and follow-up of intracranial inflammatory pathology. Selective angiography was helpful in the compartmental localization of the abscess in the interhemispheric subdural space, adjacent to the falx and tentorium by virtue of the hypertrophied tentorial meningeal arteries and vascular displacement. CT scans are also useful in follow-up of cerebral abscess after micropaque barium has been injected into the cavity as in this patient.

Brain Abscess↗
PubMed1978

Muscle growth during neonatal undernutrition and subsequent rehabilitation in the rat.

The growth of the rat calf muscle has been followed radiographically during neonatal undernutrition and subsequent catch-up. The following observations were made: (1) The mean calf muscle width of rats reared in litters of 16 was 20% less than that of those reared in litters of 8. (2) There was no significant difference between the sexes in the degree of growth retardation brought about by suckling the pups in large litters. (3) By the end of the experiment, females had caught up in both muscle width and muscle length, the males had caught up in muscle length (identical to tibia length) but not in muscle width. (4) In male pups during undernutrition the muscle diameter was greater than in normally fed animals of the same weight (but younger). This difference was not seen in females. (5) During recovery, until a weight of about 160 g was reached, the muscle width of the neonatally undernourished rats of both sexes was less than controls of the same body weight.

Animals↗
PubMed1978

Catch-up growth in the rat skull after retardation during the suckling period.

In rats whose growth was restricted by rearing in large litters the skull was less affected than the spine and the brain case less than the face. No sex difference was apparent during undernutrition but on subsequent rehabilitation females had caught up to controls in four out of five skull measurements within 4 weeks and by the end of the experiment the skulls of the neonatally undernourished females were the same size and shape as the controls. In the case of males, however, the skull of the undernourished rats never attained the same width as the controls.

Age Factors↗
PubMed1978

A longitudinal radiographic study of the growth of the rat skull.

The growth of the skull of the rat was longitudinally from 23 to 140 day PC from radiographs. Four measurements were made on each animal at each age studied. The velocity graphs of these measurements showed that for two, namely neurocranium length and bizygomatic width, the peak rate of growth occurred before birth. Viscerocranium length and neurocranium width showed peak rates after birth. Males became significantly larger than females in each of the absolute measurements studied, but in cranial index and facial index there were no significant differences between the sexes. Both these indices showed strain differences when compared to the results obtained by other workers.

Age Factors↗
PubMed1977

Polyamines and their biosynthetic decarboxylases in various tissues of the young rat during recovery from undernutrition.

1. Weanling male and female rats were undernourished for 4 weeks and then rehabilitated by allowing ad libitum feeding. 2. During rehabilitation polyamine-biosynthetic enzymes were examined in the liver, spleen and quadriceps and gastrocnemius muscles. 3. During the first few hours of rehabilitiation there was a marked increase in liver weight, accompanied by a very marked increase in ornithine decarboxylase activity. Increases in the activity of this enzyme in other tissues did not occur until between 2 and 7 days of rehabilitation, at which time there were further increases in enzyme activity in the liver. 4. S-Adenosylmethionine decarboxylase activity also showed marked fluctuations in activity in all the tissues examined. 5. Hepatic putrescine and spermidine concentrations also varied during rehabilitation, but permine concentration remained relatively constant. Both spermine and spermidine were at normal concentrations in the liver from the 10th days of rehabilitation onwards. 6. In all of the tissues examined there were marked sex differences in the parameters studied, particularly in splenic and muscular ornithine decarboxylase activity. 7. In the tissues of the male rats, changes in polyamine synthesis paralled changes in nucleic acid and protein synthesis.

Adenosylmethionine Decarboxylase↗