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Biomedical subjects

S Parker

Publications and source records attributed to S Parker.

At least 235 records · Page 13Linked to original sources
PubMed1976

Surface alterations in calf lymphocytes oxidized by sodium periodate.

In order to investigate alterations in surface structure in transformed lymphocytes, calf submandibular lymph node cell suspensions were oxidized with NaIO4. Oxidezed lymphocytes were morphologically transformed and had higher rates of DNA synthesis by 2 days after treatment. These results were prevented by reduction of the cell suspension with NaBH4, or by neuraminidase treatment of cells prior to oxidation. The amount of 125I-labeled Agaricus bisporus lectin bound to cells immediately after oxidation and the affinity constant for binding were increased over 2-fold, while cells immediately following oxidation and reduction showed decreased receptors with still higher affinity for the lectin compared to untreated cells. The amount of Phaseolus vulgaris lectin bound to oxidezed cells was also increased, but affinity was unchanged. Immediately following oxidation and reduction, these receptor sites were unchanged in number and affinity from untreated cells. In contrast, the number and affinity of receptors for concanavalin A were not changed immediately after oxidation or oxidation and reduction. In order to define the extent of compositional changes in surface glycoprotein receptors, plasma membranes were isolated from frozen calf submandibular lymph nodes. Compared to untreated plasma membranes, oxidezed membranes had similar contents of galactose, mannose, N-acetylglucosamine, N-acetylgalactosamine, fucose, and amino acids. Sialic acid content of oxidized membranes was reduced when measured by thiobarbituric acid assay. Sialic acids of untreated plasma membranes co-chromatographed with N-glycolylneurominic acid and N-acetylneuraminic acid, while those of oxidized membranes co-chromatographed with N-glycolylneuraminic acid and 5-acetamido-3,5-dideoxy-L-arabino-7-aldehydo-2-heptulosonic acid. Therefore, specific surface conformational changes in certain classes of membrane glycoproteins are associated with mild Malapradian oxidation of membrane sialic acids. These temporally precede NaIO4-induced transformation of calf lymphocytes. This is consistent with an hypothesis of membrane-mediated stimulation of lymphocyte transformation.

Animals↗
PubMed1976

The resistance of putative premalignant liver cell populations, hyperplastic nodules, to the acute cytotoxic effects of some hepatocarcinogens.

The hypothesis that liver carcinogenesis may have as an important facet the early selection of carcinogen-resistant cells was tested in animals in which putative premalignant hepatocyte populations, hyperplastic nodules, were induced by 2-acetylaminofluorene or by ethionine. Hyperplastic nodules were observed to be resistant to the acute necrogenic effects of 2 hepatotoxins, CCl4 and dimethylnitrosamine, under conditions in which liver cell necrosis occurred in the liver surrounding the nodules. In addition, although [methyl-3H]dimethylnitrosamine was taken up to an equal degree in nodules and normal liver, the interactions with DNA, RNA, and protein in hyperplastic nodules were found to be about 50% less than in control liver. Hyperplastic nodules showed a marked decrease in uptake of [9-14C]-2-acetylaminofluorene, a finding that could account for the large decrease in labeling of DNA, RNA, and protein by [9-14C]-2acetylaminofluorene observed in the nodules. The results are consistent with and support the hypothesis that new hepatocyte populations that appear prior to cancer, during liver carcinogenesis, have as an important biological property a resistance to the cytotoxic effect of hepatocarcinogens. The basis for this resistance might be a decrease in uptake and/or a reduction in the level of activation of carcinogens.

2-Acetylaminofluorene↗
PubMed1975

Ratio scale measurement of the perceived lengths of lines.

In Experiments 1 and 2, magnitude and category estimates of perceived line length difference were used to rank order 36 pairs of lines with respect to the psychological length difference between the lines forming a pair. In Experiment 3 magnitude estimates of line length ratios were used to order the same 36 pairs with respect to the psychological length ratio between the lines comprising a pair. A nonmetric analysis of the rank-order of the difference and ratio judgments was used to construct a ratio scale of perceived line length. Perceived line length was found to be a power function of physical line length with an exponent of .46. In Experiments 4 and 5, magnitude and category estimates of line length similarity were obtained. A nonmetric analysis of these data indicated that similarity judgments were monotonic inverses of judgments of psychological ratios.

Adolescent↗
PubMedDate not supplied

The inter-rater reliability and internal consistency of a clinical evaluation exercise.

OBJECTIVE: To assess the internal consistency and inter-rater reliability of a clinical evaluation exercise (CEX) format that was designed to be easily utilized, but sufficiently detailed, to achieve uniform recording of the observed examination. DESIGN: A comparison of 128 CEXs conducted for 32 internal medicine interns by full-time faculty. This paper reports alpha coefficients as measures of internal consistency and several measures of inter-rater reliability. SETTING: A university internal medicine program. Observations were conducted at the end of the internship year. PARTICIPANTS: Participants were 32 interns and observers were 12 full-time faculty in the department of medicine. The entire intern group was chosen in order to optimize the spectrum of abilities represented. Patients used for the study were recruited by the chief resident from the inpatient medical service based on their ability and willingness to participate. INTERVENTION: Each intern was observed twice and there were two examiners during each CEX. The examiners were given a standardized preparation and used a format developed over five years of previous pilot studies. MEASUREMENTS AND MAIN RESULTS: The format appeared to have excellent internal consistency; alpha coefficients ranged from 0.79 to 0.99. However, multiple methods of determining inter-rater reliability yielded similar results; intraclass correlations ranged from 0.23 to 0.50 and generalizability coefficients from a low of 0.00 for the overall rating of the CEX to a high of 0.61 for the physical examination section. Transforming scores to eliminate rater effects and dichotomizing results into pass-fail did not appear to enhance the reliability results. CONCLUSIONS: Although the CEX is a valuable didactic tool, its psychometric properties preclude reliable assessment of clinical skills as a one-time observation.

Clinical Competence↗
PubMedDate not supplied

Perioperative rate-related silent myocardial ischemia and postoperative death.

A case is presented that demonstrates heart rate (HR)--related silent myocardial ischemia occurring preoperatively, subsiding intraoperatively, then recurring and leading to a post-operative cardiac death in a patient undergoing peripheral vascular surgery. This case illustrates that patients may have an ischemic threshold for HR whereby recurrent depression of the ST segment may occur during increase of HR to rates as low as 80 to 85 beats per minute (bpm), even in the absence of acute blood pressure (BP) changes. Myocardial ischemia may be HR related; however, the authors are not aware of a case that demonstrates repeated episodes of rate-related ischemia occurring at HRs well below the 100 bpm traditional definition of tachycardia. The authors conclude that patients at risk for perioperative myocardial ischemia should be identified and the hemodynamic management of these patients should include control of HR. This implies control of the physiologic variables that influence HR, along with the use of beta-adrenergic blockers. This case also demonstrates the value of Holter monitoring for ischemia, which, when done preoperatively, can detect patients at risk for unfavorable cardiac outcomes. Ischemia monitoring also may be useful during the intraoperative and postoperative periods, a time when ischemia is often silent and undetected. The early recognition of ischemia would allow for anti-ischemic interventions, which could decrease the morbidity and mortality of patients at risk for perioperative cardiac complications.

Arrhythmias, Cardiac↗
PubMedDate not supplied

Water uptake of soft lining materials from osmotic solutions.

OBJECTIVES: The water uptake characteristics of soft lining materials are of obvious importance in that they are expected to function in the oral environment. Results for Novus (Hygenic Corp., Akron, OH, USA) show a very high uptake from distilled water. Despite this high uptake, Novus appears to function satisfactorily in the mouth. High water uptake of soft lining materials has been attributed to the presence of water soluble impurities that, on immersion, form solution droplets; the driving force for the uptake being the osmotic gradient between the droplets and the external solution. Uptake should therefore be less from ionic solutions. The object of this study was to test the applicability of this theory to Novus and two experimental soft lining materials. METHODS: Water uptake of two experimental materials and Novus has been determined from distilled water and two saline solutions (0.45 and 0.9 M). After 196 days specimens were desorbed to constant weight and then subjected to a second sorption cycle. RESULTS: Novus had the highest uptake from distilled water at approximately 18%, the experimental materials having an uptake approximately 7%. Desorptions were all rapid, minimum weight being reached within 1-2 days. Uptakes of the second sorptions from water were all higher. Uptake from saline solutions was approximately 12% for all materials, uptake from 0.9 M saline being the lowest. Second sorption results from solution were similar to the first. CONCLUSION: The results obtained support the theory that the high water uptake of elastomeric materials is osmotically driven.

Adsorption↗
PubMedDate not supplied

Effects of in utero exposure to alcohol upon male rats.

Ethanol ingestion by pregnant women can result in the development of the fetal alcohol syndrome in their progeny. To investigate the late consequences of maternal ethanol ingestion upon male progeny, pregnant dams were administered ethanol-containing liquid diets from the 12th day of gestation to 10 days postpartum and their male progeny were compared to those of offspring obtained from dams isocalorically fed a liquid diet without alcohol in which Dextri-Maltose isocalorically replaced the ethanol of the ethanol-containing diet and those of dams fed a standard rat chow ad libitum. A significant decrease in body weight at birth (p less than 0.0001), at weaning, and at 55 days of age (postpuberty) (p less than 0.005) was found for the in utero ethanol-exposed animals as compared to that of the animals obtained from the two control groups. Anogenital distances and indices (measures of masculinity) in the male progeny were reduced (p less than 0.001) on days 1 and 5 in the alcohol-exposed animals as compared to those of the two control groups. Testes and prostate-seminal vesicle weights of the alcohol-exposed animals were reduced on day 55 (p less than 0.05) and again on day 110 (p less than 0.01) as compared to those of the two control groups. Similarly, serum testosterone and luteinizing hormone levels were reduced significantly on day 55 (p less than 0.05) in the alcohol-exposed animals but not in the controls. No difference was noted at 110 days of age in testosterone and LH (luteinizing hormone) levels between the various groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

The acoustic qualities of Bora vowels.

Bora contains the vowel system /i e a o i w/, where /i/ is high, central, open, unrounded and /w/ is high, back, open, unrounded. A contrast between /i/ and /u/ is exceedingly rare in the languages of the world. An opposition between a central and a back vowel which are otherwise identical is theoretically significant since it shows that the binary feature [+/- back] is too weak to encode all phonological contrasts along the front/back dimension. However, previous analyses of languages containing such oppositions are based primarily on impressionistic transcriptions without instrumental confirmation. This study contributes to the debate by providing acoustic evidence supporting the minimal contrast between /i/ and /w/ in Bora. The results indicate that these phonemes have identical F1 values, but /i/ yields higher F2 and F3 measurements than /w/, in keeping with their reported difference in backness.

Adult↗