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Biomedical subjects

P Walker

Publications and source records attributed to P Walker.

At least 235 records · Page 13Linked to original sources
PubMed1983

Enzyme-linked immunoassays for antibodies against Vibrio cholerae.

Glutaraldehyde-treated V. cholerae organisms bind firmly to the surfaces of plastic microELISA plates, thus providing a stable immobilized antigen for use in enzyme-linked immunosorbent assays (ELISA). Serum absorption and ELISA-inhibition experiments indicate that, in addition to detecting natural antibodies in normal rat serum, the immobilized antigen may be used to quantitate specific anti-V. cholerae antibodies induced in rats by injection of live organisms. Apart from serotypically specific anti-lipopolysaccharide (LPS) antibodies, the reaction with immobilized organisms seems to involve antibodies common to Inaba and Ogawa serotypes; it is suggested that these antibodies are primarily directed against antigens of the outer membrane protein complex of V. cholerae cells. These findings have led to the development of an indirect ELISA method which quantitates levels of antibodies that react with heat-sensitive surface antigens of V. cholerae without involvement of anti-LPS antibodies. When used in conjunction with the indirect LPS-ELISA, the test has been found to provide a more detailed description of the serum antibody responses of rats to parenteral injections of live V. cholerae than has been reported previously.

Animals↗
PubMed1982

Nucleotide sequence of satellite DNA contained in the eliminated genome of Ascaris lumbricoides.

Several restriction endonuclease fragments isolated from highly repetitive satellite DNA of the chromatin eliminating nematode Ascaris lumbricoides var. suum have been cloned. Each type of restriction fragment corresponds to a different variant of the same related ancestral sequence. These variants differ by small deletions, insertions and single base substitutions. Restriction and DBM blot analyses show that members of the same variant class are tandemly linked and therefore are physically separated from other variant classes. A comparison of all the determined sequences establishes a 121 bp long and AT rich consensus sequence. There is evidence for an internal short range periodicity of 11 bp length, indicating that the Ascaris satellite initially may have evolved from an ancestral undecamer sequence. The satellite DNA sequences are mostly but not entirely eliminated from the presumptive somatic cells during chromatin diminution. We have no evidence for transcriptional activity of satellite DNA at any stage or tissue analyzed.

Animals↗
PubMed1982

Thallium myocardial imaging: recent experience using a coronary vasodilator.

Thallium-201 myocardial imaging is an important test in the assessment of patients with suspected coronary artery disease. Techniques differ in detail, reliability and in patient acceptability. Three techniques have been compared. Thirty-two-patients were studied in three groups. In the first group (15 patients) exercise thallium scans were compared with scans following an intravenous vasodilator (dipyridamole). In the second group (12 patients) intravenous dipyridamole and oral dipyridamole thallium scans were compared. In the third group (five patients) combined oral dipyridamole and exercise scans were assessed. There were no major differences in the first two groups but the combined test showed a marked increase in image quality and diagnostic yield. Thallium scanning is simplified considerably by the use of oral dipyridamole, without loss of diagnostic quality of safety. It promises to be the method of choice for stress scanning, and is ideal in patients unable to tolerate maximum exercise. The combined exercise--dipyridamole scan helps to evaluate complex problems, particularly those with less severe coronary insufficiency, and can be done without the use of a treadmill.

Administration, Oral↗
PubMed1982

Visual memory and stimulus repetition effects.

Recent investigations of memory for randomly configured patterns indicate that visual memory can involve distinct short-term and long-term components. The appearance of a visual recency effect that is confined to the last-presented item is believed to result from the active visualization of this item during the retention interval. Studies of the retention of familiar visual information have also suggested that the short-term effects observed are a result of active visualization. In a review of these studies, however, we argue that the effects obtained with familiar visual information are not necessarily a result of active visualization and, indeed, may not involve anything other than long-term visual memory. For example, Rabbitt and Vyas (1979) observed a visual recency effect in a serial choice reaction time task involving familiar information. That this recency effect was confined to the final item accords with the results obtained with unfamiliar visual information. However, this choice reaction time task did not require subjects to remember previous stimuli, so it is unlikely that they actively visualized them. With the case for a distinct short-term visual memory currently resting on the recency effect interpreted as reflecting a process of active visualization, this result is especially important. In the second part of the present paper, we report a series of experiments that provides an understanding of the visual recency effect in the serial choice reaction time task. We conclude from these studies that this effect is not due to visualization or to a visual trace either decaying or being overwritten by a succeeding stimulus.

Attention↗
PubMed1982

Salivary gland weight and nerve growth factor in the genetically obese (ob/ob) mouse.

The salivary glands of genetically obese male mice are significantly smaller than those of lean male mice, but the salivary glands of female mice do not differ in weight. The increases in weight of salivary glands in male mice after treatment with T3 at 50, 150, or 500 ng/day or with several doses of isoproterenol were comparable on a percentage basis, but the weights in the ob/ob mice were always smaller than any of those in the lean mice. Measurements of nerve growth factor (NGF) in several tissues showed a significantly lower concentration in the salivary glands of obese female mice than in same tissue from female lean mice. There were no differences in NGF levels in brown fat or in the cortex, cerebellum, or brain stem. The concentration of epidermal growth factor, in contrast to that of NGF, was not lower in the salivary glands of obese mice. Testosterone increased the weight of the salivary glands, spleen, and kidney in obese female mice, but the weight of the salivary glands in lean animals remained significantly higher than that in the obese mice both with and without treatment. Testosterone significantly increased the NGF concentration in salivary glands, but the values in treated male mice were only one tenth those in the treated lean animals.

Animals↗
PubMed1982

Effects of neonatal hyperthyroidism on the development of the hypothalamic-pituitary-thyroid axis in the rat.

The acute and latent effects of neonatal hyperthyroidism (NH) on the hypothalamic-pituitary-thyroid axis were studied in the rat after treatment of newborn animals with L-T4 (0.4 microgram/g BW, daily) for a period of 12 days. NH was associated with a permanent reduction in body weight in both male and female rats, in addition to a delay in the attainment of peak concentrations of hypothalamic TRH and pituitary and serum TSH. Serum TSH, T4, and T3 concentrations also were significantly and permanently reduced in NH animals (P less than 0.01) after cessation of L-T4 treatment. The serum TSH secretory response to 1 microgram synthetic TRH also was evaluated in 120-day-old control and NH rats, before and after the administration of L-T4 (0.6 microgram/100 g BW for 7 days) or propylthiouracil (0.05% in the drinking water for 14 days). In the baseline state, adult NH rats had a net secretory response similar to that of controls (189.0 +/- 31.3 vs. 227.0 +/- 29.3 microgram/ml . min). Administration of T4 significantly decreased while propylthiouracil treatment significantly increased the net TSH secretory response of NH rats compared to similarly treated control rats. These data are compatible with the hypothesis that NH leads to a permanent resetting of the regulatory set-point for pituitary TSH secretion and to increased sensitivity to the feedback inhibitory effects of thyroid hormones.

Animals↗
PubMed1982

Xenobiotic cholesteryl ester formation.

1. When the novel hypolipidaemic compound 1-(4-carboxyphenoxy)-10-(4-chlorophenoxy) decane (CCD) was administered orally (250 mg/kg body weight for seven days) to rats, a lipophilic cholesterol-containing metabolite accumulated in the liver. 2. Analysis by n.m.r. spectroscopy and mass spectrometry identified the metabolite as the cholesterol conjugate of CCD. This structure was confirmed by comparison with reference material synthesized in our laboratories. 3. The xenobiotic cholesteryl ester was not further metabolized and, unlike the natural counterparts, was not transported by lipoproteins. 4. When added in vitro, the xenobiotic cholesteryl ester appeared to enhance the activity of hepatic lysosomal cholesteryl ester hydrolase and thus may contribute to the hypocholesterolaemic activity of CCD.

Animals↗
PubMed1982

Molecular cloning and sequence analysis of highly repetitive DNA sequences contained in the eliminated genome of Ascaris lumbricoides.

High molecular weight DNA from germ line and somatic cells of the DNA eliminating nematode Ascaris lumbricoides has has been isolated and digested with different restriction enzymes. The resulting DNA fragments were separated by agarose gel electrophoresis. Germ line but not somatic DNA shows a prominent band about 120 bp long as well as multiples of that length. These fragments are shown to be monomers and multimers of a highly repetitive satellite DNA, which is eliminated mostly but not completely during the process of chromatin diminution. Restriction digests, hybridization experiments and sequence analysis revealed that this eliminated satellite is composed of a whole set of different but related variant classes, all of them showing the same repeating unit length of about 120 bp. Members of the same variant class are tandemly linked and therefore physically separated from other variant classes. All satellite sequences can be derived from the same common ancestor sequence, differing only by base substitutions, insertions and deletions. There is no evidence for transcription of satellite DNA at any stage and tissues analyzed.

Animals↗
PubMed1982

The need for support services for minority pre-allied health majors.

The success of increased efforts to gain admission for larger numbers of minority students into allied health programs will require improvement in the competitiveness of minority allied health applicants. A survey of pre-allied health majors shows that, although a majority of Black and Hispanic preprofessional students have taken science courses in high school, 53.8% of Hispanic and 34% of Black students surveyed reported college science grade point averages in the C to D range. If minority students are going to become more competitive in the admissions process, they will need increased support services at the preprofessional level. To increase the ethnic representation of their student bodies, schools and colleges of allied health will have to increase recruitment efforts, incorporate diversity factors (e.g., consideration of ethnic background, sex, geographic area, and ability to surmount academic difficulties) into admissions criteria, and place a priority on developing academic enrichment programs.

Adult↗
PubMed1981

Protein degradation in human skeletal muscle tissue: the effect of insulin, leucine, amino acids and ions.

1. The protein degradation rate of human skeletal muscle was evaluated in vitro in isolated fibre bundles from the rectus abdominus muscle by measuring the tyrosine released from muscle tissue proteins. Protein metabolism in this semi-intact preparation was compared with that of the intact extensor digitorum longus muscles from rats under the same experimental conditions. 2. Protein balance was negative in both preparations, but protein synthesis and degradation were two to three times higher in the rat muscles. Tyrosine was released at a constant rate for at least 3 h of incubation independent of whether protein synthesis was inhibited or not. Disintegration of the muscle fibres more than doubled the tyrosine release rate. Human red gastrocnemius muscle showed 37% higher degradation rate compared with the predominantly white rectus abdominus muscle. The half-life of human skeletal muscle protein in vitro was estimated to be 20 days when calculated from the rate of tyrosine release. 3. The addition of leucine to the incubation medium decreased the rate of protein degradation, which was further decreased by the addition of other amino acids. Insulin did not influence the protein degradation rate during 2 h of incubation. This did not reflect a lack of sensitivity to insulin of the preparation, since protein synthesis responded to insulin. Calcium (5 mmol/l) stimulated and zinc (0.1 mmol/l) inhibited the protein degradation. 4. This experimental system may be suitable as an additional tool for evaluating protein degradation in human skeletal muscles.

Adult↗
PubMed1981

Effect of thyroxine, testosterone, and corticosterone on nerve growth factor (NGF) and epidermal growth factor (EGF) concentrations in adult female mouse submaxillary gland: dissociation of NGF and EGF responses.

Testosterone propionate (TP) and corticosterone acetate (CA) were administered alone and in combination with T4 to assess the effect on submaxillary gland (SMG) nerve growth factor (NGF) and epidermal growth factor (EGF) concentrations in adult female mice. Mice were treated for 5 or 10 days. SMG NGF, and EGF concentrations were measured by specific RIA techniques. Mean SMG NGF (0.68 +/- 0.08 microgram/mg protein) and EGF (0.58 +/- 0.05 microgram/mg protein) concentrations were similar in control mice. T4 (0.4 microgram/g BW, sc, daily) significantly increased mean SMG NGF and EGF concentrations to 469% and 347%, respectively, of control values after 5 days and to 1190% and 568%, respectively, after 10 days of treatment. TP (25 microgram/g BW, sc, every 2 days) significantly increased mean SMG NGF and EGF concentrations to 734% and 767%, respectively, of control values at 5 days and to 1971% and 1953%, respectively, at 10 days. T4 and TP resulted in no further significant increases in either SMG NGF or EGF concentrations above the levels observed after TP alone. CA (25 microgram/g BW, sc, daily) increased mean SMG NGF, but not EGF, concentrations at both 5 and 10 days. Moreover, T4 and CA appeared to exert an additive effect on NGF. In contrast to the observations in adult female mice, T4 increased mean SMG NGF concentrations to 178% of control levels in adult male mice, but had no significant effect of SMG EGF concentrations. These data indicate that T4 and TP modulate SMG NGF and EGF concentrations in adult female mice. T4, however, appears to have a preferential effect on NGF on both male and female mice, unlike the equal effect on TP on both NGF and EGF. CA, like T4, also appears to increase NGF, but not EGF, concentrations in adult female SMG. The present results suggest separate regulatory mechanisms for T4, TP, and CA on SMG NGF and EGF biosyntheses.

Animals↗
PubMed1981

Nerve growth factor in human umbilical cord serum: demonstration of a veno-arterial gradient.

An heterologous radioreceptor assay (RRA) for nerve growth factor (NGF) has been developed to measure NGF in human umbilical cord serum. The RRA uses mouse NGF (mNGF) as iodination material and as standard and a rat pheochromocytoma clonal line of cells (PC-12) as a source of NGF receptor (KD = 3.8 X 10(-9)M). Human cord serum exhibited parallel displacement of radiolabeled NGF in the RRA. Umbilical vein and artery NGF concentrations were measured in 22 healthy, full-term infants. The mean and (SEM) umbilical vein NGF concentration (30.4 +/- 3.2 pM/ml) significantly exceeded the mean umbilical artery NGF concentration (22.4 +/- 3.3 pM/ml) (p less than 0.05). Cord serum also produced a positive bioassay response (neurite outgrowth) in PC-12 cells, and this response was inhibited by anti-hNGF antiserum. These results are compatible with placental synthesis and secretion of NGF and suggest the possibility that NGF may play a role in autonomic and perhaps central nervous system maturation in the human fetus.

Fetal Blood↗
PubMed1980

Radioimmunoassay for mouse nerve growth factor (NGF). Effects of thyroxine administration on tissue NGF levels.

A sensitive and specific radioimmunoassay (RIA) has been developed for beta-nerve growth factor (NGF) purified from the submaxillary gland of the adult male mouse. The RIA is sensitive to 13 pg/assay tube with an intra-assay coefficient of variation of 7% and an interassay coefficient of variation of 11.8%. Of the substances tested for immunological cross-reactivity in the RIA, only mouse epidermal growth factor caused significant displacement of the radiolabeled ligand; 11% at a dose of 10 microgram/ml. Mouse tissue extracts diluted out parallel to the standard curve. The effects of altered thyroid function on tissue NGF concentration in adult male mice were studied using the RIA. Thyroxine administration (25 microgram T4 i.p. daily for 12 days) caused significant increases in submaxilllary gland and liver NGF content and concentration (P less than 0.001) compared to controls but had no significant effect on heart and kidney NGF levels. Propylthiouracil treatment (0.05% PTU in the drinking water for 21 days) led to a marked increase in thyroid gland weight (550% of control) but had no significant effect on NGF concentration in any of the organs studied with the exception of kidney where a 75% reduction in NGF concentration was observed. These studies indicate that thyroid hormones increase NGF content and concentration in the submaxillary gland and liver of adult male mice and are suggestive of increased NGF synthesis. Thyroid hormones may therefore play an important regulatory role in NGF metabolism in peripheral tissues of the adult mouse.

Animals↗
PubMed1980

Free thyroid hormone concentrations during postnatal development in the rat.

Sprague-Dawley rats were sacrificed by decapitation at 5, 7, 12, 14, 22, 26, 32, and 40 days of age. Adult animals (175 to 225 g) were also studied. Serum-free thyroxine (FT4) concentrations rose rapidly between 5 and 12 days to levels similar to adult concentrations, whereas the percentage of FT4 was relatively high between 5 and 12 days before declining to adult values by 14 days. Serum-free triiodothyronine (FT3) concentrations rose progressively to attain peak concentrations at 26 days and subsequently declined to adult levels by 40 days. The percentage FT3 rose in parallel with the FT3 concentrations to peak values at 22 to 26 days before declining to adult levels. FT4/thyroid-stimulating hormone (TSH) and FT3/THS ratios increased progressively through 22 days of age in parallel with the FT3/FT4 ratio. These data indicate that free thryoid hormone concentrations follow essentially the same developmental profile as do total thyroid hormone concentrations. Progressive maturation of the negative feedback control mechanism for the pituitary-thyroid axis, as assessed by the FT4/TSH and FT3/TSH ratios, occurs through 14 days. However, the continued rise in FT3 concentrations, FT3/TSH, and FT3/FT4 ratios through 26 days suggests a further resetting of the setpoint of the pituitary-thyroid axis possibly related to the stress of weaning.

Age Factors↗