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Biomedical subjects

D Walker

Publications and source records attributed to D Walker.

At least 343 records · Page 19Linked to original sources
PubMed1984

EEG and visual evoked potentials of conscious man during moderate hypothermia.

Five conscious, normal humans were cooled by water immersion until their core temperatures were near 33.5 degrees C. When hypothermic at this level, small shifts of EEG frequencies to more theta and beta and less alpha activity occurred in comparison to normothermia. There was no significant change in the amplitude of the EEG. Although 10-20% increases in the latency of peaks in the visual evoked potential occurred in some subjects when hypothermic, this was not statistically significant, nor was the slight amplitude reduction. The results confirm for conscious, unanesthetized humans that moderate hypothermia to the level of 33.5 degrees C is on the borderline for significant alteration of brain electrical activity by cold, a general conclusion that was known previously only for anesthetized or immobilized humans and other mammals.

Adult↗
PubMed1984

Asymmetric replication of hepatitis B virus DNA in human liver: demonstration of cytoplasmic minus-strand DNA by blot analyses and in situ hybridization.

In situ and blot hybridization techniques have been used with strand- and region-specific probes to characterize the forms of hepatitis B virus (HBV) DNA in the liver of a patient with chronic active hepatitis B. The hepatocytes contain a heterogeneous population of rapidly migrating DNA species in the 0.5-1.4 kb position that are localized predominantly in the cytoplasm and are of minus-strand polarity. The findings indicate that the replication is asymmetric, with separate pathways for plus- and minus-strand synthesis of HBV DNA; that viral DNA synthesis is initiated at a site near the nick in the minus strand of virion DNA; and that actively replicating forms of HBV DNA can be identified at the cellular level by in situ hybridization.

Cytoplasm↗
PubMed1984

Pulmonary artery sling.

Pulmonary artery sling is a rare cause of respiratory distress the embryological origin of which is not known. Two patients with this abnormality, both of whom are now thriving, are described. Surgery was necessary at the age of 5 1/2 years in one child, who also had an atrial septal defect. The other child, at the age of 2 years, shows improvement of her wheezing, cough, and breathlessness despite having had neither surgical nor medical treatment.

Female↗
PubMed1984

Imaging of unilateral hydronephrosis in an experimental animal model. With special reference to magnetic resonance.

In an experimental animal model of partial ureteral obstruction, three different modalities--excretory urography, real-time ultrasound and magnetic resonance--were used for imaging of the unilateral hydronephrotic rabbit kidney. Urography demonstrated well the anatomy of the renal pelvis, the site and the degree of obstruction. Real-time ultrasound and magnetic resonance imaging were both capable of demonstrating compartments of renal parenchyma in addition to the pelveocaliceal dilatation. With magnetic resonance, the renal vessels could be demonstrated. Blood flow velocity in renal arteries and veins was determined with the Doppler technique.

Animals↗
PubMed1983

Identification of the glucose transporter in rat skeletal muscle.

The glucose transporter in the plasma membrane of rat skeletal muscle has been identified by two approaches. In one, the transporter was detected as the polypeptide that was differentially labeled by photolysis with [3H]cytochalasin B in the presence of L- and D-glucose. [3H]Cytochalasin B is a high-affinity ligand for the transporter that is displaced by D-glucose. In the other, the transporter was detected by means of its reaction with rabbit antibodies against the purified glucose transporter from human erythrocytes. By both procedures, the transporter was found to be a polypeptide with a mobility corresponding to a molecular weight of 45,000-50,000 upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Animals↗
PubMed1983

The effects of proglumide on cholecystokinin-, bombesin-, and glucagon-induced satiety in the rat.

Intraperitoneal (IP) administration of the glutaramic acid derivative proglumide inhibited satiety induced by all IP doses of cholecystokinin octapeptide (CCK-OP) in 3-hour food-deprived intact rats. Proglumide did not influence satiety when administered alone and did not inhibit satiety induced by IP glucagon. While proglumide did not inhibit satiety induced by low doses of IP bombesin, it partially and significantly inhibited the satiety effects produced by high doses of this peptide. Since bombesin is a known secretagogue for CCK in several species, these results indicate that while bombesin and CCK act independently to induce satiety, the effect induced by high doses of bombesin is mediated, in part, by the release of endogenous CCK or a structurally related peptide. Furthermore, these results illustrate that proglumide is a specific antagonist of CCK-induced satiety and is, therefore, a potentially useful tool for investigating the physiologic role of this peptide in the control of food intake.

Animals↗
PubMed1983

The glucose transport system of muscle plasma membranes: characterization by means of [3H]cytochalasin B binding.

A membrane-rich preparation was isolated from adult rat skeletal muscle in low salt media and further fractionated in sucrose gradients. Fraction F2, with a relative density of 1.092-1.119, consisted of sealed membrane vesicles which were enriched in plasma membrane markers. These vesicles were capable of stereospecific D-glucose uptake which was sensitive to cytochalasin B (CB). The membranes were also enriched in high affinity [3H]CB binding activity (Kd of 0.28 microM). [3H]CB binding to the glucose carrier of these plasma membranes, estimated as the fraction of binding protectable by D-glucose, ranged between 2.5 and 7.4 pmol/mg protein in several membrane preparations. The amount of [3H]CB binding to muscle membranes from newborn and adult rats was not markedly different. Trypsin, at low concentrations, altered the molecular weight of several membrane components, without affecting [3H]CB binding. Higher concentrations of trypsin abolished [3H]CB binding. Both 2,4-dinitrofluorobenzene (0.1 mM) and N-ethylmaleimide (15 mM) inhibited [3H]CB binding; inhibition by these reagents was prevented by inclusion of micromolar concentrations of CB in the reaction mixture. Several procedures that extracted specific proteins enriched the D-glucose-sensitive [3H]CB binding to the protein-depleted membranes. Antibody raised against the glucose carrier of human red cell membranes cross-reacted with a polypeptide of Mr about 45K of muscle membranes which might represent the glucose carrier.

Animals↗
PubMed1983

Progressive multifocal leukoencephalopathy: a burnt-out case.

A patient with Hodgkin's disease developed progressive multifocal leukoencephalopathy (PML), documented by brain biopsy to be associated with JC virus infection. His disease progressed over several months, resulting in severe neurological deficit, but then stabilized with little or no further clinical progression during the remaining year of his life. Histopathological evaluation of the brain at autopsy supported the clinical impression that brain infection was arrested. Whereas the brain biopsy exhibited the histological features of active PML including giant bizarre astrocytes, at postmortem examination brain lesions appeared inactive, with regression of astrocytic changes and elimination of oligodendroglial inclusions. Similarly, JC virus antigen, present in the brain biopsy, was not detected in the autopsied brain. This case provides further evidence that PML is not invariably fatal and that clinical and cytological remission can occur.

Adult↗
PubMed1983

The effect of sucrose on the rate of de novo sucrose biosynthesis in leaf protoplasts from spinach, wheat and barley.

Protoplasts from the leaves of wheat, spinach, and barley were found to synthesize [14C]sucrose from 14CO2 at rates comparable with those of the parent tissue. CO2 fixation and sucrose biosynthesis ceased virtually immediately when the light was switched off. The effect of sucrose pretreatment on the rate of de novo sucrose biosynthesis was found to vary with leaf age and with plant species. Protoplasts from young wheat and spinach leaves showed an apparent stimulation of the rate of sucrose biosynthesis after sucrose pretreatment. In protoplasts from mature leaves of spinach, sucrose pretreatment produced inhibition. After sucrose pretreatment protoplasts from mature spinach leaves showed low rates of CO2 fixation, and sucrose biosynthesis compared with controls. Conversely, with protoplasts from mature leaves of wheat and barley, the rate of CO2 fixation was unchanged and there was little or no effect on the rate of sucrose biosynthesis after sucrose pretreatment. Preincubation with sucrose had no effect on the activity of sucrose-phosphate synthetase (EC 2.4.1.14), cytoplasmic fructose-1,6-bisphosphatase (EC 3.1.3.11), or UDPglucose pyrophosphorylase (EC 2.7.7.9) from spinach leaves. It was concluded that there is no direct feedback inhibition of sucrose on the sucrose biosynthetic pathway in leaves of spinach, wheat, and barley. The mechanism of inhibition of sucrose biosynthesis by sucrose in spinach remains to be elucidated.

Carbon Dioxide↗
PubMed1983

Insulin binding to differentiating muscle cells in culture.

Saturable binding of 125I-labelled insulin was detected on L6 myoblasts grown in monolayers. Binding was proportional to the number of cells and was pH sensitive, decreasing above pH 7.0. Binding also decreased with increasing temperature in the range 22-37 degrees C. Binding of insulin over a range of hormone concentrations (10(-10)-10(-6) M) was analyzed by Scatchard plots. The data are compatible with the coexistence of two components with Kd of 3 and 190 nM. The number of both types of binding sites increased with cell differentiation (upon alignment and cell fusion), when expressed either per unit protein, DNA, or surface membrane cholesterol. On the other hand, their association constants did not vary. Binding of insulin to a nonfusing mutant of L6 cells resembled binding to the parent myoblasts before alignment.

Animals↗
PubMed1983

The effects of hypoxia on glucose turnover in the fetal sheep.

The origin of the hypoxia-induced rise in fetal blood glucose concentration in fetal sheep of 124-135 days was investigated. Hypoxia was induced in pregnant sheep and fetuses with chronically implanted vascular catheters by causing the ewes to breathe 9% O2 and 3% CO2 in N2 for 60 min. The rise in fetal plasma glucose caused by a 60% reduction in maternal PaO2 was associated with a 50% fall in plasma insulin concentration. The fall in insulin and rise in glucose was prevented by the alpha-adrenergic blocking agent phentolamine but not by the beta-antagonist propranolol. Turnover of glucose in the fetus under these conditions was measured with [6-3H] and [U-14C] glucose. Hypoxia reduced fetal glucose consumption despite the hyperglycaemia. After 30 min of hypoxia there was no evidence of fetal production of glucose but by 60 min substantial production was evident. The reduced fetal consumption and increased production of glucose was inhibited by phentolamine but not by propranolol. It is concluded that in the fetal sheep hypoxia induced hyperglycaemia is first caused by reduced consumption of glucose and thus fetal glycogen stores are not depleted. If the hypoxia persists fetal blood glucose is elevated further by fetal production of glucose.

Animals↗
PubMed1983

Thromboxane synthetase inhibitors in septic shock.

Thromboxane (TX) has been reported to cause mortality in endotoxin or septic shock. Cyclooxygenase inhibition improves survival in gram-negative or gram-positive shock. The exact level in the prostaglandin system of which the protection occurs is unknown. This study was designed to compare the effects of a cyclooxygenase inhibitor (indomethacin, IND) to a thromboxane synthetase inhibitor (IMI) on survival and on the production of Tx and prostacyclin (PGI2) in a clinically relevant rat gram-negative sepsis model. Three groups were studied: 1) control (N = 35) animals received E coli only; 2) IND (N = 35) treated animals received 3 mg/kg IP; 3) IMI (N = 35) treated animals received 30 mg/kg IP. All drugs were given 1 h after an IP injection of E coli (LD70) organisms. In this model only IND significantly improved survival. IND and IMI significantly blocked the production of Tx seen in septic shock. IND blocked PGI2 production whereas IMI increased the production. These results show that Tx may not be important in the irreversible stages of shock. Shunting prostaglandin production to PGI2 with thromboxane synthetase inhibitors needs to be considered when using this group of compounds. The mechanism of protection by IND remains unknown.

Animals↗