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Biomedical subjects

D Lawson

Publications and source records attributed to D Lawson.

At least 73 records · Page 4Linked to original sources
PubMed1994

Fatal parathyroid hormone-related protein-induced humoral hypercalcemia of malignancy in a 3-month-old infant.

Parathyroid hormone-related protein (PTHrP) is the factor responsible for the syndrome of humoral hypercalcemia of malignancy (HHM). The syndrome is well documented in adult cancer patients, but has not previously been described in young children. We report the case of a 3-month-old infant who developed refractory hypercalcemia (peak total calcium 13.8 mg/dl; normal 8.5-10.5, ionized calcium 3.3 meq/l; normal 2.0-2.5) associated with a high-grade, poorly differentiated malignant hepatic sarcoma. Parathyroid hormone (intact) levels were suppressed (7.5 pg/ml; normal 10-65). Fractional excretion of phosphate was markedly elevated (73.5%; normal 8%-20%) as were urinary cAMP levels (12.48 nmol/dl glomerular filtrate; normal 1.83-4.47) suggesting a PTH-like effect. Increased levels of PTHrP were present both in the serum (4.9 pmol/l; normal for adults < 1.5) and ascitic fluid (6.1 pmol/l). Since previous studies have demonstrated a potential role for PTHrP in the regulation of embryonal tissue differentiation and transmembrane calcium flux, our observation of elevated PTHrP levels associated with the development of a poorly differentiated hepatic sarcoma in a young infant may provide insight into the molecular mechanisms underlying HHM. We suggest that serum or plasma PTHrP levels be determined in all children with hypercalcemia of malignancy in whom the hypercalcemia cannot otherwise be explained.

Carcinoma, Hepatocellular↗
PubMed1994

Activation sequence of discrete brain areas during cognitive processes: results from magnetic field tomography.

Magnetic field tomography is a technique for extracting 3-dimensional estimates of current density in the brain, from non-contact, non-invasive measurements of the magnetic field generated by the brain. It allows visualisation of both cortical and subcortical focal activation patterns at millisecond intervals, and the relative time difference between active cortical areas. We have used this technique to study the activation history of discrete brain regions associated with the preparation for, initiation and inhibition of movement, and movement itself in a CNV paradigm. The strongest focal activities are found within well defined cortical regions, namely the auditory (A1), sensorimotor (SM1), medial parietal area (MPA) and anterior supplementary motor area (SMA). For the movement condition, activation history differs for the warning stimulus and the stimulus initiating movement.

Acoustic Stimulation↗
PubMed1994

Distribution of lactotroph subpopulations in different regions of the rat pituitary.

In this study, we examined the distribution of lactotrophs in different regions of pituitaries of ovariectomized (OVX) rats either untreated or treated with estradiol, progesterone or a combination of estradiol and progesterone. Anterior pituitaries were cut into inner and outer zones. Each of these regions was enzymatically dispersed and the resulting cells subjected to density sedimentation through a discontinuous Percoll gradient. The light and heavy cell subpopulations obtained were compared with cells not subjected to Percoll (unseparated cells). Cell numbers were determined and prolactin positive cells were assessed by immunocytochemistry. In OVX rats, the percentage of lactotrophs in the unseparated cell fraction of the outer zone was significantly (P < 0.05) lower than that in the inner zone. Estradiol increased the percentage of PRL cells in all cell populations, but the effect on inner zone light cells was significantly less than on any other type of cells. Progesterone given alone did not affect the percentage of lactotrophs in pituitary compared to untreated OVX rats nor did it alter the effects of estradiol. When the number of lactotrophs was calculated, the unseparated cells of inner and outer zone were equivalent except in the untreated OVX group where there was a significantly greater number of lactotrophs in the outer zone. In untreated OVX rats there was an equal distribution of lactotrophs between light and heavy cells in both inner and outer zones. Estradiol significantly increased the number of PRL cells in both zones and the effect was greater in the heavy cell fractions especially in the outer zone. In contrast, progesterone decreased the number of PRL positive cells in both zones and across cell types, but this effect was most pronounced in the outer zone. Progesterone also decreased the total pituitary cell number and this effect was greater than could be accounted for by the decrease in lactotroph numbers. We conclude that, except in untreated OVX rats, the numbers of lactotrophs in inner and outer zones are similar. The results also indicate that estradiol and progesterone can significantly alter the proportion and/or numbers of PRL positive cells within pituitary zones and may also affect cells that are not identified as PRL positive.

Animals↗
PubMed1994

Rapid chromosome identification by oligonucleotide-primed in situ DNA synthesis (PRINS).

We describe a method for rapid identification of chromosomes at metaphase, and quantification of chromosomes in interphase, by annealing oligonucleotide primers, derived from chromosome-specific subsets of repeated DNA families, to the DNA of cytological preparations, and enzymatic extension with the incorporation of labelled nucleotides. The method is equally applicable to normal cells or those from somatic cell hybrids. Where the labelled product is too small or of too low a copy number to be readily seen after the single extension reaction, we have developed a method for cyclic amplification of the labelled DNA, enabling clear visualization of the signal.

Animals↗
PubMed1993

Detection of airborne cocaine and heroin by high-throughput liquid-absorption preconcentration and liquid chromatography-electrochemical detection.

A high-throughput liquid-absorption preconcentrator (HTLAP) for rapid and/or ultrasensitive detection and analysis of trace contaminants samples air at a rate of 600-700 l/min and collects analytes from vapors or aerosols at an efficiency of 40-60% into a small volume of liquid absorbent dripping at a rate of 0.1-2 ml/min. These features combine to reduce the lower detection limit (LDL) of available analytical instrumentation by a factor of > 1000 and/or to permit faster sampling and far more rapid on-site air monitoring than were previously practicable. LDLs of ca. 1:10(13) (v/v) of alkaloids have been achieved with LC and electrochemical detection. The HTLAP is directly adaptable to most liquid-phase analyzers. The small rate of liquid collection is also compatible with available interfaces to mass spectrometers. Moreover, the HTLAP permits detection and quantitation of polar or highly reactive compounds that cannot be readily analyzed by conventional preconcentration and GC.

Air Pollutants↗
PubMed1993

Stability and long-term durability of Raman spectroscopy.

OBJECTIVE: The purpose of this study was to assess in the clinical setting the reliability and long-term stability of Raman spectroscopy as implemented in the RASCAL multiple gas analyzer, and to describe/analyze failure modes that manifest in regular use. METHODS: Twenty-one RASCAL analyzers were tested for accuracy and precision. Without any prior external calibration or alignment, all gas analyzers were systematically tested over a consecutive 36-hour period with standard gas mixtures. Data were analyzed by evaluating the difference between the predicted value and observed value (bias residual) as reported by each RASCAL: All service data (29 months) also were analyzed for information on durability and failure modes. RESULTS: The RASCAL exhibited a significant tendency to overread high concentrations of agent (isoflurane/enflurane); 4 of 16 instruments misread an agent by more than +/- 0.30%. Four of 16 instruments could not properly identify volatile agents in low concentrations (0.31 vol%). Inventory records show that water contamination led to the replacement of gas sample sets an average of 1.5 +/- 1.2 times per case over the 29-month period. Although many instruments had not been externally calibrated for over 63 days, linearity proved acceptable for CO2, O2, N2O, and N2. A rationale for instrument behavior and major failure modes, based on the instrument design, was developed. CONCLUSIONS: The manufacturer's suggested calibration intervals (30 days) were found to be more than adequate for reliable gas analysis using Raman spectroscopy. Without the benefit of frequent calibrations and as time passes, volatile agent quantification can be expected to drift significantly upward.

Anesthesiology↗
PubMed1993

Reduction of plasma prolactin by acute administration of CB-154 in ovariectomized F344 and Holtzman rats treated with diethylstilbestrol: a comparison of RIA and Nb2 lymphoma bioassay.

Fischer 344 (F344) and Holtzman Sprague-Dawley female rats were ovariectomized and implanted with a s.c. Silastic capsule of diethylstilbestrol (DES). At 1, 4 and 8 weeks of DES exposure, blood samples were obtained by infraorbital sinus puncture under light ether anesthesia before and 2 hours after s.c. administration of CB-154 (2.5 mg/rat). The plasma obtained was assayed for prolactin by radioimmunoassay (RIA) and Nb2 lymphoma cell bioassay (BA). At 1 week of DES treatment plasma prolactin in F344 rats measured by RIA was decreased by CB-154 (approximately 60%) whereas the level measured by BA was not changed and the BA:RIA ratio was increased from 2.4 +/- 0.2 to 4.8 +/- 0.9. CB-154 decreased plasma prolactin levels at 4 weeks but the effect seen by RIA (approximately 80%) was greater than that seen by BA (approximately 60%) and the BA:RIA ratio was increased (2.2 +/- 0.2 vs 3.4 +/- 0.5). By 8 weeks of DES exposure, CB-154 was as effective in reducing the levels measured by BA (approximately 89%) as those measured by RIA (approximately 85%) and the BA: RIA was not affected by the dopamine agonist. In Holtzman rats CB-154 decreased prolactin levels measured by RIA and BA to the same extent at both 1 and 4 weeks resulting in no change in the BA:RIA ratio, but at 8 weeks the BA:RIA was decreased by CB-154 (2.1 +/- 0.1 to 1.7 +/- 0.1). As was observed in F344 rats, the reduction in plasma prolactin induced by CB-154 increased as the duration of DES treatment increased (1 week approximately 45%; 4 weeks approximately 55-60%; 8 weeks approximately 80-85% inhibition) regardless of assay method. It is concluded that DES increases the BA:RIA ratio of plasma prolactin and that acute CB-154 treatment increases, decreases or does not change the BA:RIA ratio depending on the strain of rat used and the duration of DES treatment.

Animals↗
PubMed1993

Verapamil and aspirin modulate platelet-mediated vasomotion in arterial segments with intact or disrupted endothelium.

OBJECTIVES: This study was designed to examine the effects of verapamil and aspirin, which decrease thromboxane A2 and serotonin release, on the modulation of vascular tone by platelets. BACKGROUND: Aggregating platelets cause constriction of de-endothelialized arterial segments through thromboxane A2 and serotonin release. These cells cause relaxation of arterial segments with intact endothelium through release of the endothelium-derived relaxing factor. METHODS: Healthy subjects were given either no drug, verapamil or aspirin for > or = 5 days before their platelets were obtained. The effects of platelets obtained from subjects before and after treatment with aspirin or verapamil on the tone of rat aortic rings were determined. RESULTS: As expected, control platelets (before verapamil or aspirin treatment) induced concentration-dependent relaxation of rat aortic rings with intact endothelium and a concentration-dependent contraction of de-endothelialized rings. Verapamil treatment enhanced (p < 0.02) the platelet-mediated relaxation in rings with intact endothelium and abolished platelet-mediated constriction (p < 0.01) in the de-endothelialized rings. Aspirin treatment also abolished (p < 0.05) platelet-mediated constriction of the de-endothelialized rings. The de-endothelialized rings contracted normally in response to the synthetic thromboxane A2 analogue U46,619, as well as to serotonin, indicating that the vascular smooth muscle response to thromboxane A2 and serotonin was intact. CONCLUSIONS: This study provides evidence for the modulation of platelet-mediated vasoconstriction of de-endothelialized arterial segments by prior treatment of subjects with verapamil or aspirin. In clinical syndromes characterized by endothelial dysfunction or disruption, treatment with verapamil or aspirin may modify platelet-vessel wall interactions.

Animals↗
PubMed1993

Purification and properties of transgelin: a transformation and shape change sensitive actin-gelling protein.

We have purified the transformation and shape change sensitive isoform of an actin associated polypeptide doublet previously described by us (Shapland, C., P. Lowings, and D. Lawson. 1988. J. Cell Biol. 107:153-161) and have shown that it is evolutionarily conserved as far back as yeast. The purified protein: (a) binds directly to actin filaments at a ratio of 1:6 actin monomers, with a binding constant (Ka) of approximately 7.5 x 10(5) M-1; and (b) causes actin filament gelation within 2 min. Although these activities are controlled by ionic strength (and may be mediated by positively charged amino acid residues) the molecule remains as a monomer irrespective of ionic conditions. EM reveals that the addition of this protein to actin filaments converts them from a loose, random distribution into a tangled, cross-linked meshwork within 1 min, and discrete tightly aggregated foci after 10 min. By use of an "add-back" cell permeabilization system we can rebind this molecule specifically to actin filaments in cells from which it has previously been removed. Since the protein is transformation sensitive and gels actin, we have named it transgelin.

Amino Acid Sequence↗
PubMed1993

Does dopamine inhibit or stimulate prolactin release in vitro? The effects of dopamine concentration and duration of in vivo estradiol treatment.

Prolactin release was examined from pituitary explants of ovariectomized, Fischer 344 rats at various times of estradiol treatment. The explants were acutely exposed to concentrations of dopamine from 0 to 10(-4) M and the concentration of prolactin in the resulting incubation medium was determined by radioimmunoassay. At 1 and 2 weeks of estradiol treatment, prolactin release from explants of Fischer 344 rats was not inhibited by 10(-6) or 10(-5) M dopamine when compared with release from explants exposed to no dopamine, whereas dopamine at doses of 10(-7) and 10(-8) M significantly stimulated prolactin release. By 3 or 4 weeks of estradiol treatment, the stimulatory effects of the low doses of dopamine were not evident and higher doses significantly inhibited prolactin release. These data indicate that dopamine can inhibit, stimulate, or produce no change in prolactin secretion and that these effects depend upon the concentration of dopamine used and the duration of estradiol treatment to which the animals are subjected.

Animals↗
PubMed1992

The effects of estradiol on pituitary responsiveness to dopamine in vitro: a comparison of ovariectomized Fischer 344 and Holtzman rats.

The objective of this study was to determine if the effectiveness of dopamine as an inhibitor of prolactin is altered by estradiol in strains of rats which show marked differences in estrogen-induced pituitary hyperplasia. Groups of Fischer 344 and Holtzman Sprague-Dawley rats were ovariectomized and implanted with Silastic capsules of estradiol. Rats were sacrificed by rapid decapitation following a brief period of ether anesthesia at 2, 4, 6, 8 weeks (F-344) or at 2 and 8 weeks (Holtzman) of estradiol treatment. The pituitary was removed and cut into fragments which were either snap frozen for initial prolactin content measurements or incubated for 60 min in the presence or absence of dopamine (1 x 10(-6) M). Prolactin was measured in the plasma, in sonicates of the pituitary and in the incubation medium by double antibody radioimmunoassay. Pituitary weight and plasma levels of prolactin were significantly less in Holtzman rats compared to Fischer 344 females at 2 or 8 weeks of estradiol treatment but pituitary concentrations of prolactin were not different between the two strains. Pituitary fragments from Fischer 344 rats studied at 2 and 4 weeks of estradiol treatment did not respond to the removal of dopamine in vitro whereas pituitary fragments from Holtzman rats obtained at 2 weeks of estradiol treatment did release significantly more prolactin in the absence than in the presence of dopamine. Pituitary fragments taken from Fischer 344 rats at 6 and 8 weeks were responsive to dopamine whereas pituitary tissue from Holtzman rats was not responsive at 8 weeks. The data indicate that temporal differences in responsiveness to the inhibitory effects of dopamine occur in strains which are susceptible or resistant to the formation of pituitary tumors following prolonged estradiol treatment.

Analysis of Variance↗
PubMed1992

Temporal effects of estradiol and diethylstilbestrol on pituitary and plasma prolactin levels in ovariectomized Fischer 344 and Holtzman rats: a comparison of radioimmunoassay and Nb2 lymphoma cell bioassay.

An Nb2 lymphoma cell bioassay (Nb2BA) and a radioimmunoassay (RIA) were used to compare plasma and pituitary levels of prolactin in ovariectomized Fischer 344 (F344) and Holtzman rats treated with either diethylstilbestrol (DES) or estradiol for up to 8 weeks. The objectives were to determine whether there were temporal differences in prolactin responses in strains with different genetic predispositions to estrogen-induced pituitary tumor formation and to determine whether the results of the two assay methods were equivalent. All rats were ovariectomized for 7 days and all except controls received subcutaneous Silastic implants of DES or 17 beta-estradiol and were sacrificed at intervals from 2 days to 8 weeks later. Pituitary content and plasma levels of prolactin were determined by Nb2BA and RIA and the ratio of these measurements was calculated. DES induced a significant increase in pituitary prolactin in F344 rats by 2 days of treatment, as measured by RIA. Pituitary content increased to a peak by Day 4, after which a gradual decline occurred until the end of the experiment. Nb2BA measurements were similar to those obtained by RIA, except at 8 weeks, when the content determined by Nb2BA was significantly higher than the content determined by RIA. When estradiol was given to F344 rats a pattern of increase and subsequent decrease in pituitary content similar to that seen with DES was observed and levels measured by Nb2BA and RIA were essentially equivalent. Plasma levels of prolactin in DES-treated F344 rats increased exponentially through the 8 weeks, and the Nb2BA measurements were significantly greater than levels determined by RIA throughout the treatment period. Estradiol treatment produced a pattern of change in plasma levels of prolactin similar to that observed with DES, except that RIA and Nb2BA measurements were not different. Comparable results were obtained in Holtzman rats, except plasma levels were not increased to the same degree as seen in F344 rats. From these results, we conclude that DES, but not estradiol, can selectively increase the secretion of prolactin that is more bioactive than immunoreactive and that this effect of DES is observed in F344 and Holtzman rats, although F344 rats released more prolactin in response to estrogens than did Holtzman females.

Animals↗
PubMed1992

Immunolocalization of the intermediate filament-associated protein plectin at focal contacts and actin stress fibers.

The distribution of plectin in the cytoplasm of Rat1 and glioma C6 cells was examined using a combination of double and triple immunofluorescence microscopy and interference reflection microscopy. In cells examined shortly after subcultivation (less than 48 h), filamentous networks of plectin structures, resembling and partially colocalizing with vimentin filaments, were observed as reported in previous studies. In cells kept attached to the substrate without growth for periods of 72 h to 8 days (stationary cultures), thick fibrillary plectin structures were observed. These structures were located at the end of actin filament bundles and showed co-distribution with adhesion plaques (focal contacts), vinculin, and vimentin. Only relatively large adhesion plaques (dash-like contacts) were decorated by antibodies to plectin, smaller dot-like contacts at the cell edges remained undecorated. Moreover, in stationary Rat1 cells plectin structures were found to be predominantly colocalized with actin stress fibers. However, after treatment of such cells with colcemid, plectin's distribution changed dramatically. The protein was no longer associated with actin structures, but was distributed diffusely throughout the cytoplasm. After a similar treatment with cytochalasin B, plectin's association with stress fibers again was completely abolished, although stress fibers were still present. The association of plectin with focal contact-associated intermediate filaments was demonstrated also by immunogold electron microscopy of quick-frozen, deep-etched replicas of rat embryo fibroblasts. These data confirm previous reports suggesting a relationship between intermediate filaments on the one hand, and actin stress fibers and their associated plasma membrane junctional complexes, on the other. Furthermore, the data establish plectin as a novel component of focal contact complexes and suggest that plectin plays a role as mediator between intermediate filaments and actin filaments.

Actins↗
PubMed1991

The Trypanosoma brucei cytoskeleton: ultrastructure and localization of microtubule-associated and spectrin-like proteins using quick-freeze, deep-etch, immunogold electron microscopy.

We have used a combination of quick-freezing/deep-etching and colloidal gold immunocytochemistry (i) to analyze the molecular organization of the microtubular membrane skeleton and the flagellum of Trypanosoma brucei, and (ii) to localize two defined cytoskeletal proteins within these structures. The cell body of trypanosomatids is enveloped by a membrane skeleton consisting of a tightly packed array of microtubules which are closely associated with the cell membrane. The membrane-oriented face of these microtubules is richly decorated with microtubule-associated proteins, which form intermicrotubule and microtubule-membrane linkers. In contrast, the cytoplasmic faces of the microtubules have a smooth, nondecorated appearance. A previously identified, highly repetitive microtubule-associated protein is confined to the membrane-oriented face of the microtubular array, suggesting that the function of this protein may be that of a microtubule-membrane linker. Quick-freezing has also been used to reveal the geometric organization of the paraflagellar rod structure in the flagellum, its interaction wit the cell body, and a unique series of fleur-de-lis-like molecules which link this organelle to axonemal microtubules. Immunohistochemistry using an antibody against human erythrocyte spectrin suggests that these linker structures may contain ancestral spectrin-like molecules.

Animals↗
PubMed1991

Variable resistance loadings in anaerobic power testing.

The aim of this study was to establish optimal test conditions for maximal anaerobic testing on a frictionloaded bicycle ergometer. Power and work outputs of 15 subjects during a 60-s all-out effort were tested under five conditions on a specially modified Monark ergometer. Test conditions were produced by altering the commencement resistance loading and either holding it constant (0.065C, 0.075C kg/kg. BW) for the entire duration of the 60-s work test or by reducing it by a specific amount to a more manageable load if pedalling rate dropped below 90 rpm (0.075R, 0.085R, 0.095R kg/kg. BW). Resistance and pedalling rate were continuously monitored with power outputs being determined every 100 ms, breath by breath oxygen consumption (VO2) was measured and capillary blood lactate (HLa) analyzed before and 5 min post each test condition. The test condition with the highest initial load (0.095R) produced the greatest peak power (PP). The reduced test procedure with the higher initial loads resulted in the greatest mean power (MP) and total work outputs (0.095R and 0.085R). Post-exercise blood HLa was not significantly different in any test condition. Peak power and MP correlated highly with both body weight (r = 0.77-0.85 and r = 0.75-0.83) and lean body weight (r = 0.84-0.88 and r = 0.90). During the last 30 s of the test, subjects reached between 90-100% of their measured maximal aerobic capacity (VO2max). The results of this study indicate that for a 60-s maximal all-out effort, a reduced test condition with a high initial resistance setting is required to produce the highest anaerobic test parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗