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Biomedical subjects

W J Thompson

Publications and source records attributed to W J Thompson.

At least 109 records · Page 6Linked to original sources
PubMed1985

Purification and characterization of high-affinity cyclic adenosine 5'-monophosphate phosphodiesterases from human acute myelogenous leukemic cells.

Soluble, high-affinity cyclic adenosine 3':5'-monophosphate (cyclic AMP) phosphodiesterases extracted from blast cells of patients with acute myelogenous leukemia have been characterized by physical, kinetic, and immunological criteria and fractionated to a high degree of purity. Procedures used in this study were similar to those used to purify the high-affinity enzyme from dog kidney. Two forms of high-affinity enzyme were found in blast cells. Form A was similar to the known type IV phosphodiesterases, including those of normal lymphocytes and monocytes. It showed a molecular weight near 60,000, a rate of hydrolysis of cyclic AMP 7 to 10 times that of cyclic guanosine 3':5'-monophosphate (cyclic GMP), competitive inhibition by cyclic GMP for cyclic AMP hydrolysis, and identical immunoreactivity by Western transfer analysis. This enzyme form was purified to apparent homogeneity by physical criteria but showed a low maximum velocity relative to other phosphodiesterase forms. A second, different form of high-affinity phosphodiesterase (Form B) was also resolved and partially purified. By comparison with Form A, this enzyme eluted from diethylaminoethyl cellulose at slightly lower ionic strength, had a lower molecular weight, appeared specific for cyclic AMP as substrate, showed no inhibition of cyclic AMP hydrolysis by cyclic GMP, and displayed no immunological cross-reactivity to the Mr 60,000 enzyme. Neither enzyme form was activated by calmodulin or proteolysis, whereas both showed comparable inhibition by 6,7-dimethoxy-1-veratrylisoquinoline, 1-methyl-3-isobutylxanthine, and 1,3-dimethylxanthine.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1985

Adipocyte cyclic nucleotide phosphodiesterase activation by vanadate.

The addition of vanadate (Na3VO4) to intact isolated rat adipocytes stimulated cAMP phosphodiesterase activity (Type IV) in the particulate (P2) fraction. Vanadate increased the Vmax of the Type IV phosphodiesterase activity without affecting its apparent substrate affinity. Na3VO4 also stimulated cAMP hydrolysis of cell-free particulate and cytosolic fractions, but this activation required the presence of reduced glutathione (GSH). The mixture of vanadate and glutathione appeared as an emerald green solution (V-GSH complex), which was shown by EPR to contain vanadyl ion. No effect of either GSH or Na3VO4 alone on cell-free particulate cAMP phosphodiesterase activity was observed; however, Na3VO4, alone or in combination with GSH, stimulated cGMP hydrolysis in this subcellular fraction. The V-GSH complex increased the Vmax of the particulate cAMP phosphodiesterase activity without affecting its apparent Km. The activating effect of the complex was rapid in onset, persistent over 30 minutes, and reversible. The EC50 for activation of the particulate cAMP phosphodiesterase was approximately 5 microM Na3VO4 (maintaining the GSH:Na3VO4 molar ratio at 2:1); maximal stimulation was achieved at 0.1 mM Na3VO4. Purified microsomal membranes showed activation similar to that of the P2 fraction, while only a 60% stimulation was observed in purified plasma membranes. The V-GSH complex increased basal insulin-activated Type IV phosphodiesterase activity to a common maximal level. Detergent-solubilized cAMP-phosphodiesterase from the P2 fraction was stimulated 2.5-fold by the V-GSH complex. Limited trypsin treatment of P2 membranes activated cAMP phosphodiesterase and abolished the stimulatory effect of the V-GSH complex. These results are generally consistent with the hypothesis that V-GSH complex activates Type IV phosphodiesterase by an indirect mechanism, which appears to involve predominantly membrane bound components that may be biologically important enzyme regulatory elements.

Adipose Tissue↗
PubMed1984

2,4-Diamino-5-cyano-6-halopyridines: a new class of cyclic AMP phosphodiesterase inhibitors with therapeutic potential.

2,4-Diamino-5-cyano-6-halopyridines have been described previously as oral insulinotropic agents and have been found recently to have bronchodilatory properties. In the present report the synthesis of the iodo compound is newly described, and it is established that HI- or HBr-mediated condensation and cyclization of malononitrile in 1,2-dichloroethane yield selectively the 5-cyanopyridine derivatives. The pyridine derivatives were found to constitute a new class of potent cyclic AMP phosphodiesterase inhibitors. Inhibition of purified dog kidney cyclic AMP phosphodiesterase was of the mixed type. Since cyclic AMP phosphodiesterase inhibitors are known to enhance glucose-induced insulin secretion and to activate glucose production by the liver, the finding that the pyridine derivatives described here inhibited cyclic AMP phosphodiesterase opens new avenues of interpretation for their insulinotropic action as well as for the paradoxical lack of improvement of glucose disposal by elevation of insulin after oral drug administration. Cyclic AMP phosphodiesterase inhibition also has the potential of explaining the bronchodilatory effects of these drugs.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1984

Investigation of chewing patterns in deep-bite malocclusions before and after orthodontic treatment.

A knowledge of chewing provides a better understanding of normal jaw movement and can help form a basis for assessing the effects of malocclusion on jaw function. This study was conducted to describe the effects of deep-bite malocclusion on masticatory function and to determine what changes may occur with orthodontic correction. Five subjects, each exhibiting deep overbite in the early permanent or adult dentition, were selected for this study. Two subjects had Class II, Division 1 malocclusions, and the other three had Class I malocclusions. By means of the "replicator system" jaw movements during border movements and unilateral chewing were recorded and analyzed by computer plots. The typical chewing pattern of all five subjects was characterized by midsagittal opening, wide lateral closing movements, tooth gliding, and a pause at the intercuspal position and during swallowing. Comparison of these findings with chewing data from normal children in previous studies indicated that the deep-bite malocclusion did not create a major disturbance in chewing. Some differences between the preoperative and postoperative condition were noted, however. Prior to treatment, three subjects showed a nearly vertical chewing cycle which avoided tooth contact at the border path. Following treatment, all subjects showed a greater coincidence between the closing chewing path and the lateral border movement. This indicated more gliding tooth contact after treatment. Following deep-bite correction, the border paths showed a refinement of the intercuspal position (IP) and an increased steepness in lateral tooth guidance near IP. The total vertical component of tooth guidance was reduced by treatment.

Adolescent↗
PubMed1983

The effect of N6-phenylisopropyladenosine on the regulation of fat cell hexose transport, glucose oxidation and fatty acid release by insulin and catecholamines.

N6-Phenylisopropyladenosine was employed in the absence of endogenous adenosine to explore the influence exerted by the R-site over the antagonistic interaction of insulin and catecholamines on several parameters of fat cell metabolism. When no hormones were present, N6-phenylisopropyladenosine had little or no effect; however, the nucleoside potentiated insulin inhibition of catecholamine-stimulated events, such as lipolysis, and, conversely, diminished or blocked catecholamine inhibition of insulin-stimulated processes, such as 2-deoxyglucose uptake, glucose oxidation and esterification, even under conditions where N6-phenylisopropyladenosine, alone, was ineffective in reversing catecholamine actions.

Adenosine↗
PubMed1983

Lack of segmental selectivity in elimination of synapses from soleus muscle of new-born rats.

The elimination of polyneuronal innervation from neonatal rat soleus muscle was studied by comparing the extent of synapse loss by motor neurones emerging through each of the two spinal nerves (L4 and L5) supplying the muscle. The fraction of muscle fibres receiving innervation from the L4 spinal nerve declined from an average of 75% in 6-day-old animals (when all fibres are polyneuronally innervated) to 18% in animals older than 16 days (when almost all muscle fibres are singly innervated). By comparison innervation by the L5 spinal nerve declined from 99% of the fibres at 6 days to 83% of the fibres after 16 days. As a result of synapse elimination there is a greater reduction in the innervation of the muscle by the L4 nerve. The difference in loss of muscle fibres innervated by L4 vs. L5 was not, however, due to a greater degree of synapse elimination of L4 motor nerve terminals. As shown by measurements of the sizes of motor units, both L4 and L5 have units which on average are about four to five times larger at 6 days than at the conclusion of synapse elimination. Thus L4 and L5 motor neurones undergo approximately the same degree of size reduction. The apparently disproportionate loss of muscle innervation by the L4 nerve is explained by the fact that L4 usually contains only a small portion of the total of soleus motor neurones. I therefore conclude that there is no selective loss of synapses based on spinal origin of motor neurones.

Animals↗
PubMed1982

Cyclic AMP does not modulate hexose uptake of serum-deprived BHK-21 fibroblasts.

We have studied the uptakes of the glucose analogs, 2-deoxyglucose (2DG), and 3-O-methylglucose (3OMG) in serum-deprived BHK-21 fibroblasts. Incubation for 4 hours with 0.25 mM 1-methyl-3-isobutylxanthine (MIX) increased cellular cyclic AMP 3 to 15 fold, without affecting the initial rates of uptake of these sugars. Incubation with 100 nM insulin, doubled hexose uptake without affecting cyclic AMP. Insulin did not modify the cyclic AMP response to MIX; nor did MIX alter the hexose uptake response to insulin. There was no effect of 0.1 mM L-isoproterenol (ISO) or 0.1 mM prostaglandin E1 (PGE1) on cyclic AMP. PGE1 slightly stimulated uptake of 2DG but not 3OMG; ISO did not affect hexose uptake. We conclude that cyclic AMP does not directly regulate hexose uptake in these cells.

1-Methyl-3-isobutylxanthine↗
PubMed1982

Isolation and enrichment of the gastric chief cells of the rat.

The isolation and enrichment of the gastric chief cells of the rat are described. Ultrastructural examination showed 85% enrichment from a mixed population of mucosal cells following their centrifugation through a discontinuous Percoll gradient. When compared to homogenates of the initial mixed cell population, the enriched chief cell population showed over a three-fold increase in pepsin(ogen) content. Preliminary experiments showed that a combination of the secretagogues histamine and carbamylcholine caused a significant increase in pepsin release from enriched chief cell preparations and a concomitant decrease in their pepsin content as compared to untreated cells. The results obtained in this study indicate the feasibility of employing this procedure for the isolation of gastric chief cells for the in vitro study of secretagogue regulation of pepsin secretion.

Animals↗
PubMed1982

Dislocations of the lower cervical spine.

In 34 cases of cervical spine facet dislocation treated between 1975 and 1979, the dislocations were reduced by closed methods and immobilized in the halo thoracic brace. If closed reduction was unsuccessful, open reduction and fusion were performed. There is a high incidence of failure of closed reduction and halo thoracic immobilization in patients with minimal or no neurologic deficit. Bilateral facet dislocation was more frequently associated with severe neurologic injury than was unilateral facet dislocation, Use of closed reduction is time consuming, often unsuccessful, and may result in neurologic deterioration. Patients with facet dislocations and minimal neurologic injury are at risk of late instability following halo thoracic brace immobilization, and therefore open reduction and posterior cervical fusion may be advisable for them. However, surgical fusion carries a high incidence of long-term neck pain and stiffness, and is indicated only in patients at risk of developing late instability.

Adolescent↗
PubMed1981

Evidence for convertible forms of soluble uterine cyclic nucleotide phosphodiesterase.

The cyclic nucleotide phosphodiesterase (3':5'-cyclic nucleotide 5'-nucleotidohydrolase, EC 3.1.4.17) systems of many tissues show multiple physical and kinetic forms. In contrast, the soluble rat uterine phosphodiesterase exists as a single enzyme form with non-linear Lineweaver-Burk kinetics for cyclic AMP (app. Km of approx. 3 and 20 microM) and linear kinetics for cyclic GMP (app. Km of approx. 3 microM) since the two hydrolytic activities are not separated by a variety of techniques. In uterine cytosolic fractions, cyclic AMP is a non-competitive inhibitor of cyclic GMP hydrolysis (Ki approx. 32 microM). Also, cyclic GMP is a non-competitive inhibitor of cyclic AMP hydrolysis (Ki approx 16 microM) at low cyclic GMP/cyclic AMP substrate ratios. However, cyclic GMP acts as a competitive inhibitor of cyclic AMP phosphodiesterase (Ki approx 34 microM) at high cyclic GMP/cyclic AMP substrate ratios. When a single hydrolytic form of uterine phosphodiesterase, separated initially by DEAE anion-exchange chromatography, is treated with trypsin (0.5 microgram/ml for 2 min) and rechromatographed on DEAE-Sephacel, two major forms of phosphodiesterase are revealed. One form elutes at 0.3 M NaOAc- and displays anomalous kinetics for cyclic AMP hydrolysis (app. Km of 2 and 20 microM) and linear kinetics for cyclic GMP (app. Km approx. 5 microM), kinetic profiles which are similar to those of the uterine cytosolic preparations. A second form of phosphodiesterase elutes at 0.6 M NaOAc- and displays a higher apparent affinity for cyclic AMP (app. Km approx. 1.5 mu) without appreciable cyclic GMP hydrolytic activity. These data provide kinetic and structural evidence that uterine phosphodiesterase contains distinct catalytic sites for cyclic AMP and cyclic GMP. Moreover, they provide further documentation that the multiple forms of cyclic nucleotide phosphodiesterase in mammalian tissues may be conversions from a single enzyme species.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1981

Cytochalasin inhibition of isolated rat gastric parietal cell function.

Submicrogram concentrations (0.04-0.29 microM) of the microfilament disrupting agents cytochalasins D, E, and B (CD, CE, CB) were shown to inhibit secretagogue-stimulated 14C-aminopyrine accumulation (AP) in isolated rat gastric mucosal parietal cells. The microtubule disrupting agent colchicine had little influence on AP accumulation. Histamine- and dibutyryl cyclic AMP (DbcAMP)-stimulated AP accumulation was inhibited with an order of potency CD greater than CE approximately equal to CB. CB inhibition of these secretagogue actions was, however, only approximately 65-70% of the maximal stimulated response, whereas CD and CE caused 100% inhibition. On the other hand, carbamylcholine-stimulated AP accumulation was inhibited 100% by all cytochalasins tested with an order of potency CD approximately equal to CE greater than CB. These data are discussed in relation to acid secretagogue-induced morphological changes involving actin filament organization in parietal cells.

Actins↗