Biomedical subjects

L Lavoie

Publications and source records attributed to L Lavoie.

At least 19 recordsLinked to original sources

PubMed2001

Specific inhibition by hGRB10zeta of insulin-induced glycogen synthase activation: evidence for a novel signaling pathway.

Grb10 is a member of a family of adapter proteins that binds to tyrosine-phosphorylated receptors including the insulin receptor kinase (IRK). In this study recombinant adenovirus was used to over-express hGrb10zeta, a new Grb10 isoform, in primary rat hepatocytes and the consequences for insulin signaling were evaluated. Over-expression of hGrb10zeta resulted in 50% inhibition of insulin-stimulated IRK autophosphorylation and activation. Analysis of downstream events showed that hGrb10zeta over-expression specifically inhibits insulin-stimulated glycogen synthase (GS) activity and glycogen synthesis without affecting insulin-induced IRS1/2 phosphorylation, PI3-kinase activation, insulin like growth factor binding protein-1 (IGFBP-1) mRNA expression, and ERK1/2 MAP kinase activity. The classical pathway from PI3-kinase through Akt-PKB/GSK-3 leading to GS activation by insulin was also not affected by hGrb10zeta over-expression. These results indicate that hGrb10zeta inhibits a novel and presently unidentified insulin signaling pathway leading to GS activation in liver.

Animals↗

PubMed2001

Atrioventricular interval optimization and exercise tolerance.

Modern pacemakers offer many programming options regarding the AV interval including the ability to vary AV intervals depending on whether atrial activity is paced or spontaneous and to shorten AV intervals with increasing rates. To determine if optimization of these features improves exercise tolerance, 14 patients with intact sinus node function and AV block treated with dual chamber pacemakers were enrolled in a randomized double-blind crossover trial. Doppler echocardiographic measurements of cardiac index and mitral flow were assessed over a range of programmable AV intervals at rest to determine each patient's optimal AV interval. Eleven patients completed serial graded exercise tests with spiroergometry after randomly programming the AV interval three ways in a crossover manner: fixed AV interval = 150 ms without rate adaptation (150/Fixed), fixed AVinterval = 150 ms with rate adaptation (150/R), or optimized AV interval with rate adaptive AV interval shortening (optimized/R). Exercise capacity was determined by maximum oxygen uptake. Ten men and four women, age 64 +/- 8 years, were enrolled. At rest, optimization of the AVintervalimproved the cardiac index by 21% (P < 0.001) and mitral flow by 13.4% (P < 0.001) when compared to least-favorable AV intervals. During exercise, no differences in maximum heart rates were noted. Maximum oxygen uptake was increased in both groups with rate adaptive AVinterval shortening when compared tofixed AVinterval without rate adaptation: 13.9% (adjusted P < 0.04) and 14.6% (adjusted P < 0.02) in optimized/R and 150/R, respectively. No differences were noted between optimized/R and 150/R. In conclusion, rate adaptive AV interval shortening improved exercise tolerance independent of changes in heart rate. However, optimization of the AV interval with Doppler echocardiography at rest did not further improve exercise capacity.

Atrial Function↗

PubMed1999

Regulation of glycogen synthase in rat hepatocytes. Evidence for multiple signaling pathways.

We examined the signaling pathways regulating glycogen synthase (GS) in primary cultures of rat hepatocytes. The activation of GS by insulin and glucose was completely reversed by the phosphatidylinositol 3-kinase inhibitor wortmannin. Wortmannin also inhibited insulin-induced phosphorylation and activation of protein kinase B/Akt (PKB/Akt) as well as insulin-induced inactivation of GS kinase-3 (GSK-3), consistent with a role for the phosphatidylinositol 3-kinase/PKB-Akt/GSK-3 axis in insulin-induced GS activation. Although wortmannin completely inhibited the significantly greater level of GS activation produced by the insulin-mimetic bisperoxovanadium 1,10-phenanthroline (bpV(phen)), there was only minimal accompanying inhibition of bpV(phen)-induced phosphorylation and activation of PKB/Akt, and inactivation of GSK-3. Thus, PKB/Akt activation and GSK-3 inactivation may be necessary but are not sufficient to induce GS activation in rat hepatocytes. Rapamycin partially inhibited the GS activation induced by bpV(phen) but not that effected by insulin. Both insulin- and bpV(phen)-induced activation of the atypical protein kinase C (zeta/lambda) (PKC (zeta/lambda)) was reversed by wortmannin. Inhibition of PKC (zeta/lambda) with a pseudosubstrate peptide had no effect on GS activation by insulin, but substantially reversed GS activation by bpV(phen). The combination of this inhibitor with rapamycin produced an additive inhibitory effect on bpV(phen)-mediated GS activation. Taken together, our results indicate that the signaling components mammalian target of rapamycin and PKC (zeta/lambda) as well as other yet to be defined effector(s) contribute to the modulation of GS in rat hepatocytes.

Animals↗

PubMed1997

Identification and characterization of two distinct intracellular GLUT4 pools in rat skeletal muscle: evidence for an endosomal and an insulin-sensitive GLUT4 compartment.

In skeletal muscle, acute insulin treatment results in the recruitment of the GLUT4 glucose transporter from intracellular vesicular structures to the plasma membrane. The precise nature of these intracellular GLUT4 stores has, however, remained poorly defined. Using an established skeletal-muscle fractionation procedure we present evidence for the existence of two distinct intracellular GLUT4 compartments. We have shown that after fractionation of crude muscle membranes on a discontinuous sucrose gradient the majority of the GLUT4 immunoreactivity was largely present in two sucrose fractions (30 and 35%, w/w, sucrose; denoted F30 and F35 respectively) containing intracellular membranes of different buoyant densities. Here we show that these fractions contained 44+/-6 and 49+/-7% of the crude membrane GLUT4 reactivity respectively, and could be further discriminated on the basis of their immunoreactivity against specific subcellular antigen markers. Membranes from the F30 fraction were highly enriched in transferrin receptor (TfR) and annexin II, two markers of the early endosome compartment, whereas they were significantly depleted of both GLUT1 and the alpha1-subunit of (Na++K+)-ATPase, two cell-surface markers. Insulin treatment resulted in a significant reduction in GLUT4 content in membranes from the F35 fraction, whereas the amount of GLUT4 in the less dense (F30) fraction remained unaffected by insulin. Immunoprecipitation of GLUT4-containing vesicles from both intracellular fractions revealed that TfR was present in GLUT4 vesicles isolated from membranes from the F30 fraction. In contrast, GLUT4 vesicles from the F35 fraction were devoid of TfR. The aminopeptidase, vp165, was present in GLUT4 vesicles from both F30 and F35; however, vesicles isolated from F30 contained over twice as much vp165 per unit of GLUT4 than those isolated from F35. The biochemical co-localization of vp165/GLUT4 was further substantiated by double-immunogold labelling of ultrathin muscle sections. Overall, our data indicate the presence of at least two internal GLUT4 pools: one possibly derived from an endosomal recycling compartment, and the other representing a specialized insulin-sensitive GLUT4 storage pool. Both pools contain vp165.

Aminopeptidases↗

PubMed1997

The molar ratios of alpha and beta subunits of the Na+-K+-ATPase differ in distinct subcellular membranes from rat skeletal muscle.

The Na+-K+-ATPase consists of alpha and beta subunits proposed to function as an alpha-beta heterodimer. Skeletal muscle is characterized by expression of alpha1, alpha2, beta1, and beta2 subunit isoforms. The relative molar proportions of each subunit or each protein isoform are not known, yet their subcellular distribution and expression in muscles of different fiber types are markedly different. In this study, the molar ratio of each pump subunit isoform was measured in purified membranes from skeletal muscle and compared with those in kidney and brain microsomes. Recombinant proteins were used as standards to quantitate each isoform by immunoblotting in combination with measurements of [3H]ouabain binding. The results indicate that in kidney microsomes, which express predominantly alpha1 and beta1 isoforms, the alpha:beta subunit molar ratio is approximately 1:1. In brain microsomes, the sum of all alpha (alpha1, alpha2, and alpha3) and all beta (beta1 and beta2) subunits also yielded a molar ratio of approximately 1:1. In contrast, in red (oxidative) skeletal muscles, the all alpha:beta subunit ratio was 0.2 in plasma membranes and 0.4 in intracellular membranes. The ratio of alpha2 subunits to alpha1 subunits ranged from 1.6 in surface membranes to up to 7 in internal membranes, while the beta1 subunits exceeded the beta2 subunits by approximately 4-fold in all membrane fractions. Thus, intracellular membranes of red skeletal muscles contain primarily alpha2 and beta1 subunits. When these intracellular membranes were further subfractionated by velocity gradient centrifugation, the alpha2:beta1 subunit ratio was 0.5 in the faster migrating (larger) membranes and 1.0 in the slower migrating (smaller) ones. This was due to a progressive decrease in abundance of the beta1 subunits without a change in the concentration of alpha2 subunits per unit protein. The Na+-K+-ATPase hydrolytic activity was higher in the larger vesicles than in the smaller ones along the sucrose gradient. These results suggest that the ratio of beta to alpha subunits may serve to regulate the catalytic activity of the Na+-K+-ATPase in skeletal muscle.

Animals↗

PubMed1996

Insulin-induced translocation of Na+-K+-ATPase subunits to the plasma membrane is muscle fiber type specific.

We have previously shown that an acute insulin treatment induces redistribution of the alpha 2- and beta 1- isoforms of the Na+-K+-ATPase from intracellular membranes to plasma membranes detected on subcellular fractionation of mixed muscles and immunoblotting with isoform-specific antibodies (H. S. Hundal et al. J. Biol. Chem. 267: 5040-5043, 1992). In the present study we give both biochemical and morphological evidence that this insulin effect is operative in muscles composed mostly of oxidative (red) fibers but not in muscles composed mostly of glycolytic (white) fibers. The redistribution of the Na+-K+-ATPase alpha 2- and beta 1-isoforms after insulin injection was detected in membranes isolated from and muscles (soleus, red gastrocnemius, red rectus femoris, and red vastus lateralis) but not in membranes from white muscles (white gastrocnemius, tensor fasciae latae, white rectus femoris, and white vastus lateralis). After insulin injection, the potassium-dependent 3-O-methylfluorescein phosphatase activity of the enzyme was higher by 22% in the plasma membrane-enriched fraction and lower by 15% in the internal membrane fraction isolated from red but not from white muscles. Quantitative immunoelectron microscopy of ultrathin muscle cryosections showed that in vivo insulin stimulation augmented the density of Na+-K+-ATPase alpha 2- and beta 1- isoforms at the plasma membrane of soleus muscle by 80 and 124%, respectively, with no change in white gastrocnemius muscle. The effect of insulin to increase the content of Na+-K+-ATPase alpha 2- and beta 1-subunits in isolated plasma membranes was still observed when glycemia was prevented from dropping by using hyperinsulinemic-euglycemic clamps. We conclude that the insulin-induced redistribution of the alpha 2- and beta 1-isoforms of the Na+-K+-ATPase from an intracellular pool to the plasma membrane in restricted to oxidative fiber-type skeletal muscles. This may be related to the selective expression of beta 1-subunits in these fibers and implies that the beta 2-subunit, typical of glycolytic muscles, does not sustain translocation of alpha 2 beta 2-complexes.

Animals↗

PubMed1995

The GLUT4 glucose transporter and the alpha 2 subunit of the Na+,K(+)-ATPase do not localize to the same intracellular vesicles in rat skeletal muscle.

The GLUT4 glucose transporter and the alpha 2 subunit of the Na+,K(+)-ATPase of rat skeletal muscle are two proteins which redistribute from intracellular membranes to plasma membranes following in vivo insulin stimulation. Here we show that although both proteins co-segregate after subcellular fractionation of unstimulated rat hindlimb muscles, they do not share the same intracellular residence inside the muscle fibre. By immunogold single- and double-labeling on ultrathin muscle cryosections with specific antibodies, the GLUT4 glucose transporter and the Na+,K(+)-ATPase alpha 2 subunit were observed on different vesicular structures within the cell. GLUT4 was detected on subsarcolemmal and perinuclear membranes, and at the junction between myofibrillar A and I bands where triads are localized. The alpha 2 subunit of the Na+,K(+)-ATPase was observed at the plasma membrane and in distinct subsarcolemmal vesicles and intermyofibrillar membranes. Quantitative analysis of double-labeling of GLUT4 and Na+,K(+)-ATPase alpha 2 subunit revealed that less than 6% of the two proteins co-localize in the same continuous vesicular structures. The differential intracellular localization of the two proteins was further confirmed by immunopurification of GLUT4-containing membranes from muscle homogenates, in which the alpha 2 subunit of the Na+,K(+)-ATPase was found only at the same extent as the alpha 1 subunit of the enzyme, a protein exclusively present at the plasma membrane.

Animals↗

PubMed1994

Catheter ablation using radiofrequency or low-energy direct current in pediatric patients with the Wolff-Parkinson-White syndrome.

Percutaneous ablation of accessory pathways was performed in 22 consecutive children and adolescents (9 boys and 13 girls, age range 8 to 18 years). Low-energy direct current (DC) was used exclusively in the first 6 patients, whereas ablation was performed with radiofrequency energy in the following 16. Accessory pathways were located in the left free wall in 15 patients, were posteroseptal in 3, were in the right free wall in 3 and were anteroseptal in 1. A concealed accessory pathway was present in 7 patients (32%). There was no significant difference in clinical or electrophysiologic variables between both groups. Catheter ablation was successful in the initial 6 patients using low-energy DC, as compared with 13 of 16 patients using radiofrequency ablation. Low-energy DC was successful as a backup power source in all 3 patients who had unsuccessful radiofrequency ablation. There was no complication. The median procedural and fluoroscopic times for successful ablation were 2.5 hours and 49 minutes, respectively (p = NS between both power sources). Accessory pathway conduction recurred in 2 patients (33%) who had low-energy DC as compared with 1 (6%) who had radiofrequency ablation (p = NS). These 3 patients had successful reablation of their accessory pathways. In children and adolescents with accessory pathways, both new power sources compare favorably, with an overall success rate of ablation of 100% (22 of 22 patients). Radiofrequency ablation should be used initially because it does not require general anesthesia and is associated with a lower rate of recurrence of accessory pathway conduction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1993

Results of a comparative study of low energy direct current with radiofrequency ablation in patients with the Wolff-Parkinson-White syndrome.

OBJECTIVE: To compare two new power sources for catheter ablation in patients with the Wolff-Parkinson-White syndrome. DESIGN: 120 consecutive patients with accessory pathways had catheter ablation. Low energy direct current (DC) was used in the first 60 patients and radio-frequency current in the next 60 patients. SETTING: Electrophysiological laboratory of a large heart institute. PATIENTS: 72 men and 48 women (mean (SD) age 35 (14) years (range 9-75)). The accessory pathways were in the left free wall in 73 patients. They were posteroseptal in 35 patients, in the right free wall in five, and anteroseptal in seven. There was no significant difference in the clinical or electrophysiological variables between the two ablation groups. RESULTS: Catheter ablation with low energy direct current was successful in 55/60 patients (92%) and radiofrequency energy was successful in 52/60 patients (87%). Low energy direct current was also successful in four of the eight patients in whom radiofrequency ablation had failed. Radiofrequency ablation was successful in two of the five patients in whom low energy direct current ablation had failed. The mean (SD) procedure and fluoroscopy times for successful ablation were 3.2 (1.5) h and 61 (40) min respectively. These times were similar for both power sources. Accessory pathway conduction recurred in 17 patients (28%) who had low energy direct current and four patients (7%) who received radiofrequency energy (p < 0.004). All patients with recurrence of an accessory pathway had successful re-ablation. CONCLUSIONS: Both new power sources successfully ablated accessory pathways, (overall success rate 94% (113/120 patients)). Radiofrequency ablation, however, did not require general anaesthesia and was associated with a significantly lower rate of recurrence of accessory pathway conduction. Therefore radiofrequency should be used initially for ablation. Low energy direct current may be most useful as a back-up in patients in whom radiofrequency ablation fails.

Adolescent↗

PubMed1993

Insulin increases the Na(+)-K(+)-ATPase alpha 2-subunit in the surface of rat skeletal muscle: morphological evidence.

The cellular localization of the alpha 2-subunit of the Na(+)-K(+)-ATPase was defined by immunoelectron microscopy, and the effect of insulin on the amount of alpha 2-immunoreactive subunits on the cell surface was quantitated. Two protocols were used for tissue fixation and immunolocalization. Protocol 1 was characterized by fixation with 2% paraformaldehyde, use of a monoclonal antibody, and detection with 3-nm-diameter gold-labeled Fab fragments or 10-nm gold-labeled immunoglobulin G. Protocol 2 was characterized by fixation with 4% paraformaldehyde plus 0.1% glutaraldehyde, use of a polyclonal antibody, and detection with 10-nm gold-labeled protein A. In control muscle, the alpha 2-subunit of the Na(+)-K(+)-ATPase was present at the plasma membrane and in intracellular tubular and vesicular structures located in subsarcolemmal and triadic regions. Acute insulin stimulation increased the number of immunolabeled alpha 2-subunits in the plasma membrane after both fixation protocols. The gain in the plasma membrane ranged from 1.5- to 3.7-fold and was significant at the level of P < 0.005. These results provide morphological quantitative evidence that the alpha 2-subunit of the Na(+)-K(+)-ATPase is present both at the plasma membrane and intracellularly in mammalian skeletal muscle and that insulin acutely increases its abundance in the muscle surface.

Animals↗

PubMed1993

Opposite effects of hyperglycemia and insulin deficiency on liver glycogen synthase phosphatase activity in the diabetic rat.

The specific effect of hyperglycemia on the reported decrease in liver glycogen synthase phosphatase activity was studied in STZ-induced diabetic rats with normal fasting insulinemia. Four groups of animals were investigated: control (nondiabetic), diabetic hyperglycemic (STZ), diabetic normoglycemic (STZ followed by 3-day phloridzin treatment), and a diabetic normoglycemic group injected with glucose to reinstate hyperglycemia. None of the treatments significantly altered fasting plasma insulin and glucagon concentrations. We found that hepatic synthase phosphatase activity decreased in STZ-induced diabetic rats and was further markedly reduced when glycemia was normalized in the diabetic animals. This additional decrease in phosphatase activity was almost fully reversed when hyperglycemia was restored by acute glucose infusion of the normoglycemic diabetic rats. In parallel, the levels of liver G6P and F6P were markedly reduced in the diabetic normoglycemic rats and restored with reinstatement of hyperglycemia. In contrast, liver microsomal glucose-6-phosphatase activity was enhanced and glucokinase activity was lowered in all diabetic groups, regardless of glycemia. Our results indicate that hyperglycemia per se counteracts part of the loss of hepatic synthase phosphatase in diabetic animals and provokes the stable conversion of synthase phosphatase from a less active to a more active form.

Animals↗

PubMed1993

Characterization and measurement of prostate-specific antigen using monoclonal antibodies.

Monoclonal and polyclonal antibodies were produced using a pure preparation of prostate-specific antigen (PSA) as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). By SDS-PAGE, the apparent molecular weight of PSA was about 33 kD. Eighty-four monoclonal antibodies were produced, 77 of which bind PSA with an affinity higher than 10(9) M-1. Use of these monoclonal antibodies to study the immunological characteristics of PSA revealed the presence of 4 epitopes. Injection of PSA into goats resulted in a production of polyclonal antibodies with high affinity. These polyclonal antibodies were purified by affinity chromatography and adsorbed on plastic tubes. By an immunometric assay, we have also demonstrated that polyclonal antibodies bind PSA at a fifth epitope that is different from those of monoclonal antibodies. Using an iodinated monoclonal antibody and polyclonal antibodies adsorbed on plastic tubes, a sensitive immunoradiometric assay could be developed, and a further increase in sensitivity could be achieved by using a mixture of 2 monoclonal antibodies. The serum PSA levels in 2,250 patients measured with this immunoradiometric assay were identical to the values determined by Tandem-R, although the present assay reached a minimum detectable value of 0.05 ng/ml compared with 0.2 ng/ml by Tandem-R.

Animals↗

PubMed1992

Distinct oxidoresistance phenotype of human T47D cells transfected by rat glutathione S-transferase Yc expression vectors.

We have investigated the role of a glutathione S-transferase (GST) with inherent peroxidase activity in the cellular defense against lipid peroxidation and free radical-mediated oxidative damage. Stable transfectants of human T47D cells were generated which express recombinant rat GST-Yc from a human cytomegalovirus promoter-based expression vector. Among several GST-Yc transfectants characterized, two of them contained, respectively, 2- and 3-fold higher GST activity than parental cells or control transfectants and, respectively, 4-5- and 8-10-fold higher selenium-independent glutathione peroxidase activity. Cellular growth kinetics and rates of [3H]thymidine incorporation showed that both transfectants were more resistant to oxidative shocks mediated by cumene hydroperoxide or singlet oxygen generated by photosensitized rose bengal than were T47D cells and control transfectants. In contrast, a T47D transfectant, which expressed high levels of recombinant selenoglutathione peroxidase and showed enhanced resistance to cumene hydroperoxide (Mirault, M.-E., Tremblay, A., Beaudoin, N., and Tremblay, M. J. (1991) J. Biol. Chem. 266, 20752-20760), was as sensitive as parental cells to singlet oxygen. No difference was found in growth sensitivity to 1-h shock treatments with the quinonoid drug daunomycin, irrespective of GST-Yc or selenoglutathione peroxidase overexpression in these cells.

Animals↗

PubMed1992

Hepatic vagotomy does not alter plasma insulin response to a low dose injection of glucose.

It has been reported that insulin concentration is altered by a hepatic vagotomy following intraperitoneal glucose injection (0.3 g/kg) resulting in supraphysiological blood glucose concentrations. On the other hand, neural activity of the hepatic vagus nerve has been shown to be substantially reduced by lower doses (0.05 g/kg intraportal; 0.1 g/kg intravenous). The present study was conducted in order to examine the role of the hepatic vagus nerve in insulin response after intraperitoneal injections of 0.1 and 0.3 g/kg of glucose. Measurements were made 5 days after section of this branch. In a first experiment, arterial glucose and insulin concentrations were not affected by the hepatic vagotomy following injections of either 0.1 or 0.3 g/kg of glucose. The same finding was also found in a second experiment in which portal glucose and insulin levels were measured after injection of 0.1 g/kg of glucose. These results suggest that large changes in neural activity are needed for the hepatic vagus nerve to influence the insulin response.

Animals↗

PubMed1992

Success, safety, and late electrophysiological outcome of low-energy direct-current ablation in patients with the Wolff-Parkinson-White syndrome.

BACKGROUND: Percutaneous ablation of accessory pathways with the use of a defibrillator can be accomplished with high-energy direct-current (DC) shocks of 150-400 J, but complications include cardiac tamponade and sudden cardiac death, mostly resulting from significant electrical arcing and barotrauma. A new low-energy DC power source with a brief time-constant capacitive discharge delivers shocks of 2-40 J and eliminates or greatly reduces arcing. This report describes our initial experience with this device in 60 consecutive patients (mean age, 34 years; range, 9-67 years) with Wolff-Parkinson-White syndrome. Accessory pathways were located in the left free wall in 36 patients, in the right free wall in two, were posteroseptal in 18, and anteroseptal in four. Most patients (77%) had their initial diagnostic electrophysiological study and catheter ablation during the same session. METHODS AND RESULTS: Selective ablation of accessory pathways was successful in 55 patients (92%). The mean cumulative energy was 312 +/- 284 J and the mean creatine kinase MB peak (normal, 0-30 units) was 42 +/- 27 units. Patients with left free wall accessory pathways required less procedure time for ablation (2.7 +/- 0.8 versus 3.6 +/- 1.5 hours, p less than 0.0007) and less fluoroscopy time (46 +/- 24 versus 66 +/- 33 minutes, p less than 0.002). Complications were limited to transient pericarditis (three patients), one iliac artery dissection, and cardiac tamponade probably caused by catheter repositioning in the coronary sinus (one patient). An electrophysiological study was repeated in 50 of the 55 successful cases at a mean of 9 +/- 5 months. This study was normal in 48 of 50 (96%) patients. CONCLUSIONS: Low-energy DC ablation is safe and effective treatment for accessory pathways in children and adults. The long-term outcome is excellent as documented by electrophysiological restudy.

Adult↗

PubMed1991

Hormone-stimulated glucose production from glycogen in hepatocytes from streptozotocin diabetic rats.

The contribution of hormone-stimulated glycogenolysis to hepatic glucose production was studied in hepatocytes from streptozotocin diabetic rats. To this end, the activation of glycogen phosphorylase by glucagon, vasopressin, and the alpha 1-adrenergic agonist phenylephrine was compared in hepatocytes from normal and diabetic rats and related to glycogen content, glucose production, and microsomal glucose-6-phosphatase activity. Streptozotocin-induced diabetes reduced the glycogen content and the amount of total (a + b) phosphorylase in hepatocytes proportionally to the severity of the disease. In cells from severely diabetic rats (group 1), the responsiveness of activation of phosphorylase to the hormones was reduced by about half, consistent with a 45% reduction in total phosphorylase. In addition, the sensitivity of phosphorylase activation to all hormones investigated was decreased by about 1 order of magnitude or more in cells of this group. In hepatocytes from rats with milder diabetes (group 2), maximal phosphorylase activation reached an intermediate value between that of the control group and of group 1. In response to all hormones investigated, group 2 diabetic rat hepatocytes produced less glucose than control rat liver cells, while in group 1 there was no increase in glucose production at all, presumably because glycogen concentration was too low. However, in group 2 diabetic rat hepatocytes, glucagon-stimulated glucose production, unlike phosphorylase activation, did not show decrease sensitivity, presumably because glucose-6-phosphatase activity is increased by diabetes. Our results thus indicate that hormone-stimulated liver glycogenolysis is unlikely to contribute to enhanced glucose production in insulin-deficient diabetes, despite increased glucose-6-phosphatase activity.

Animals↗

PubMed1991

Low energy direct current ablation in patients with the Wolff-Parkinson-White syndrome: clinical outcome according to accessory pathway location.

Forty-five patients with the Wolff-Parkinson-White syndrome underwent direct current (DC) ablation using a low energy power source (Cardiac Recorders). Anodal shocks of 10-40 joules were given to either a 6 French quadripolar catheter (Bard), a 7 French bipolar contoured catheter (Bard), or a 7 French deflectable catheter with a 4-mm distal electrode (Mansfield). The indifferent electrode consisted of a large patch that was positioned under the left scapula. There were 26 males and 19 females, with a mean age of 34 years (range 9-67). Accessory pathways were located in the left free wall in 30 patients (67%) and were posteroseptal in 15 patients (33%). The shortest ventriculoatrial interval during mapping (89 +/- 21 msec), the mean cumulative amount of energy per patient (322 +/- 283 joules), and the mean CK-MB rise (45 +/- 30 units, normal 0-30 units) were not significantly different between both groups. Ablation was successful in 29/30 patients (97%) with a left free-wall accessory pathway, and in 13/15 patients (87%) with a posteroseptal accessory pathway. All three patients with failure of ablation had multiple accessory pathways, and two of these patients had Ebstein's anomaly. Patients with left free-wall and posteroseptal accessory pathways, respectively, differed significantly in terms of: total session time (4.1 +/- 1 hours vs 5.3 +/- 1.3, p = 0.0001), total procedure time for ablation (2.6 +/- 0.8 hours vs 3.2 +/- 1.2, P = 0.02), and fluoroscopy time (46 +/- 24 min vs 64 +/- 29, P = 0.006). In 13 patients (29%) with a concealed accessory pathway, these variables were not significantly different from patients with overt preexcitation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Increased synthase phosphatase activity is responsible for the super-activation of glycogen synthase in hepatocytes from fasted obese Zucker rats.

Addition of 60 mM glucose caused a similar partial activation of glycogen synthase in hepatocytes isolated from overnight fasted Wistar rats and from fasted lean Zucker (Fa/fa?) rats. In contrast, the activation went rapidly to completion in cells from fasted obese (fa/fa) rats. Subsequent addition of 4 microM microcystin, a potent inhibitor of type 1 and type 2A protein phosphatases, induced a rapid inactivation of glycogen synthase, which occurred at a similar rate in all three types of hepatocytes. This suggests that the super-activation of glycogen synthase in hepatocytes from fasted obese rats is not due to a lower synthase kinase activity. Glycogen synthase phosphatase was quantitatively assayed in broken-cell preparations from the same livers, with exogenous synthase b as substrate. The synthase phosphatase activity in the fa/fa livers was 3-fold higher than that in the livers from both lean Zucker rats and Wistar rats. This difference has to be attributed to an increased synthase phosphatase activity of the glycogen-bound protein phosphatase-1 in livers of fasted obese rats. The results suggest that in the latter animals the available insulin exceeds the insulin resistance of the liver. The resulting overexpression of the insulin-dependent synthase-phosphatase-1G activity may explain the super-activation of glycogen synthase in response to a glucose challenge.

Animals↗