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Biomedical subjects

D Steinberg

Publications and source records attributed to D Steinberg.

At least 289 records · Page 16Linked to original sources
PubMed1976

Triglyceride, diglyceride, monoglyceride, and cholesterol ester hydrolases in chicken adipose tissue activated by adenosine 3':5'-Monophosphate-dependent protein kinase. Chromatographic resolution and immunochemical differentiation from lipoprotein lipase.

Hormone-sensitive lipase and cholesterol ester hydrolase of chicken adipose tissue were markedly activated by adenosine 3':5'-monophosphate (cAMP)-dependent protein kinase (on the average, 235 to 275%; occasionally as much as 1000%). Diglyceride and monoglyceride hydrolases were also activated, but to a lesser extent (60 to 87%). The activation of all four hydrolases was inhibited by protein kinase inhibitor and reversed by the addition of exogenous protein kinase. Following activation by cAMP-dependent protein kinase, all four hydrolases were deactivated in a Mg2+-dependent reaction and then reactivated to or near initial levels on incubation with cAMP and Mg2+-ATP. The reversible deactivation is assumed to reflect activity of one or more protein phosphatases. The maximum activation obtainable for the four hydrolases decreased when the tissue had been previously exposed to glucagon, indicating that the glucagon-induced activation was probably similar to or identical with the activation demonstrated in cell-free preparations. The pH optima for the four hydrolase activities were similar (7.13 to 7.38). Although the absolute activities and relative degrees of kinase activation differed according to the particular emulsified substrates used, the results do not rule out the possibility that all four hydrolase activities are referable to a single hormone-sensitive hydrolase. Hormone-sensitive acyl hydrolases were separated from lipoprotein lipase by heparin-Sepharose affinity chromatography. Lipoprotein lipase was active against triolein, diolein, and monoolein, but not cholesterol oleate. Incubation of lipoprotein lipase with exogenous protein kinase, cAMP, and Mg2+ATP had no effect on any of the three hydrolase activities. Lipoprotein lipase was further purified to homogeneity and used to prepare antiserum in rabbits. The immunoglobin G fraction from these antisera completely inhibited lipoprotein lipase eluted from heparin-Sepharose columns. However, the hormone-sensitive hydrolase activities (not retained on heparin-Sepharose affinity chromatography) were not inhibited by anti-lipoprotein lipase immunoglobin G, and anti-lopoprotein lipase immunoglobin G did not affect the activation process in crude fractions. Thus, hormone-sensitive lipase and lipoprotein lipase, functionally distinct enzymes, have been physically resolved and immunochemically distinguished. Apparently lipoprotein lipase activity is not regulated, at least directly, by cAMP-dependent protein kinase.

Adenosine Triphosphate↗
PubMed1976

Uptake and degradation of low density lipoprotein by swine arterial smoot muscle cells with inhibition of cholesterol biosynthesis.

We have previously proposed on the basis of studies in hepatectomized animals that low density lipoproteins are degraded at a significant rate by peripheral tissues. To test the capacity of one peripheral cell type to catabolize low density lipoprotein, cultures of swine aortic smooth muscle cells were incubated with homologous 125I-labeled low density lipoprotein and uptake and degradation measured. Degradation of 125I-labeled low density lipoprotein to products soluble in trichloroacetic acid showed an initial lag period of 1--2 h after which the rate increased and remained linear for the following 15 h. Rates of degradation increased sharply with low density lipoprotein concentration over the lower range (from 0--25 mug protein/ml) and then more slowly up to the highest concentration tested, 300 mug protein/ml. Even at very low concentrations, 1 mug low density lipoprotein protein/ml (less than 10% of the plasma low density lipoprotein concentration), the in vitro degradation rate (per kg of smooth muscle cells) exceeded the in vivo degradation rate (per kg of total body weight). To the extent that smooth muscle cells are representative of other peripheral cells, the results support the proposal that peripheral degradation of low density lipoprotein apoprotein may be quantitatively important. The rate of incorporation of labeled acetate into sterols was suppressed in cells incubated with whole serum, low density and very low density lipoproteins, or suspensions of free cholesterol. In this respect, the results were similar to those observed in human skin fibroblasts studied concurrently. However, high density lipoprotein inhibited sterol synthesis by about 25% in swine smooth muscle cells while it had no effect in human skin fibroblasts.

Animals↗
PubMed1976

Binding, internalization, and degradation of low density lipoprotein by normal human fibroblasts and by fibroblasts from a case of homozygous familial hypercholesterolemia.

Skin fibroblasts from a patient with homozygous familial hypercholesterolemia (HFH) were compared with normal skin fibroblasts with regard to binding, internalization, and degradation of iodinated human low density lipoprotein (LDL). Like other cell lines from HFH patients, the mutant cells showed no suppression of sterol synthesis by LDL. Surface binding, measured at 0 degrees to eliminate the appreciable internalization that was shown to occur at 37 degrees, was on the average slightly less for HFH cells than normal cells at low LDL concentrations but comparable or even greater at high LDL concentrations (greater than 60 mug of LDL protein per ml). A major defect observed was in the rate of internalization of LDL at 37 degrees, which was only 1-10% of that in normal cells. LDL degradation was also markedly reduced but not to the same extent. Thus, a larger fraction of the LDL taken up appeared to be degraded by the mutant cells. The most striking defect observed, then, was not in surface binding of LDL but in rate of LDL internalization. While this might be secondary to a defect in specific binding sites of LDL, the magnitude of the observed differences in binding at low temperature seems too small to account for the huge differences in internalization (13- to 115-fold).

Adult↗
PubMed1976

Low density and high density lipoprotein turnover following portacaval shunt in swine.

Turnover of 125I-low density lipoprotein (LDL) and of 131I-high density lipoprotein (HDL) was determined before and after end-to-side portacaval shunt in eight swine. LDL (d 1.019-1.063) and HDL (d.1.09-1.21) were isolated by ultracentrifugation and iodinated by the iodine monochloride technique. Immediately postoperatively there was no consistent change in the fractional catabolic rate (FCR) of LDL compared to preoperative control values, while in all animals FCR of HDL was significantly increased (by as much as 300%). After recovery from surgery, neither LDL nor HDL catabolic rates were significantly elevated above control values in four swine. However, plasma levels of LDL and HDL protein, and of LDL and HDL cholesterol were significantly reduced 10-12 weeks after the portacaval shunt. The reduced levels of LDL and HDL associated with normal fractional clearance rates imply a reduction in synthesis of LDL and HDL following portal diversion.

Animals↗
PubMed1975

The effects of free fatty acid infusion on glucose metabolism in normal and streptozotocin-treated dogs.

By means of a novel technique for direct intravenous infusion of free fatty acids (FFA) into conscious dogs, it was found that the elevation of FFA levels in normal animals leads to a marked increase in insulin release and to a decrease in plasma glucose concentration. Dogs with streptozotocin-induced diabetes were used for FFA infusion in order to test whether peripheral glucose utilisation would be suppressed by FFA in the absence of the usual insulin response. Diabetic dogs receiving a constant infusion of intravenous glucose were given infusions of oleic acid after control periods of 2-3 hours. Constant intravenous infusion of U-14C-glucose into the diabetic dogs indicated that FFA infusion caused an average transient drop of 36,8% in glucose flux. After 1 1/2 hours of FFA infusion the flux returned to the former rates. Because no change in plasma glucose levels was found during FFA infusion our results can be explained only by a drop in hepatic glucose production concomitant with an equal drop in peripheral glucose utilisation.

Animals↗
PubMed1975

Cholesterol esterase in rat adipose tissue and its activation by cyclic adenosine 3':5'-monophosphate-dependent protein kinase.

A high level of cholesterol esterase activity, comparable to that of hormone-sensitive triglyceridase, has been demonstrated in rad adipose tissue. Essentially all of the activity was in the isolated adipocytes, primarily in the 100,000 times g supernatant fraction of the adipocytes. Cholesterol esterase activity in the 100,000 times g supernatant fraction was increased 40 plus or minus 16% by incubation with ATP (0.5 mM), Mg-2+ (1.25 mM), and cyclic adenosine 3':5'-monophosphate (cyclic AMP) (10 muM), conditions which also activated hormone-sensitive triglyceridase. Protein kinase inhibitor (rabbit skeletal muscle) blocked activation, and activation was restored by the addition of excess protein kinase (bovine skeletal muscle). In extracts prepared from adipocytes first incubated for 5 min with 10 muM epinephrine and 1 mM theophylline, there was no cyclic AMP-dependent cholesterol esterase activation, implying that the enzyme had been activated by a similar mechanism in the intact cell. The physiological role of this high level of cholesterol esterase activity in adipose tissue is unclear. Its relationship to hormone-sensitive triglyceride lipase, with which it extensively co-fractionates, and its possible involvement in fat mobilization remain to be determined.

Adipose Tissue↗
PubMed1975

Enzymes regulating glycogen metabolism in swine subcutaneous adipose tissue. I. Phosphorylase and phosphorylase phosphatase.

Glycogen phosphorylase from swine adipose tissue was purified nearly 700-fold using ethanol precipitation, DEAE-cellulose adsorption, AMP-agarose affinity chromatography, and agarose gel filtration. The purified enzyme migrated as one major and several minor components during polyacrylamide gel electrophoresis. Activity was associated with the major component and at least one of the minor components. The molecular weight of the disaggregated, reduced, and alkylated enzyme, estimated by polyacrylamide gel electrophoresis performed in the presence of sodium dodecyl sulfate, was 90,000. Stability of the purified enzyme was considerably increased in the presence of AMP. The isoelectric pH of the enzyme in crude homogenates was 6.3. The sedimentation coefficient of the purified enzyme (7.9 S) and that in crude homogenates (7.3 S) was determined by sucrose density gradient sedimentation. Optimal pH for activity was between pH 6.5 and 7.1. Apparent Km values for glycogen and inorganic phosphate were 0.9 mg/ml and 6.6 mM, respectively. The Ka for AMP was 0.21 mM. Enzyme activity was increased by K2SO4, KF, KCl, and MgCl2 and decreased by NaCl, Na2SO4, D-glucose, and ATP. Inhibition by glucose was noncompetitive with the activator AMP; inhibition by ATP was partially competitive with AMP. The purified enzyme was activated by incubation with skeletal muscle phosphorylase kinase. Enzyme in crude homogenates was activated by the addition of MgCl2 and ATP; activation was not blocked by addition of protein kinase inhibitor, suggesting that phosphorylase kinase in homogenates of swine adipose tissue is present largely in an activated form. Deactivation of phosphorylase a by phosphorylase phosphatase was studied using enzyme purified approximately 200-fold from swine adipose tissue by ethanol precipitation, DEAE-cellulose chromatography, and gel filtration. The Km of the adipose tissue phosphatase for skeletal muscle phosphorylase a was 6 muM. The purified swine adipose tissue phosphorylase, labeled with 32-P, was inactivated and dephosphorylated by the adipose tissue phosphatase. Dephosphorylation of both skeletal muscle and adipose tissue substrates was inhibited by AMP and glucose reversed this inhibition. Several lines of evidence suggest that AMP inhibition was due to an action on the substrate rather than on the enzyme. We have previously reported that the system for phosphorylase activation in rat fat cells differs in some important characteristics from that in skeletal muscle. However, both swine fat phosphorylase and phosphorylase phosphatase have major properties very similar to those described for the enzymes from skeletal muscle.

Adenosine Monophosphate↗
PubMed1975

Enzymes regulating glycogen metabolism in swine subcutaneous adipose tissue. II. Glycogen synthase.

Glycogen synthase from swine adipose tissue was purified to apparent homogeneity using ethanol precipitation, DEAE chromatography, and affinity chromatography utilizing glucosamine 6-phosphate as the ligand. The purified enzyme migrated as a single protein component during electrophoresis on polyacrylamide gels at pH 7.3 although some protein failed to enter the running gel. Enzyme incubated with sodium dodecyl sulfate (SDS) migrated as one component (mol wt similar to 90,000) on SDS-polyacrylamide gel electrophoresis. The enzyme was relatively unstable at all stages of the purification procedure, but stability was increased in the presence of glucose 6-phosphate, UDPG, or glycerol. The isoelectric point of the purified enzyme and of enzyme activity in crude homogenates was pH 4.8. The sedimentation coefficient of the enzyme in crude homogenates was 8.5 S. The pH-activity profile showed an optimum at pH 7.8 in the absence of glucose 6-phosphate but no definable optimum between pH 7.0 and 9.2 in its presence. The Km of glycogen synthase I for UDPG was 250 muM in the absence and 37 muM in the presence of glucose 6-phosphate; the K-a for glucose 6-phosphate was 18 mu-M. The K-m of glycogen synthase D for UDPG was 130 mu-M in the presence of glucose 6-phosphate; the Ka for glucose 6-phosphate was 1 mM. The anions sulfate and phosphate activated the enzyme when assays were performed in the absence of glucose 6-phosphate. Fluoride produced activation of enzyme assayed either in the presence or in the absence of glucose 6-phosphate.

Adipose Tissue↗
PubMed1975

Family unit in a children's psychiatric hospital.

The need for effective management of disorders of parent/child relationships is repeatedly stressed. Despite the bulk of theoretical work on the subject there is little information on the practical management of the clinical problems that arise. We describe a unit designed and staffed for the management of such disorders. In our view it meets a need in a way that could be difficult or impossible for most paediatric, psychiatric, and social services as they are at present organized.

Child↗
PubMed1975

Platelet hypersensitivity and intravascular coagulation in paroxysmal nocturnal hemoglobinuria.

The patient described had paroxysmal nocturnal hemoglobinuria associated with recurrent arterial as well as venous thrombosis. Study of platelet function revealed hypersensitivity to epinephrine, adenosine 5'phosphate (ADP) and collagen as judged by their ability to aggregate platelets as well as to release 14C serotonin. The release of total nucleotides was also markedly increased over normal with all aggregating agents. The abnormality was localized to the platelet since aggregation occurred when the patient's platelets were resuspended in normal plasma but not when normal platelets were incubated in the patient's plasma. Presumptive evidence for ongoing intravascular coagulation was an increase in fibrinogen derivatives of heavier molecular weight than the native protein presumably a result of thrombin action. However, factor XII was not activated and fibrinolysis was not increased. Complement component levels and antithrombin concentrations were also normal. The findings in this case suggest that hypersensitive platelets may contribute to the intravascular coagulation that is manifested by the increased incidence of thrombosis in patients with paroxysmal nocturnal hemoglobinuria.

Adenosine Diphosphate↗
PubMed1975

The management of acute myelogenous leukemia.

Although definite improvement in the treatment of acute myelogenous leukemia has taken place, the outlook for patients remains grim. The current aggressive approach to treatment, entailing a program of chemotherapy which almost invariably produces bone marrow aplasia and considerable toxicity, has been the subject of some controversy. Selected aspects of management are discussed.

Adrenal Cortex Hormones↗
PubMed1975

Symptomatic treatment of agoraphobia and social phobias: a follow-up study.

1. Twenty-six out of 28 out-patients with agoraphobia and social phobias who had originally been treated with phenelzine or placebo in a double-blind clinical trial were followed up for a mean period of one year. During the follow-up period patients received further pharmacotherapy or behaviour therapy, except that those patients originally receiving placebo were not allowed therapy with monoamine oxidase inhibitors. 2. Ratings of phobic and additional symptoms, social adjustment and degree of personality disorder were made after one year by one of the authors (D.S.) who had no prior knowledge of the treatment each patient had received. 3. There were no significant differences in any of the ratings between the patients of the two groups, but those originally receiving placebo had more additional treatment in the follow-up period. Patients continuing to receive phenelzine frequently experienced a return of symptoms if the drug was withdrawn before six months treatment had elapsed. 4. Degree of personality disorder showed a significant negative correlation (p = -0.6) with improvement in the phenelzine group but not in those receiving placebo originally. 5. Improvement in social adjustment items was less than improvement in symptoms at follow-up. The implications of this are discussed. 6. The results suggest that phenelzine is of comparable efficacy to other symptomatic treatments for agoraphobia and social phobias, but that it acts mainly by symptom suppression. Prolonged treatment in patients with personality disorders is not indicated, for improvement is less likely and the dangers of dependence are greater.

Agoraphobia↗