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Biomedical subjects

D Stribling

Publications and source records attributed to D Stribling.

31 records · Page 2Linked to original sources
PubMed1984

Post-natal development of interscapular (brown) adipose tissue in the guinea pig: effect of environmental temperature.

The post-natal development of interscapular brown adipose tissue (BAT) was studied in the guinea pig by monitoring changes in DNA, triglycerides and mitochondrial protein as well as the activity of cytochrome oxidase and atractyloside insensitive GDP-binding. The results demonstrate that neonatal brown fat develops into a tissue with the gross characteristics of white adipose tissue. In this respect the post-natal development of guinea pig BAT is analogous to that of the tissue in man. Furthermore the apparent transformation is not irreversible since cold exposure (+4 degrees C) of adult guinea pigs for six weeks resulted in restoration of cytochrome oxidase, GDP-binding, etc, to levels characteristic of neonatal BAT. However, the interscapular fat pad temperature response to noradrenaline and the presence of 32 000 mol. wt mitochondrial inner membrane protein indicate that the tissue retains thermogenic activity even in warm acclimated adult guinea pigs.

Adipose Tissue, Brown↗
PubMed1983

Identification of two mitochondrial GDP-binding sites in rat brown adipose tissue.

Scatchard analysis of specific guanosine-diphosphate-([3H]GDP-) binding to rat brown-adipose-tissue mitochondria revealed two distinct binding sites with apparent dissociation constants (Kd) of approximately 0.05 and 2.0 microM. Binding to both sites was insensitive to atractyloside. Reducing the pH of the binding medium from 7.1 to 6.6 caused marked reductions in the Kd of both sites, but at pH 7.6, the dissociation constants were increased about 3-fold. Acute treatment of rats with noradrenaline, 1 h before sacrifice, increased the maximum number of binding sites (Bmax, pmol/mg mitochondrial protein) of both sites and also increased the dissociation constants. The Bmax of the lower-affinity site was elevated in rats exposed to 5 degrees C or fed a palatable cafeteria diet for 10 d, compared to control animals, with the greater changes occurring in the cold-adapted group. The high-affinity site was unaltered by cold adaptation or cafeteria feeding. These results indicate the presence of two distinct nucleotide-binding sites in brown-fat mitochondria, both of which may be involved in thermogenesis.

Adenosine Diphosphate↗
PubMed1983

Effects of selective (beta-1 and beta-2) and nonselective beta adrenoceptor antagonists on the cardiovascular and metabolic responses to isoproterenol: comparison with ICI 141,292.

Six groups of four dogs were studied under pentobarbital anesthesia. Plasma levels of free fatty acids (FFA), glucose, insulin and lactate were measured after four challenges with isoproterenol (0.125 micrograms/kg/min i.v. for 10 min). In control animals, infusion of isoproterenol elevated plasma FFA, glucose, insulin and lactate, raised heart rate and lowered diastolic blood pressure. Propranolol lowered resting heart rate and blocked all the isoproterenol-induced responses. Atenolol (beta-1-selective antagonist) slowed resting heart rate and blocked FFA and heart rate responses. ICI 118,551 (beta-2-selective antagonist) blocked the glucose, insulin and lactate responses and the fall in diastolic blood pressure. Selectivity was lost at higher doses. ICI 141,292 (potent beta-1-selective antagonist and modest partial agonist) exhibited beta-1-selective blockade against both cardiovascular (heart rate) and metabolic (FFA) receptors. Partial agonist activity was also beta-1-selective, but there was no evidence of agonist activity at the metabolic receptors.

Adrenergic beta-Antagonists↗
PubMed1982

Factors affecting tryptophan-induced hypoglycaemia in rats.

The mechanisms whereby tryptophan administration leads to hypoglycaemia in some groups of rats but not others have been investigated. Animals insensitive to tryptophan are rendered responsive by adrenalectomy. This effect is reversed by steroid replacement. Turnover studies with [2-3H]glucose show that hypoglycaemia in sensitive animals is associated with a decrease in glucose synthesis. Tryptophan administration causes a marked and sustained increase in plasma glucagon concentrations in all animals. The locus of the inhibition of gluconeogenesis in tryptophan-sensitive animals is the reaction catalysed by phosphoenolpyruvate carboxykinase. The sensitivities to tryptophan of gluconeogenesis in isolated hepatocytes from normal and adrenalectomized animals were similar. Cells from chronically streptozotocin-diabetic animals required higher concentrations of the amino acid for the same effect. These results are discussed in relation to previous discrepancies in the literature, and a unifying hypothesis for tryptophan-induced hypoglycaemia is proposed.

Adrenalectomy↗
PubMed1982

Endotoxin and tryptophan-induced hypoglycaemia in rats.

Pretreatment of rats with increasing, but non-lethal, doses of endotoxin was associated with a parallel increase in sensitivity to induction of hypoglycaemia by tryptophan. Acutely streptozotocin-diabetic animals became hypoglycaemic with endotoxin alone, and this was increased further by tryptophan. Variations in tryptophan sensitivity between rat populations cannot be explained by previous history of exposure to endotoxin. Endotoxin abolished the increase in tryptophan dioxygenase activity caused by triamcinolone, but not that caused by tryptophan. Triamcinolone was effective, however, when given together with tryptophan to endotoxin-treated rats. The activity of tryptophan dioxygenase in vivo and in liver cells in vitro is unchanged by exposure to endotoxin at 1 mg/kg body wt. Turnover studies indicated that hypoglycaemia resulted from inhibition of gluconeogenesis. There was no evidence to support a role for insulin in this process and results were consistent with an endotoxin-mediated hepatic insensitivity to glucagon. They also suggested that quinolinate, rather than 5-hydroxytryptamine, may be the intracellular agent responsible for inhibition of gluconeogenesis.

Animals↗
PubMed1978

Purification and characterization of the class-II D-fructose 1,6-bisphosphate aldolase from Escherichia coli (Crookes' strain).

A new form of the class-II D-fructose 1,6-bisphosphate aldolase (EC 4.1.2.13) of Escherichia coli (Crookes' strain) was isolated from an extract of glycerol-grown bacteria. It has a higher molecular weight (approx. 80000)than previous preparations of the enzyme and closely resembles the typical class-II aldolase from yeast in size and amino acid composition. On the other hand, its kinetic behaviour is not typical of a class-II aldolase. The enzyme has no requirement for thiol compounds either for stability or activity, added K+ ions have no effect, and the optimum pH for the cleavage activity is unusually high. The class-II enzymes from the prokaryote E. coli and the eukaryote yeast show no immunological identity. However, the similarity of their structures suggests that they have evolved from a common ancestor.

Amino Acids↗
PubMed1974

Properties of the phosphonomethyl isosteres of two phosphate ester glycolytic intermediates.

The enzymic synthesis of the 1-phosphonomethyl isostere of fructose 1,6-diphosphate in which the 1-phosphate (-OPO(3)H(2)) is replaced by the phosphonomethyl group (-CH(2)PO(3)H(2)) is described. The kinetic properties of this fructose diphosphate isostere and of 4-hydroxy-3-oxobutylphosphonic acid, an isostere of dihydroxyacetone phosphate, with aldolase (EC 4.1.2.13), fructose diphosphatase (EC 3.1.3.11) and glycerol phosphate dehydrogenase (EC 1.1.1.8) are described (see Table 1).

Alkaline Phosphatase↗
PubMed1973

Purification and characterization of two fructose diphosphate aldolases from Escherichia coli (Crookes' strain).

Two fructose diphosphate aldolases (EC 4.1.2.13) were detected in extracts of Escherichia coli (Crookes' strain) grown on pyruvate or lactate. The two enzymes can be resolved by chromatography on DEAE-cellulose at pH7.5, or by gel filtration on Sephadex G-200, and both have been obtained in a pure state. One is a typical bacterial aldolase (class II) in that it is strongly inhibited by metal-chelating agents and is reactivated by bivalent metal ions, e.g. Ca(2+), Zn(2+). It is a dimer with a molecular weight of approx. 70000, and the K(m) value for fructose diphosphate is about 0.85mm. The other aldolase is not dependent on metal ions for its activity, but is inhibited by reduction with NaBH(4) in the presence of substrate. The K(m) value for fructose diphosphate is about 20mum (although the Lineweaver-Burk plot is not linear) and the enzyme is probably a tetramer with molecular weight approx. 140000. It has been crystallized. On the basis of these properties it is tentatively assigned to class I. The appearance of a class I aldolase in bacteria was unexpected, and its synthesis in E. coli is apparently favoured by conditions of gluconeogenesis. Only aldolase of class II was found in E. coli that had been grown on glucose. The significance of these results for the evolution of fructose diphosphate aldolases is briefly discussed.

Amino Acids↗
PubMedDate not supplied

Aldose reductase in the etiology of diabetic complications: 2. Nephropathy.

The progression of diabetic nephropathy can be arrested by an improvement in diabetic control. High glucose concentrations increase the flux through the aldose reductase pathway, and it has been proposed that this may contribute to renal damage. Aldose reductase is present in both the glomerulus and the renal tubule. Biochemical changes associated with increased sorbitol production have been demonstrated in animal models, including myo-inositol depletion, reduced Na+-K+ ATPase activity, and activation of the pentose phosphate and glucuronate-xylose pathways. Selective inhibition of aldose reductase reverses these biochemical changes and prevents some of the structural and functional abnormalities in diabetic rats. The potential beneficial effects of aldose reductase inhibitors on diabetic kidney disease in man are at present being investigated.

Aldehyde Reductase↗
PubMedDate not supplied

Aldose reductase in the etiology of diabetic complications. 3. Neuropathy.

Aldose reductase has been shown to be present in both autonomic and somatic nerves. Activation of this enzyme and the polyol pathway has been demonstrated in diabetic animal models to cause a range of biochemical, functional, and structural consequences that include the accumulation of sorbitol and fructose; axoglial dysjunction; paranodal demyelination; abnormalities in axonal transport, blood flow, and vascular permeability; and resistance to ischemic transmission of action potentials. These data provide an insight into the range of processes that if activated may either singly or in combination result in altered patterns of nerve function and structural alterations in diabetic neuropathy. In animal models of diabetes, it has been shown that inhibition of aldose reductase can modify these diabetes-induced changes. It is hoped that the results of large-scale controlled trials will provide clinical evidence to support these data.

Aldehyde Reductase↗