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Biomedical subjects

J Bremer

Publications and source records attributed to J Bremer.

At least 109 records · Page 6Linked to original sources
PubMed1982

The metabolism of fatty acids in hepatocytes isolated from triiodothyronine-treated rats.

1. The effect of triiodothyronine on the metabolism of palmitate, oleate and erucate in isolated rat hepatocytes was studied. 2. In triiodothyronine-treated rats increased oxidation and decreased triacylglycerol formation from palmitate and oleate was observed. For erucate triiodothyronine caused increased oxidation, but had no significant effect on esterification. 3. Glucagon had no effect on the fatty acid metabolism in hepatocytes from triiodothyronine-treated rats, whereas it stimulated the oxidation in hepatocytes from normal rats. Still, after treatment with triiodothyronine, the oxidation of fatty acids was significantly higher than in glucagon-stimulated normal hepatocytes. 4. In isolated rat liver mitochondria triiodothyronine raised the activity of the outer carnitine palmitoyltransferase (EC 2.3.1.21). The activity of the total carnitine palmitoyltransferase was elevated only slightly in isolated mitochondria from triiodothyronine-treated rats. These effects were similar to those seen in fasted rats. 5. Triiodothyronine had no significant influence on the concentration of long-chain acyl-CoA or alpha-glycerophosphate in isolated rat hepatocytes.

Animals↗
PubMed1982

Metabolism of very long-chain monounsaturated fatty acids (22:1) and the adaptation to their presence in the diet.

Unadapted rats and other animal species have a limited capacity to metabolize monounsaturated fatty acids with 22 carbons (22:1). Excess amounts in the diet of fats containing these fatty acids cause a transient accumulation (lipidosis) of triacylglycerol in the heart and other tissues but not in the liver, which seems to export the 22:1 fatty acids as very low density lipoproteins to the blood plasma. The acute lipidosis most probably is explained by a slow oxidation of 22:1 acyl-CoA by the mitochondrial acyl-CoA dehydrogenase combined with an inhibitory effect of this CoA ester on the oxidation of acyl-CoA esters of a more "normal" chain length. Other fatty acid metabolizing enzymes also show slow reaction rates with the 22:1 fatty acids. Upon continued feeding of diets with 22:1 fatty acids, an adaptation takes place and the lipidosis disappears. This adaptation coincides with the development of an increased capacity to chain-shorten the 22:1 fatty acids, especially in the liver, but also in the heart. The chain-shortening seems to be due to a partial beta-oxidation of the 22:1 fatty acids by the peroxisomal beta-oxidation enzyme system which shows an increased activity in adapted rats. In such rats, less 22:1 fatty acids circulate in the plasma very low density lipoproteins than in unadapted rats. The drug clofibrate (ethyl-p-chlorophenoxyisobutyrate) which induces increased activity of the peroxisomal beta-oxidation enzymes, provides partial protection against the lipidosis in unadapted animals. Hydrogenated fish oil (containing different 22:1 isomers and many fatty acids with trans double bonds) is more efficient as an inducer of the chain-shortening of erucic acid in the liver than is rapeseed oil, which contains only one 22:1 fatty acid isomer and no fatty acids with trans double bonds. The hydrogenated fish oil causes less lipidosis than does rapeseed oil when diets containing the same amount of 22:1 fatty acids are fed. It is suggested that CoA esters that are poorly oxidized by the mitochondria (e.g., esters of erucic acid, of some fatty acids with trans double bonds, and of clofibric acid) may trigger the adaptation process.-Bremer, J., and K. R. Norum. Metabolism of very long-chain monounsaturated fatty acids (22:1) and the adaptation to their presence in the diet.

Acyl Coenzyme A↗
PubMed1981

The effect of fasting on the activity of liver carnitine palmitoyltransferase and its inhibition by malonyl-CoA.

The effect of fasting on palmitoyl-CoA: carnitine palmitoyltransferase (EC 2.3.1.21) in rat liver mitochondria and its inhibition by malonyl-CoA has been investigated. The activity of the outer carnitine palmitoyltransferase (transferase I) is nearly doubled after 24 h fasting, while the activity of total carnitine palmitoyltransferase (transferase I + II) increases only about 25%. The inhibition of the increased outer transferase by malonyl-CoA is decreased in fasting rats. The results suggest that carnitine palmitoyltransferase less sensitive to malonyl-CoA is exposed on the outer surface of the inner mitochondrial membrane in fasting, thus reducing the latency of the enzyme.

Acyl Coenzyme A↗
PubMed1981

Clofibrate.

Explore the source record for details and available documents.

Animals↗
PubMed1981

Content analysis of helping group interactions: toward a developmental perspective.

Age comparative content analyses were carried out for eleven support-discussion groups. Comparisons of six groups of elderly persons and five groups of college youth revealed that the older more frequently discuss bodily changes, family relations, significant others and external sources of self respect. The young were more concerned with physical vulnerabilities. The elderly were more likely to discuss matters in terms of the past. The results are considered in the light of a life stage developmental conception of group behavior which could have implications for helping interventions.

Adolescent↗
PubMed1980

Regulation of palmitate esterification/oxidation by glucagon in isolated hepatocytes: the role of alpha-glycerophosphate concentration.

Lipolysis was measured as the disappearance of [3H]glycerol previously incorporated into triacylglycerol, diacylglycerol and phosphatidic acid. There was no effect of glucagon on the lipolysis of any of these lipids. A transient increase in cellular alpha-glycerophosphate was induced by addition of glycerol during incubation. This resulted in an immediate and temporary decrease in oxidation and increase in esterification of palmitate while the uptake of palmitate from the incubation medium was unchanged. The change in alpha-glycerophosphate was also correlated with a transient drop in acyl-CoA and acylcarnitine. The lactate/pyruvate ratio was increased by the glycerol addition, but was still elevated for some while after the transient change in alpha-glycerophosphate. Similar effects were obtained by addition of dihydroxyacetone instead of glycerol. It is concluded that fatty acid esterification/oxidation can be changed by variations in the concentration of alpha-glycerophosphate, and that glucagon acts on lipid metabolism by decreasing the level of this metabolite.

Animals↗
PubMed1980

Thermodynamic aspects of translocation of reducing equivalents by mitochondria.

The "poise" in which there is no net transport of reducing equivalents mediated by glutamate and aspartate movements across the mitochondrial membrane has been studied using nonrespiring liver mitochondria, supplied with a given extramitochondrial ATP/ADP ratio. Absorbance shifts in safranine have been used as a probe to estimate the membrane potential generated under these conditions. Measurements of the asymmetric distribution of substrate anions and of reducing potential across the limiting membrane gave estimated differences of between 2.2 and 3.3 kcal when the ATP/ADP ratio in the suspending medium was about 30. The estimated membrane potential under these conditions was about 140 mV. All of the above parameters were decreased in a corresponding manner when the ATP/ADP ratio imposed from outside was decreased. A strong inflection in the slope of correlated parameters was obtained when the ATP/ADP ratio was below about 0.5. On the other hand, there was a linear relationship between the membrane potential and the asymmetric poise of reducing equivalents and of carbon metabolites. It is concluded that the poise of reducing equivalents mediated by the malate-aspartate shuttle is determined principally by the membrane potential through its effect on the electrogenic exchange of glutamate and aspartate.

Adenosine Diphosphate↗
PubMed1980

Pyruvate carboxylase and propionyl-CoA carboxylase as anaplerotic enzymes in skeletal muscle mitochondria.

Oxygen uptake in skeletal muscle mitochondria respiring on pyruvate or on acetylcarnitine plus propionylcarnitine is stimulated 3--4-fold by bicarbonate. The stimulation is highly dependent on ATP. The respiration rate obtained amounts to 1/4-1/3 of the rate obtained with pyruvate-malate in the presence of ADP. With decreasing ATP/ADP ratios in the medium, a decreasing stimulation by bicarbonate is obtained. Similar results were obtained with heart mitochondria. With ATP added, a pyruvate-dependent build up of citric acid cycle intermediates takes place in incubations with skeletal muscle mitochondria amounting to about 0.5 nmol x min-1 x mg protein-1. In 14CO2-fixation experiments, the activity of pyruvate carboxylase (EC 6.4.2.1) amounts to about 3 nmol x min-1 x mg protein-1 under similar conditions. With propionylcarnitine plus acetylcarnitine a similar stimulation of respiration and fixation of bicarbonate is observed. In this case the respiration and the propionyl-CoA carboxylase (EC 6.4.1.3) is less inhibited by ADP. The results are discussed in relation to the regulation of the level of citric acid cycle intermediates in muscle tissues. It is concluded that pyruvate carboxylase is an important anaplerotic enzyme in skeletal muscle mitochondria.

Acetylcarnitine↗
PubMed1980

Patterns of peptides and protein-associated-peptide complexes in psychiatric disorders.

Peptidic neurones may be considered as multisignal intergrators and transducers. When formation or release of peptide outstrips genetically determined breakdown capacity, overflow of peptides to the body fluids and urine may be expected. In this paper, pathological urinary chromatographic patterns of peptides are shown for genetic, functional and mixed disorders. Part symptoms of the disorders may be induced with the biologically isolated and purified peptides as well as with chemically synthesized peptides.

Adolescent↗
PubMed1979

Arsenite inhibits beta-oxidation in isolated rat liver mitochondria.

A partial inhibition of acylcarnitine oxidation by arsenite in rat liver mitochondria has been studied. This inhibition is confined to the thiolase(s). The inhibition was observed also in the presence of malate, indicating no selective effect on ketogenesis. Ketogenesis from acetyl-CoA was inhibited by arsenite. Mitochondrial CoA was acylated by acylcarnitine nearly as rapidly in the presence of arsenite as in its absence. Thus, arsenite did not interfere with the availibility of CoA in the mitochondria. No effect of arsenite on enzymes of beta-oxidation other than the thiolase(s) was observed. When arsenite and acylcarnitine were added simultaneously to mitochondria, there was a delay before maximal inhibition of oxygen uptake occurred. When the mitochondria were preincubated with arsenite before addition of acylcarnitine, the inhibitory effect on oxygen utilization was initially large, but then partially repealed. Similar time delays were observed in the activity of acetoacetyl-CoA thiolase of disrupted mitochondria depending on the sequence of arsenite and acetoacetyl-CoA addition. It is suggested that substrate and arsenite complete for the reactive sulfhydryl group at the active site of the thiolase(s).

Acetyl-CoA C-Acetyltransferase↗
PubMed1979

The stimulation of erucate metabolism in isolated rat hepatocytes by rapeseed oil and hydrogenated marine oil-containing diets.

1. The metabolism of palmitate and especially of erucate was studied in hepatocytes isolated from rats fed for 3 weeks a diet containing peanut oil (diet, 1), rapeseed oil (diet 2) and partially hydrogenated marine oil (diet 3). 2. The metabolism of palmitate was not significantly influenced by the diet. The rapeseed oil diet caused 1.4 fold and 1.3 fold increase and marine oil diet 3 fold and 2.2 fold increase in the oxidation and chain-shortening respectively of [14-14C]erucic acid in isolated hepatocytes. 3. Cyanide and antimycin A did not inhibit the chain-shortening of erucate in liver cells of rats fed rapeseed oil and peanut oil. The high capacity of the chain-shortening system in hepatocytes of marine oil-fed rats was partially inhibited. 4. Inhibition of the transfer of fatty acids into the mitochondria by lowering the intracellular carnitine concentration and/or by addition of (+)-decanoyl-carnitine resulted in a very pronounced apparent stimulation of the chain-shortening of erucic acid. It is suggested that the chain-shortening system may be virtually independent of the mitochondria, unless the availability of the extramitochondria NAD+ and/or NADP+ is rate-limiting under conditions of extremely low redox potential of the mitochondria. 5. Feeding marine oil or rapeseed oil to the rats induced a 30% increase in catalase activity, a 25--30% increase in urate oxidase activity and a 50% increase in the total CoA in the liver compared to rats fed peanut oil. 6. It is suggested that the increased metabolism of erucate in hepatocytes of marine oil and rapeseed oil-fed rats may be due to the increase in ther peroxisomal beta-oxidation.

Animals↗
PubMed1978

Comparative biochemistry of beta-oxidation. An investigation into the abilities of isolated heart mitochondria of various animal species to oxidize long-chain fatty acids, including the C22:1 monoenes.

Rates of acylcarnitine oxidation by isolated heart mitochondria from various animal species were measured polarographically, and by using a spectrophotometric assay [see Osmundsen & Bremer (1977) Biochem. J. 164, 621-633]. Polarographic measurements do not give a correct guide to abilities to beta-oxidize very-long-chain acylcarnitines, in particular C22:1 fatty acylcarnitines. 2. No significant species differences were detected in the abilities to beta-oxidize various C22:1 fatty acylcarnitines. Significant species differences were, however, detected when rates of beta-oxidation were correlated with rates of respiration brought about by very-long-chain acylcarnitines. We concluded that some aspects of oxidative metabolism (possibly the oxidation of tricarboxylic acid-cycle intermediates) are inhibited by very-long-chain fatty acids in some species (e.g. the rat and the cat but not in others (e.g. the pig and the rabbit). 3. It is proposed that the pattern of variation of rates of oxidation of various acylcarnitines (as measured spectrophotometrically) of various chain lengths can be used as a guide to the chain-length specificities of the acyl-CoA dehydrogenases of beta-oxidation (EC 1.3.99.3).

Animals↗
PubMed1978

The effect of acylcarnitines on the oxidation of branched chain alpha-keto acids in mitochondria.

The oxidation of 14C-labelled branched-chain alpha-keto acids corresponding to the branched-chain amino acids valine, isoleucine and leucine has been studied in isolated mitochondria from heart, liver and skeletal muscle. 1. Heart and liver mitochondria have similar capacities to oxidize these alpha-keto acids based on protein content. Skeletal muscle mitochondria also show significant activity. 2. Half maximum rates are obtained with approximately 0.1 mM of the alpha-keto acids under optimal conditions. Added NAD and CoA had no effect on the oxidation rate, showing that endogenous mitochondrial NAD and CoA are required for the oxidation. 3. Addition of carnitine esters of fatty acids (C6--C16), succinate, pyruvate, or alpha-ketoglutarate inhibited the oxidation of the branched chain alpha-keto acids, especially in a high-energy state (no ADP added). In heart mitochondria the addition of AD (low-energy state) decreased the inhibitory effects of acylcarnitines of medium chain length or of pyruvate, and abolished the inhibitory effect of succinate. It is suggested that the oxidation rate is regulated mainly by the redox state of the mitochondria under the conditions used. 4. The results are discussed in relation to the regulation of branched-chain amino acid metabolism in the body.

Animals↗
PubMed1978

The effects of clofibrate feeding on the metabolism of palmitate and erucate in isolated hepatocytes.

The metabolism of palmitate and erucate has been investigated in hepatocytes isolated from control rats and from rats fed 0.3% clofibrate. Clofibrate increased the oxidation of [1-14C]palmitate 1.5 to 2-fold while the esterification was decreased. At a high concentration of palmitate (1.5 mM), the total rate of fatty acid metabolism was stimulated. Clofibrate stimulated both the oxidation (3.5 to 5-fold) and the esterfication (1.7-fold) of [14-14C]erucate. Erucate undergoes chain-shortening in isolated liver cells. This chain-shortening was stimulated at least 2-fold by clofibrate feedings. The isolated mitochondrial fraction from clofibrate-fed rats showed an increased capacity for oxidation of short-chain acylcarnitines (including acetylcarnitine), while the oxidation of palmitoyl- and erucoylcarnitine showed little change. It is suggested that erucate is shortened by the recently detected beta-oxidation system of peroxisomes.

Acyltransferases↗