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At least 703 records · Page 39Linked to original sources
PubMed1988

Effects of short-term dehydroepiandrosterone treatment on serum and pancreatic insulin in Zucker rats.

Lean and obese female Zucker rats were treated with 0.6% dehydroepiandrosterone (DHEA) from 5 until 10 wk of age and comparisons made to both ad libitum--fed and weight-matched groups. Within genotype, body weights and cumulative food intakes of DHEA and weight-matched groups were not different. Fat pad weights of DHEA rats were significantly lower than those of non-treated groups. Pancreatic insulin content, whether expressed per pancreas or per gram pancreas, was not lowered by DHEA treatment. Fasting serum insulin levels were not altered in lean rats but were significantly lower in DHEA obese rats than in either nontreated obese group. Glucose metabolism (conversion to CO2, fatty acids or glyceride-glycerol) in isolated adipocytes was similar in all groups except that obese rats had greater glyceride-glycerol production than lean rats. Glucose conversion to CO2 in soleus muscle was lower in obese rats than in lean rats. Basal and insulin-stimulated glycogen production was lower in DHEA and weight-matched obese rats than in any other group. Ad libitum-fed lean rats had higher insulin-stimulated glycogen production than DHEA lean and all groups of obese rats. Short-term DHEA treatment of obese Zucker rats lowers serum insulin levels without improvement of insulin resistance in peripheral tissues and without lowering pancreatic insulin content.

Adipose Tissue↗
PubMed1974

An early response to gibberellic Acid not requiring protein synthesis.

Cell-free extracts from gibberellic acid-treated barley (Hordeum vulgare L. cv. Himalaya) aleurone layers show phosphorylcholine glyceride transferase activity greater than that from control layers. The increase in activity is not prevented by a mixture of amino acid analogs nor by cordycepin under conditions in which it is demonstrated that the analogs and the cordycepin are entering the cells in effective concentrations. We conclude therefore that the GA(3)-dependent increase in phosphorylcholine glyceride transferase activity (which occurs within the first 4 hours of GA(3) treatment) does not require RNA synthesis or protein synthesis.

Journal Article↗
PubMed1981

Organelle Membranes from Germinating Castor Bean Endosperm: II. ENZYMES, CYTOCHROMES, AND PERMEABILITY OF THE GLYOXYSOME MEMBRANE.

Glyoxysome ghosts were isolated from germinating castor bean endosperms using established methods. Electron microscopic examination showed that some matrix material was retained within the glyoxysomal membrane. Two cytochrome reductases and phosphorylcholine glyceride transferase co-sedimented with the alkaline lipase, a known component of the glyoxysome membrane, in sucrose gradient centrifugation of osmotically shocked glyoxysomes. The activities of these enzymes in the glyoxysome membranes were compared to those in the endoplasmic reticulum relative to phospholipid content. On this basis, the phosphorylcholine glyceride transferase was 10-fold more active in the endoplasmic reticulum, whereas the lipase was 50-fold more active in the glyoxysome membrane. The cytochrome reductases were only 2-fold more active in the endoplasmic reticulum, indicating that they are components of the two membranes. Difference spectroscopy of the glyoxysome membrane suspension revealed the presence of a b5-type cytochrome similar to that found in the endoplasmic reticulum. Since the glyoxysome membrane is apparently derived from the endoplasmic reticulum, components of the endoplasmic reticulum such as these are likely to be incorporated into the glyoxysome membrane during biogenesis.Enzyme activities involving the cofactors NADH or CoA were measurable in broken, but not in intact, glyoxysomes. Thus, it appears that cofactors for enzymes within the organelle cannot pass through the membrane.

Journal Article↗
PubMed1981

Effects of Cyanide on Rates and Products of Fatty Acid Synthesis by Chloroplasts Isolated from Spinacia oleracea.

Cyanide inhibited unesterified fatty acid synthesis but stimulated glyceride synthesis from [1-(14)C]acetate when Spinacia oleracea chloroplasts were incubated in basal media. Both unesterified fatty acid and glyceride accumulation were inhibited when chloroplasts were incubated in a diacylglycerol mode. Stimulation of chloroplast fatty acid synthesis by either exogenous coenzyme A or Triton X-100 was almost completely abolished in the presence of cyanide. Stearoyl-ACP desaturation is considered to be inhibited to a greater extent than is fatty acid synthesis de novo.

Journal Article↗
PubMed1980

The lipid composition of human epididymis.

In the present study the lipid composition of human epididymidis is reported. The total lipids represented 1.25 per cent of the total wet weight of the tissue. The phospholipids formed 64 per cent, cholesterol 12 per cent and glycerides 24 per cent of the total lipids. In patients with obstruction of efferent ducts, the total lipids were increased due to the significant in creases observed in glycerides and cholesterol of the epididymidis. There was a marked fall in epididymal phospholipids due to a fall in phosphatidyl choline and phosphatidyl ethanolamine.

Adult↗
PubMed1975

Non-ionic surfactants and membrane transport of thioridazine in goldfish.

Polysorbate 80, which has been widely used in studies of the effects of surfactants on drug absorption, increases the rate of absorption of some drugs at concentrations near its critical micelle concentration (cmc). To determine whether all non-ionic surfactants were capable of inducing this effect, the effects of six commercial non-ionic surfactants on thioridazine absorption in goldfish have been compared with the effect of polysorbate 80. The reciprocal death time (T-1) determined when the fish were immersed in the solution under study was the index of absoprtion rate used. Not all surfactants tested increased T-1. Cremophor EL (polyoxyethylated castor oil), Atlas G1295 (a polyoxyethylene fatty glyceride), Atlas G1300 (a polyoxyethylene glyceride ester) had no effect below their cmc's. Those surfactants that did increase T-1 [polysorbate 80 (a polyoxyethylene lanolin derivative), G2162 (a polyoxyethylene oxypropylene monosterate) and Renex 650 (a polyoxyethylene alkyl aryl ether)] display the concentration-dependent behaviour reported previously - a decrease in absorption rate when the surfactant concentration is increased above its cmc. The factor determining whether or not the surfactant will increas absorption rate appears to be the configuration of the surfactant molecule rather than its hydrophile-lipophile balance or its surface activity.

Animals↗
PubMed1983

Isolation and characterization of the Neurospora crassa endoplasmic reticulum.

The endoplasmic reticulum from Neurospora crassa was identified by monitoring the activity of the putative enzyme marker phosphatidylcholine glyceride transferase. After differential centrifugation of a cell homogenate, phosphatidylcholine glyceride transferase activity initially copurified with plasma membrane H+-ATPase. However, isopycnic centrifugation of the whole-cell homogenate on a linear sucrose gradient separated the two enzyme activities into different fractions. The lighter membrane fraction exhibited characteristics that have been associated with the endoplasmic reticulum in other organisms: (i) the inclusion of magnesium caused this light membrane fraction to shift to a higher density on the gradient; (ii) it was highly enriched in cytochrome c reductase, an endoplasmic reticulum marker in other systems; and (iii) the morphology of the light fraction with and without added magnesium was clearly distinguishable from that of the plasma membrane fraction by electron microscopy. A reinvestigation of the location of chitin synthetase confirmed its association with the plasma membrane fraction even after separation of the lighter fractions.

Adenosine Triphosphatases↗
PubMed1993

Processing of lipid-modified prolipoprotein requires energy and sec gene products in vivo.

The kinetics of processing of glyceride-modified prolipoprotein that accumulated in globomycin-treated Escherichia coli has been found to be affected by sec mutations, i.e., secA, secE, secY, secD, and secF, and by metabolic poisons which affect proton motive force (PMF). The effect of sec mutations on processing of glyceride-modified prolipoprotein in vivo was not due to a secondary effect on PMF. Neither a secF mutation nor metabolic poisons affected the processing of previously accumulated proOmpA protein in vivo, suggesting that the requirements for functional sec gene products and PMF are specific to the processing of lipoprotein precursors by signal peptidase II.

Anti-Bacterial Agents↗
PubMed1963

NATURE OF THE LIPIDS OF SOME LACTIC ACID BACTERIA.

Ikawa, Miyoshi (University of California, Berkeley). Nature of the lipids of some lactic acid bacteria. J. Bacteriol. 85:772-781. 1963.-Lactobacillus casei, L. plantarum, Leuconostoc mesenteroides, Pediococcus cerevisiae, and Streptococcus faecalis were grown on a lipid-free medium, and the amounts of acetone-soluble lipids, acetone-insoluble phospholipids, and unextracted or bound lipid in the cells were estimated. Neutral glycerides appeared to be absent, or present only in traces, in L. casei and S. faecalis. L. plantarum, L. mesenteroides, and P. cerevisiae, in addition to containing glycerides, appeared to contain glycolipids of glucose and galactose. Glycerol was present in the phospholipid fraction of all the organisms, and, in addition, galactose was present in L. mesenteroides. Paper chromatography of hydrolysates of the phospholipid fractions showed the absence of the usual phospholipid nitrogen bases, serine, ethanolamine, and choline, in these organisms. Microbiological assays of lyophilized unextracted cells for myo-inositol and choline also showed that lipids containing these components occurred in very small amounts at most. The principal ninhydrin-reacting substance in the phospholipid fraction of L. casei, L. plantarum, P. cerevisiae, and S. faecalis was lysine, which seemed to be exclusively of the l configuration. The principal ninhydrin-reacting substance in the L. mesenteroides phospholipid fraction was d-alanine. These amino acids appeared to be bound in components of the phospholipid fraction and not free.

Enterococcus faecalis↗
PubMed1976

Effect of propylthiouracil-induced hypothyroidism on phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin synthesis in chick liver microsomes.

Biosynthesis of phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin was studied in liver endoplasmic reticulum obtained from newly hatched chicks which were made hypothyroid by feeding 0.2% propylthiouracil. In vitro measurements were made of the specific activities of phosphorylcholine-glyceride (cholinephosphotransferase (EC 2.7.8.2), hosphorylethanolamine-glyceride (ethanolamine-phosphotransferase (EC 2.7.8.1)), and phosphorylcholine-ceramide (ceramide cholinephosphotransferase (EC 2.7.8.3)) transferases in control and hypothyroid chick liver for a period of 40 days. The specific activity of all three transferases began to decline after the chicks were on the propylthiouracil-containing diet for 5 days and steadily declined, reaching levels 10-15% of the controls after 15 days. These low levels were maintained for as long as the chicks were on this diet. Administration of L-thyroxine (15 mug/100 g of body weight) to the hypothyroid chicks caused a marked increase in the specific activities of all three transferases, reaching levels similar to those seen in the control chicks in 36-48 h. The specific activities then declined as the chicks were maintained on the diet of propylthiouracil, reaching the former low levels after 120 h. Administration of cycloheximide alone to the hypothyroid chicks caused a rise in the specific activities of the transferases after 24 h approximately equal to that caused by thyroxine alone, while thyroxine and cycloheximide together were no different than either alone. These studies indicate that in some manner circulating thyroxine controls the activities of enzymes involved in the biosynthesis of phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin in chick liver endoplasmic reticulum. There was no evidence that induction of hypothyroidism by propylthiouracil had any effect on the activities of these enzymes in the CNS.

Animals↗
PubMed2002

Adipose tissue sensitization to insulin induced by troglitazone and MEDICA 16 in obese Zucker rats in vivo.

The putative role played by insulin sensitizers in modulating adipose tissue lipolysis in the fasting state was evaluated in obese conscious Zucker rats treated with troglitazone or beta,beta'-tetramethylhexadecanedioic acid (MEDICA 16) and compared with nontreated lean and obese animals. The rates of appearance (R(a)) of glycerol and free fatty acid (FFA), primary intra-adipose reesterification, and secondary reuptake of plasma FFA in adipose fat were measured using constant infusion of stable isotope-labeled [(2)H(5)]glycerol, [2,2-(2)H(2)]palmitate, and radioactive [(3)H]palmitate. The overall lipolytic flux (R(a) glycerol) was increased 1.7- and 1.4-fold in obese animals treated with troglitazone or MEDICA 16, respectively, resulting in increased FFA export (R(a) FFA) in the troglitazone-treated rats. Primary intra-adipose reesterification of lipolysis-derived fatty acids was enhanced twofold by insulin sensitizers, whereas reesterification of plasma fatty acids was unaffected by either treatment. Despite the unchanged R(a) FFA in MEDICA 16 or the increased R(a) FFA induced by troglitazone, very low density lipoprotein production rates were robustly curtailed. Total adipose tissue reesterification, used as an estimate of glucose conversion to glyceride-glycerol, was increased 1.9-fold by treatment with the insulin sensitizers. Our results indicate that, in the fasting state, insulin sensitizers induce, in vivo, a significant activation rather than suppression of adipose tissue lipolysis together with stimulation of glucose conversion to glyceride-glycerol.

Adipose Tissue↗
PubMed1995

Transgenic GLUT-4 overexpression in fat enhances glucose metabolism: preferential effect on fatty acid synthesis.

GLUT-4 expression varies widely among normal humans and those with obesity and diabetes. Using the alpha P2 promoter/enhancer ligated to the human GLUT-4 gene, we created transgenic mice to study the impact of alterations in GLUT-4 expression selectively in adipocytes on glucose homeostasis and body composition. Here we investigated molecular mechanisms for enhanced glucose tolerance and obesity in these mice. [U-14C]glucose incorporation into triglycerides, glyceride-glycerol, glyceride-fatty acids, CO2, and lactate was measured in adipocytes incubated at 3, 0.5, and 3 microM glucose with or without maximally stimulating insulin. In nontransgenic and transgenic mice, the major pathway for glucose metabolism shifts from lipogenesis at tracer glucose concentration to glycolysis at physiological glucose concentration. In transgenic adipocytes incubated at 3 microM glucose, metabolism via all major pathways is enhanced by 8.6- to 38-fold in the absence of insulin and 3- to 13-fold in the presence of insulin. At physiological glucose concentration, constitutive metabolism to triglycerides, CO2, and lactate is two- to threefold greater in transgenic than in nontransgenic adipocytes. De novo fatty acid synthesis is preferentially increased: 31-fold for basal and 21-fold for insulin-stimulated compared with nontransgenic adipocytes. Thus overexpression of GLUT-4 in adipocytes of transgenic mice results in increased glucose metabolism in all major pathways, with differential regulation of the pathways involved in lipogenesis.

Adipocytes↗
PubMed1975

Plasma triglyceride secretion in squirrel monkeys: effects of nicotine.

The acute effects of intravenous nicotine on the appearance of plasma triglycerides have been studied in anaesthetised squirrel monkeys given Triton-WR 1339. At both dose levels studied, 4 and 10 mug/kg/30 sec, nicotine caused a stimulation in the rate of accumulation of plasma glycerides, the larger dose producing the greater effect. Nicotine caused a transient elevation in plasma free fatty acids (FFA), also in proportion to the dose given. It is suggested the changes in plasma glycerides are due to enhanced hepatic secretion secondary to increased plasma FFA. The administration of Triton-WR 1339 caused a rapid and sustained fall in plasma cholesterol concentrations. This fall was similar to that observed in plasma Triton and evidence is presented to suggest that Triton and cholesterol are removed from the circulation by a similar mechanism. There was no effect of nicotine on plasma cholesterol. The implications of the effects of nicotine of plasma triglycerides in relation to coronary heart disease are discussed briefly.

Animals↗
PubMed1972

Precursor-product relationship between pools of very low density lipoprotein triglyceride.

The process of removal of triglyceride from the plasma may involve a sequential conversion of larger to smaller glyceride-rich lipoproteins. This has been studied within the species of lipoproteins comprising the very low density lipoproteins (VLDL) which transport the bulk of endogenously formed triglyceride. Palmitic acid-(14)C which was used to label the plasma glycerides was administered either as a prolonged constant infusion or as a pulse label. The specific activity-time curves of triglyceride fatty acids (TGFA) were analyzed both in total VLDL and in two subfractions of VLDL. The nature of the curves for total VLDL that were observed during the constant infusions were consistent with slow isotopic equilibration of precursors of VLDL-TGFA or with the presence of a precursor-product relationship between different components of VLDL-TGFA. The curves did not indicate any detectable differences in (fractional) turnover rates of independently metabolized pools of VLDL-TGFA. Differences in the specific activity-time curves of TGFA in two subfractions of VLDL (Sf > 100 and Sf 20-100) were consistent with a precursor-product relationship between TGFA in the two subfractions; again there was no indication of significant differences in (fractional) turnover rates. The specific activity-time curves of TGFA in the two subfractions of VLDL that were obtained with single injections of radio-palmitate showed a consistent difference in the rates at which TGFA became labeled in the two subfractions, being slower in the Sf 20-100 fraction. The findings from all experiments when considered together, were compatible with a precursor-product relationship that suggested that larger VLDL were converted to progressively smaller species as triglyceride was being removed.

Adolescent↗
PubMed1986

Glucose, acetate, and lactate metabolism in perirenal adipose tissue of fetal and newborn calves.

Rates of utilization of glucose, acetate, and lactate and activities of selected enzymes were determined in vitro to characterize the nature of lipogenesis and metabolite utilization in perirenal adipose tissue from 6- to 7-month old fetal and 3- to 4-h-old unsuckled newborn calves. Contribution of the pentose phosphate cycle to glucose metabolism was estimated using specifically labeled glucose. Rates of fatty acid synthesis from all three substrates and oxidation of glucose were much greater in fetal than in newborn adipose tissue. In fetal adipose tissue, acetate and lactate were major sources of carbon for fatty acid synthesis; glucose functioned mainly by metabolism via the pentose phosphate cycle to provide reducing equivalents for fatty acid synthesis and by incorporation into glyceride glycerol for fatty acid esterification. Pentose phosphate cycle contributed 58 and 12% to glucose metabolism in adipose tissue of fetal and newborn calves, respectively. Adipose tissue metabolism of newborn calves was characterized by greatly depressed rates of fatty acid synthesis despite high enzyme activities and elevated rates of glyceride glycerol synthesis.

Acetates↗
PubMed1983

Muscle carnitine deficiency: fatty acid metabolism in cultured fibroblasts and muscle cells.

L-carnitine, as little as 25nM, greatly increased oxidation of palmitate by carnitine-depleted cultured human skin fibroblasts from normal subjects, and from two patients with muscle carnitine deficiency. Carnitine stimulated oxidation of labeled palmitate by cultured muscle cells from rat, normal humans, or patients with muscle carnitine deficiency. Carnitine reduced incorporation of palmitate into glycerides in normal fibroblasts, and it may thereby counteract cellular accumulation of glycerides in cells. Fibroblasts from patients with muscle carnitine deficiency took up labeled carnitine at a normal rate. Dexamethasone increased palmitate oxidation by normal human fibroblasts and muscle cells of rat, and normal and muscle carnitine-deficient humans. The results parallel the reported effectiveness of carnitine, glucocorticoids, or medium-chain triglycerides in treatment of these patients.

Adolescent↗
PubMed1997

Endogenous energy production by mature boar spermatozoa.

When incubated in the absence of exogenous substrates, washed boar spermatozoa maintained a high energy charge potential (ECP) for at least 5 h. Addition of 3-chloro-1-hydroxypropanone, an inhibitor of triosephosphate isomerase and glyceraldehyde 3-phosphate dehydrogenase, at any time caused the ECP to decline and fructose-1,6-bisphosphate, dihydroxyacetone phosphate and glycerol to accumulate. There appear to be two endogenous substrates that are degraded ultimately to produce the triosephosphates which allow the cells to produce lactate for the mitochondrial synthesis of ATP. One substrate generates minor amounts of glycerol 3-phosphate whereas the other substrate degrades to glycerol and may be di-glycerides, or tri-glycerides, or both.

Acetone↗
PubMed1982

Parenteral nutrition: current status and concepts.

Parenteral nutrition is regarded as a form of nutrition in some countries and as an extension of intravenous fluid therapy in others. The optimum clinical application of parenteral nutrition as a form of therapy requires detailed knowledge of the nutrient solutions themselves, including the commonly used solutions such as dextrose, soybean oil emulsion, synthetic crystalline L-amino acid solutions; older solutions such as xylitol, protein hydrolysates; and newer solutions such as glycerides and special purpose amino acid solutions. Additionally, information has accumulated over the past 10 years, leading to the rational use of vitamins and trace elements in parenteral nutrition. Metabolism of the substrates has been correlated with known pathways of intermediary metabolism in normal, starved and stressed subjects. Several new concepts have arisen: a) Infusion of excessive quantities of dextrose results in lipogenesis and increased carbon dioxide production. Hyperalimentation of this type is being replaced by infusion of lesser quantities of dextrose, supplemented by intravenous infusion of lipid as a calorie source. b) Protein hydrolysates and racemic synthetic crystalline amino acid solutions have been replaced by synthetic crystalline L-amino acid solutions. c) A new fat emulsion based on safflower oil is competing successfully with the traditional soybean oil emulsion. d) Newer substrates are being explored. These include branched chain amino acids, keto analogues of amino acids, synthetic glycerides and maltose. e) Deficiencies of essential fatty acids, trace elements and vitamins have been studied in patients on long term parenteral nutrition and their mechanisms elucidated. Official recommendations for intravenous administration of these nutrients have been made. f) Several techniques have been applied in several circumstances, including protein sparing therapy, cyclic nutrition, home therapy, and parenteral nutrition in liver and renal failure. Parenteral nutrition is now used extensively, not only in major hospitals where the resources of a team approach with physician, nurse, pharmacist and dietitian are available, but also in smaller hospitals where all of these facilities may not be at hand. However, whatever the setting, the principles behind the clinical application of parenteral nutrition should be well understood by those involved, including current approaches to safe preparation and infusion of parenteral nutrition solutions.

Amino Acids↗