Search PubMed⌕ Search

Biomedical subjects

R O Scow

Publications and source records attributed to R O Scow.

At least 37 records · Page 2Linked to original sources
PubMed1986

Effect of epinephrine and other lipolytic agents on intracellular lipolysis and lipoprotein lipase activity in 3T3-L1 adipocytes.

3T3-L1 adipocytes were used to test the hypothesis that hormone-sensitive lipolysis and lipoprotein lipase activity might be regulated in a reciprocal manner. Intracellular lipolysis was stimulated by catecholamine, dibutyryl cAMP, and ACTH, but not by glucagon. The effects of epinephrine on lipolysis were blocked by the beta-antagonist propanolol but not by the alpha-antagonist phentolamine. Hormone-stimulated lipolysis was not changed by acute (45 min) or chronic (2 days) treatment of the cells with insulin whereas the latter treatment augmented lipoprotein lipase activity about fivefold. Epinephrine did not affect the lipoprotein lipase activity of insulin-stimulated cells. Withdrawal of glucose from the medium decreased lipoprotein lipase activity and the effect of epinephrine on lipolysis. Effects of lipolytic agents on activity of lipoprotein lipase were variable and concentration-dependent. Lipoprotein lipase activity was decreased only by concentrations of epinephrine greater than those inducing maximal intracellular lipolysis, and the decrease in activity occurred about 30 min after the increase in glycerol release. There seems to be no relationship between the level of activity of lipoprotein lipase and the maximal rate of hormone-stimulated lipolysis in 3T3-L1 cells. Unlike in adipose tissue and adipocytes of rats, hormone-stimulated lipolysis and lipoprotein lipase activity in murine 3T3-L1 adipocytes appear to be regulated independently.

Adipose Tissue↗
PubMed1986

Effect of the combined lipase deficiency mutation (cld/cld) on ultrastructure of tissues in mice. Diaphragm, heart, brown adipose tissue, lung, and liver.

Lipoprotein lipase and hepatic lipase activities are very low in tissues of mice born with genetic combined lipase deficiency (cld/cld). Consequently, if allowed to suckle, the mice develop severe hyperlipemia and die within 3 days. The ultrastructure of capillaries and parenchymal cells in tissues that normally contain lipoprotein lipase and hepatic lipase was studied in tissues from cld/cld and unaffected mice 6 to 24 hours of age. Capillaries in tissues from suckled cld/cld mice were packed with numerous abnormally shaped chylomicrons. There was close contact between surfaces of chylomicrons and the luminal plasma membrane of endothelium. Chylomicrons were sometimes found between endothelial cells and in the subendothelial space in heart, lung, and liver, and in the lumen of lung alveoli. In contrast, capillaries of suckled unaffected mice contained very few chylomicrons, and the subendothelial spaces and lung alveoli were free of chylomicrons. Myocytes of diaphragm and heart from suckled cld/cld mice did not contain lipid droplets, whereas brown adipocytes contained a few small droplets. Parenchymal cells in diaphragm, heart, brown adipose tissue, and lung from suckled unaffected mice contained numerous large lipid droplets. Hepatocytes of suckled cld/cld mice contained small irregularly shaped lipoprotein particles (100 A) in endoplasmic reticulum and Golgi, numerous large lysosomes containing small lipoprotein particles, lipid spheres and lamellar structures, and no intracellular lipid droplets, whereas hepatocytes of suckled unaffected mice contained larger lipoprotein particles (400 A), large lipid droplets, and very few lysosomes. Triacylglycerol of chylomicrons from cld/cld mice was readily hydrolyzed by bovine lipoprotein lipase in vitro, and this effect was not augmented by heat-inactivated serum, indicating that the chylomicrons contained adequate amounts of apoprotein C-II. Thus, the large amount of chylomicrons in capillaries and small amount of lipid droplets in cells of suckled cld/cld mice reflect the very low level of lipoprotein lipase activity in these animals. The findings in hepatocytes indicate that lipoprotein metabolism in liver is markedly disturbed in cld/cld mice.

Adipose Tissue, Brown↗
PubMed1985

Effect of pH on visualization of fatty acids as myelin figures in mouse adipose tissue by freeze-fracture electron microscopy.

We studied the effect of pH on visualization of fatty acids as myelin figures in young mouse epididymal adipose tissue. Fatty acid content of the tissue was increased to 12.4 nmol/mg wet weight by treating the tissue with 380 microM isoproterenol at pH 7.4 for 15 min in the absence of glucose and albumin. Myelin figures were found in freeze-fracture replicas of isoproterenol-treated tissue fixed with glutaraldehyde at pH 7.4 and then incubated and glycerinated at pH 8.1. Myelin figures were seen in replicas as concave or convex laminated sheets and long cylindrical multilamellar structures in fat cells and extracellular space. Myelin figures were sometimes seen in cells extending from the surface of intracellular lipid droplets, the site of lipolysis, to the cell surface and extracellular space. Myelin figures were not found in isoproterenol-treated tissue fixed at pH 7.4 and processed at pH 7.0. Smooth-surfaced droplets, instead, were found in these tissues in the extracellular space. Neither myelin figures nor smooth-surfaced droplets were found in tissues treated with insulin and glucose (to reduce fatty acid content to 1.4 nmol/mg), fixed at pH 7.4 and processed at either pH 8.1 or pH 7.0. Lowering pH of the media to 4.5 during processing of tissues treated with isoproterenol at pH 9.0 caused disappearance of myelin figures and appearance of smooth-surfaced droplets in the extracellular space. Myelin figures were found in replicas of tissue treated with isoproterenol for 15 min at pH 7.4, incubated 10 min at pH 8.4, quick-frozen and then freeze-fractured, indicating that formation of myelin figures was not dependent on glutaraldehyde fixation and glycerol infiltration of the tissue. Our findings show that excess fatty acids in adipose tissue can be visualized as myelin figures if the tissue is exposed to pH 8.1-9.0 and maintained at or above pH 7.4, or as smooth-surfaced droplets if the tissue is processed at pH 7.0 or 4.5. We conclude that myelin figures formed under these conditions are composed primarily of partially ionized fatty acids (acid-soaps), and that the smooth-surfaced droplets in the extracellular space are composed of un-ionized (protonated) fatty acids.

Adipose Tissue↗
PubMed1985

Combined lipase deficiency (cld/cld) in mice. Demonstration that an inactive form of lipoprotein lipase is synthesized.

Combined lipase deficiency, cld, is a recessive mutation within the T/t complex of mouse chromosome 17. Mice homozygous for this defect display severe functional deficiencies of lipoprotein lipase and the related hepatic lipase. They develop massive hyperchylomicronemia and die within 3 days when allowed to suckle. Heart, diaphragm muscle, and brown adipose tissue of 1-day-old cld/cld and unaffected mice incorporated in vivo [35S]methionine into a protein that could be immunoprecipitated by antilipoprotein lipase serum. The immunoprecipitated protein in all tissues had the same Mr as bovine lipoprotein lipase as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The proportion of radioactivity in the lipoprotein lipase band to that in total protein was 0.02% in tissues of cld/cld mice and 0.01% in tissues of unaffected mice. There was 2-6 times more lipoprotein lipase-like protein (determined by immunoassay) in tissues of defective mice than in those of unaffected mice. These findings indicate that the cld mutation did not cause deletion of the structural gene for lipoprotein lipase. Lipoprotein lipase activity in heart, diaphragm muscle, brown adipose tissue, and lung of cld/cld mice was less than 5% of that in tissues of unaffected mice. This low activity could be inhibited more than 85% by antilipoprotein lipase serum, but not by nonimmune serum. It is concluded that tissues in cld/cld mice synthesize a lipoprotein lipase-like protein which has subnormal catalytic activity.

Adipose Tissue, Brown↗
PubMed1985

Lipid filling and lipolysis in adipose tissue and cells.

Fatty acids are transported from circulating blood lipoproteins to adipocytes during lipid filling of adipose tissue and from adipocytes to the capillary lumen during lipid mobilization. Our studies with chylomicrons and lipid monolayers show that ampipathic fatty acids formed by the action of lipoprotein lipase locate and move in the interface between lipid and the aqueous phase. Our studies on brown and white adipose tissue show that fatty acids formed by the action of lipoprotein lipase on chylomicrons at the capillary endothelial surface and by the action of hormone sensitive lipase on intracellular lipid droplets locate in an interfacial continuum composed of the outer leaflets of the plasma membrane of cells and the lumenal leaflets of intracellular membranes. Ampipathic fatty acids can be visualized with electron microscopy as lamellar structures. In fixed tissue fatty acids which overcrowd the interfacial continuum form lamellar extensions of the external leaflet of membranes at different sites along their transport route. In adipose tissue of fed animals lamellar structures extend from chylomicrons at the capillary endothelial surface through trans-endothelial channels to adipocytes marking the route of transport of fatty acids during lipid filling of adipose tissue. In adipose tissue of fasted animals lamellar structures extend from intracellular lipid droplets through intracellular channels to the plasma membrane of adipocytes marking the route of fatty acid transport during lipid mobilization. In adipocytes from brown adipose tissue of cold-stressed young animals lamellar structures extend from intracellular lipid droplets to the outer mitochondrial chamber marking the route of transport of fatty acids to mitochondria for oxidation and heat production.

Adipose Tissue↗
PubMed1984

Uptake of plasma triacylglycerol by a muscular artery in the rat: an ultrastructural study.

The uptake of plasma triacylglycerol by the dorsalis pedis artery in the rat was studied using intravenous infusion of an emulsion of triacylglycerol at a rate of 2.3 mumol per min for 1.5 or 5 h. Electron microscopy revealed lipid droplets in the arterial lumen near the endothelium and in the medial smooth muscle cells (SMC), but not in the endothelial cells or in the extracellular space. Lamellar structures with a periodicity of 40 A developed in the arterial tissue when glutaraldehyde-fixed specimens were incubated at +25 degrees C before postfixation in osmium. Lamellae were present at the luminal and basal surfaces and within endothelial cells, and also in the medial extracellular space associated with the plasma membrane of SMC, in the intracellular channels and near and inside the mitochondria of the medial SMC. No lipid droplets or lamellae were found in the arterial tissue of the control rats. The findings indicate that plasma triacylglycerol is not taken up by the arterial tissue as intact lipid particles, but that these are hydrolyzed at the luminal surface of the endothelium, the lipolytic products then being transferred to the medial SMC for re-esterification and storage in the form of triacylglycerol. The lamellar structures found in the fixed and incubated arterial tissue are thought to represent fatty acids produced by the lipolysis of triacylglycerol during incubation, and we suggest that the transport of fatty acids from the arterial lumen to the medial SMC occurs by lateral movement in a continuum of cell membranes.

Animals↗
PubMed1984

Lipolysis and fatty acid transport in rat heart: electron microscopic study.

Lamellar structures with a periodicity of 50 A developed in myocytes of glutaraldehyde-fixed heart tissues from young and adult rats when the tissues were incubated with tannic acid (pH 7.4) at 25 degrees C. The increase in lamellar structures (P less than 0.025) was accompanied by a significant decrease in intracellular lipid droplets (P less than 0.025), indicating that tissue lipase was active in fixed tissue and that the lamellar structures were probably composed of fatty acids formed by lipolysis. The lamellar structures in myocytes were located in the lumen of intracellular channels near lipid droplets and mitochondria and in the outer compartment of mitochondria. Lamellar structures were found at the periphery of chylomicrons, in intraendothelial channels, and in extracellular space of incubated fixed tissues from chylomicron-injected young rats. Chylomicron-lipid disappeared from capillaries (P less than 0.025) and lamellar structures with wide interlamellar spacings (80-1,000 A) developed in the extracellular space surrounding capillaries (P less than 0.025) in unfixed heart tissue from chylomicron-injected fasted young rats when the tissue was incubated without tannic acid; lamellar structures did not develop in similarly treated tissue from uninjected rats. Thus the lamellar structures found in extracellular space represent fatty acids derived from lipolyzed chylomicrons. We conclude that fatty acids produced by lipolysis in incubated heart accumulated and spread in an interfacial continuum of external leaflets of cell membranes extending from the capillary lumen to extracellular space and from intracellular lipid droplets to the interior of mitochondria in myocytes. When fatty acids overcrowded the continuum, they formed lamellar extensions of the continuum at different sites along its course through the tissue.

Aging↗
PubMed1983

Purification and characterization of rat lingual lipase.

Lingual lipase was highly purified from serous glands of rat tongue. Protein containing lipolytic activity was precipitated with 30-60% saturated ammonium sulfate from the 100,000 X g supernatant of a homogenate of the glands, resuspended in buffered solution, treated and precipitated with acetone at -20 degrees C, and redissolved in buffered solution at pH 5.4. This protein was further purified by hydrophobic chromatography on ethyl agarose; it was eluted with a micellar solution of sodium taurodeoxycholate, oleic acid, and monooleoylglycerol at pH 6.3. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed this fraction consisted of one major protein band, with Mr = 51,000, and several minor bands. A similar value for Mr of protein with lipolytic activity was obtained when acetone-precipitated protein was subjected to gel filtration on Sephadex G-200 indicating that 51,000 is the Mr of an active form of lingual lipase. Lingual lipase purified from rat tongue had a specific activity of 230 units/mg of protein (unit = micromoles of fatty acid formed/min at 37 degrees C). Purified lingual lipase hydrolyzed immediately long chain triacylglycerol to diacylglycerol and fatty acid in medium containing 17 mM sodium taurodeoxycholate and 3.3 mM CaCl2 at pH 5.4. It then hydrolyzed diacylglycerol, and later monoacylglycerol, but at rates 1:6 and 1:20, respectively, of that for triacylglycerol. The activity of lingual lipase in the presence of sodium taurodeoxycholate and CaCl2 was decreased only 33% when pH of the incubation medium was increased to 6.5. This indicates that lingual lipase, which is known to be active in stomach, could act in the small intestines.

Animals↗
PubMed1983

Movement of lipolytic products to mitochondria in brown adipose tissue of young rats: an electron microscope study.

Lipolysis occurred and lamellar structures with a periodicity of 40 A developed in glutaraldehyde-fixed brown adipose tissue of suckling rats when the tissue was incubated at 25 degrees C. The lamellar structures were found in capillaries, associated with chylomicrons, in intracellular channels of capillary endothelium, in extracellular space, and in channels near lipid droplets in adipocytes in tissue of fed rats injected intravenously with chylomicrons. They were also found in channels near mitochondria and inside mitochondria in adipocytes in incubated-fixed tissue of rats exposed to 4 degrees C for 2 hr or unsuckled overnight. In addition, aqueous spaces developed adjacent to lipid droplets in incubated tissue of cold-exposed and unsuckled rats. Development of lamellar structures under conditions causing lipolysis and accumulation of fatty acids in fixed tissue indicated the lamellae were composed primarily of fatty acids. We conclude that fatty acids formed by lipolysis of chylomicrons in tissue from fed rats accumulated in a continuum of the outer leaflets of cell membranes extending from capillary lumen to lipid droplets of adipocytes, and fatty acids formed by lipolysis of intracellular lipid in tissue from cold-exposed or unsuckled rats accumulated mostly in a continuum extending from lipid droplets to the interior of mitochondria. When fatty acids overcrowded the continuum in fixed tissue, they formed lamellar extensions of the continuum at different sites along its course through the tissue.

Adipose Tissue, Brown↗
PubMed1982

Continuity of intracellular channels with extracellular space in adipose tissue and liver: demonstrated with tannic acid and lanthanum.

Tannic acid was used to demonstrate continuity of intracellular channels with extracellular space in white adipose tissue of adult rats, brown adipose tissue of suckling rats, and liver of diabetic rats. Electron-opaque material resulting from treatment of glutaraldehyde-fixed tissue with tannic acid was found in extracellular space, invaginations of cell surfaces, vesicles, and intracellular channels. Electron-opaque material was present in channels that surrounded lipid droplets in both white and brown adipocytes and in hepatocytes. The small distance between the lumen of marked channels and lipid droplets in adipocytes indicates that a monolayered structure, perhaps a leaflet of membrane lining the channel. Similar findings were obtained in brown adipose tissue using lanthanum instead of tannic acid to mark intracellular channels continuous with extracellular space. Since endoplasmic reticulum is the primary site of triacylglycerol synthesis in adipocytes, marked channels near lipid droplets may be elements of endoplasmic reticulum. Some of the channels marked with tannic acid in hepatocytes contained lipoprotein particles, whereas others were located, in relation to mitochondria and lipid droplets, in the same sites as endoplasmic reticulum in untreated tissue. This indicates that some of the channels marked with tannic acid in hepatocytes are endoplasmic reticulum. Presence of electron-opaque material in intracellular channels and vesicles, but not in cytoplasm, of treated tissue indicates the channels and vesicles were open to extracellular space during treatment with tannic acid or lanthanum and, furthermore, that their membranes were continuous with plasma membrane.

Adipose Tissue↗
PubMed1982

Transfer of human lymph chylomicron constituents to other lipoprotein density fractions during in vitro lipolysis.

To ascertain whether chylomicron constituents would be transferred to low density lipoprotein (LDL, d 1.019-1.063 g/ml) and high density lipoprotein (HDL, d 1.063-1.21 g/ml) density fractions during lipolysis in the absence of other lipoproteins, the in vitro effect of bovine milk lipoprotein lipase on human thoracic duct lymph chylomicrons in the presence of albumin was examined. In incubations without lipase, over 90% of chylomicron constituents remained in the 1.006 g/ml supernate, and large particles ranging in diameter mainly from 750-6000 A were observed by electron microscopy. After the addition of lipase, lipolysis ranged from 69.0-94.6% and numerous collapsed particles with redundant surface were seen, as well as smaller particles within the LDL and HDL density region. With lipolysis, the majority of chylomicron cholesterol and phospholipid mass was transferred to LDL and HDL, while chylomicron apolipoprotein (apo) A-I, A-II, and C-II mass was transferred mainly to HDL. Utilizing either radioiodinated apoA-I and apoA-II reassociated with chylomicrons or radiolabeled chylomicrons, a similar redistribution of apoA-I and apoA-II radioactivity was noted with lipolysis. In contrast, chylomicron apoB (mainly B-48) radioactivity was transferred predominantly to LDL with lipolysis. These data are consistent with the concept that during lymph chylomicron triglyceride hydrolysis, chylomicron apolipoproteins, cholesterol, and phospholipid can be transferred to the LDL and HDL density regions in the absence of acceptor particles.

Animals↗
PubMed1980

Accumulation of lipid in muscular arteries of short-term diabetic rats. An electron microscope study.

Lipid accumulation in muscular (pulmonary, coronary and tibial) arteries and elastic (aorta and pulmonary) arteries of streptozotocin diabetic (65 mg/kg) rats was studied with an electron microscope. Arterial tissue specimens taken 4 days after the induction of diabetes showed lipid deposits in smooth muscle cells in the muscular arteries of 9 out of 24 diabetic rats, but in none of the 17 control rats. Histochemically the lipid was identified as triacylglycerol. Lipid accumulation was not seen in the elastic arteries of either diabetic or control rat. The diabetic animals with lipid deposits had slightly but significantly higher plasma glucose concentrations (p < 0.02), higher non-esterified fatty acids levels (p < 0.01), and lower concentrations of plasma insulin (p < 0.02) than those without arterial deposits. The amount of lipid deposited in the arteries was closely related to the plasma non-esterified fatty acid level, which was in the ranges 0.8-1.1 mmol/l in diabetic rats without deposits, and 1.1-2.4 mmol/l in those with deposits. The findings suggest that lipid accumulations in smooth muscle cells of muscular arteries during acute diabetes could result from the high plasma non-esterified fatty acid concentrations.

Animals↗
PubMed1980

Transport of lipid across capillary endothelium.

Fatty acids, monoacylglycerol, cholesterol, and phospholipids are taken up from blood by many different tissues. These substances, which are strongly amphipathic at physiological pH, are poorly soluble in water and neutral lipids (tyriacylglycerol nd cholesteryl ester). They are transported in blood as components of lipoprotein particles or, in the case of fatty acids, s monomers bound to albumin. Fatty acids derived from the diet are carried as triacylglycerol in chylomicrons and very low density lipoprpoteins (VLDL). Phospholipids and cholesterol absorbed from intestines are also transported in chylomicrons and VLDL. We propose that transport of fatty acids and monoacylglycerol from chylomicrons Tand VLDL) across capillary endothelium in extrahepatic tissues requires 1) conversion of chylomicron triacylglycerol to amphipathic lipids (fatty acids and monoacylglycerol) by lipoprotein lipase at the capillary surface, 2) location and lateral movement of ipolytic products in a continuous interface composed of the chylomicron surface film and the external leaflet of plasma and intracellular membranes of endothelial and parenchymal cells, and 3) removal of lipolytic products from the interface in endoplasmic reticulum where they are reesterified to traicylglycerol and accumulate between leaflets of endoplasmic reticulum. We suggest that cholesterol and phospholipids from chylomicrons, and fatty acids from plasma albumin, also cross capillary endothelium by lateral movement in cell membranes.

Capillary Permeability↗
PubMed1979

Lipolysis and lipid movement in a membrane model. Action of lipoprotein lipase.

The action of purified bovine milk lipoprotein lipase on tri[3H]oleoylglycerol and the effect of albumin on movement of lipolytic products at an argon-water interface were studied in a specially designed tricomparted trough. The amount of trioleoylglycerol applied was 14 times that needed to cover the surface of the aqueous subphase (0.1 M Tris . HCl, pH 7.4) with a monolayer. It is concluded that trioleoylglycerol was present in lenses on the surface of the aqueous subphase, that hydrolysis by lipoprotein lipase occurred in or near the lipid/argon-water interface, and that lipolytic products immediately located and spread throughout the interface, displacing substances with lower spreading pressures from the interface. Addition of albumin to the aqueous subphase accelerated markedly the desorption of oleic acid and monooleoylglycerol from the interface and thereby enhanced lipolysis. When albumin was not contiguous with the site of hydrolysis, oleic acid and monooleoylglycerol readily moved in the interface to the area of contact with albumin where they were desorbed from the interface. These findings support the hypothesis of transport of lipolytic products by lateral movement in cell membranes.

Animals↗