Biomedical subjects

L Dory

Publications and source records attributed to L Dory.

30 records · Page 2Linked to original sources

PubMed1985

Heterogeneity of dog interstitial fluid (peripheral lymph) high density lipoproteins: implications for a role in reverse cholesterol transport.

The heterogeneity of dog interstitial fluid (peripheral lymph) high density lipoprotein (HDL) was investigated and compared to plasma HDL. Interstitial fluid and plasma HDL of normal and cholesterol-fed dogs was subfractionated by ultracentrifugation and affinity and molecular weight sieving chromatography. Both plasma (P) and interstitial fluid (L) HDL can be subfractionated into a larger fraction (P-I and L-I) and a smaller one (P-II and L-II). Cholesterol feeding induces a large increase in the P-I and L-I component of HDL, but the increase in L-I is far greater in proportion than that of P-I. Furthermore, L-I of cholesterol-fed dogs appears to be almost exclusively discoid in shape, while only approximately 15% of particles in P-I are discoidal. The discoid HDL of L-I is reflected in its chemical composition: 28% unesterified cholesterol, 6% cholesteryl ester, 45% phospholipid, and 21% protein. It contains large amounts of apoE in addition to apoA-I and apoA-IV. We found that the association of apoE with discoid particles is frequent, but not necessary. Calculations based on known protein mass and quantitation of discoid particles on electron micrographs suggest that the concentration of discoid particles in the peripheral lymph of cholesterol-fed dogs is about fourfold that of the plasma of the same animal. These findings provide strong circumstantial evidence for the peripheral formation of discoid HDL, perhaps as an early event in reverse cholesterol transport.

Animals↗

PubMed1984

Changes in plasma apo B, apo E, apo A-I, and apo A-IV concentrations in dogs consuming different atherogenic diets.

To define the relationship between apoprotein levels and plasma cholesterol concentration in dogs, we measured the cholesterol, apo B, apo E, apo A-IV, and apo A-I levels in 6 dogs fed a synthetic diet (Diet I), and in 5 dogs fed dog chow supplemented with lard, cholesterol, bile salts, and propylthiouracil (Diet II). The diet-induced hypercholesterolemia exceeded 900 mg/dl in dogs fed Diet I and was accompanied by a 12-fold increase in apo B, a 30-fold increase in apo E, an 8-fold increase in apo A-IV, and a 1 1/2-fold increase in apo A-I. By contrast, the hypercholesterolemia averaged 1300 mg/dl in dogs fed Diet II and was accompanied by a 12-fold increase in apo B, an 11-fold increase in apo E, a 3-fold increase in apo A-IV, and a 5-fold decrease in apo A-I levels. When 3 of the Diet I dogs were switched to dog chow, their plasma cholesterol, apo B, and apo E levels dropped to 30% of their peak value within 7 days. The change in apo B and apo E levels was found to be highly correlated with the change in plasma cholesterol concentrations in each of the Diet I animals (r2 ranged from 0.92 to 0.99 for both apoproteins). A strong linear relationship was also observed between apo E and apo B (r2 ranged from 0.94 to 0.98), indicating that the plasma apo E to apo B ratio remained constant in these animals as the hypercholesterolemia progressed or regressed.

Animals↗

PubMed1983

Lipoproteins and apolipoproteins in peripheral lymph of normal and cholesterol-fed dogs.

Prenodal peripheral lymph was used as a model of interstitial fluid to obtain information on the composition of lipoproteins and apolipoproteins which are in direct contact with peripheral cells. Lipoproteins resembling plasma lipoproteins in size and electrophoretic mobility were present in the prenodal peripheral lymph of control as well as cholesterol-fed dogs. Most of the lipoproteins in control dogs were high density lipoproteins, both in the plasma and in the lymph. Cholesterol feeding resulted in an increased concentration of lipoprotein particles with decreased electrophoretic mobility (beta-VLDL and, in plasma, HDLc) and decreased concentration of HDL, both in plasma and in lymph. Size distribution of lipoproteins was also markedly altered by cholesterol feeding; most of the lipoproteins were present as IDL and VLDL both in plasma and in lymph. Judged by agarose gel chromatography, the size of the lymph HDL as consistently larger than plasma HDL in both groups of dogs. Furthermore, it appears that cholesterol feeding increased the size of an HDL subfraction, partially resolved by agarose chromatography, both in lymph and plasma. All apolipoproteins present in plasma were also present in lymph. Cholesterol feeding resulted in 3-10-fold increases in plasma apo B, E, and A-IV while apo A-I was drastically decreased. These changes were reflected in lymph to different degrees depending on the size of the lipoprotein fraction containing the individual apolipoproteins. Our findings provide direct evidence that the large, cholesterol-rich, 'atherogenic' lipoproteins found in the plasma of cholesterol-fed dogs (beta-VLDL) are also present in the interstitial fluid and presumably interact with peripheral cells. Our studies furthermore suggest modification of plasma HDL by peripheral cells and/or de novo assembly of an HDL subfraction. The utilization of this animal model may thus provide a direct approach to the study of the interaction of lipoproteins with peripheral cells.

Animals↗

PubMed1983

Lecithin:cholesterol acyltransferase-mediated modification of discoidal peripheral lymph high density lipoproteins: possible mechanism of formation of cholesterol-induced high density lipoproteins (HDLc) in cholesterol-fed dogs.

Peripheral lymph high density lipoproteins (HDL) of the cholesterol-fed dog differ in a number of characteristics from plasma HDL of the same animal. Their high content of free cholesterol, phospholipid, apoprotein E, and apoprotein A-IV, their greater heterogeneity in size, and the presence of many discoidal particles suggest that a portion of lymph HDL is assembled within the interstitial fluid. The present experiments demonstrate that the endogenous lecithin:cholesterol acyltransferase (LCAT) activity of whole peripheral lymph of the cholesterol-fed dog is far less (less than 1%) than that found in the plasma of the same animal (0.3 nmol/hr per ml versus 40.6 nmol/hr per ml). Addition of partially purified LCAT to whole lymph induced many changes in the chemical composition of peripheral lymph lipoproteins. After incubation with LCAT, the free cholesterol and phospholipid contents of lymph HDL decreased, from 17% to 12% and from 46% to 33%, respectively, whereas cholesteryl ester content increased from 7% to 13%. These changes were accompanied by a mass transfer of apoprotein E and cholesterol to the p less than 1.05 g/ml fraction, the complete disappearance of the discoidal particles, and a decrease in size heterogeneity of lymph HDL. These results suggest that, in the cholesterol-fed dog, cholesterol efflux into the interstitial spaces may occur in the absence of significant LCAT activity. Furthermore, our studies suggest that the subsequent reaction between lymph HDL and LCAT within the vascular compartment leads to the generation of apoprotein E and cholesteryl ester-rich cholesterol-induced HDL.

Animals↗

PubMed1983

Characterization of dog peripheral lymph lipoproteins: the presence of a disc-shaped "nascent" high density lipoprotein.

The distribution, chemical, and apoprotein composition of plasma and peripheral lymph lipoproteins were compared in control and cholesterol-fed dogs. In both groups of animals, the agarose electrophoretic patterns of plasma and lymph lipoproteins were similar. In hypercholesterolemic dogs, beta-very low density lipoprotein, beta-migrating intermediate density lipoprotein, and HDLc were major components both in plasma and lymph, providing evidence for a potential interaction of these atherogenic particles with macrophages and other peripheral cells. The chemical composition and physical appearance of peripheral lymph HDL was markedly different from that of plasma HDL (high density lipoprotein), especially in the cholesterol-fed animals. Lymph HDL had a higher cholesterol to protein ratio and a markedly increased free cholesterol content (free cholesterol to cholesteryl ester ratio of 1.7 as opposed to 0.2 in plasma HDL in cholesterol-fed animals). The phospholipid content of lymph HDL was higher than that of plasma HDL, while the protein content was lower. A significant proportion of lymph HDL obtained from cholesterol-fed dogs was in the form of disc-shaped particles stacked in rouleau structures. Changes in plasma apolipoprotein concentrations due to cholesterol feeding were reflected in peripheral lymph to different degrees, depending largely on the relative size of the lipoproteins containing the individual lipoproteins. A considerable enrichment of lymph HDL with apoE and apoA-IV was observed by both immunochemical and electrophoretic methods. In lymph HDL from control and cholesterol-fed dogs, the apoE/apoA-I and apoA-IV/apoA-I ratios were several-fold elevated, compared to those of plasma HDL. It is concluded, therefore, that during cholesterol feeding a substantial portion of interstitial HDL is assembled de novo in the periphery as a crucial stage of reverse cholesterol transport to the liver. It is likely that further modification occurs upon entry to plasma and exposure to lecithin:cholesterol acyltransferase, possibly leading to generation of HDLc. Alternatively, these particles may be directly and rapidly removed by the liver.

Animals↗

PubMed1982

The effect of anesthesia or restraint on triacylglycerol turnover in the rat.

A comparison of triacylglycerol metabolism was made among anesthetized, restrained and unanesthetized-unrestrained rats. The method utilized for the comparison was the determination of triacylglycerol turnover following the intravenous injection of [3H]glycerol. Peak appearance of triacyl[3H]glycerol was 25 min in unanesthetized-unrestrained rats but 35 and 45 min in restrained and anesthetized rats, respectively. Using serial plasma triacylglycerol determinations as an index of steady-state in all three groups, it was found that only the anesthetized and unanesthetized-unrestrained animals could be used for kinetic analysis. In these two animal preparations, apparent fractional catabolic rates were calculated and found to be lower in anesthetized (0.014 min-1) compared to unanesthetized-unrestrained animals with chronic indwelling cannulas (0.029 min-1). Apparent total catabolic rates, calculated from the plasma triacylglycerol mass and estimated plasma volume, were reduced by 50% in anesthetized animals. It is concluded that wide differences in triacylglycerol metabolism exist in these rat preparations which should be considered in the interpretation of future studies. The unanesthetized-unrestrained rat model may represent the closest approximation to the normal physiologic state.

Anesthesia, General↗

PubMed1981

Metabolic fate of VLDL apolipoproteins B and E in hepatectomized rats.

The metabolic fate of VLDL apolipoproteins B and E was examined in functionally hepatectomized rats. 1 h after hepatectomy, there was almost complete absence of ultracentrifugally isolated VLDL lipid and protein, including apolipoproteins B and E. Analysis of apolipoprotein concentrations by electroimmunoassay showed hepatectomy did not affect the total serum concentrations of apolipoproteins B and E; thus, hepatectomy caused a redistribution of these apolipoproteins from VLDL to higher density lipoproteins. In the LDL (d = 1.03--1.063 g/ml) fraction, hepatectomy, increased the concentrations of free cholesterol (40%), esterified cholesterol (57%) and protein (18--67%), due to an increase in apolipoproteins B (22--48%) and E (250--300%). After hepatectomy, the HDL fraction accumulated the greatest total amount of apolipoprotein E. Since the majority of apolipoprotein E was isolated in the d greater than 1.21 g/ml fraction after sequential ultracentrifugation, the redistribution of apolipoproteins B and E was further defined by fractionation of serum on 5 M agarose columns. Electroimmunoassay of the column fractions showed that the apolipoprotein B peak eluted before the apolipoprotein E peak. Although a considerable portion of apolipoprotein E eluted with A-I, the peak of apolipoprotein E eluted before the A-I peak in both groups. These data suggest that a portion of apolipoprotein E is associated with particles which are similar than LDL but are larger than A-I-rich HDL. Hepatectomy caused an accumulation of apolipoprotein B in LDL, and apolipoprotein E and cholesterol in particles which were smaller than LDL and may represent LDL1. It is likely that under normal physiological conditions the liver plays a role in the removal of these apolipoprotein E-rich particles which are derived, at least in part, from the metabolism of VLDL.

Animals↗

PubMed1981

Plasma lipids, lipoproteins, and triglyceride turnover in eu- and hypo-thyroid rats and rats on a hypocaloric diet.

Lipid and lipoprotein concentration, and triglyceride turnover were studied in control, thyroidectomized, and pair-fed control rats (pair-fed to match the food intake of the thyroidectomized rats). Thyroidectomy induced a significant increase in plasma cholesterol (and low density lipoprotein) concentrations and a decrease in plasma triglyceride (and very low density lipoprotein) concentrations. Changes in similar direction but of smaller magnitude were observed in the plasma of the pair-fed control rats. To further investigate triglyceride metabolism in these three groups of animals, triglyceride turnover was studied in fasted, unrestrained, and unanesthetized rats, following injection of [2-3H]glycerol. Peak incorporation of [2-3H]glycerol into plasma triglyceride occurred in all three groups of animals at 25 min after precursor administration, although the maximal incorporation was substantially lower in the thyroidectomized group than in either of the control groups. Thereafter, plasma triglyceride radioactivity decayed monoexponentially with a half-life of 24 +/- 1 min for both normal and pair-fed control rats, compared with the half-life of 41 +/- 3 min observed in the thyroidectomized rats. The calculated apparent fractional catabolic rates were thus 0.029 min-1 for both control groups and only 0.017 min-1 for the thyroidectomized animals. The apparent total catabolic rates of plasma triglyceride were 299 +/- 11, 138 +/- 11, and 48 +/- 4 micrograms triglyceride . min-1 for the normal controls, pair-fed controls, and thyroidectomized rats, respectively. These data further emphasize the importance of thyroid hormones in regulating plasma lipid and lipoprotein metabolism and, specifically, indicate that hypothyroidism results in a reduction of triglyceride secretion into, and the removal from, circulation. Furthermore, evidence was presented that the decreased caloric intake of the hypothyroid animals cannot, in itself, account for this observation.

Animals↗

PubMed1981

Rat plasma lipoproteins and apolipoproteins in experimental hypothyroidism.

Hyperlipidemia associated with hypothyroidism is well documented in man and several animal species. The effect of hypothyroidism on apolipoprotein metabolism in the absence of complicating factors such as high cholesterol or fat content in the diet is virtually unknown. Hypothyroidism was therefore induced in male Sprague-Dawley rats by radiothyroidectomy (RTx-treated) or treatment with propylthiouracil (PTU-treated). Both treatments resulted in an over 90% decrease in circulating thyroid hormone concentrations accompanied by a 50-100% increase in plasma cholesterol and a 20-40% reduction in plasma triglyceride concentrations. Plasma apo E and apo B concentrations increased by 100% in the PTU-treated group and 40-50% in the RTx-group. Apo A-I increased 10 and 30% in the RTx- and PTU-treated rats, respectively, while the concentration of apo A-IV was not altered. A large increase in the low-density (LDL) and high-density lipoprotein (HDL) protein was observed and accompanied by a marked reduction of very low density lipoprotein (VLDL) in the hypothyroid rats. The electrophoretic pattern of plasma lipoproteins in the hypothyroid rats was changed by the appearance of a slow pre-beta band shown to be beta-VLDL. A redistribution of apo B occurred within the lipoprotein fractions. Apo B content in the VLDL fraction decreased and a large increase was noted in LDL. The major portion of the apo E and apo A-I increment was recovered in the HDL and to a lesser degree in LDL. An accumulation of apo E-rich larger HDL particles, resembling HDLc in apolipoprotein composition and distinct from the apo A-I-containing species, was observed by column chromatography. The results presented are consistent with the hypothesis that hypothyroidism in the rat may induce an accelerated production of VLDL catabolic remnants, including LDL, but at the same time reduce the rate of removal of these lipoproteins from the circulation.

Animals↗

PubMed1981

Fate of apolipoproteins C-1, C-iii, and E during lipolysis of human very low density lipoproteins in vitro.

The apoprotein and lipid composition of HDL-like products arising from lipolysis of human VLDL was studied. The VLDL was perfused through beating rat hearts in the absence of serum to avoid possible alteration of the primary products of lipolysis due to apoprotein exchange with serum lipoproteins. The lipolytic products were separated by gel filtration to obviate possible losses of apoproteins from the lipoproteins during ultracentrifugation. Apoprotein B, E, C-II, and C-III were quantitated by electroimmunoassay and lipids were determined by chemical methods. During perfusion, a 50% hydrolysis of the VLDL triacylglycerols was associated with the appearance of 11% of the apoC-II, 30% of the apoC-III, and 20% of apoE of the VLDL in HDL-like particles as isolated by agarose gel filtration. The shift of the apoproteins to these particles was associated with a similar redistribution of cholesterol, phospholipid, and cholesteryl ester. The lipid composition of the HDL-like particles was cholesterol (15.1 +/- 4.0%), phospholipid (37.8 +/- 3.2%), cholesteryl ester (34.2 +/- 2.6%), and triglyceride (12.9 +/- 3.2%). The particles possessed a hydrated density of 1.063-1.21 g/ml and were spherical, with particle diameters (mean 124 +/- 36 A, range 50-160 A) that were comparable to the diameter (140 A) estimated from calculations of the surface to volume ratio, assuming a spherical particle consisting of a neutral lipid core surrounded by cholesterol, phospholipid, and protein. No discoidal forms or rouleau structures were observed in the HDL-sized fraction isolated by gel filtration. The HDL-like fraction could be resolved further by heparin-Sepharose chromatography into an unretained fraction containing predominantly apoC-III with apoE and apoC-II, and a retained fraction containing apoC-III and apoE. Small amounts of apoE were also recovered in extremely small particles that are normally observed in the d > 1.21 g/ml fraction after ultracentrifugation. No apoC-II or C-III was observed in this fraction. Incubation of VLDL with lipoprotein lipase, mobilized from hearts by heparin perfusion, yielded results that were similar to those with the perfused heart. Hearts perfused with VLDL removed apoB but not apoC-II, C-III, E, or phospholipids from the perfusate. It is concluded that the initial products of VLDL catabolism include spherical particles, similar in size to HDL, that contain apoC-II, C-III, E, cholesterol, cholesteryl esters, and phospholipids. ApoE is also released as a small extensively delipidated particle.-Tam, S. P., L. Dory, and D. Rubinstein. Fate of apolipoproteins C-II, C-III, and E during lipolysis of human very low density lipoproteins in vitro.

Animals↗

PubMed1979

Secretion of cholesterol-rich lipoproteins by perfused livers of hypercholesterolemic rats.

Rats maintained on a high-fat diet supplemented with propylthiouracil develop a hypercholesterolemia, an increased serum level of apolipoprotein (apo) E, abnormal very low density lipoproteins (VLDL) and low density lipoproteins (LDL), and a fatty liver which contains cholesterol ester as its major lipid. The fatty liver secretes apoE into a recirculating perfusate at a significantly higher rate and produces cholesterol ester-rich, apoC-deficient VLDL with slower electrophoretic mobility than the triacylglycerol-rich VLDL produced by perfused normal livers. LDL, secreted in significant quantities by the perfused fatty liver, but not by the normal liver, is also cholesterol rich and contains apoE as well as apoB. The incorporation of [(3)H]leucine into apoVLDL and apoLDL secreted by the livers of the hypercholesterolemic animals and the apoVLDL secreted by the normal liver corresponds to the pattern visualized when the apoproteins are separated by polyacrylamide gel electrophoresis. Similar patterns are noted when non-recirculating perfusates are studied. These results indicate that the cholesterol ester-rich, apoC-deficient VLDL and the apoE-containing LDL found in the serum of hypercholesterolemic rats are not solely catabolic remnants of VLDL and chylomicrons but are secreted by the liver. Separation of the perfusate lipoproteins by agarose gel filtration revealed that most of the apoE secreted by the livers of hypercholesterolemic rats is found in the VLDL and LDL, whereas apoE secreted by the normal livers is distributed equally between VLDL, high density lipoproteins, and a low molecular weight fraction which corresponds to the virtually delipidated apoprotein. Thus the distribution of apoE among the lipoprotein fractions may be related to the total amount of cholesterol being transported in the circulation.

Animals↗

PubMed1978

The catabolism of human and rat very low density lipoproteins by perfused rat hearts.

The catabolism of human and rat 125I-labelled very low density lipoproteins (VLDL) was compared by perfusing the lipoproteins through beating rat hearts. Triacylglycerol was removed from the VLDL to a greater extent than the protein moiety, leaving remnants containing relatively more apo-B and less apo-C. The change in apo-C content of the remnants correlated with the loss of triacylglycerol. The extent of removal of triacylglycerol from the rat and human VLDL was similar and in most cases appeared to saturate the heart lipoprotein lipase. The remnants were slightly smaller in size than the VLDL, and included particles which appeared to be partially emptied. In addition to remnants of d less than 1.019 g/ml, iodinated lipoproteins derived from rat and human VLDL were recovered at d 1.019-1.063 and 1.063-1.21 g/ml. The former contained largely cholesterol and cholesteryl esters, while phospholipids were the dominant lipid in the latter. An average of 40% of the 125I-labelled apoprotein lost from the VLDL was associated with the perfused hearts. Very little d 1.019-1.063 g/ml lipoprotein was produced from low (physiological) concentrations of rat VLDL, most of the lipoprotein being removed by the heart. However, lipoproteins of density 1.019-1.063 g/ml were formed from human VLDL at all concentrations in the perfusate, as well as from higher concentrations of the rat VLDL. Agarose gel filtration of lipoproteins following heart perfusion with human VLDL revealed large aggregates containing particles which resemble low density lipoproteins (LDL) in electron microscopic appearance and apoprotein composition, since they contain largely apo-B. These data suggest that at normal concentrations rat VLDL are almost completely catabolised and taken up by the heart without the formation of LDL, while LDL is produced from human VLDL at all concentrations.

Animals↗