PubMed Health⌕ Search

Biomedical subjects

V S LeQuire

Publications and source records attributed to V S LeQuire.

At least 19 recordsLinked to original sources
PubMed1988

Intestinal lipoprotein synthesis in control and hypercholesterolemic rats.

Previous studies in our laboratory have shown that very-low-density lipoproteins (VLDL) synthesized by the intestine of the diet-induced hypercholesterolemic rat are enriched in cholesteryl esters and unesterified cholesterol compared with intestinal VLDL from control rats. In these studies, we isolated and characterized nascent intestinal Golgi intermediate-density lipoproteins (IDL, d 1.006-1.040 g/ml) and studied isotope incorporation into apoliproteins of Golgi VLDL from control and hypercholesterolemic rats. IDL were triacylglycerol-rich lipoproteins but contained more cholesteryl ester and protein than the corresponding Golgi VLDL fractions. IDL from hypercholesterolemic rats were enriched in cholesteryl esters to a greater extent than IDL from control rats. The apolipoprotein patterns of IDL fractions were the same as those of intestinal Golgi VLDL, consisting of apolipoproteins (apo) B-48, A-I and A-IV. Time-course isotope incorporation curves for apo A-I and A-IV in Golgi VLDL were similar, but they differed from curves for apo B-48. None of these curves was markedly altered in the hypercholesterolemic rat. We conclude that the major effect of increased dietary cholesterol on intestinal lipoprotein biosynthesis is to increase the percentage of cholesteryl esters in Golgi lipoproteins. Dietary cholesterol does not alter the apolipoprotein composition of Golgi lipoproteins, nor does it have a significant effect on the pattern of isotope incorporation into apolipoproteins of Golgi VLDL. The effect of cholesteryl ester enrichment on the subsequent metabolism of these particles in the circulation and the effect of these particles on hepatic lipoprotein production remain to be determined.

Animals↗
PubMed1988

Identification of lipoprotein-binding proteins in rat liver Golgi apparatus membranes.

The low density lipoprotein (LDL) receptor has been shown to be a plasma membrane glycoprotein responsible for the cellular binding and endocytosis of plasma lipoproteins. Inasmuch as the Golgi apparatus has been shown to participate in glycoprotein processing and in the assembly of plasma lipoproteins by hepatic and intestinal epithelial cells, the present studies were designed to test the hypothesis that lipoprotein receptors are present within Golgi membranes. Utilizing ligand blotting with a variety of iodinated lipoproteins, several lipoprotein-binding proteins were identified in rat liver Golgi membranes at apparent molecular weights (Mr) 200,000, 160,000, 130,000, 120,000, 100,000, 80,000, and 70,000. The 130,000 protein was the most prominent and was identified as the mature LDL receptor by its binding characteristics and an Mr characteristic of the plasma membrane receptor. Enzymatic deglycosylation studies suggested that the 120,000 and 100,000 proteins were LDL receptor precursors lacking sialic acid. Antibody to the LDL receptor recognized all the bands on immunoblots except the 70,000 protein, with the 130,000 protein being the most prominent. Isolation of the Golgi fractions in the presence of protease inhibitors did not eliminate any of the proteins recognized by the antibody but did result in sharper bands on the blots. Additionally, we investigated the hypothesis that conditions that regulate plasma membrane LDL receptors also cause detectable changes in receptors in Golgi membranes. All the binding proteins were increased in Golgi membranes from rats treated with 17-alpha-ethynylestradiol. Colchicine caused an accumulation of 120,000 Mr protein, suggesting blockage of final sialylation in the trans Golgi. When protein synthesis was inhibited by cycloheximide, there was no reduction of mature LDL receptors in Golgi membranes, consistent with recycling of receptors through this organelle.

Animals↗
PubMed1987

Beta-adrenergic receptor properties of a pulmonary alveolar type II cell preparation from the adult rat.

The pulmonary alveolar type II cell synthesizes and secretes phosphatidylcholine (PC), a major component of surfactant, above basal level in response to beta-adrenergic stimulation. The investigation of the specific receptor which mediates these events was the topic of this study. Freshly isolated type II cells from adult rats were disrupted in a French pressure cell, and crude particulate fractions were recovered and used in assays for binding of the radioligand (-)-3-[125I]-iodocyanopindolol. The receptor had high affinity for beta-adrenergic agents, and specific binding to the receptor was saturable and reversible. The KD value obtained by kinetic means (19.6 pM) was in close agreement with that obtained by Scatchard (21.5 pM) and Hill (21.3 pM) analyses of steady-state binding data. The Scatchard correlation coefficients and Hill plot coefficients were close to 1, indicative of a single class of binding sites which displays no cooperativity. The specificity for catecholamine agonists and stereoselectivity observed were appropriate for a beta-adrenergic receptor. Use of selective drugs identified the presence of both beta 1- and beta 2-adrenergic receptor subtypes (1:3, respectively) on this cell type.

Animals↗
PubMed1984

Intestinal lipoprotein synthesis. Comparison of nascent Golgi lipoproteins from chow-fed and hypercholesterolemic rats.

Hypercholesterolemia, induced by a cholesterol-enriched diet, is associated with distinctive modifications in the serum lipoproteins of a variety of species. Present in the serum of these animals are several classes of lipoproteins enriched in cholesteryl esters and apolipoprotein E. To investigate the role of intestinal lipoprotein synthesis in diet-induced hypercholesterolemia, we characterized nascent lipoproteins retrieved from Golgi apparatus-rich fractions of intestinal epithelial cells from chow-fed control and hypercholesterolemic rats. To eliminate chylomicrons from the preparations, rats were fasted overnight prior to the experiments. Golgi very low density lipoproteins (d less than 1.006 g/ml) from control rats were triglyceride-rich lipoproteins that migrated slightly slower than pre-beta migrating serum very low density lipoproteins. These particles contained apoproteins B-240, A-IV, and A-I. Golgi very low density lipoproteins from hypercholesterolemic rats were likewise triglyceride-rich lipoproteins migrating electrophoretically like control Golgi very low density lipoproteins and they contained apoproteins B-240, A-IV, and A-I. However, these latter particles contained less triglyceride and more cholesterol compared to control Golgi very low density lipoproteins. In addition, by radioisotope incorporation studies, Golgi very low density lipoproteins from hypercholesterolemic rats contained relatively more apoprotein A-IV (21.6 vs. 11.0%) and less apoprotein B-240 (17.0 vs. 27.0%) than found in control Golgi very low density lipoproteins. Approximately 60% of the total apoprotein radioactivity was found in apoprotein A-I in both preparations. We conclude that intestinal lipoprotein synthesis is modified by diet-induced hypercholesterolemia. The significance of these modifications with respect to the marked hypercholesterolemia observed in these animals remains to be determined.

Animals↗
PubMed1982

Hepatic Golgi lipoproteins: precursors to plasma lipoproteins in hypercholesterolemic rats.

Two classes of nascent lipoproteins can be isolated from Golgi apparatus-rich fractions of liver from hypercholesterolemic rats. Golgi very low density lipoproteins (VLDL, d less than 1.006 g/ml) are enriched in cholesteryl esters and are similar in many respects to hypercholesterolemic plasma B-VLDL. Golgi low density lipoproteins (LDL, d 1.006-1.05 g/ml) are cholesteryl ester-rich beta-migrating lipoproteins similar to hypercholesterolemic plasma LDL. To determine if this latter lipoprotein is a precursor to plasma LDL, control and hypercholesterolemic rats were injected with Triton WR 1339 (400 mg/kg) to block intravascular lipoprotein catabolism, followed in 30 min with 100 microCi [3H]leucine. At time intervals up to 3 hours after [3H]leucine injection, rats were killed, and plasma lipoproteins and, in some experiments, Golgi lipoproteins were isolated. Three hours after radioisotope injection, 52% of the total lipoprotein radioactivity was found in the plasma VLDL of hypercholesterolemic rats compared to 82% in chow-fed control rats. Twenty-four percent of the total lipoprotein radioactivity appeared in the plasma IDL fraction in hypercholesterolemic rats, while only 3% was found in the same fraction in control rats. After Triton, the time course of specific activities of the Golgi and plasma lipoproteins was consistent with Golgi VLDL and LDL being precursors to plasma VLDL and IDL, respectively. The time course of specific activities of the tetramethylurea-insoluble proteins of plasma and Golgi lipoproteins provided additional evidence in support of this relationship. Furthermore the composition of plasma VLDL and IDL after Triton injection resembled their hepatic Golgi counterparts. We conclude that the liver of the hypercholesterolemic rat synthesizes, assembles, and secretes a cholesteryl ester-enriched VLDL and a cholesteryl ester-rich, beta-migrating LDL. The former is a precursor to plasma VLDL while the latter is a precursor to plasma IDL.

Animals↗
PubMed1981

beta-Adrenergic induced synthesis and secretion of phosphatidylcholine by isolated pulmonary alveolar type II cells.

Rat pulmonary alveolar type II cells isolated by trypsinization and discontinuous density gradient ultracentrifugation were maintained in primary culture for 48 hours. The cultured type II cells responded to beta-adrenergic, but not cholinergic, agonists by an increase in the rate of synthesis and also secretion of 3H-phosphatidylcholine. The beta-adrenergic agonists, isoproterenol and terbutaline, 10 microM, caused a 1.7-fold increase in the rate of synthesis of 3H-phosphatidylcholine after a 4-hour incubation. At this time, there was also an increase in the cAMP content of the cultured cells. Terbutaline, 10 microM, caused a 4.9-fold increase in the rate of secretion of 3H-phosphatidylcholine after a 1-hour incubation. The beta-adrenergic effect on both synthesis and secretion by type II cells was blocked by propranolol. 8-Br-cAMP, 100 microM, but not 8-Br-cGMP, mimicked the beta-adrenergic effect on both synthesis and secretion of 3H-phosphatidylcholine. The increased rate of 3H-phosphatidylcholine induced by beta-adrenergic agonists was unaffected by colchicine. These data are consistent with the hypothesis that both synthesis and secretion of pulmonary surfactant are under adrenergic control operating through a beta-receptor and the adenylate cyclase system. These data also suggest that synthesis and secretion of pulmonary surfactant are independent processes. The possibility of other neural or hormonal mechanisms is not excluded.

Adrenergic beta-Agonists↗
PubMed1980

Electron paramagnetic resonance and saturation transfer electron paramagnetic resonance studies on erythrocytes from goats with and without heritable myotonia.

Erythrocytes from myotonic goats, an animal model of heritable myotonia, and normal goats were studied using electron paramagnetic resonance (EPR) and saturation transfer electron paramagnetic resonance (ST-EPR) spin labeling techniques. Three fatty acid spin labels with the nitroxide moiety at progressively greater distances from the carboxyl group were used to monitor different regions within the erythrocyte membrane. Since spin labels have been shown to induce hemolytic and morphologic alterations in erythrocytes, conditions for minimizing these alterations were first defined by hemolysis studies and scanning electron microscopy. Using these defined conditions for our studies we observed no significant differences in any of the EPR or ST-EPR parameters for normal and myotonic goat erythrocytes with any of the fatty acid spin labels used. Our results do not support the theory that myotonia is the result of a generalized membrane defect characterized by increased membrane fluidity as determined by fatty acid spin labels.

Animals↗
PubMed1980

Isolation and characterization of hepatic Golgi lipoproteins from hypercholesterolemic rats.

The feeding of cholesterol-rich diets alters the serum lipoproteins of a number of mammalian species. These lipoproteins are characterized by the presence of several classes of particles enriched in cholesteryl esters and apolipoprotein E (apo E). It was the aim of this study to determine whether one or more of these particles arises by de novo hepatic synthesis by characterizing nascent lipoproteins isolated from the hepatic Golgi apparatus of hypercholesterolemic rats. Characterization of these lipoproteins afforded the opportunity to assess morphologic, biochemical, and biophysical properties of newly synthesized lipoproteins before enzymatic alterations and apoprotein transfer known to occur after secretion into the plasma compartment. Golgi very low density lipoproteins (VLDL, d < 1.006 g/ml) from hypercholesterolemic rats contained nearly four times the total cholesterol mass found in control Golgi VLDL. They exhibited electrophoretic mobility intermediate between beta and pre-beta and were devoid of apo C. A second population of hepatic Golgi lipoproteins was isolated from hypercholesterolemic rats at 1.006--1.040 g/ml d. These low density lipoproteins were smaller than VLDL, displayed beta electrophoretic mobility, were enriched in cholesteryl esters, and contained apo E as well as apo B. The fatty acid composition of the core lipids of the nascent lipoproteins was found to reflect that of dietary triglyceride. The liver of the hypercholesterolemic rat thus plays an active role in dietary-induced hypercholesterolemia by synthesizing a modified VLDL and a low density lipoprotein resembling serum low density lipoprotein.

Animals↗
PubMed1979

The composition and calcium transport activity of the sarcoplasmic reticulum from goats with and without heritable myotonia.

Studies were conducted on purified sarcoplasmic reticulum isolated from myotonic goats, an animal model of heritable myotonia. When compared to sarcoplasmic reticulum from normal goats, fragmented sarcoplasmic reticulum from the myotonic goat had (1) increased levels of calcium, (2) increased rates of calcium uptake and efflux, (3) an increased sialic acid content, and (4) an increased content of saturated fatty acids. These differences support the concept of a structural and functional defect as a basis for the abnormal contraction-relaxation characteristics of myotonia.

Animals↗
PubMed1972

Role of plasma lipoproteins in cortisone-induced fat embolism.

The clinical syndrome of fat embolism can be a complication in patients who have suffered long-bone fracture, and has been associated with a number of conditions in which bone fracture is not a factor. The origin of embolic fat (bone marrow or depot fat versus plasma lipoproteins) has been debated. To test the hypothesis that alterations in the composition of plasma very-low-density lipoproteins (VLDL) could lead to their coalescence and subsequent impaction in pulmonary vasculature, New Zealand white rabbits were injected intramuscularly with 25 mg of cortisone twice a day for 2, 4, 6, 11 and 12 days. Blood samples were obtained from unanesthetized animals prior to the cortisone treatment and at sacrifice. Pulmonary fat embolism that was similar histologically to that found in the human patient with the clinical syndrome was produced in all rabbits treated for 4-12 days. After the fourth day, all animals were hyperlipidemic. There was a tenfold increase in plasma VLDL concentration and the mean particle diameter of the VLDL was increased from 620 A to 1016 A. The proportion of triglyceride (TG) was increased, protein (PR) and phospholipid (PL) were decreased and total cholesterol (TC) was unaltered (untreated controls: PR, 16.4%; TG, 58.5%; PL, 19.2%; TC, 6.7% and cortisone-treated: PR, 8.4%; TG, 75.1%; PL, 11%; TC, 6.4%). The lipid composition of pulmonary embolic fat from rabbits treated with cortisone for 6 or 11 days was TG, 81%; PL, 13% and TC, 6%. VLDL from similarly treated rabbits had a lipid composition of TG, 79%; PL, 14.5% and TC, 6.6%. The TC concentration of bone marrow and depot fat from animals treated with cortisone for 11 days was <1%, and the PL concentration was <2%. These data support the hypothesis that plasma lipoproteins, primarily the VLDL, when altered in size and composition can coalesce into globules of sufficient size to occlude peripheral capillaries.

Adipose Tissue↗
PubMed1970

Identity of very low density lipoprotein apoproteins of plasma and liver Golgi apparatus.

In the rat, very low density lipoproteins isolated from hepatocyte Golgi apparatus, liver perfusates, and whole plasma appear identical in many respects. With specific immunochemical techniques and polyacrylamide-gel electrophoresis it can be demonstrated that the very low density lipoproteins from all three sources contain the same major lipoprotein apoproteins.

Animals↗