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Biomedical subjects

A Angel

Publications and source records attributed to A Angel.

At least 55 records · Page 3Linked to original sources
PubMed1990

Preparing and analyzing fractured archaeological fibers.

A technique was developed to prepare archaeological fiber cross sections for electron microscopic examination and x-ray analysis. Use of this new method allows chemical and morphological information to be obtained from the interior of a single fiber or yarn. Fibers are fractured while frozen and then freeze dried. Following mounting and carbon coating, fibers are examined by scanning and backscatter electron microscopy and then analyzed by using energy-dispersive spectrometry. Elemental distribution is mapped by using image-processing software. In this report, the described technique is employed in the examination of ancient fibers from three different long-term storage environments (moist buried, dry buried, museum stored). Data obtained by examining the interior of fibers such as these provide insight into the conditions of a fiber's growth, the treatments applied during the fiber's processing and use, and the conditions in which the fiber was stored.

Archaeology↗
PubMed1990

Dietary fish oils limit adipose tissue hypertrophy in rats.

Total body mass, fat pad mass, and fat cell size were examined after feeding rats diets containing 20% triglycerides from fish oil or lard. Although food consumption, weight gain, and fat balance on the two diets were similar, lard-fed rats had 77% more fat in perirenal fat pads and 51% more fat in epididymal fat pads compared with fish oil-fed rats. There was no difference between the two groups in fat cell number in each region; however, adipocytes were significantly smaller in fish oil-fed rats. Thus dietary fish oil appears to limit triglyceride accumulation in adipose tissue and thereby limit fat cell trophic growth.

Adipose Tissue↗
PubMed1990

Changes in dietary lipid saturation modify fatty acid composition and high-density-lipoprotein binding of adipocyte plasma membrane.

Binding of rat high-density lipoprotein (HDL) to adipocyte plasma membranes appears to be mediated by specific protein-recognition sites, but membrane lipids may also affect these interactions. To study the effect of dietary fatty acid composition on adipocyte-membrane phospholipid composition and HDL binding, male Wistar rats (250 +/- 10 g) were fed diets high in polyunsaturated (20% wt:wt sunflowerseed oil) or saturated and monounsaturated fatty acids (20% lard, by weight). Sunflower-oil vs lard feeding significantly increased the polyunsaturated fatty acid content of membrane diacylglycerophospholipids and the (22:0 and 24:0) content of long-chain fatty acids of sphingomyelin (p less than 0.05) from epididymal and perirenal adipocyte plasma membranes. Concomitant with these changes in membrane phospholipid composition, sunflower-oil vs lard treatment significantly increased the maximum binding capacity (Bmax) of 125I-labeled HDL2 (p less than 0.05). These results show that feeding polyunsaturated fatty acids enhanced HDL2 Bmax of adipocyte plasma membranes, possibly as a consequence of altering the fatty acid composition of membrane phospholipids.

Adipose Tissue↗
PubMed1990

Dietary polyunsaturated fatty acids enhance the uptake of high-density lipoprotein cholesterol ester by rat adipocytes.

Compared with diets high in saturated and monounsaturated fatty acids (20% lard by weight), diets high in polyunsaturated fatty acids (20% sunflower oil) alter the fatty acid composition of rat adipocyte plasma membranes and enhance HDL2 binding. We examined the effect of these two diets on HDL1 and HDL2 apolipoprotein and cholesterol uptake by adipocytes isolated from perirenal and epididymal adipose tissue of male Wistar rats. Consistent with selective cellular uptake. HDL esterified cholesterol uptake was 3-10-fold higher than predicted from HDL apolipoproteins associated with adipocytes. Dietary polyunsaturated fatty acids significantly enhanced apolipoprotein and esterified-cholesterol uptakes from HDL2 by perirenal adipocytes. This effect of dietary fat composition was adipose-region (perirenal greater than epididymal) and HDL-subfraction (HDL2 greater than HDL1) specific. Thus, diet-induced changes known to alter membrane phospholipid composition and increase HDL2 binding are also associated with enhanced HDL2-esterified-cholesterol uptake by adipocytes.

Adipose Tissue↗
PubMed1990

Alterations of "sleeping time" in the rat induced by drugs which modulate central monoaminergic systems.

The effects of adrenoceptor agonists and antagonists have been determined on "sleeping time" in the rat--that is, with the animal immobile and adopting a sleeping posture. Alterations in their gross behaviour patterns were assessed also. The specific alpha 2-adrenoceptor agonists (yohimbine, WY 26393, RX 781094 and RS 21361) decreased sleeping time, as did the beta-adrenoceptor agonist clenbuterol. The specific alpha 2-adrenoceptor agonist clonidine gave a large increase in sleeping time at doses in excess of 25 micrograms kg-1. The same effect was seen with the beta-antagonist propranolol and the specific beta 2-antagonist ICI 118551.

Adrenergic alpha-Agonists↗
PubMed1990

Selective uptake of cholesteryl ester from high density lipoproteins by plasma membranes of adipose tissue.

The interaction between high density lipoproteins (HDL) and adipose tissue is an important pathway for cholesterol and cholesteryl ester flux. In intact fat cells, a disproportionately greater net uptake of cholesteryl ester occurs subsequent to lipoprotein binding than would have been predicted from a consideration of holoparticle uptake alone. To characterize the early events in this process, cholesteryl hexadecyl ether, a nonmetabolizable, accumulative marker of cholesteryl ester, was incorporated into canine HDL2, and its uptake by omental adipocyte plasma membranes was measured in relation to the binding of HDL2, which in this animal species is enriched in apolipoprotein A-I and free of apolipoprotein E. The dose-response profile for HDL2 binding was consistent with a single lipoprotein binding site at all concentrations of HDL2, whereas uptake of cholesteryl ester from HDL2 was biphasic, suggesting a high affinity site at low HDL2 concentrations and a low affinity site at high lipoprotein concentrations. Pronase treatment stimulated binding twofold and this was accompanied by a parallel twofold stimulation of cholesteryl ester uptake. EDTA, on the other hand, reduced binding and uptake of cholesteryl ester by 20%, indicating partial dependence upon divalent cations. The proportion of HDL2 cholesteryl ester accumulated by plasma membranes relative to HDL2 protein bound was not altered by either pronase or EDTA, despite the fact that these agents had opposite effects upon binding. In dissociation studies, a portion of membrane-associated HDL2 did not equilibrate with exogenous HDL2 and a greater proportion of the cholesteryl ester failed to dissociate. A stepwise mechanism for cholesteryl ester uptake, involving (i) saturable, high affinity HDL2 binding to cell surface sites, (ii) vectoral, HDL2 concentration-dependent delivery of cholesteryl ester to the membrane, and (iii) cholesteryl ester sequestration into a nonexchangeable membrane compartment, appears to be independent of metabolic energy or cell processing.

Adipose Tissue↗
PubMed1990

Enhanced binding of phospholipase-A2-modified low density lipoprotein by human adipocytes.

Recognition of low density lipoprotein (LDL) by human adipocytes is not dependent on the classical LDL (apoprotein B-E) receptor. To assess whether LDL phospholipids have a role in adipocyte-LDL interactions, binding studies were carried out with human LDL modified with cobra venom phospholipase A2 (PLA2) and freshly isolated adipocytes and purified adipocyte plasma membranes prepared from surgical biopsies. LDL incubated with PLA2 showed increased monoacylphospholipid content, decreased diacylphospholipid content, and increased anodic migration on agarose gel electrophoresis. LDL cholesterol, triglyceride, and protein content remained unchanged. Typically, modification of 16 and 47% of LDL phospholipids enhanced specific binding of 125I-labelled LDL to plasma membranes progressively from 3.1 micrograms LDL bound/mg membrane protein (control) to 5.8 and 28.2 micrograms LDL bound/mg membrane protein, respectively. Nonspecific binding was not altered significantly. Excess unlabelled native LDL and high density lipoprotein (HDL3) effectively inhibited binding of PLA2-modified LDL. Freshly isolated adipocytes also showed enhanced binding and uptake of PLA2-modified LDL (0.1 vs. 0.9 micrograms LDL/10(6) cells x 2 h), control vs. modified). The results demonstrate that alterations of LDL phospholipids significantly enhance LDL binding and suggest a regulatory role for phospholipids in lipoprotein-cell interaction. Furthermore, the results support the view that human adipose tissue may be involved in the metabolism of modified lipoproteins, in vivo.

Adipose Tissue↗
PubMed1989

Transfer of free and esterified cholesterol from low-density lipoproteins and high-density lipoproteins to human adipocytes.

Cholesterol stored in human adipose tissue is derived from circulating lipoproteins. To delineate the cholesterol transport function of LDL and HDL, the movement of radiolabelled esterified cholesterol and free cholesterol from labelled LDL and HDL to human adipocytes was examined in the present study. LDL and HDL were enriched and labelled in esterified cholesterol with [14C]cholesterol by the action of plasma lipid transfer proteins and lecithin-cholesterol acyltransferase. Doubly labelled (3H,14C) LDL and HDL were prepared by exchanging free [3H]cholesterol into the 14C-labelled lipoproteins. 14C-labelled lipoprotein and 3H-labelled lipoprotein were also prepared separately and mixed to yield a mixed doubly labelled lipoprotein. Relative to the total amount added, proportionally more free than esterified cholesterol was transferred to the adipocytes upon incubation with any doubly labelled LDL and HDL. The calculated mass of free and esterified cholesterol transferred, however, varied with different labelled lipoproteins. 3H- and 14C-labelled LDL or HDL transferred 2-3-fold more esterified than free cholesterol while the reverse occurred with the mixed doubly labelled LDL or HDL. Thus, free cholesterol-depleted particles preferentially transferred cholesterol ester to the fat cells. In the presence of the homologous unlabelled native lipoprotein, the transfers of free and esterified cholesterol from labelled LDL or HDL were specifically inhibited. Selective transfer of esterified cholesterol relative to apoprotein was also observed when esterified cholesterol uptake from both LDL and HDL was assayed along with the binding of 125I-labelled lipoprotein. The cellular accumulation of cholesterol ether-labelled HDL (a non-hydrolyzable analogue of cholesterol ester) exceeded that of cholesterol ester consistent with significant hydrolysis of the latter physiological substrate. These results demonstrate preferential transfer of free cholesterol and esterified cholesterol over apoprotein for both LDL and HDL in human adipocytes. Furthermore, the data suggest that the cholesterol ester transport function of LDL and HDL can be enhanced by free cholesterol depletion and cholesterol ester enrichment of the particles, and affirms a role for adipose tissue in the metabolism of lipid-modified lipoproteins.

Adipose Tissue↗
PubMed1989

Hypothyroidism reduces HDL binding to rat liver cells.

The plasma clearance rate of high density lipoprotein is reduced in the hypothyroid rat. Because the liver is an important site of HDL-cholesterol catabolism, the present study was undertaken to investigate whether thyroid hormone deficiency affects binding of HDL to liver cells. Male Wistar rats were made hypothyroid by feeding propylthiouracil (0.1% w/w). Liver cells were isolated by in situ perfusion of the liver with a buffered collagenase solution. 125I-labelled rat HDL binding to isolated liver cells was carried out at low temperature on ice. For both control and hypothyroid rat liver cells, 125I-HDL binding was significantly inhibited by excess unlabelled rat HDL and also by human HDL3 and human LDL but was unaffected by the addition of 10 mM EDTA. From Scatchard analysis of dose-response studies, hypothyroid cells displayed a lower HDL binding capacity (P less than 0.01) and a higher binding affinity (P less than 0.025) compared to control cells. These results suggest that thyroid hormone affects the expression of the HDL binding site in liver cells which may contribute to the reduced HDL clearance in the hypothyroid animal.

Animals↗
PubMed1989

Proteolytic degradation of HDL1 on the fat cell surface is nutritionally regulated.

The importance of plasma HDL apolipoprotein concentration as a predictor of atherosclerotic risk is well recognized, yet the processes of HDL modification and degradation in various cells are not clearly understood. We examined the characteristics of HDL1 apolipoprotein degradation and cellular uptake by rat adipocytes and determined the effects of fasting on these processes. Epididymal and perirenal adipocytes were isolated from male Wistar rats (310 +/- 4 g) fed ad libidum and incubated with 5 micrograms of rat 125I-labeled HDL1 (d: 1.07-1.10 g/mL) mL-1 for 2 h at 37 degrees C. Cellular uptake of HDL1 was calculated as the trichloroacetic acid precipitable radioactivity associated with adipocytes following incubation. Intracellular and medium degradation of HDL1 were determined as trichloroacetic acid soluble 125I counts associated with cells and measured in the postincubation medium, respectively. Fifty to sixty percent of cellular uptake and degradation of HDL1 was inhibited by the addition of 25-fold excess unlabeled HDL. HDL1 degradation measured in the medium was 10- to 12-fold greater than cellular uptake of HDL1 apolipoproteins. Intracellular degradation of HDL1 was negligible. The presence of EDTA in the incubation medium reduced HDL1 degradation measured in the medium, but enhanced HDL1 cellular uptake. Conditioned medium separated from cells after 2 h of incubation at 37 degrees C in the absence of HDL and subsequently incubated with 125I-labeled HDL1 for an additional 2 h at 37 degrees C, degraded less than 5% of HDL compared with degradation in the presence of cells. These results suggest that rat adipocytes degrade, or modify, HDL1 particles, possibly by interactions with cell surface proteases.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1989

The effects of space travel on the nervous system.

The translation of man from terrestrial to an extra terrestrial environment is accompanied by an upset in the servo-control of movement engendered by the removal of the normal gravitational signal. Unfortunately the "natural" response of the nervous system, to ocular and vestibular confusion, is to cause varying degrees of sickness which can only be avoided by choice of suitable space travellers i.e., those who are least upset by gravitational chaos. This will remain so until much more is learned about the fundamental physiological mechanisms whereby man maintains a correct head/trunk, head/eye, trunk/limb and eye/limb positional coordination and why if these are upset man's natural response is to vomit.

Eye Movements↗
PubMed1989

Effect of massive obesity on low and high density lipoprotein binding to human adipocyte plasma membranes.

Adipose tissue is a major cholesterol storage organ in man, and turnover of this slowly exchangeable pool is dependent on low and high density lipoproteins which deliver and remove cholesterol from this site. To determine whether lipoprotein binding is altered in the obese state, we examined the binding of low density lipoprotein (LDL) and high density lipoprotein (HDL2 and HDL3) to purified adipocyte plasma membranes obtained from omental fat depots of massively obese patients (BMI greater than 40 kg/m2) and lean subjects. The specific binding and uptake of 125I-HDL2 and 125I-HDL3 were greater for obese than for lean adipocytes. Scatchard analysis of binding studies using purified adipocyte plasma membranes and varying amounts of labeled HDL2 or HDL3 demonstrated a higher binding affinity (lower Kd) for HDL2 and higher binding capacity (Bmax) value for both HDL2 and HDL3 in obese as compared to lean. 125I-LDL specific binding was somewhat lower in obese than in lean membranes but this difference was not statistically significant. The cholesterol content of isolated omental adipocytes expressed on a cellular basis or as the cholesterol/triglyceride ratio (mg chol/g of lipid) were similar in the obese and lean subjects. Furthermore, 125I-LDL, 125I-HDL2 or 125I-HDL3 specific binding did not correlate with cellular cholesterol content or with cholesterol/triglyceride ratio. These findings indicate that lipoprotein binding to adipocytes is altered in obesity and is characterized by up-regulation of HDL (particularly HDL2) binding with little change in LDL binding. We conclude from this study that obesity has a profound effect on the expression of HDL binding sites in human adipocytes and that LDL and HDL binding in fat cells are regulated differently.

Adipose Tissue↗
PubMed1989

Scanning electron microscopy of very small fat cells and mature fat cells in human obesity.

To determine the effect of obesity on the size distribution of fat cell populations in human adipose tissue, omental fat tissue biopsies were obtained from lean, moderately obese, and massively obese patients. The size distributions of adipocytes from lean and obese fat tissues examined by the scanning electron microscopic method were bimodal, consisting of populations of very small fat cells and mature fat cells, in contrast to collagenase-derived isolated cells that showed only the large mature fat cells. The very small fat cell population represented 21 to 26% of the total fat cell number in the lean and in both obese groups. In contrast, preparations of human fat cells isolated by the collagenase method systematically excluded the very small fat cells. In massive obesity, both cell populations participated in the hyperplastic growth but only the larger mature fat cells increased in size, implying that these two cell populations differ in their physiological role.

Adipose Tissue↗
PubMed1988

Composition, morphology and distribution of high-density lipoproteins in plasma and peripheral lymph: effect of feeding cholesterol and saturated fat.

In euthyroid dogs fed a diet rich in cholesterol and saturated fat, the cholesterol concentration in both plasma and peripheral lymph increased progressively with the appearance of HDLc (d 1.006-1.063). This HDLc fraction was heterogeneous and could be separated into 'slow' and 'fast' migrating fractions by Pevikon block electrophoresis. On SDS-polyacrylamide gel electrophoresis, plasma 'slow' HDLc was appreciably enriched in apolipoprotein (apo) E, while plasma and lymph 'fast' HDLc were apo E-poor. In contrast, no apo E was visible in lymph 'slow' HDLc in either plasma or lymph HDL2 fractions (d 1.087-1.21). The interstitial HDL fractions containing apo A-IV ('fast' HDLc and HDL2) were also rich in free cholesterol, implying that apo A-IV-containing particles are involved in reverse cholesterol transport. Plasma and peripheral lymph HDL2 and 'fast' HDLc cholesterol/protein ratios were not different, whereas lymph 'slow' HDLc was 24% that of plasma, indicating that interstitial 'slow' HDLc was poor in cholesterol compared to plasma. This marked reduction in lymph 'slow' HDLc cholesterol suggests that this particle was either selectively retarded from egress by the endothelial barrier, or that interstitial 'slow' HDLc represents a depleted particle involved in the delivery of cholesterol to peripheral tissues. These findings taken together support the hypothesis that interstitial 'slow' HDLc may represent a particle involved in cholesterol ester delivery, in contrast with HDL2 and 'fast' HDLc, which could serve as an efflux acceptor of tissue free cholesterol. This study demonstrates significant heterogeneity of interstitial peripheral lymph lipoproteins compared to plasma lipoproteins, and indicates selective distribution of these particles in the extravascular space.

Animals↗
PubMed1988

Weight loss in massive obesity: reciprocal changes in plasma HDL cholesterol and HDL binding to human adipocyte plasma membranes.

Human obesity is frequently associated with elevated plasma triglyceride and cholesterol concentrations and reduced high density lipoprotein (HDL) cholesterol, abnormalities that commonly revert to normal levels with weight loss. This study was undertaken to examine possible mechanism(s) associated with the changes in plasma HDL cholesterol concentrations in massively obese patients after weight loss. Ten massively obese patients (two men and eight women, age = 37.8 +/- 2.4 years) were studied before, during, and after 1 year of weight loss and weight maintenance following gastric stapling. Total cholesterol and low density lipoprotein cholesterol were within the normal range for sex and age before weight loss and did not change significantly during or after weight reduction. In the females, HDL cholesterol concentrations increased from 0.96 +/- 0.06 mmol/L to 1.23 +/- 0.3 mmol/L (mean +/- SEM, n = 8, P less than .05) with weight reduction. In the two men, plasma HDL cholesterol concentrations were, respectively, 1.22 and 0.65 mmol/L before and 1.23 and 0.98 mmol/L after weight loss. Specific binding of 125I-HDL2 and 125I-HDL3 to purified plasma membranes was determined using abdominal and omental fat depot before and after weight loss in six of the ten obese patients. An average reduction of 30% to 40% in 125I-HDL2 and 125I-HDL3 binding capacity to these membranes occurred after weight loss. Furthermore, a positive correlation (r = .65, n = 10, P less than .05) was observed between plasma HDL cholesterol and triglyceride concentrations before weight loss but not after weight loss (r = .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1988

Characterization of high-density lipoprotein binding to rat adipocytes and adipocyte plasma membranes.

The interaction of high-density lipoproteins (HDL) with adipocytes is important in the regulation of cellular cholesterol flux. To study the mechanisms of HDL binding and cellular processing, we incubated adipocytes isolated from epididymal and perirenal adipose tissue of male Wistar rats (300 g) with HDL1 (1.07-1.10 g/mL) and HDL2 (1.10-1.14 g/mL) fractions separated from rat plasma by gradient ultracentrifugation. Freshly isolated adipocytes were incubated with 125I-labeled HDL for 2 h at 37 degrees C to determine cell-associated uptake and degradation. Adipocytes from both fat regions showed significant cell-associated HDL1 and HDL2 uptake and very high medium degradation (2- to 6-fold higher than uptake). To assess 125I-labeled HDL binding independent of cellular metabolism, we purified adipocyte plasma membranes from isolated adipocytes and used them in binding assays. Binding of HDL1 and HDL2 in the membrane system was 85-95% specific, sensitive to high NaCl concentrations, and abolished by pronase treatment. In contrast to HDL2 binding, the maximum HDL1 binding to perirenal plasma membranes was significantly higher than its binding to epididymal membranes (7.2 +/- 1.3 vs. 4.4 +/- 0.2 micrograms/mg, n = 6, p less than 0.05). This increment in HDL1 binding to perirenal membranes represented an EDTA- sensitive, calcium-dependent component. These results indicate that HDL binding to adipocyte plasma membranes depends on both adipose tissue region and HDL subtype. The membrane binding characteristics, taken together with the cellular uptake results, suggest that adipocytes bind and metabolize HDL and that this interaction may involve a protein receptor.

Adipose Tissue↗