Biomedical subjects

M L Garg

Publications and source records attributed to M L Garg.

At least 19 recordsLinked to original sources

PubMed1992

Essential fatty acid metabolism in cultured human airway epithelial cells.

To characterize essential fatty acid metabolism of human airway epithelium, we examined the capacity of epithelial cells to incorporate and desaturate/elongate 18:2(n - 6) and the turnover of phospholipid fatty acyl chains in these cells. Epithelial cells were cultured for 5-7 days and incubated with [1-14C]18:2(n - 6) (1 microCi, 100 nmol). The essential fatty acid profile of the cells was readily modified by 18:2(n - 6) supplementation to culture medium. After 4 h incubation, 32 +/- 5.6 nmol of [1-14C]18:2(n - 6) was incorporated into phospholipids (65 +/- 9.5%, of which 74% was incorporated into phosphatidylcholine (PC)) and neutral lipid (31 +/- 10%) per mg protein of cultured cells. 30 +/- 8% of [1-14C]18:2(n - 6) incorporated, was converted to homologous trienes, tetraenes and pentaenes, the major products being 20:3(n - 6) and 20:4(n - 6). The conversion of 18:2(n - 6) was time-dependent and donor age-related. A higher proportion of 20:3(n - 6) and 20:4(n - 6) was incorporated into phosphatidylinositol (PI) and phosphatidylethanolamine (PE). About 10-15% of total products formed from 18:2(n - 6) was released from membrane to culture medium. Both 20:4(n - 6) and 20:5(n - 3) inhibited 18:2(n - 6) incorporation and desaturation. Rate of incorporation of 18:2(n - 6) was more than either 18:1(n - 9) or 16:0. With pulse-chase studies, the half-life of 18:2(n - 6) in PC, PI and PE was estimated to be 5.5, 6.0 and 7.3 h, respectively. These data indicate active metabolism of essential fatty acids in human airway epithelial cells. This metabolism may play a key role in the regulation of membrane properties and function in these cells.

Carbon Radioisotopes↗

PubMed1992

Desaturation of linoleic acid in the small bowel is increased by short-term fasting and by dietary content of linoleic acid.

The rate of desaturation of linoleic acid (18:2(n - 6)) and level of arachidonic acid (20: 4(n - 6)) in mucosal microsomes from small intestine of rats fasted for 24 h or fed diets of different fatty acid composition was examined. Fasting or feeding a diet high in linoleic acid increased delta 6-desaturase activity, a rate-limiting enzyme in the arachidonic acid biosynthetic pathway in the jejunum. After fasting, delta 6-desaturase activity was also enhanced in the ileum. Feeding a diet rich in n - 3 fatty acids had no significant effect on delta 6-desaturase activity in jejunal or ileal mucosal microsomes. Following fasting, arachidonic acid content of microsomal total phospholipids increased in the jejunum with a concomitant decrease in linoleic acid content. Arachidonic acid and 18:2(n - 6) concentration remained unchanged in ileal microsomes after short-term food withdrawal. Feeding a diet containing n - 3 fatty acids lowered the content of 20:4(n - 6) and increased 20:5(n - 3) and 22:6(n - 3) levels in both jejunal and ileal microsomes. These data indicate that the level of 20:4(n - 6) and the biosynthesis of 20:4(n - 6) by desaturation-chain elongation of 18:2(n - 6) in the rat enterocyte responds rapidly to change in physiological conditions such as fasting and dietary fat composition.

Animals↗

PubMed1992

Addition of long-chain polyunsaturated fatty acids to formula for very low birth weight infants.

Thirty-four premature infants who were appropriate for gestational age and weighing less than 1500 g at birth were fed "preemie" SMA-24 formula, "preemie" SMA-24 formula manufactured to contain C20 and C22 omega 6 and omega 3 fatty acids (LCPE-SMA), or expressed milk (EBM). Blood samples were drawn from a small arm vein during the first week of life and after 28 days of feeding. The fatty acid content of plasma phospholipids was determined. Infants fed SMA-24 had a high content of 18:2 omega 6 in plasma phospholipids. Feeding LCPE-SMA normalized plasma phospholipid levels of C20 and C22 omega 6 and omega 3 fatty acids to be similar to levels of C20 and C22 omega 6 and omega 3 fatty acids found in infants fed EBM, and significantly higher than characteristic levels for infants fed SMA-24. Feeding LCPE-SMA or EBM results in a balanced incorporation of C20 and C22 omega 6 and omega 3 fatty acids into phospholipids derived from the liver or perhaps the small intestine.

Fatty Acids↗

PubMed1991

Effect of automobile exhaust on the distribution of trace elements and its modulation following Fe, Cu, and Zn supplementation.

The effect of automobile exhaust on the distribution of trace elements with special reference to Pb and its modulation following Cu, Zn, and Fe supplementation, in mouse organs, has been studied using Energy Dispersive X-ray Fluorescence technique. Seven elements, namely K, Fe, Cu, Zn, Br, Rb, and Pb, were detected in all the organs. The maximum concentration of Pb was found in lungs followed by that in liver and kidney. The effect of automobile exhaust was found to be significant on the concentrations of Fe and Pb; their concentrations were found to increase in all the organs. However, the concentrations of Cu and Zn were found to be decreased significantly in the liver. In the animals given Fe, Cu, or Zn supplementation along with motor exhaust, the percentage change in the concentration of Pb in lungs was decreased, and that of Fe was increased significantly. In kidney, no significant change was observed for the animals given Cu and Zn, whereas for animals given Fe, the level of Pb decreased significantly. In liver, the reduction in the level of Zn in the exhaust-exposed animals was made up and the level of Pb was reduced following Zn supplementation. These results clearly indicate that Fe and Zn play an important role in Pb metabolism and tend to lower the absorption of Pb. The effect of Fe is more pronounced than that of Zn, whereas the effect of Cu seems to be insignificant.

Administration, Inhalation↗

PubMed1991

Dietary fat: exogenous determination of membrane structure and cell function.

Evidence indicates that principal features of the membrane involve structural organization of lipids in the form of a bilayer with functional proteins either bound to the bilayer surface or inserted into the bilayer and interacting within specific domains in the lipid milieux. In homeotherms, intrinsic and extrinsic factors apparently form the basis for determination of membrane lipid composition and thus membrane physicochemical properties. Moreover, many intrinsic metabolic controls, such as fatty acid desaturation and phospholipid biosynthesis, may be attenuated by change in the nature of the extrinsic or dietary influence. This review will focus on the role of dietary fat as a determinant of subcellular structural constituents to illustrate that feeding nutritionally adequate diets differing in fatty acid composition can induce physiological transitions in membrane function involving the activity of enzymes responsible for synthesis of membrane constituents, hormone-activated functions and expression of activity in the cell nucleus.

Animals↗

PubMed1991

Primary care teaching physicians' losses of productivity and revenue at three ambulatory-care centers.

This study reports two years of basic data concerning University of Illinois clerkship students, their teaching faculty, and their patients at three community health centers. Students from four classes (1985, 1986, 1987, and 1988) were studied in 1985 and 1986. The faculty were family physicians, internists, and pediatricians who provided 20% of the undergraduate medical education for the last 30 months of a four-year curriculum. The study's goal was to develop estimates of the primary care teaching physicians' productivity, to compare them with the productivity of physicians not involved in teaching, and to provide estimates of revenue shortfalls that occurred for the physicians who were teaching. The estimated productivity of the teaching physicians, working 29 hours a week in ambulatory-care settings, was lower by 30-40% when they were teaching medical students than the productivity of nonteaching physicians regionally and nationally. The average patient-care revenue loss for a full-time-equivalent faculty member per full-time-equivalent student for 1985 was estimated to be $27,531 (regional comparison) or $21,143 (national comparison). The corresponding figures for 1986 were $24,294 and $21,525, respectively. The study's results should be useful to those who are planning to establish ambulatory-care delivery systems and also to directors of existing ambulatory-care delivery systems who may be contemplating accepting medical students.

Community Health Centers↗

PubMed1991

Fish oil-enriched diet is mucosal protective against acetic acid-induced colitis in rats.

Products of arachidonic acid metabolism are elevated in patients with inflammatory bowel disease and this elevation is correlated with disease activity. Eicosapentaenoic acid competes with arachidonic acid and alters eicosanoid biosynthesis. In this experiment, the possibility that eicosapentaenoic acid could be used in the treatment of inflammatory bowel disease was investigated by determining the effect of 6 weeks of a fish oil-supplemented diet, enriched in eicosapentaenoic acid, on colonic and ileal morphology, histology, and in vivo fluid absorption in rats with 4% acetic acid-induced colitis. The results of an eicosapentaenoic acid-enriched diet were compared with results of saturated and polyunsaturated fatty acid-enriched diets. In rats with misoprostol pretreated acetic acid-induced colitis, an eicosapentaenoic acid-enriched diet reversed net colonic fluid secretion to absorption and prevented macroscopic and histologic injury, compared with saturated and poly-unsaturated fatty acid-enriched diets, which did not. The fish oil mucosal protective effect occurred in the presence of a 30-fold enhancement of PGE2 synthesis. In rats with non-misoprostol pretreated acetic acid-induced colitis, an eicosapentaenoic acid-enriched diet returned ileal fluid absorption to control levels, as compared with saturated and polyunsaturated fatty acid-enriched diets, which did not. In conclusion, a fish oil (eicosapentaenoic acid)-enriched diet, but not a saturated- or a polyunsaturated-enriched diet, protected colonic and ileal net fluid absorption in an experimental model of inflammatory bowel disease.

Acetates↗

PubMed1990

Alteration of the lipid composition of rat testicular plasma membranes by dietary (n-3) fatty acids changes the responsiveness of Leydig cells and testosterone synthesis.

Experiments were conducted to assess whether changing dietary fat composition altered phospholipid composition of rat testicular plasma membranes in a manner that altered receptor-mediated action of luteinizing hormone (LH)/human chorionic gonadotropin (hCG). Weanling rats were fed diets that provided high or low cholesterol intakes and that were enriched with linseed oil, fish oil or beef tallow for 4 wk. Feeding diets high in (n-3) fatty acids decreased plasma and testicular plasma membrane 20:4(n-6) content. A marked reduction of the 22:5(n-6) content and an increase in the 22:6(n-3) content of testicular plasma membrane was found only in animals fed fish oil. A decrease in binding capacity of the gonadotropin (LH/hCG) receptor in the plasma membrane, with no change in receptor affinity, was observed for animals fed either linseed oil or fish oil diets. Dietary treatments that raised plasma membrane cholesterol content and the cholesterol to phospholipid ratio in the membrane were associated with increased binding capacity of the gonadotropin receptor. Feeding diets high in 18:3(n-3) vs. those high in fish oil altered receptor-mediated adenylate cyclase activity in a manner that depended on the level of dietary cholesterol. Feeding diets high in cholesterol or fish oil increased basal and LH-stimulated testosterone synthesis relative to that in animals fed the low cholesterol diet containing linseed oil. It is concluded that changing the fat composition of the diet alters the phospholipid composition of rat testicular plasma membranes and that this change in composition influences membrane-mediated unmasking of gonadotropin receptor-mediated action in testicular tissue.

Adenylyl Cyclases↗

PubMed1990

Intestinal microsomes: polyunsaturated fatty acid metabolism and regulation of enterocyte transport properties.

Recent evidence has suggested that transport of nutrients from the lumen to the interior of the gastrointestinal epithelium and exit of nutrients from the enterocyte to the circulation is governed by physicochemical properties of brush border and basolateral membranes, respectively. The main determinants of membrane properties are phospholipid, cholesterol, and fatty acyl chain composition (chain length and degree of unsaturation). Lipid synthesis occurs in enterocyte microsomes and the fine tuning of lipid composition is done at other subcellular sites by deacylation-reacylation or by changing the polar head group (e.g., by phosphatidylethanolamine methyltransferase). The present paper will focus on the mechanisms by which enterocyte membranes adapt functional properties in response to external stimuli. It is proposed that under the influence of internal or external stress, the enzymes of lipid metabolism in microsomes are modulated. These changes in lipid synthesis are reflected in other subcellular membranes, changing their physicochemical status and thus transport phenomena. One of the initial events appears to be alteration in desaturase enzyme activity. Our results suggest that desaturase activity and the fatty acyl profiles of the intestinal mucosal phospholipid rapidly respond to physiological conditions such as fasting and dietary fat treatment.

Animals↗

PubMed1990

Critical period programming of intestinal glucose transport via alterations in dietary fatty acid composition.

Intestinal adaptation occurs in response to physiological or pathological processes that include resection, aging, diabetes, radiation, lactation, chronic alcohol feeding, and feeding diets of varying lipid, protein, or carbohydrate composition. The mechanisms involved in the adaptive response include alterations in morphology, cell kinetics, digestive enzyme activity, transport, membrane lipid composition, and enzymes involved in lipid metabolism. This discussion will review the effect of aging and alterations in dietary fatty acid composition on the small intestine. In addition, it may be possible to program the intestinal response to aging by feeding diets of differing fatty acid composition during the critical period of weaning. Alterations in the ratio of polyunsaturated to saturated fatty acids in the diet modifies the age-associated changes in the intestinal uptake of glucose. The changes occur rapidly, progressively, and irreversibly, suggesting that the intestinal uptake of glucose is subject to critical period programming. The mechanism by which diet may modify the ability of the intestine to up- or down-regulate glucose transport requires further investigation.

Animals↗

PubMed1990

Interactions of saturated, n-6 and n-3 polyunsaturated fatty acids to modulate arachidonic acid metabolism.

Anti-thrombotic effects of omega-3 (n-3) fatty acids are believed to be due to their ability to reduce arachidonic acid levels. Therefore, weanling rats were fed n-3 acids in the form of linseed oil (18:3n-3) or fish oil (containing 20:5n-3 and 22:6n-3) in diets containing high levels of either saturated fatty acids (hydrogenated beef tallow) or high levels of linoleic acid (safflower oil) for 4 weeks. The effect of diet on the rate-limiting enzyme of arachidonic acid biosynthesis (delta 6-desaturase) and on the lipid composition of hepatic microsomal membrane was determined. Both linseed oil- or fish oil-containing diets inhibited conversion of linoleic acid to gamma-linolenic acid. Inhibition was greater with fish oil than with linseed oil, only when fed with saturated fat. delta 6-Desaturase activity was not affected when n-3 fatty acids were fed with high levels of n-6 fatty acids. Arachidonic acid content of serum lipids and hepatic microsomal phospholipids was lower when n-3 fatty acids were fed in combination with beef tallow but not when fed with safflower oil. Similarly, n-3 fatty acids (18:3n-3, 20:5n-3, 22:5n-3, and 22:6n-3) accumulated to a greater extent when n-3 fatty acids were fed with beef tallow than with safflower oil. These observations indicate that the efficacy of n-3 fatty acids in reducing arachidonic acid level is dependent on the linoleic acid to saturated fatty acid ratio of the diet consumed.

Animals↗

PubMed1989

Hypotriglyceridemic effect of dietary n - 3 fatty acids in rats fed low versus high levels of linoleic acid.

The effect of dietary alpha-linolenic acid (linseed oil) or eicosapentaenoic acid (fish oil) on serum and liver triacylglycerol levels in rats fed diets rich in saturated fatty acids (hydrogenated beef tallow) versus high in linoleic acid (safflower oil) was examined. Feeding fish oil with hydrogenated tallow lowered the serum triacylglycerol concentration while the combination of fish oil and safflower oil failed to do so. Inclusion of fish oil in the hydrogenated tallow diet lowered the triacylglycerol constant in level tissue whereas inclusion of linseed oil had no significant effect. Feeding of linseed oil or fish oil in the safflower oil diet resulted in lowering of the liver triacylglycerol levels. These results suggest that dietary fish oil may have greater hypotriglyceridemic effects in individuals/populations eating diets high in saturated fats compared with those consuming mainly polyunsaturated vegetable oils rich in n - 6 fatty acids.

Animals↗

PubMed1989

Omega-3 fatty acids increase the arachidonic acid content of liver cholesterol ester and plasma triacylglycerol fractions in the rat.

Recent studies have demonstrated that dietary fish oils rich in eicosapentaenoic acid (C20:5,omega 3) lower the content of arachidonic acid and its metabolites in plasma and tissue phospholipids. The present study examined the fatty acid composition of cholesterol ester and triacylglycerol fractions from plasma and livers of rats fed diets enriched with saturated fatty acids (beef tallow), alpha-linolenic acid (linseed oil) or eicosapentaenoic acid (fish oil). Feeding diets containing linseed oil or fish oil for 28 days increased arachidonic acid (C20:4,omega 6) levels in the cholesterol ester fraction of liver and in the triacylglycerol fraction of the plasma lipids. Plasma cholesterol esters were depleted of C20:4,omega 6 after feeding of the diet containing either linseed oil or fish oil. The changes in C20:4,omega 6 content cannot be explained by alterations in cholesterol ester or triacylglycerol pools of plasma and liver. These results suggest that the decrease in phospholipid C20:4,omega 6 content generally observed after fish oil consumption may be partly due to a shift of C20:4,omega 6 from phospholipid to the triacylglycerol and/or cholesterol ester pools in the same tissue. Triacylglycerols and cholesterol esters may therefore play a buffering role in the homeostatic maintenance of tissue phospholipid levels of arachidonic acid.

Animals↗

PubMed1989

Influence of dietary fat composition on intestinal absorption in the rat.

Omega-3 fatty acids influence the function of the intestinal brush border membrane. For example, the omega-3 fatty acid eicosapentaenoic acid (20:5 omega 3) has an antiabsorptive effect on jejunal uptake of glucose. This study was undertaken to determine whether the effect of feeding alpha-linolenic acid (18:3 omega 3) or EPA plus docosahexaenoic acid (22:6 omega 3) on intestinal absorption of nutrients was influenced by the major source of dietary lipid, hydrogenated beef tallow or safflower oil. The in vitro intestinal uptake of glucose, fatty acids and cholesterol was examined in rats fed isocaloric diets for 2 weeks: beef tallow, beef tallow + linolenic acid, beef tallow + eicosapentaenoic acid/docosahexaenoic acid, safflower oil, safflower oil + linolenic acid, or safflower oil + eicosapentaenoic acid/docosahexaenoic acid. Eicosapentaenoic acid/docosahexaenoic acid reduced jejunal uptake of 10 and 20 mM glucose only when fed with beef tallow, and not when fed with safflower oil. Linolenic acid had no effect on glucose uptake, regardless of whether it was fed with beef tallow or safflower oil. The jejunal uptake a long-chain fatty acids (18:0, 18:2 omega 6, 18:3 omega 3, 20:4 omega 6, 20:5 omega 3 and 22:6 omega 3) and cholesterol was lower in safflower oil than with beef tallow. When eicosapentaenoic acid/docosahexaenoic acid was given with beef tallow (but not with safflower oil), there was lower uptake of 18:0, 20:5 omega 3 and cholesterol. The demonstration of the inhibitory effect of linolenic acid or eicosapentaenoic acid/docosahexaenoic acid on cholesterol uptake required the feeding of a saturated fatty acid diet (beef tallow).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Fish oil prevents change in arachidonic acid and cholesterol content in rat caused by dietary cholesterol.

Rats were fed diets high in either saturated fat (beef tallow) or alpha-linolenic acid (linseed oil) or eicosapentaenoic and docosahexaenoic acids (fish oil) with or without 2% cholesterol supplementation. Consumption of linseed oil and fish oil diets for 28 days lowered arachidonic acid content of plasma, liver and heart phospholipids. Addition of 2% cholesterol to diets containing beef tallow or linseed oil lowered 20:4 omega 6 levels but failed to reduce 20:4 omega 6 levels when fed in combination with fish oil. Feeding omega 3 fatty acids lowered plasma cholesterol levels. Addition of 2% cholesterol to the beef tallow or linseed oil diet increased plasma cholesterol concentrations but not when fish oil was fed. Feeding the fish oil diet reduced the cholesterol content of liver, whereas feeding the linseed oil diet did not. Dietary cholesterol supplementation elevated the cholesterol concentration in liver in the order: linseed oil greater than beef tallow greater than fish oil (8.6-, 5.5-, 2.6-fold, respectively). Feeding fish oil and cholesterol apparently reduced 20:4 omega 6 levels in plasma and tissue lipids. Fish oil accentuates the 20:4 omega 6 lowering effect of dietary cholesterol and appears to prevent accumulation of cholesterol in plasma and tissue lipids under a high dietary load of cholesterol.

Animals↗

PubMed1989

Dietary saturated fat level alters the competition between alpha-linolenic and linoleic acid.

Male weanling rats were fed semi-synthetic diets high in saturated fat (beef tallow) vs high in linoleic acid (safflower oil) with or without high levels of alpha-linolenic acid (linseed oil) for a period of 28 days. The effect of feeding these diets on cholesterol content and fatty acid composition of serum and liver lipids was examined. Feeding linseed oil with beef tallow or safflower oil had no significant effect on serum levels of cholesterol. Serum cholesterol concentration was higher in animals fed the safflower oil diet than in animals fed the beef tallow diet without linseed oil. Feeding linseed oil lowered the cholesterol content in liver tissue for all dietary treatments tested. Consumption of linseed oil reduced the arachidonic acid content with concomitant increase in linoleic acid in serum and liver lipid fractions only when fed in combination with beef tallow, but not when fed with safflower oil. Similarly, omega 3 fatty acids (18:3 omega 3, 20:5 omega 3, 22:5 omega 3, 22:6 omega 3) replaced omega 6 fatty acids (20:4 omega 6, 22:4 omega 6, 22:5 omega 6) in serum and liver lipid fractions to a greater extent when linseed oil was fed with beef tallow than with safflower oil. The results suggest that the dietary ratio of linoleic acid to saturated fatty acids or of 18:3 omega 3 to 18:2 omega 6 may be important to determine the cholesterol and arachidonic acid lowering effect of dietary alpha-linolenic acid.

Animals↗

PubMed1989

Intestinal aspects of lipid absorption: in review.

The rapidly evolving field of lipid absorption is reviewed with the thrust of new knowledge focused on the interpendency of the luminal and cellular phases of absorption. To date little attention has been paid to factors that regulate the phospholipid biosynthesis in the enterocyte. The availability of 20:4 omega 6 may be the rate-limiting factor for phospholipid synthesis. The source of 20:4 omega 6 is unknown, whether it be synthesized de novo the enterocyte or entirely originating from degradation of bile phospholipid. It has been established that dietary fat can modulate the enterocyte membrane lipid composition and transport properties. Specified fats such as as fish oils rich in 20:5 omega 3 and 22:6 omega 3 have been implicated as protective against hypercholesterolemia. However, the effects of these dietary fats on the transport of nutrients across the enterocyte are not yet known, nor are the mechanisms responsible for the adaptive responses of the brush border identified.

Animals↗

PubMed1989

Fish oil prevents effect of high cholesterol diet on active intestinal transport of galactose.

We tested the hypothesis that diets containing fish oils prevent the effects of a high cholesterol diet on the morphology and nutrient uptake of the intestine. Isocaloric semisynthetic diets were supplemented with beef tallow or fish oil containing low or high amounts of cholesterol and were fed to growing female Wistar rats for 14 days, after which the in vitro jejunal and ileal uptake of glucose, galactose, long-chain fatty acids, and cholesterol was determined. Feeding cholesterol with beef tallow was associated with a 12% decrease in the jejunal mucosal surface area. Feeding fish oil decreased jejunal mucosal surface area by 24%, as compared with the beef tallow diet, but the reduction was increased to 42% when fish oil and cholesterol were fed together. Ileal surface area was unaffected by varying the major source of dietary lipid, or by adding cholesterol. Despite the effect of fish oil on the mucosal surface area, the jejunal and ileal uptake of saturated as well as unsaturated long-chain fatty acids and cholesterol was similar in the four diet groups. Cholesterol supplementation enhanced the jejunal uptake of high concentrations of galactose only when fed with beef tallow, i.e., feeding fish oil prevented the enhancing effect of cholesterol on galactose uptake observed when beef tallow was fed. Thus, (i) a fish oil diet prevents the enhancing effect of cholesterol on jejunal active transport of galactose, an effect not explained by the reduction in jejunal mucosal surface area observed with the fish oil diet; (ii) these dietary manipulations result in a clear dissociation of the morphological from the transport adaptation of the intestine; and (iii) substitution of fish oil for beef tallow as the major source of lipid in the diet prevents the influence of cholesterol on the active intestinal transport of galactose.

Animals↗