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J M Dietschy

Publications and source records attributed to J M Dietschy.

At least 91 records · Page 5Linked to original sources
PubMed1983

Synthesis and coenzyme A-dependent esterification of cholesterol in rat intestinal epithelium. Differences in cellular localization and mechanisms of regulation.

The current studies were undertaken to characterize the localization and regulation of cholesterol synthesis and acyl-CoA:cholesterol acyltransferase activity in rat intestinal crypt and villus cells. Both parameters were determined in groups of animals with widely varying sterol fluxes across the intestinal mucosa. In animals on control diet the rates of cholesterol synthesis, measured by the incorporation of [3H]water per mg of protein, were similar along the villus/crypt axis in the jejunum, whereas in the ileum, villus cells were significantly more active than crypt cells. In both areas, however, the majority of total synthetic activity was found in cells from the crypts and lower villi. In contrast, the highest specific and total acyl-CoA:cholesterol acyltransferase activity was recovered in the villus cells of the jejunum and ileum. Dietary cholesterol did not affect sterol synthesis in any of the cell fractions but increased acyl-CoA:cholesterol acyltransferase activity approximately 2-fold in jejunal cell fractions. Inhibition of cholesterol absorption or sequestration of intestinal bile acids stimulated sterol synthetic activity up to 7-fold, and this occurred mainly in the lower villus and crypt cells in both jejunum and ileum. An increased demand for lipoprotein cholesterol, generated by triglyceride feeding, similarly was associated with enhanced synthetic rates. However, unlike cholesterol feeding, these manipulations did not increase acyl-CoA:cholesterol acyltransferase activity in any of the villus cell fractions. These studies suggest, therefore, that the intracellular pools of cholesterol that regulate the rate of cholesterol synthesis and the rate of cholesterol esterification are functionally distinct.

Animals↗
PubMed1983

Dissociation of hepatic cholesterol synthesis from hepatic low-density lipoprotein uptake and biliary cholesterol saturation in female and male hamsters of different ages.

These studies were carried out in order to examine the relationship between the rate of uptake of low-density lipoproteins (LDL) by the liver and the rates of hepatic and extrahepatic cholesterol synthesis and biliary cholesterol content. Female hamsters fed a regular chow diet manifested a rate of hepatic sterol synthesis that was several-fold higher than that in age-matched males maintained on the same diet. Synthesis in the small intestine did not show a corresponding sex difference, but the overall rate in the remaining tissues of the carcass was significantly lower in the females than in the males. Thus, although the proportion of newly synthesized sterol produced by the liver was substantially greater in the females, this was balanced by a smaller contribution from the extrahepatic compartment so that whole-body sterol synthesis was similar in the females and males. Sterol synthesis in the whole animal declined markedly with age in both the females and males, and this was due principally to a reduction in extrahepatic synthesis. Despite the higher rate of hepatic synthesis in females, the rate of uptake of [14C]sucrose-labeled, homologous LDL by the liver was similar in females and males. In males, the adrenal gland transported the labeled LDL at a much higher rate than in females, but in the other extrahepatic tissues the rate of LDL uptake was similar in both groups. The level of cholesterol carried in the various plasma lipoprotein fractions and the relative cholesterol content of gallbladder bile were also similar in females and males. Thus, in this experimental model, the rate of LDL transport by the liver and extrahepatic tissues, the amount of cholesterol carried in plasma lipoproteins and the degree of biliary cholesterol saturation were not directly related to the rates of endogenous hepatic and extrahepatic sterol synthesis.

Aging↗
PubMed1983

In vivo modulation of rat liver acyl-coenzyme A:cholesterol acyltransferase by phosphorylation and substrate supply.

Rats were infused intravenously with a bolus of mevalonolactone or cholesterol-rich chylomicron and microsomes prepared from the livers at times up to 2 h after the infusion. Acyl-CoA cholesterol acyltransferase (ACAT) activity was measured in the microsomes under conditions that define the activity state of the enzyme which recent evidence suggests may depend on the degree of phosphorylation of the enzyme. ACAT activity was increased by both treatments. Some of the observed increase could be attributed to an increase in the supply of substrate cholesterol to the enzyme. The remaining change in activity was consistent with a change in the activity state of ACAT occurring in vivo in response to the influx of cholesterol to the enzyme.

Acyltransferases↗
PubMed1983

Dual modulation of hepatic and intestinal acyl-CoA: cholesterol acyltransferase activity by (de-)phosphorylation and substrate supply in vitro.

Acyl-CoA: cholesterol acyltransferase (ACAT) activity in microsomes from rat liver and rat intestinal epithelial cells was increased by incubation of the microsomes with the 100 000 x g supernatant fraction in the presence of ATP/MgCl2 and NaF. The measured activity was further increased by including cholesterol-rich liposomes in the preincubation. The ACAT activity in rat liver microsomes could be inhibited by preincubation in the presence of 100 000 x g supernatant and MgCl2 and microsomes preactivated by ATP/MgCl2 could also be inhibited in this way. The results suggest that ACAT activity in vitro is modulated by substrate supply and also reversibly by an ATP-dependent process which may be protein phosphorylation.

Acyltransferases↗
PubMed1983

Rates of receptor-dependent and -independent low density lipoprotein uptake in the hamster.

By using a constant infusion technique in the hamster, rates of uptake of [14C]sucrose-labeled hamster low density lipoprotein (hamLDL) and methylated hamster LDL (MehamLDL) were directly measured in 15 tissues. From these measurements the magnitude of LDL receptor-dependent and receptor-independent lipoprotein transport was calculated. The whole-animal clearance of hamLDL equaled 547 microliters/hr per 100 g of body weight. LDL clearance per g of tissue was highest in the liver (114 microliters/hr per g), ovary (43), spleen (36), adrenal gland (29), and intestine (24) and was lowest in fat (0.75), brain (0.35), and muscle (0.26). When adjusted for organ weight, the sum of the absolute clearance rates in all of the tissues examined equaled the rate of whole-animal LDL turnover. Liver accounted for 73%, and the jejunum and ileum combined accounted for 7% of whole-animal clearance. The 12 other tissues each accounted for only a minor portion of LDL clearance. Rates of uptake of Me-hamLDL were much less in many tissues and accounted for only 6-12% of the uptake of LDL in the liver, ovary, adrenal gland, lung, and kidney. However, this receptor-independent uptake was quantitatively more important in the intestine (44%) and spleen (72%) and accounted for essentially all LDL uptake in organs such as muscle, skin, and brain. Thus, in the hamster, most LDL is taken up and degraded by the liver. This uptake process is greater than 90% mediated by the LDL receptor and manifests saturation kinetics. Finally, cholestyramine feeding increases receptor-mediated LDL transport in the liver but in no other tissue studied.

Adrenal Glands↗
PubMed1983

Cholesterol synthesis and low density lipoprotein uptake are regulated independently in rat small intestinal epithelium.

We have compared the rates of low density lipoprotein (LDL) uptake and cholesterol synthesis in the rat intestine. By using a constant infusion technique, total and receptor-independent uptake was determined with homologous rat LDL (rLDL) and methylated human LDL (Me-hLDL), respectively. The absolute rates of sterol synthesis were measured with [1-(14) C]-octanoate and [3H]water. The rates of rLDL uptake in whole gut segments were similar along the length of the small intestine, whereas the rates of sterol synthesis varied over a 5-fold range and were highest in the duodenum and distal ileum. When the mucosal epithelium was fractionated along the villus/crypt axis, both rLDL and Me-hLDL clearance by the enterocytes increased approximately 3-fold in going from the upper villus to the crypt cell fractions, in both jejunum and ileum. In both the whole gut segments and isolated cells, approximately 60% of LDL uptake was receptor dependent. When the rates of rLDL cholesterol uptake were calculated and related to the absolute rates of sterol synthesis in the same cell fractions in vivo, both processes were found to be distributed similarly along the villus/crypt axis. Furthermore, the majority of mucosal cholesterol (64-86%) was derived from local synthesis rather than from rLDL uptake at all locations along the intestinal villus. Finally, when sterol synthesis in the epithelial cells was varied up to 7-fold by feeding cholesterol, triglyceride, cholestyramine, or surfomer, rLDL uptake was essentially unchanged. Thus, in intestinal epithelial cells in vivo, the rate of LDL uptake was constant under circumstances in which changing needs for cellular cholesterol were met by changes in the rates of sterol synthesis.

Animals↗
PubMed1983

Cholesterol synthesis in vivo and in vitro in the WHHL rabbit, an animal with defective low density lipoprotein receptors.

These studies were undertaken to measure rates of synthesis of digitonin-precipitable sterols in vivo and in vitro in control rabbits (New Zealand (NZ) control) and in homozygous Watanabe heritable hyperlipidemic rabbits (WHHL) that lack receptors for low density lipoproteins (LDL). The plasma cholesterol concentration in NZ control fetuses equaled 79 mg/dl, rose to 315 mg/dl 12 days after birth, and fell to 80 mg/dl in young adult animals. At these same ages, cholesterol concentrations in the WHHL animals equal 315, 625, and 715 mg/dl, respectively. The rate of whole animal sterol synthesis in vivo, expressed as the mumol of [3H]water incorporated into sterols per hr per kg of body weight, was lower in the WHHL animals than in the NZ controls both in the fetuses (108 vs 176) and in the adult animals (48 vs 66). In adult NZ controls the content of newly synthesized sterols (rate of sterol synthesis) per g of tissue was highest in the liver (538 nmol/g per hr), adrenal gland (438), small bowel (371), and ovary (225) while lower rates of synthesis were found in 15 other tissues. In the WHHL rabbits a higher content of [3H]sterols was found only in the adrenal gland (2,215) while synthesis was suppressed in the liver (310), colon, lung, and kidney, and was unchanged in the remaining organs. These findings were confirmed by measurements of rates of sterol synthesis in the same tissues in vitro. When whole organ weight was taken into consideration, the tissues that were the major contributors to whole body sterol synthesis in both types of rabbits were liver, small bowel, skin, and carcass. However, it was the lower rate of synthesis in the liver of the WHHL animals that alone accounted for the lower rate of whole animal sterol synthesis seen in these rabbits. These studies demonstrate that in WHHL animals that lack LDL receptors and that have very high levels of circulating LDL cholesterol, the rate of cholesterol synthesis in nearly all tissues is normal but in the liver is significantly suppressed. Only the adrenal gland manifested enhanced synthesis. Such findings suggest that in the WHHL rabbit where LDL receptor activity is reduced and plasma LDL levels rise, mechanisms other than receptor-mediated LDL uptake may act to deliver cholesterol to the cells of the various organs and to the liver.

Adrenal Glands↗
PubMed1983

Absolute rates of cholesterol synthesis in rat intestine in vitro and in vivo: a comparison of different substrates in slices and isolated cells.

In an effort to localize small intestinal sterol synthesis both along the length of the intestine and along the villus-crypt axis, we defined the optimal conditions to measure absolute rates of digitonin-precipitable sterol (DPS) synthesis in whole intestinal slices and in isolated epithelial cells. When [1-(14)C]acetate and [1-(14)C]octanoate were compared in midgut slices, [1-(14)C]octanoate was preferentially metabolized to CO(2) and DPS. Because of its rapid intramitochondrial degradation, [1-(14)C]octanoate effectively swamped-out other sources of acetyl CoA (C(2)) and achieved rates of C(2) flux into DPS virtually identical to the absolute rates determined with [(3)H]water. On the other hand, unlabeled acetate decreased the apparent C(2) flux from [1-(14)C]octanoate into DPS, but not into CO(2), in a dose-dependent fashion up to 8 mM. Under comparable incubation conditions, intestinal epithelial cells isolated by the EDTA chelation technique differed from slices in several respects. First, DPS synthesis from the various substrates was proportional to time only for 30 min compared to 90 min in slices. Second, the preferred (14)C-labeled substrate for DPS and CO(2) synthesis was acetate rather than octanoate. Third, neither of the (14)C-labeled substrates achieved the rates of synthesis found with [(3)H]water. Fourth, sterol synthesis from any of the substrates was essentially zero in the absence of glucose in the incubation medium. When the optimal rates of sterol synthesis in vitro were estimated using [(3)H]water in villus and crypt cell fractions of the jejunum and ileum, all ileal fractions were more active. However, ileal villus cells exceeded the jejunal villus cells by 5.2-fold in their capacity to incorporate [(3)H]water into DPS, whereas the crypt cell fractions differed by only 1.4-fold. The majority of the sterol synthetic capacity resided in the lower villus region in both the proximal and distal intestine and the crypts accounted for about 30% and 14%, respectively, of the total found in the jejunum and ileum. A similar distribution pattern along both the vertical and horizontal axes of the intestine was found after [(3)H]water administration in vivo, although under these conditions the proportion recovered in the crypts increased to 38% and 31%, respectively, of the total [(3)H]DPS found in the jejunum and ileum. These studies demonstrate that [(3)H]water yields optimal rates of sterol synthesis both in intestinal slices and in isolated epithelial cells and is incorporated into DPS mainly in cells of the lower villus and crypt region both in vitro and in vivo.-Stange, E. F., and J. M. Dietschy. Absolute rates of cholesterol synthesis in rat intestine in vitro and in vivo: a comparison of different substrates in slices and isolated cells.

Acetates↗
PubMed1983

Sterol synthesis in vivo in 18 tissues of the squirrel monkey, guinea pig, rabbit, hamster, and rat.

This study was undertaken to measure and compare the rates at which digitonin-precipitable sterols (DPS) were synthesized in vivo in the major organs of five different animal species. These rates were assessed by measuring the velocity at which [3H]water was incorporated into DPS in the intact animal. The animals used were chosen to include species that carried most of their plasma cholesterol either predominantly in high (rat, hamster) or low (guinea pig) density lipoproteins (HDL and LDL, respectively) or more evenly distributed between the LDL and HDL fractions (monkey and rabbit). Whole animal sterol synthesis was much higher in the rat (16.1 mumol/hr) than in the other four species (2.9-4.6 mumol/hr) when normalized to a constant body weight of 100 g. This uniquely high rate of sterol synthesis could be attributed predominantly to an extremely high rate of incorporation of [3H]water into DPS by the liver of the rat. When expressed per g of tissue, the highest content of newly synthesized sterol in all species was found in tissues such as adrenal gland, ovary, and gastrointestinal tract. However, the content of [3H]DPS in the liver varied markedly from a high of 2279 nmol/hr per g in the rat to a low of only 109 nmol/hr per g in the guinea pig. Consequently, when expressed as a percentage of total body synthesis, the whole liver of the rat contained 51% of the [3H]DPS while this figure was much lower in the monkey (40%), hamster (27%), rabbit (18%), and guinea pig (16%). Thus, in all species except the rat, the major sites for sterol synthesis appeared to be the gastrointestinal tract, carcass (predominantly the muscle), and skin. In addition, even though the content of newly synthesized sterol per g of adrenal gland was higher than in nearly any other tissue in all of the species examined, it was further demonstrated that in the rat most of this [3H]DPS was derived from the blood (and, therefore, ultimately from the liver) whereas in the other species it was largely synthesized locally within the gland. Thus, these studies demonstrated that in many species the liver is quantitatively far less important as a site for sterol synthesis than previously believed and, as a correlate of this, most sterol utilized by extrahepatic tissues is largely synthesized locally within those tissues.

Animals↗
PubMed1983

Alteration of the degree of biliary cholesterol saturation in the hamster and rat by manipulation of the pools of preformed and newly synthesized cholesterol.

Our studies compared the effects of changing the availability of newly synthesized and preformed cholesterol by various dietary manipulations on biliary cholesterol secretion in the hamster and rat. In hamsters fed a plain pelleted diet, only 2%-5% of biliary cholesterol was derived directly from newly synthesized sterol. Cholestyramine feeding, through a stimulation of hepatic sterol synthesis, increased this fraction fivefold but did not change total biliary cholesterol output. The relative cholesterol content increased significantly due to a reduction in bile acid and phospholipid output. In contrast, biliary cholesterol output was increased several-fold in hamsters fed a fat-free diet. These animals also manifested a pronounced increase in whole-body sterol synthesis, this being due principally to an increase in hepatic sterol synthesis. Although this resulted in the transport of much more newly synthesized cholesterol directly into bile, this did not account for the disproportionately high rate of biliary cholesterol output. Such excess sterol was derived predominantly from a preformed source. Unlike hamsters, rats fed the fat-free diet manifested a marked reduction in hepatic and whole-body sterol synthesis, bile acid pool size, and bile acid and cholesterol output in bile. These studies demonstrate that when hepatic cholesterol synthesis increases in response to a need for more sterol in the body, a greater proportion of biliary cholesterol is derived directly from newly synthesized sterol, but total biliary cholesterol output is unchanged. In contrast, when more cholesterol is synthesized than is needed to maintain cholesterol balance, biliary cholesterol output may increase. Such excess biliary sterol is derived predominantly from a preformed source rather than from the transport of newly synthesized sterol directly across the canalicular membrane.

Animals↗
PubMed1982

Correlation of low and high density lipoprotein binding in vivo with rates of lipoprotein degradation in the rat. A comparison of lipoproteins of rat and human origin.

These studies were done in the rat to correlate the ability of low and high density lipoproteins of rat (rLDL and rHDL) and human (hLDL and hHDL) origin to bind in vivo to specific tissues with the rates at which these same lipoprotein fractions were cleared from the circulation. The adrenal gland and liver manifested the greatest amounts of rLDL binding in vivo, but activity also was found in spleen, lung, kidney, ovary, and intestine. In contrast, little or no such binding was found utilizing either methyl-rLDL or hLDL. rHDL containing E apoprotein bound to the same group of tissues although in lesser amounts, except in the case of ovary and adrenal gland which bound disproportionately greater amounts of rHDL than rLDL. In keeping with these marked differences in tissue binding, the clearance of rLDL from the plasma equaled 847 +/- 36 microliters/h/100 g of rat while that of methyl-rLDL and hLDL was only 368 +/- 8 and 363 +/- 11 microliters/h/100 g of rat, respectively. When the steady state plasma level of rLDL was raised 2.5-fold, the clearance decreased slightly to 705 +/- 20 microliters/h/100 g of rat. The clearance of hLDL remained constant, however, at about 350 microliters/h/100 g of rat even when the plasma hLDL level was raised to very high values. The clearance of rHDL and hHDL equaled 644 +/- 16 and 408 +/- 13 microliters/h/100 g of rat, respectively, reflecting the more similar rate of binding of rHDL and hHDL to the tissues of the rat. Rates of whole animal sterol synthesis were lowered from 28 mumol/h to 8.8 mumol/h or 13 mumol/h by fasting and cholesterol feeding, respectively, and stimulated to 71 mumol/h by cholestyramine treatment. Under these same conditions, hepatic cholesterol synthesis could be lowered from the normal rate of 15 mumol/h to 4.2 mumol/h and raised to 50 mumol/h. None of these treatments, however, affected the plasma clearance of rLDL and rHDL. In contrast, treatment with ethinyl estradiol increased by 3-fold both the hepatic binding and the whole animal plasma clearance of rLDL. Following resection of approximately two-thirds of the liver under carefully controlled metabolic conditions, there was no change in the rate of hepatic cholesterol synthesis or rLDL binding in the remaining liver, but the clearance of chylomicrons, rLDL, and rHDL diminished by 67%, 26%, and 17%, respectively, suggesting that in the rat the liver was responsible for the degradation of approximately 97%, 39%, and 27%, respectively, of these lipoprotein fractions.

Animals↗
PubMed1982

Relative rates of sterol synthesis in the liver and various extrahepatic tissues of normal and cholesterol-fed rabbits. Relationship to plasma lipoprotein and tissue cholesterol levels.

The relative rates of sterol synthesis in the liver and ten extrahepatic tissues of normal and cholesterol-fed rabbits were determined by measuring the rates of incorporation of [1-14C]octanoate into digitonin-precipitable sterols by tissue slices. In normal rabbits the rate of sterol synthesis in the liver was very low compared to that in several extrahepatic tissues, particularly the small intestine. The rate of synthesis in the small intestine showed marked regional variation, with the highest rate occurring in the section proximal to the entry of the common bile duct and the lowest rate in the mid-sections of the intestine. The regional differences in intestinal sterol synthesis correlated inversely with the cholesteryl ester content of the tissue. Rabbits fed the cholesterol diet developed marked hypercholesterolemia, with much of the additional cholesterol appearing in the VLDL and LDL fractions. The cholesteryl ester content of the liver, small intestine and various other extrahepatic tissues increased significantly. Coincident with these changes was a marked suppression of sterol synthesis, not only in the liver, but also in the small intestine, adrenal gland, kidney, lung, spleen and ovary. Thus, the rabbit, like the guinea pig, normally exhibits a very low rate of hepatic sterol synthesis compared to that found in other species such as the rat, squirrel monkey and baboon and, furthermore, manifests feedback inhibition of both hepatic and extrahepatic sterol synthesis when dietary cholesterol intake is increased. This general suppression of synthesis correlates with an accumulation of cholesteryl ester in the tissues which, in turn, presumably is related to the uptake of lipoprotein cholesterol from the hypercholesterolemic plasma that develops under such dietary conditions.

Adrenal Glands↗
PubMed1982

Biological activity, lipoprotein-binding behavior, and in vivo disposition of extracted and native forms of Salmonella typhimurium lipopolysaccharides.

Although phenol-extracted gram-negative bacterial lipopolysaccharides (LPS) have been used to study the properties of endotoxins for many years, nothing is known about the behavior of native (unextracted) LPS in vivo. Accordingly, we have compared extracted and native forms of LPS with regard to their biological activity, their ability to bind to plasma high density lipoproteins (HDL), and their fate after intravenous injection into rats. The LPS of Salmonella typhimurium G-30 were labeled with [(3)H]galactose, and whole bacteria, bacterial outer membranes, outer membrane fragments (harvested from the bacterial culture supernatant), and phenol extracts of the bacteria were prepared. After defining the LPS, phospholipid, and protein composition of these preparations, we compared the activity of the LPS in phenol extracts and membrane fragments in two assays. In both the limulus lysate assay and the rabbit pyrogen test, the LPS in phenol extracts were slightly more potent than the LPS in membrane fragments. We next studied the ability of the LPS in each preparation to bind to rat lipoproteins in vitro, and each preparation was then injected intravenously into rats for measurements of LPS-HDL binding and tissue uptake in vivo. Two patterns of lipoprotein binding were observed. Less than 25% of the LPS in both outer membranes and whole bacteria bound to HDL in vitro. When the outer membranes and whole bacteria were injected into rats, their LPS again bound poorly to HDL and they were rapidly removed from plasma into the liver and spleen. In contrast, >50% of the LPS in both culture supernatant membrane fragments and phenol-water extracts bound to HDL in vitro. When these preparations were injected into rats, approximately 50% of the LPS in the membrane fragments and phenol-water extracts bound to HDL and remained in the plasma over the 10-min study period. Moreover, the LPS in these preparations accumulated in the ovary and the adrenal gland, two tissues that use HDL-cholesterol for hormone synthesis. Binding to HDL thus greatly influenced the plasma half-life and tissue uptake of both extracted and native LPS. We conclude that extraction of S. typhimurium LPS with phenol does not significantly alter the biological activity or the lipoprotein binding behavior of the LPS and that the in vivo fates of phenol-extracted and membrane fragment LPS are essentially identical. The results thus provide important support for many previous studies that have used phenol-extracted LPS to mimic the activities of native LPS in vivo. However, the only native LPS that resembled the behavior of extracted LPS were the LPS that had been shed from the bacteria in fragments of membrane that had reduced amounts of protein and phospholipid. Removal of LPS from other outer membrane constituents, whether by chemical extraction or by a natural process of surface shedding, thus alters the behavior of the LPS; the most important feature of this alteration appears to be the ability of these LPS to bind readily to HDL.

Adrenal Glands↗
PubMed1981

Kinetic parameters of the lipoprotein transport systems in the adrenal gland of the rat determined in vivo. Comparison of low and high density lipoproteins of human and rat origin.

These studies were done to characterize the rate of uptake of high (HDL) and low (LDL) density lipoprotein cholesterol by the adrenal gland of the rat under in vivo conditions. Animals were pretreated for 4 days with 4-aminopyrazolo[3,4-d]pyrimidine to essentially eliminate endogenous plasma lipoproteins and with aminoglutethimide for 1 h to block conversion of cholesterol to adrenal hormones. Such animals were then infused with varying amounts of HDL and LDL from both human and rat plasma, and this led to rapid accumulation of cholesterol, both free and esterified, in the adrenal glands over the subsequent 4-h period of observation. This uptake process was linear with respect to time and manifested saturation kinetics with respect to the steady state level of plasma lipoprotein cholesterol. When human lipoproteins were infused, the maximal rate of cholesterol uptake was approximately 0.45 mg/pair of adrenal glands/h for both HDL and LDL; however, the half-maximal rate of uptake (Km) was achieved at a plasma HDL cholesterol concentration of only 12 mg/dl while a concentration of 61 mg/dl was required to achieve the same velocity with LDL. When similar experiments were carried out with rat HDL, the Km equaled 7.2 mg/dl and a maximal rate of uptake of 0.32 mg/pair of adrenal glands/h was achieved. It was not possible to obtain complete kinetic curves using rat LDL, but at physiological plasma concentrations, there was no difference in the rate of cholesterol uptake from LDL of rat or human origin. When large amounts of both HDL (5.8 times Km) and LDL (3.1 times Km) were infused into the same animals, the rate of cholesterol uptake essentially equaled the sum of the maximal transport rates for the two lipoproteins. These data provide additional support for the concept that the adrenal gland (and ovary) of the rat can take up HDL and LDL cholesterol by separate mechanisms. However, from the quantitative data on the kinetics of these uptake processes, it is apparent that in this species HDL cholesterol must be the major substrate for the synthesis of adrenal hormones.

Adrenal Glands↗
PubMed1981

Binding of Salmonella typhimurium lipopolysaccharides to rat high-density lipoproteins.

These studies were undertaken to investigate the binding of gram-negative bacterial lipopolysaccharides (LPS) to high-density lipoproteins (HDL) of rat plasma. Purified Salmonella typhimurium LPS, intrinsically labeled with [3H]-galactose, bound rapidly in vitro to isolated rat HDL. Maximal binding of LPS to HDL occurred when LPS and HDL were incubated with lipoprotein-free plasma (rho greater than 1.21 g/ml). Since LPS, when purified, form large aggregates, we tested the hypothesis that disaggregation of LPS enhances LPS-HDL binding. We found that calcium chloride (1 mM), an agent which prevents LPS disaggregation, inhibited binding of LPS to HDL by interfering with the modification of LPS by lipoprotein-free plasma. Conversely, sodium deoxycholate (0.15 g/dl), which disaggregates LPS, greatly increased binding of LPS to HDL in the absence of lipoprotein-free plasma. Analysis of labeled LPS by sodium deodecyl sulfate-polyacrylamide gel electrophoresis showed only minor differences in the sizes of LPS molecules before and after binding to HDL, suggesting that chemical modification of LPS is not required for binding. The results provide evidence that disaggregation increases the binding of LPS to HDL.

Animals↗
PubMed1981

Sites of tissue binding and uptake in vivo of bacterial lipopolysaccharide-high density lipoprotein complexes: studies in the rat and squirrel monkey.

When gram-negative bacterial lipopolysaccharides (LPS) are injected intravenously into the rabbit or rat, they bind to plasma lipoproteins, particularly high density lipoproteins (HDL). The present studies were performed to examine the mechanisms by which LPS-HDL complexes are removed from the circulation and taken up by various tissues. Our approach was to compare the sites of specific tissue binding and uptake of HDL and of LPS-HDL complexes in the rat and squirrel monkey. In the rat, binding of homologous 125I-HDL was demonstrated principally in the adrenal gland, ovary, liver, and spleen. [3H]LPS-HDL complexes (produced in vitro by incubating Salmonella typhimurium [3H]LPS with rat HDL and lipoprotein-free plasma) bound to the same tissues, but with apparently lower affinities. The specificity of binding of both 125I-HDL and [3H]LPS-HDL to these organs was demonstrated in two ways. First, tissue binding of both radiolabeled preparations was swamped out by raising the circulating levels of HDL-cholesterol from 32 to 140 mg/dl. Second, treatment of the animals with dexamethasone abolished specific binding of both HDL preparations to the adrenal gland while administration of adrenocorticotropin increased the specific adrenal binding of the two preparations. The steady-state plasma clearance rate for 125I-HDL equaled 774 +/- 29 microliters/h and was significantly lower (557 +/- 39 microliters/h) for the LPS-HDL complex, a finding that presumably reflected the lesser ability of the various tissues to bind the LPS-HDL complex. Binding studies were also done in the squirrel monkey, an animal that has the same level of circulating HDL cholesterol as the rat, but nearly three times more cholesterol in low density lipoproteins. Specific binding of homologous 125I-HDL and [3H]LPS-HDL was again found principally in the adrenal gland and liver. The results indicate that the sites of tissue uptake of bacterial LPS are strongly influenced by binding of LPS to HDL. In particular, LPS-HDL binding may be an important determinant of the extent to which LPS are taken up by the adrenal gland during bacterial sepsis.

Adrenal Glands↗