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Biomedical subjects

A C Ross

Publications and source records attributed to A C Ross.

105 records · Page 6Linked to original sources
PubMed1982

Retinol esterification by rat liver microsomes. Evidence for a fatty acyl coenzyme A: retinol acyltransferase.

To explore the nature of retinyl ester synthesis by liver microsomes, membranes prepared from rat or cat liver were incubated under various conditions with [3H] retinol dispersed in dimethyl sulfoxide. When [3H]retinol, buffer, and microsomes were incubated together (basal conditions), some [3H]retinol esterification was consistently observed. However, the rate of esterification could be increased 6- to 11-fold by addition of either palmitoyl-CoA (100 microM) or a fatty acyl CoA-generating system. To determine whether the fatty acid used to esterify [3H]retinol under basal conditions might be derived from an endogenous pool of fatty acyl-CoA associated with the microsomal preparation, microsomes were pretreated at pH 7.4 with 0.5 M hydroxylamine, a reagent that reacts with coenzyme A thioesters to form hydroxamates. This pretreatment reduced the basal reaction by 69%. However, hydroxylamine-treated microsomes still retained acyltransferase activity, as shown by a 24- to 40-fold increase in retinyl ester synthesis after addition of palmitoyl-CoA. When microsomes were incubated with both [3H]retinol and [14C]palmitoyl-CoA of known specific radioactivities, the ratio of 14C to 3H in newly synthesized retinyl palmitate was essentially equal to that of its putative substrates, indicating that [14C]palmitate did not undergo significant isotope dilution prior to acylation of [3H]retinol. These experiments provide direct evidence for retinol esterification catalyzed by a microsomal acyl-CoA:retinol acyltransferase and indirect evidence for a pool of fatty acyl-CoA in isolated liver microsomes that is available to react with [3H]retinol to form esterified retinol.

Acyltransferases↗
PubMed1982

Retinol esterification by mammary gland microsomes from the lactating rat.

Because vitamin A in milk is largely present as esterified retinol while blood plasma predominantly contains unesterified retinol, experiments were conducted to determine whether membranes from the lactating mammary gland are able to synthesize retinyl esters in vitro. When microsomes from rats lactating for 7 to 14 days were incubated with [(3)H]retinol dispersed in dimethylsulfoxide, some [(3)H]retinol esterification was observed (147 pmol/5 min per 0.5 mg protein). However, 3- to 7-fold increases in retinyl ester synthesis could be achieved by supplying either a fatty acyl CoA-generating system or preformed fatty acyl CoA thioesters; thus, the major activity in vitro has the characteristics of a fatty acyl CoA: retinol acyltransferase. Both long-chain and medium-chain fatty acyl CoA esters stimulated [(3)H]-labeled retinyl ester synthesis in vitro. Concordantly, analysis of the retinyl ester pattern of rat milk demonstrated the presence of eight different esters of retinol ranging in fatty acyl chain length from 8 to 18 carbons. Retinol esterification by microsomes was maximal at neutral pH (7.1) in the presence of approximately 50 micro M palmitoyl CoA, and was linear with time of incubation for at least 5 min. Retinyl ester synthesis increased with the apparent concentration of [(3)H]retinol to approximately 200 nmol/ml, but was also dependent on the ratio of retinol relative to total microsomal protein in the incubation mixture. These experiments demonstrate for the first time retinol esterification by mammary gland membranes and point to the hypothesis that free retinol from plasma is esterified in this organ before secretion of retinyl esters in milk.-Ross, A. C., Retinol esterification by mammary gland microsomes from the lactating rat.

Animals↗
PubMed1980

The binding protein for retinoic acid from rat testis cytosol: isolation and partial characterization.

This study reports the isolation and partial characterization of a soluble protein with binding specificity for retinoic acid from rat testis cytosol. Cytosol, labeled in vitro by incubation with [14C]retinoic acid, was fractionated by a series of procedures that included ion exchange chromatography on DEAE-Sepharose and on DEAE-cellulose, gel filtration on Sephadex (G-50, and preparative polyacrylamide gel electrophoresis. The resulting cytosol bindin; protein for retinoic acid had been purified approximately 16,000-fold, with recovery of 11% of the specifically bound [14C]retinoic acid. The purified binding protein was homogeneous on disc gel electrophoresis at pH 4.5 or in the presence of SDS, but displayed microheterogeneity on isoelectric focusing, where both a major and a minor band with apparent isoelectric points near 4.7 were observed. Purified retinoic acid binding protein had a molecular weight of approximately 14,600, and an ultraviolet absorption spectrum with two maxima near 277 and 346 nm. The fluorescence intensity of retinoic acid bound to the cytosol binding protein was approximately 30-times greater than that of retinoic acid in solution in any of five organic solvents, suggesting that retinoic acid is highly immobilized when bound to the cytosol binding protein. The properties of the rat testis cytosol binding protein for retinoic acid were compared directly with those of the testis cytosol binding protein for retinol and of serum retinol-binding protein. The two cytosol binding proteins were much more similar to each other than to the serum transport protein, from which they differed in a number of properties, including which they differed in a number of properties, including molecular size, affinity for prealbumin, immunological reactivity, and absorption and fluorescence spectral characteristics.

Amino Acids↗
PubMed1979

Intracellular binding proteins for retinol and retinoic acid: comparison with each other and with serum retinol-binding protein.

Soluble proteins with binding specificity for either retinol or retinoic acid were isolated from rat testis cytosol. The characteristics of the purified cytosolic protein were compared both with each other, and directly with those of serum retinol-binding protein (RBP). Substantial similarities were observed between the two cytosol retinoid binding proteins, as well as clear differences between each of these proteins and serum RBP. The intracellular binding proteins differed from serum RBP with regard to molecular weight, immuno-reactivity, binding affinity for serum prealbumin, and ultraviolet and fluorescence spectral characteristics. The ultraviolet absorption spectrums of the cytosol binding protein for retinol (CRBP) and of the cytosol binding protein for retinoic acid (CRABP) were almost identical despite differences in the nature of the ligands bound by these two proteins.

Animals↗
PubMed1977

Use of esterified retinol to trace the degradation of chylomicrons in cholesterol-fed rabbits.

Moderately hypercholesterolemic rabbits hydrolyzed chylomicron TG at the same rate as normal animals, but were found to accumulate partially degraded intestinal lipoproteins of Sf 100-400 and Sf 20-100. These results support the hypothesis that the hypercholesterolemia induced by cholesterol feeding results at least in part from an inability to clear chylomicron remnants in proportion to the rate of their formation.

Animals↗
PubMed1977

Chylomicron remnant cholesteryl esters as the major constituent of very low density lipoproteins in plasma of cholesterol-fed rabbits.

Feeding rabbits 500 mg of cholesterol daily for 4 to 15 days greatly increased the concentration of esterified cholesterol in lipoproteins of d less than 1.006 g/ml. The origin of hypercholesterolemic very low density lipoproteins was investigated by monitoring the degradation of labeled lymph chyomicrons administered to normal and cholesterol-fed rabbits. Chylomicrons were labeled in vivo by feeding either 1) [3H]cholesterol and [14C]oleic acid or 2) [14C]cholesterol and [3H]retinyl acetate. After intravenous injection of labeled chylomicrons to recipient rabbits, [14C]triglyceride hydrolysis was equally rapid in normal and cholesterol-fed animals. Normal rabbits rapidly removed from plasma both labeled cholesteryl and retinyl esters, whereas cholesterol-fed rabbits retained nearly 50% of doubly labeled remnants in plasma 25 min after chylomicron injection. Ultracentrifugal separation of plasma into subfractions of very low density lipoproteins showed that chylomicron remnants in cholesterol-fed animals are found among all subclasses of very low density lipoproteins. Analysis of cholesteryl ester specific activity-time curves for the very low density lipoproteins subfraction from hypercholesterolemic plasma showed that nearly all esterified cholesterol in large very low density lipoproteins and approximately 30% of esterified cholesterol in small very low density lipoproteins was derived from chylomicron degradation. Apparently, nearly two-thirds of the esterified cholesterol in total very low density lipoproteins from moderately hypercholesterolemic rabbits is of dietary origin.

Animals↗
PubMed1976

Disposition of plasma cholesterol in the pregnant hypocholesterolemic rabbit.

Processes that might explain the hypocholesterolemia observed in pregnant rabbits were studied in animals fed a cholesterol-free chow diet. Excretion of endogenous steroids, measured after administration of a single intravenous dose of radioactive cholesterol, averaged 75 mg/day in controls and 96 mg/day in pregnant hypocholesterolemic rabbits. The mass of maternal plasma cholesterol transferred to the fetuses was measured in animals in which a constant plasma cholesterol specific activity was maintained. Placental transfer during the first 28 days of gestation ranged from 2 to 12 mg/day for mothers carrying litters of one to eight fetuses. It is concluded that loss of maternal plasma cholesterol due to placental transfer is small compared to loss by fecal steroid excretion. Because large decreases in plasma cholesterol concentration during pregnancy and increases at parturition were not accompanied by changes in the slopes of the specific activity-time curves, it appears most likely that cholesterol in isotopic equilibrium with plasma cholesterol is temporarily and reversibly sequestered in maternal tissues of the pregnant rabbit.

Animals↗
PubMedDate not supplied

Hysteria.

Explore the source record for details and available documents.

Female↗
PubMedDate not supplied

Effects of N-(4-hydroxyphenyl)-retinamide on the number and cytotoxicity of natural killer cells in vitamin-A-sufficient and -deficient rats.

N-(4-hydroxyphenyl)retinamide (4-HPR), a synthetic retinoid with anticarcinogenic activity, has been shown to lower the plasma retinol level rapidly and significantly. We reported previously that vitamin A-deficient rats (plasma retinol < 0.175 mumol/l) have a low number of natural killer (NK) cells in peripheral blood. To investigate the effects of 4-HPR on NK cell number and activity, two studies were conducted. In study 1, vitamin-A-sufficient rats were fed a 'therapeutic' dose of 4-HPR (2 mmol/kg of diet) for 30 days. Despite a low plasma retinol concentration (approximately 0.1 mumol/l), the number of NK cells was not reduced. Moreover, the NK cytolytic activity per cell was significantly elevated. White blood cell and differential counts were normal. In study 2, the biological activity of 4-HPR was examined in vitamin-A-deficient rats. Rats depleted of vitamin A were fed a diet containing 4-HPR (54.7 micrograms/g of diet) for 11 days. Vitamin-A-dependent processes including growth, hematocrit, lymphocyte count and the number of NK cells were restored. For comparison, another group of vitamin-A-deficient rats were repleted with retinoic acid (RA; 4.2 micrograms/g diet); this treatment also effectively restored these vitamin-A-dependent processes. Therefore, despite the plasma-retinol-lowering property of 4-HPR, treatment with this retinoid did not impair NK cell number or function. Indeed, 4-HPR showed vitamin A activity similar to RA, and may stimulate NK cell cytotoxicity.

Animals↗
PubMedDate not supplied

The role of vitamin A in natural killer cell cytotoxicity, number and activation in the rat.

The cause of low natural killer (NK) cell activity in vitamin-A-deficient rats was investigated in the current study. Cytotoxicity correlated with the percentage of NK cells (3.2.3-positive cells) in peripheral blood mononuclear cells (PBMC; r = 0.85) and spleen (r = 0.70). Lytic activity per NK cell did not differ between vitamin-A-deficient rats and controls in PBMC, whereas it did in spleen. Vitamin A deficiency did not impair the ability to produce interferon (IFN), increase lytic efficiency and expand the NK cell pool upon poly(I:C) stimulation in vivo. Nor was the in vitro activation by IFN-alpha/beta or interleukin-2 affected. Thus, vitamin A is essential for maintaining basal NK cell number and activity, but not for NK cell activation.

Animals↗