Search PubMed⌕ Search

Biomedical subjects

A E Harper

Publications and source records attributed to A E Harper.

At least 55 records · Page 3Linked to original sources
PubMed1988

Some characteristics of threonine transport across the blood-brain barrier of the rat.

Threonine entry into brain is altered by diet-induced changes in concentrations of plasma amino acids, especially the small neutrals. To study this finding further, we compared effects of various amino acids (large and small neutrals, analogues, and transport models) on transport of threonine and phenylalanine across the blood-brain barrier. Threonine transport was saturable and was usually depressed more by natural large than small neutrals. Norvaline and 2-amino-n-butyrate (AABA) were stronger competitors than norleucine. 2-Aminobicyclo[2.2.1]heptane-2-carboxylate (BCH), a model in other preparations for the large neutral (L) system, and cysteine, a proposed model for the ASC system only in certain preparations, reduced threonine transport; 2-(methylamino)isobutyrate (MeAIB; a model for the A system for small neutrals) did not. Phenylalanine transport was most depressed by cold phenylalanine and other large neutrals; threonine and other small neutrals had little effect. Norleucine, but not AABA, was a strong competitor; BCH was more competitive than cysteine or MeAIB. Absence of sodium did not affect phenylalanine transport, but decreased threonine uptake by 25% (p less than 0.001). Our results with natural, analogue, and model amino acids, and especially with sodium, suggest that threonine, but not phenylalanine, may enter the brain partly by the sodium-dependent ASC system.

Amino Acids↗
PubMed1988

Regulation of valine and alpha-ketoisocaproate metabolism in rat kidney mitochondria.

Activities of branched-chain amino acid (BCAA) aminotransferase (BCAT) and alpha-keto acid dehydrogenase (BCKD) were assayed in mitochondria isolated from kidneys of rats. Rates of transamination of valine and oxidation of keto acids alpha-ketoisocaproate (KIC) or alpha-ketoisovalerate (KIV) were estimated using radioactive tracers of the appropriate substrate from amounts of 14C-labeled products formed (14CO2 or [1-14C]-keto acid). Because of the high mitochondrial BCAT activity, an amino acceptor for BCAT, alpha-ketoglutarate (alpha-KG) or KIC, was added to the assay medium when valine was the substrate. Rates of valine transamination and subsequent oxidation of the KIV formed were determined with 0.5 mM alpha-KG as the amino acceptor; these rates were 5- to 50-fold those without added alpha-KG. Rates of CO2 evolution from valine also increased when KIC (0.01-0.10 mM) was present; however, with KIC concentrations above 0.2 mM, rates of CO2 evolution from valine declined although rates of transamination continued to rise. When 0.05 mM KIC was added to the assay medium, oxidation of KIC was suppressed by inclusion of valine or glutamate in the medium. When valine was present KIC was not oxidized preferentially, presumably because it was also serving as an amino acceptor for BCAT. These results indicate that as the supply of amino acceptor, alpha-KG or KIC, is increased in mitochondria not only is the rate of valine transamination stimulated but also the rate of oxidation of the KIV formed from valine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Alterations in phospholipid composition of egg yolks from laying hens fed choline and methionine-supplemented diets.

A trial was conducted to assess the effects of choline and methionine supplementation of the diets of hens on phospholipid composition of egg yolk. By chemical analysis, the basal diet contained 16.6% protein, 1,041 parts per million (ppm) of choline, and .53% TSAA. The energy level was 2,899 kcal ME/kg diet, with no added fat. A rapid isocratic HPLC procedure using a Waters mu Bond-NH2 column (Waters Associates, Milford, MA) was developed to quantify phospholipid components. Analysis of egg samples at peak production (36 wk of age) showed significant (P less than .05) elevations in total phospholipids, phosphatidylcholine (PC), and the ratio of PC to phosphatidylethanolamine (PE), when choline was added at 500 or 1,000 ppm. Phosphatidylethanolamine, in contrast, showed a decline with choline supplementation. Methionine supplementation (125 to 250 ppm) also caused elevations in the total phospholipid composition of the egg yolk but had only modest effects on PC and PE. There was a significant (P less than .05) correlation between the yolk weight and total phospholipid concentration, PC, and the PC:PE ratio. There was a relationship between phospholipid content and weight of eggs when diets of laying hens were supplemented with choline.

Animals↗
PubMed1987

Acceptability by rats of aqueous solutions of amino acid analogues.

Preferences differed widely when rats were offered choices between water and solutions of various natural amino acids and structurally related analogues. They avoided the branched-chain amino acid valine but preferred solutions of its isomer norvaline and of norleucine. The hydrochloride forms of ornithine and arginine were preferred to water at concentrations up to about 100 mM and avoided at 410 mM; homoarginine.HCl was never preferred and was avoided at 39 and 78 mM. Rats were indifferent to taurine and beta-alanine at most concentrations but refused these amino acids at high concentrations (205 and 410 mM, respectively). In conjunction with earlier observations on feeding behavior in response to dietary additions of amino acids, the results show that selections by rats between water and amino acid solutions cannot be used to predict choices among amino acid-containing diets.

Amino Acids↗
PubMed1987

Identification of volatile sulfur derivatives released from feathers of chicks fed diets with various levels of sulfur-containing amino acids.

Physical changes are observed in the feathers of chickens fed diets with high levels of methionine or cysteine. Chicks were fed diets chemically analyzed to contain 21% crude protein, 0.35% methionine and 0.37% cystine (basal) supplemented with DL-methionine [0.063 (control), 0.25 or 1.45%] or L-cysteine (0.203%). At 3 wk of age, the birds were weighed and the feathers scored for softness. Feather strength (i.e., force-displacement curves) was determined on feathers from the pectoral tract. A significant (P less than 0.05) reduction in body weight and an increase in feather softness were seen when chicks fed the control diet and those fed the diet with 1.45% added methionine were compared. Chicks fed the diet supplemented with 0.203% L-cysteine produced the strongest feathers; those fed diets supplemented with 1.45% DL-methionine produced the weakest feathers. Volatile sulfur compounds released from the feathers were trapped as dinitrophenyl (DNP) thioethers and were analyzed by thin-layer chromatography, high pressure liquid chromatography and mass spectrometry. More bound sulfide (P less than 0.05) was recovered from feathers of chickens fed the diet supplemented with 1.45% methionine than from feathers of chickens fed the other diets. The feather softness score was correlated (r = 0.5; P less than 0.05) with bound sulfide. Thus, consumption of a diet with a level of methionine that is approximately three times the requirement resulted in decreased growth, elevated sulfide bound to the feathers and soft, weak feathers.

Amino Acids, Sulfur↗
PubMed1987

Threonine entry into rat brain after diet-induced changes in plasma amino acids.

Passage of amino acids across the blood-brain barrier is modified by the amino acid composition of the blood. Because blood amino acid concentrations respond to changes in protein intake, we have examined associations among diet, plasma amino acid patterns, and the rate of entry of threonine into the brain. Rats were adapted for 8 h/day for 7-10 days to diets containing 6, 18, or 50% casein before receiving a single, independently varied, final meal of a diet containing 0, 6, 18, or 50% casein. After 4-7 h, they were anesthetized and infused intravenously with [14C]threonine for 5 min before plasma and brain samples were taken for determination of radioactivity and amino acid content. Plasma and brain threonine concentrations decreased as protein content increased in the diets to which the rats had been adapted. Plasma threonine concentrations increased twofold, from 1.6 to 3.0 mM, when rats adapted to 6% casein meals received a single 50% casein meal rather than a nonprotein meal; a fivefold increase, from 0.13 to 0.69 mM, occurred when rats had been previously adapted to 50% casein meals. Increasing the protein content of the final meal did not increase brain threonine concentrations. Highest and lowest rates of threonine entry into the brain occurred, respectively, in rats adapted to 6 and 50% casein meals. Changes in plasma threonine concentrations and threonine flux into brain reflected protein content of both pretreatment and final meals.

Amino Acids↗
PubMed1987

Valine entry into rat brain after diet-induced changes in plasma amino acids.

Passage of amino acids across the blood-brain barrier is assumed to be modified by amino acid composition of the blood. To gain a better understanding of the effects of protein intake on brain amino acid uptake, we examined associations among diet, plasma amino acid patterns, and the rate of entry of valine into the brain. Rats were fed (8 h/day for 7-10 days) diets containing 6, 18, or 50% casein before receiving one meal of a diet containing 0, 6, 18, or 50% casein. After 4-7 h, they were anesthetized and infused intravenously with [14C]valine for 5 min before plasma and brain samples were taken for determination of radioactivity and content of individual amino acids. As protein content of the meal was increased from 0 to 50% casein, plasma and brain concentrations of valine and most other large neutral amino acids (LNAA) increased severalfold; also the ratio of [14C]valine in brain to that in plasma decreased by greater than 50%, and the rate of valine entry into the brain increased 3.5-fold. The increase in valine flux slowed as plasma levels of LNAA, competitors for valine transport, increased. The results were far more dependent on protein content of the final meal than on that of the adaptation diet; thus changes in protein intake, as reflected in altered plasma amino acid patterns, markedly altered valine entry into the brain.

Amino Acids↗
PubMed1987

Acute effects of dietary protein on food intake, tissue amino acids, and brain serotonin.

Male rats (100 g) previously adapted to a 20% casein diet were fed diets containing from 0 to 55% of casein and were killed after 20, 60, 150, 240, or 330 min. Food intake of rats fed a protein-free diet or a diet containing greater than 35% of casein was depressed within 20 min and remained depressed for up to 5.5 h. Depressed food intake of rats fed protein-free diets was accompanied by a rapid reduction in plasma and brain total concentrations of free indispensable amino acids (IAA). Food intake depression among groups fed diets containing in excess of 35% casein was associated with elevated plasma and brain total IAA concentrations, compared with those of animals fed diets containing 15-20% of casein. No consistent relationships were observed between food or protein intakes and whole-brain concentrations of 5-hydroxytryptamine, 5-hydroxyindole-3-acetic acid, or their sum. Our results suggest that in animals fed a single diet, food intake is depressed if the total concentration of free IAA in brain either falls below a certain critical minimum or exceeds some maximum tolerable level.

Amino Acids↗
PubMed1987

Efficacy of cysteine in replacing methionine in the immune responses of broiler chicks.

Two trials were conducted to compare the effects of supplements of methionine and cysteine on the growth and immune responses of broiler chicks fed corn-soy diets. The basal diet contained 21% crude protein, 3,255 kcal metabolizable energy/kg diet, .35% methionine, .37% cysteine, and .13% choline. Additions to the basal diet were methionine (.063, .25, .85, and 1.45%), or cysteine (.203%), or a combination of methionine (.063%) and cysteine (.153%). Total antibody and 2-mercaptoethanol-resistant antibodies, immunoglobulin G (IgG), were determined in chicks inoculated intraperitoneally at 14 days of age and serially bled at 4, 7, and 10 days postinoculation. Thymus-derived (T)-cell-dependent in vivo mitogen response to phytohemagglutinin-P (PHA-P) was assessed via wing web swelling. The methionine requirement for growth (0 to 3 wk of age) was found to be no more than .413% of the diet (.35% in the basal diet plus .063% added). Addition of 1.45% methionine to the basal diet resulted in significant depression (P less than .05) in growth. The antibody responses generally peaked at 7 days postprimary inoculation. Both methionine and cystine supplementation at low levels resulted in improvement in the cell mediated PHA-P responses as well as in the IgG (T-cell-dependent) responses. High supplemental methionine (1.45%), however, caused significant (P less than .05) depressions in both responses. Equimolar additions of methionine and cysteine (16.8 mmol/kg diet) showed that cysteine was about 84 and 70% as efficacious as methionine in the IgG and the PHA-P stimulation (PHA-I), respectively, in healthy chicks.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Enhanced immune responses in broiler chicks fed methionine-supplemented diets.

Effects of feeding supplementary methionine and choline on broiler growth and immunity were examined by supplementing a corn-soybean diet that contained 21% crude protein, 3,255 kcal metabolizable energy/kg diet, .35% methionine, .37% cystine, and .13% choline. Methionine (.063, .125, .25%) and choline (.125, .25%) were dietary variables. Sulfate (.055%) was added either alone or along with methionine (.125 or .25%) and choline (.125%). In one study, the .25% methionine diet was supplemented with .121% betaine. Sodium and chloride levels were constant in all the diets. Feed and distilled water were supplied ad libitum. Total antibodies, immunoglobulin (Ig) G (2-mercaptoethanol-resistant antibodies) and IgM (2-mercaptoethanol-sensitive antibodies) were determined in 3-wk-old chicks inoculated intraperitoneally with sheep red blood cells. The thymus-derived (T)-cell-dependent in vivo mitogen response to phytohemagglutinin-P (PHA-P) was assessed via wing web swelling. The methionine requirement for growth (0 to 3 wk of age) was approximately .413% of the diet (.35% in the basal diet plus .063% added). Supplementation of the basal diet with .125% choline stimulated growth to the same extent as did the extra .063% of methionine. Addition of .055% sulfate with .125% choline did not improve the ability of the latter to spare methionine. Supplemental methionine resulted in significant (P less than .05) dose-related increases in total antibody, IgG, and response to the mitogen PHA-P, but not in IgM. There were no effects of choline on the immune variables studied. These results suggest that methionine is required for select components of the antibody response, which effect might be related to T-cell help.

Animals↗
PubMed1987

Assessment of softness properties of feathers.

An instrument to be called the "Crimp Meter" was designed and used with a conventional balance to enable the plotting of a force-displacement curve for individual feathers. A comparison of the curves described by different feathers was made by regression analysis. The type of curve described by a feather is characteristic of its tensile properties and its degree of softness. This procedure was employed to objectively confirm the observation that chicks fed toxic levels of methionine (1.45% added) in corn-soybean diets had significantly softer (P less than .001) feathers than those fed nontoxic levels of cysteine (.203% added). The basal diet was analyzed and found to contain .35% methionine and .37% cystine. This device had potential for the down-feather, wool, and fabric industries.

Animals↗
PubMed1987

Critical vitamin supplementation of broiler diets high in alfalfa juice protein.

Three trials were conducted to identify the critical vitamins in the diets of broiler-strain chicks fed alfalfa juice protein concentrate (AJPC) corn-soy diets from 0 to 3 wk of age. Vitamin supplements were added to AJPC diets. Diets were formulated to contain, parts 30/121, 40/128, 50/135, and 60/142 parts AJPC/parts total diet. Parts were used to permit usage of wet materials and still maintain about 90% dry matter. All diets were formulated to contain 20% crude protein, .93% total sulfur-containing amino acids, and 2,940 kcal metabolizable energy/kg diet. Propionic acid was added at .2% to all diets. Feeds were refrigerated (7 C) and fed out daily. The addition of choline, riboflavin, vitamin B12, vitamin A or E, folic acid, or biotin did not increase weight gains. Addition of 3 mg/kg vitamin B6 completely overcame the growth depression caused by the 50-parts AJPC diet and significant (P less than .05) growth increases (13 to 29%) were achieved with vitamin-B6 supplementation to the 60-parts AJPC diet. Depressed immune responses were completely prevented by the addition of 3 mg/kg of vitamin B6. The significant (P less than .05) increases in leg deformities observed in birds fed the 60-parts AJPC diet were also brought back to more typical values in birds fed the diet supplemented with 3 mg/kg vitamin B6. Vitamin K supplementation (.53 mg/kg) to the 60-parts AJPC diet resulted in significant decreases from 15 min in blood clotting times to 3 to 5 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗
PubMed1986

Proteins and amino acids: effects of deficiencies and specific amino acids.

Information about effects of protein and amino acid intake on carcinogenesis comes mainly from experiments on laboratory animals. In general, tumor formation and tumor growth are retarded in animals consuming protein- or amino acid-deficient diets, but the effects have been attributed mainly to reduced caloric intake or body weight. Nonetheless, some tumors grow well in animals consuming diets that contain levels of protein that are insufficient to meet their nutritional needs. Induction of tumors by chemical carcinogens or procarcinogens may be enhanced or inhibited in animals consuming a diet containing a particular level of protein, depending upon the responses of enzymes that activate or inactivate the specific compound being tested. The feeding of amino acid-deficient diets or amino acid antagonists has been proposed as an adjunct to chemotherapy. Undoubtedly, tumor development and growth can be influenced by the quantity of protein consumed by an animal, but the responses observed with specific tumors and carcinogens may differ. Therefore, it is not possible to draw general conclusions about effects of protein intake on the incidence of cancer or on the process of carcinogenesis.

Amino Acids↗
PubMed1986

Induction in rats of lysine imbalance by dietary homoarginine.

The use of dietary homoarginine (HA) to produce a lysine imbalance was examined in young rats. HA, a basic amino acid analogue, was shown earlier to compete with lysine for transport across the blood-brain barrier. Feeding a diet limiting in lysine and containing HA reduced food intake and growth; increasing dietary lysine content lessened these effects. A 3-fold increase in dietary lysine caused 10, 4, 20 and 50-fold increases in lysine concentrations in plasma, brain, liver and muscle, respectively, and reductions in ornithine concentration of brain and liver and in arginine concentration of brain. HA increased lysine levels in plasma, liver and muscle of rats fed the lysine-limiting control diet, but lysine concentrations were reduced by HA when dietary lysine was high. HA invariably lowered concentrations of lysine, ornithine and arginine in brain and ornithine concentrations in plasma and muscle. Brain concentrations of small and large neutral amino acids were unchanged by HA; an exception was glycine, which was high in the brains of rats fed HA. The HA-associated, selective reductions in levels of each basic amino acid in brain in the ratios of these concentrations to those in plasma support the concept that effects of an amino acid imbalance involve competition for amino acid entry into the brain from the blood.

Amino Acids↗