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Biomedical subjects

A E Harper

Publications and source records attributed to A E Harper.

At least 19 recordsLinked to original sources
PubMed1992

Competition for transport of amino acids into rat heart: effect of competitors on protein synthesis and degradation.

Transport of the neutral amino acids, 2-(methylamino)isobutyrate (MeAIB) and Phe, was examined in isolated rat hearts perfused by the Langendorff method. Hearts were perfused by recirculating for various time periods buffer containing [14C]-MeAIB or [14C]-Phe plus desired additions. Uptake of MeAIB was linear for approximately 30 minutes; Phe uptake was linear for a maximum of 5 minutes, and reached a steady state after 15 minutes. Km and Vmax for MeAIB were 1.1 +/- 0.03 mmol/L and 37.7 +/- 0.4 pmol/microL intracellular fluid (ICF)/min; values for Phe were 1.8 +/- 0.02 mmol/L and 364 +/- 5 pmol/microL ICF/minute. Uptake of MeAIB (0.2 mmol/L) was reduced 95% in the presence of Ser (10 mmol/L), and less severely by large neutral amino acids ([LNAA], 10 mmol/L) such as Phe and Leu (by 46% and 54%, respectively). Uptake of Phe (0.2 mmol/L) was reduced by LNAA such as Val, Leu, and Ile (by 51%, 78%, and 81%, respectively), or by commercial preparations used in parenteral nutrition, eg, Travasol or Travasol plus extra branched-chain amino acids (BCAA) (Branchamin); Ser had little effect (8% reduction). Insulin in the perfusion medium increased the fractional rate of protein synthesis. Individual BCAA at physiological concentrations (0.2 mmol/L) did not alter the rate of protein synthesis. Branchamin or Travasol plus Branchamin also had no effect on the rate of protein synthesis in heart, but did depress the rate of degradation. These studies suggest that amino acid transport into heart may be affected by normal levels of plasma amino acids, whereas protein synthesis is not.

Amino Acids↗
PubMed1992

Protein selection by rats adapted to high or moderately low levels of dietary protein.

After preliminary studies on flavor acceptability, patterns and indices of subsequent feeding behavior were monitored by computer in young rats which were adapted to 15% or 70% casein diets before being offered, sequentially, choices between flavored diet pairs in which the proportions of percentage casein were 5/65, 5/55, 5/45, 5/35 and 5/25. Similarly adapted rats received these choices in the reverse sequence. Rats adapted to 15% casein usually ate randomly from the diet pairs and selected approximately 15-30% casein; individual behaviors were prominent. The 70% casein groups avoided the higher casein diet, often within minutes (except for the first-offered 5/25 choice), and seldom selected more than 10% casein; individual differences were infrequent. Such rats also distinguished between flavored 70% and 65% casein diets. Sizes and numbers of meals and rates of eating differed for the paired diets, especially for rats adapted to 70% casein. A flavor added to the 70% casein adaptation diet was not avoided when present only in the 5% casein diet of a 5/65 choice. Rats adapted to 70% soy protein before receiving flavored 5/65 to 5/25 choices selected 20-28% soy protein, a level far above those of casein selections by rats adapted to 70% casein. Dietary adaptation and type of protein thus affect subsequent diet selection and feeding patterns and indices.

Amino Acids↗
PubMed1992

Three-day dietary intake of incarcerated and nonincarcerated adolescent males.

We collected 3-day dietary intake information from both incarcerated (n = 137) and nonincarcerated (n = 42) adolescent males to provide an objective assessment of diets of residents of a juvenile correctional facility. Average daily intake of energy, protein, 13 indicator micronutrients and of macronutrients as percent of energy were calculated. Average intakes of the total group of adolescents (n = 179) were greater than 90% of the 1980 recommended dietary allowance (RDA) for energy, protein, and 10 micronutrients. There were no statistically significant differences between black (n = 63) and white (n = 63) incarcerated subgroups and white (n = 41) nonincarcerated subjects on average measures of energy, protein, macronutrients as percent of energy, and seven micronutrients. Cumulative intakes (as a proportion of the 1980 RDA) of nonincarcerated subjects and at least one group of incarcerated subjects were significantly different for vitamin B6, folate, vitamin C, iron, sodium, and thiamin. However, average intakes of vitamin C, sodium, and iron by all groups exceeded the RDA. Overall, the total group of adolescents did not appear to be at significant nutritional risk. Folate, copper, and magnesium intakes were consistently below RDA in all groups. We suggest that these findings are not indicative of nutritional inadequacy but are, rather, cues that some RDAs may be inappropriately high.

Adolescent↗
PubMed1992

A feather-sexed strain of laying hens was more responsive to dietary supplements of choline and methionine than a vent-sexed strain.

A response surface design was used to study Cho and Met interactions with corn and soybean diets, using two strains of hens. The strains were a feather-sexed line (FS strain), and a vent-sexed line (SS strain). The diets contained 3% meat and bone meal and, on chemical analysis, 15.1% crude protein, .29% Met, .225% Cys, and 1,041 ppm of Cho. Nine diets were fed from 20 to 68 wk of age, using added Met levels ranging from 0 to 500 ppm and added Cho levels ranging from 0 to 1,500 ppm, to fix the design points. The FS strain consumed significantly more feed per day (117 versus 108 g) than the SS strain, but there were no significant differences for the 24 to 68 wk period in egg production, egg weight, or feed per dozen eggs. Three and five combinations of Met and Cho were significant in improving egg production (P less than .05) out of the eight combinations for the SS and FS strains, respectively. The best egg production for the FS strain for the period 24 to 68 wk was observed at 250 ppm Met and 1,500 ppm Cho, or 427 ppm Met and 220 ppm added Cho. The SS strain showed no significant (P greater than .05) dietary responses in egg production between 250 ppm Met and no Cho, or 427 ppm Met and either 220 or 1,280 ppm Cho. The SS strain showed no significant (P greater than .05) dietary response in egg weight to either Cho or Met.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1991

Relationship between protein intake and hepatic protein synthesis in rats.

Protein synthesis has been measured in vitro in postmitochondrial extracts from livers of rats fed levels of casein ranging from 0 to 40% by weight. The maximal capacity for protein synthesis per milligram of RNA, measured with each amino acid added at 250 mumol/L, was 40-60% higher in rats fed a protein-free diet than in those fed 6 or 15% casein. Our results suggest that the livers of rats fed a protein-free diet are primed for the synthesis of tissue proteins and, given an adequate supply of amino acids, the rate of protein synthesis would be as high as or higher than the rate in protein-replete animals. When amino acids were added to the in vitro system at concentrations found in plasma of rats fed 0, 6, 15 or 40% casein the rate of protein synthesis increased by three- to fourfold over this range, with the highest rate observed for the 15% dietary casein level. We conclude that when protein intake is below the requirement level, the rate of liver protein synthesis may be limited by amino acid supply, by the capacity of the system for protein synthesis or by both.

Amino Acids↗
PubMed1990

Dietary disproportions of amino acids in the rat: effects on food intake, plasma and brain amino acids and brain serotonin.

Food intake, growth, plasma and brain amino acid, and brain serotonin and 5-hydroxyindole-3-acetic acid (5-HIAA) concentrations were measured in rats fed low protein diets containing disproportionate amounts of large neutral amino acids (LNAA) devoid of tryptophan or histidine (tryptophan or histidine imbalance). Five-day food intakes and weight gains of rats fed the imbalanced diets were depressed. The concentration of the limiting amino acid was low in brains of rats fed diets containing LNAA that compete with either tryptophan or histidine for entry into brain. Correlations were observed between the brain concentrations of most individual LNAA and either the ratios of the plasma concentration of that LNAA to the sum of the other LNAA, or the predicted rates of influx of that LNAA. Cumulative food intakes were correlated with brain concentrations of the limiting amino acid, tryptophan or histidine. Food intakes were not consistently correlated with concentrations of serotonin and 5-HIAA because these compounds were altered only in brains of rats in the tryptophan study. Competition among amino acids for uptake into brain appears to be involved in the feeding response of the rat to dietary disproportions of amino acids, but this response is not directly related to changes in brain concentrations of serotonin and 5-HIAA.

Amino Acids↗
PubMed1979

Induction of threonine imbalance by dispensable amino acids: relation to competition for amino acid transport into brain.

The ability of low protein diets containing small neutral, dispensable amino acids to induce threonine imbalance has been examined. Diets containing amino acids which compete for threonine transport in vitro (serine, alanine, alpha-amino-n-butyrate) caused depressions of growth and food intake which could be corrected to varying degrees by adding threonine to the diet. Large neutral, indispensable amino acids, moderately inhibitory of threonine transport, also induced the imbalance. Some amino acids that had little or no effect on threonine transport in vitro (acidic amino acids and proline) did not cause growth and food intake depressions. Other non-inhibitory amino acids (arginine and lysine) caused growth depressions which were not satisfactorily corrected by additional threonine alone, but were prevented by supplements of all the indispensable amino acids including threonine. Ornithine which was also not inhibitory of threonine transport was an exception. It induced a moderate growth depression which was corrected by additional threonine. Similar studies showed that histidine or tryptophan imbalance could be induced by feeding diets containing only those large neutral amino acids which compete for histidine or tryptophan transport in vitro. These experiments show that, based on the results of transport competition experiments, it is generally possible to devise amino acid supplements which can induce a dietary imbalance of a given amino acid.

Amino Acids↗
PubMed1979

Sulfur amino acid and methyl donor status of corn-soy diets fed to starting broiler chicks and turkey poults.

Experiments were conducted to determine the effects of supplementing corn-soy-bean meal-white grease diets with sulfur amino acids and methyl group donors for starting broiler-strain chicks. The diets (23% protein and 3200 kcal ME/kg) were fed to quadruplicate lots of chicks in battery brooders. The diets were calculated to contain .37% methionine, .37% cystine, and 1499 mg/kg choline. Chemical and microbiological assays yielded values of .32% and .42% for methionine and cystine content respectively. Results of 5 chick experiments showed that supplementing this diet with .23% DL-methionine significantly (P less than .05) improved 3 week-gain (375 vs. 415 g) and feed/gain (1.54 vs. 1.47) over that obtained with the basal diet. When L-cystine and 2(CaSO4).H2O failed to give a significant (P greater than .05) response, compounds capable of donating methyl groups were fed. Significant (P less than .05) responses in gain (404 and 420) and feed/gain (1.48 and 1.51) over the basal were obtained with choline and betaine. These responses were not significantly (P greater than .05) different from that obtained with methionine. Serine and sodium formate failed to give consistent responses. Using a poult diet of 28% protein and 2800 kcal ME/kg, a significant (P less than .05) response to DL-methionine was again observed, with intermediate responses to betaine, choline, and serine. It is concluded that (within the limits of the experimental model) corn-soy type diets contain an adequate amount of total sulfur amino acid for chicks, but not poults, when sufficient choline or betaine are provided.

Amino Acids, Sulfur↗
PubMed1978

Metabolism and transport of gamma-carboxyglutamic acid.

gamma-Carboxyglutamic acid residues have beeh shown to be present in prothrombin, the other vitamin K-dependent clotting factors, and more recently in bone and kidney proteins. This amino acid is formed by a posttranslational vitamin K-dependent carboxylation of glutamyl residues in polypeptide precursors of these protens. It has now been demonstrated that this amino acid, either in the free or peptide-bound form, is not metabolically degraded by the rat, but is quantitatively excreted in the urine. In nephrectomized rats, the tissue concentration of intravenously administered gamma-carboxyglutamic acid is increased, but there is still no evidence of any oxidative metabolism of this amino acid. These amino acid is transported by kidney slices against a concentration gradient, but does not accumulate in liver, intestinal or brain tissues. Preliminary data suggest that gamma-carboxyglutamic acid may be concentrated by a carrier system different from that utilized by other amino acids.

Aminoisobutyric Acids↗
PubMed1978

Threonine metabolism in vivo: effect of threonine intake and prior induction of threonine dehydratase in rats.

The metabolic fate of threonine was investigated in young male rats fed 15% amino acid diets containing from 0.15% to 0.85% of L-threonine. Liver serine-threonine dehydratase (S-TDH) activity did not increase with increasing dietary threonine content. The level of threonine required for maximum weight gain was not greater than 0.55% of the diet (or about 600 mumoles/day). Tissue free threonine content of rats fed the diets with 0.15% or 0.3% of threonine was very low but increased sharply with increasing dietary threonine content above 0.3%. During ad libitum feeding of these diets containing L-[U-14C]threonine, rate of oxidation of threonine was low when intake was in the range of the requirement for maximum growth, but increased, thereafter as threonine intake increased. A 30-fold induction of liver S-TDH, by prior feeding of an 80% casein diet, did not result in increased oxidation of threonine when dietary threonine content was 0.15%. When dietary threonine content was increased to 0.5%, oxidation of threonine increased slightly but significantly. With 3% of threonine in the diet, rats previously fed a 15% casein diet had extremely high tissue threonine concentrations whereas those with high S-TDH activity, due to the previous feeding of the 80% casein diet, oxidized threonine rapidly and tissue threonine concentrations were elevated much less.

Animals↗