Search PubMed⌕ Search

Biomedical subjects

A E Harper

Publications and source records attributed to A E Harper.

At least 91 records · Page 5Linked to original sources
PubMed1984

Effect of dietary protein and GABA on food intake, growth and tissue amino acids in cats.

GABA at 5%, but not 3%, of a low protein diet depressed food intake and growth of kittens. Adaptation to high protein prevented these effects. When cats adapted to low or high protein were fed a meal containing GABA, plasma GABA concentration after 2 hr was 8-fold higher in the low than in the high protein group; clearance was almost complete within 6 hr. Concentrations of proline, branched-chain, other large neutral and basic (especially ornithine) amino acids increased more when cats were fed a high rather than a low protein meal; glycine decreased. At 6 hr, concentrations had consistently returned to initial levels only in the low protein group. Feeding the high protein diet ad lib increased tissue concentrations of threonine, proline and the branched-chain amino acids. Hepatic or renal GABA-aminotransferase activity was not altered in kittens fed the high protein diet. Kidney activity was 10-fold that of liver, which may contribute to the better tolerance of GABA by cats than by rats.

4-Aminobutyrate Transaminase↗
PubMed1984

Relationship between intake and rate of oxidation of leucine and alpha-ketoisocaproate in vivo in the rat.

Rates of oxidation of leucine by rats fed, ad libitum, diets containing graded amounts (0-2.4%) of leucine together with L-[1-14C]leucine were measured for 12 hours. The amount of leucine oxidized was low until dietary leucine content exceeded that needed for maximum rate of weight gain. Thereafter, the rate of leucine oxidation increased essentially linearly with increasing dietary leucine content. Rates of oxidation of alpha-ketoisocaproic acid (KIC) by rats fed, ad libitum, diets devoid of leucine to which graded amounts (0-2.05%) of KIC were added together with [1-14C]KIC were also measured for 12 hours. The amount of KIC oxidized increased as dietary KIC content oxidation studies plasma valine and alpha-ketoisovaleric acid (KIV) and plasma isoleucine and alpha-keto-beta-methylvaleric acid (KMV) concentrations were depressed when dietary levels of leucine were high. Plasma leucine and KIC concentrations were low when dietary levels of leucine were low and increased with increasing dietary leucine content. Leucine and KIC concentrations in plasma of rats fed a diet devoid of leucine did not increase in proportion to increasing dietary KIC content.

Amino Acids, Branched-Chain↗
PubMed1984

Effects on plasma amino acid concentrations and hepatic branched-chain alpha-keto acid dehydrogenase activity of feeding rats diets containing 9 or 50% casein.

Plasma concentrations of amino acids and alpha-ketoisocaproate and alpha-keto-gamma- methiolbutyrate decarboxylation activities in livers of rats trained to eat 9 or 50% casein diets for 5 hours/day, were measured one-half hour before and one-half and 3 hours after the start of the feeding period. Decarboxylation of both alpha-ketoisocaproate and alpha-keto-gamma- methiolbutyrate by liver increased significantly within one-half hour after rats had ingested either the 9 or the 50% casein diet. Liver decarboxylation activity of rats fed the 50% casein diet was from two- to fivefold higher than that of rats fed the 9% casein diet. The greatest difference was observed when calcium, NAD and coenzyme A were included in the decarboxylation assay medium. Although the activity of the branched-chain alpha-keto acid dehydrogenase increased in response to food ingestion, plasma concentrations of branched-chain amino acids also increased greatly after the ingestion of food. The similarity in the responses of alpha-ketoisocaproate and alpha-keto-gamma- methiolbutyrate decarboxylation in rats fed diets differing in protein content and subjected to different feeding regimens allows us to suggest that the branched-chain alpha-keto acid dehydrogenase is responsible, in part, for the oxidative decarboxylation of the alpha-keto acid analog of methionine. J. Nutr . 114: 1025-1034, 1984.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1983

Amino acid signals and food intake and preference: relation to body protein metabolism.

Depressed food consumption is an early response of experimental, animals to: 1) a dietary deficiency of either protein or an individual indispensable amino acid; 2) a distortion of the dietary pattern of amino acids when protein intake is low; and 3) a substantial elevation in the protein content of the diet. In each of these conditions the change in feeding behaviour is associated with alterations in concentrations of amino acids in blood but in none of them has the biochemical basis for the depressed food intake been established. The depressed food intake of rats consuming a low protein diet in which an imbalance of amino acids has been created by adding quantities of amino acids other than the one most limiting for growth, is associated with elevations in the plasma concentrations of amino acids added to create the imbalance and usually with a depression in the plasma concentration of the growth-limiting amino acid. These changes, in turn, are associated with depression of the concentration of the growth-limiting amino acid in the brain free amino acid pool. Studies in which uptake of amino acids into brain slices has been examined support the conclusion that various distortions of the plasma amino acid pattern, as the result of dietary imbalances of amino acids, can lead to depletion of the brain pool of a specific amino acid through competition between it and other amino acids in surplus in plasma for uptake into brain. The results of studies with rats in vivo of the effects on brain amino acid pools of ingestion of diets containing supplements of amino acids that compete with the growth-limiting amino acid for uptake into brain also support this conclusion. Depletion of the brain pool of the limiting amino acid as the result of feeding a diet with an amino acid imbalance can be related to overall body protein metabolism. In the young growing animal, protein synthesis is stimulated after a meal. Thus, when the diet is limiting in a single amino acid, that amino acid will be depleted from the circulating body pool. At the same time, the activities of amino acid degrading enzymes are low in animals fed a low protein diet; hence, such animals have limited capacity to degrade surpluses of amino acids. These conditions, depletion of the blood pool of the limiting amino acid and slow removal of surpluses of competing amino acids from the blood, will increase the extent of competition between other amino acids and the limiting amino acid for uptake into brain.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acids↗
PubMed1983

Atypical amino acids inhibit histidine, valine, or lysine transport into rat brain.

Transport of histidine, valine, or lysine into rat brain slices and across the blood-brain barrier (BBB) was determined in the presence of atypical nonprotein amino acids. Competitors of histidine and valine transport in slices were large neutral amino acids including norleucine, norvaline, alpha-aminooctanoate, beta-methylphenylalanine, and alpha-aminophenylacetate. Less effective were aromatic amino acids with ring substituents; ineffective were basic amino acids and omega-amino isomers of norleucine and aminooctanoate. Lysine transport was moderately depressed by homoarginine or ornithine plus arginine; large neutral amino acids were also similarly inhibitory. Histidine or valine transport across the BBB was also strongly inhibited by large neutral amino acids that were the most effective competitors in the slices (norvaline, norleucine, alpha-aminooctanoate, and alpha-aminophenylacetate); homoarginine and 8-aminooctanoate were ineffective. Homoarginine, ornithine, and arginine almost completely blocked lysine transport, but the large neutral amino acids were barely inhibitory. When rats were fed a single meal containing individual atypical large neutral amino acids or homoarginine, brain pools of certain large neutral amino acids or of arginine and lysine, respectively, were depleted.

Amino Acids↗
PubMed1982

Glucagon stimulation of phenylalanine metabolism. The effects of acute and chronic glucagon treatment.

The effects of acute and chronic glucagon treatment on phenylalanine metabolism in vivo in the rat have been investigated. A single, large dose of glucagon (2 mg/kg, i.p.) increased metabolism of a large load of phenylalanine (1.27 g/kg) via hydroxylation and transamination. The increased metabolism was associated with increased activities of hepatic phenylalanine:pyruvate aminotransferase, tyrosine aminotransferase and phenylalanine hydroxylase. In rats administered this amount of phenylalanine, the p-hydroxyphenylpyruvate dioxygenase reaction was apparently rate limiting, as indicated by increased urinary excretion of p-hydroxyphenylpyruvate and p-hydroxyphenyllactate, in addition to urinary excretion of phenylpyruvate and phenyllactate. Chronic glucagon treatment (1.25 mg/kg every 12 hr for 8 days) increased oxidation of the large phenylalanine load and urinary excretion of phenylpyruvate and phenyllactate but not p-hydroxyphenylpyruvate or p-hydroxyphenyllactate. The increased excretion of phenylpyruvate and phenyllactate was associated with an increase in hepatic phenylalanine: pyruvate aminotransferase activity. The absence of p-hydroxyphenylpyruvate in the urine and the increased oxidation of phenylalanine imply that, in rats administered glucagon chronically, flux of p-hydroxyphenylpyruvate through the p-hydroxyphenylpyruvate dioxygenase reaction was increased. A kinetic assay for phenylalanine hydroxylase based on measurement of oxygen consumption in described.

Amino Acids↗
PubMed1982

Effect of tryptophan intake on oxidation of [7a-14C]tryptophan and urinary excretion on N1-methylnicotinamide in the rat.

Oxidation of tryptophan and urinary excretion of niacin metabolites were studied in weanling rats fed ad libitum for 12 to 16 days niacin-free and nicotinamide-supplemented (20 mg/kg of diet) diets containing 15% of crystalline amino acids and from 0.04 to 1.0% of L-tryptophan. N1-methylnicotinamide was measured in urine collected during the last 3 days of the feeding period. After the feeding period, rats were placed in metabolic cages, and each rat was given 4 g (dry weight) of diet containing a tracer dose of DL-[7a-14C]tryptophan. Expired CO2 was collected hourly for 10 hours. In both the niacin-free and nicotinamide-supplemented groups, weight gains increased with increasing increments of tryptophan up to about 0.16% L-tryptophan. With more than 0.16% of L-tryptophan, the amount of N1-methylnicotinamide excreted per day by both groups of rats increased linearly with increasing tryptophan intake, but proportionately less N1-methylnicotinamide was excreted when the dietary tryptophan level was 1.0%. The amount of tryptophan oxidized per 10 hours increased linearly with increasing dietary tryptophan levels between 0.16 and 1.0%. Therefore, the decline in excretion of N1-methylnicotinamide with the 1.0% tryptophan level could not be accounted for by increased oxidation. These results suggest that after the tryptophan requirement for growth is met, the amount of tryptophan oxidized and converted to nicotinamide is directly proportional to the level of tryptophan intake up to about 3 times the requirement for growth. The tryptophan requirement of the growing rat fed niacin-free and nicotinamide-supplemented diets estimated from the inflection points of N1-methylnicotinamide excretion curves was in good agreement with the requirement of about 100 mumoles/day determined from the growth curve.

Animals↗
PubMed1982

Effect of nicotinamide intake on urinary excretion of N1-methylnicotinamide and oxidation of [7a-14C]tryptophan in the rat.

Oxidation of tryptophan and urinary excretion of N1-methylnicotinamide were studied in weanling rats fed ad libitum for 10 days 12% casein diets containing from 0 to 500 mg of nicotinamide per kilogram of diet. N1-methylnicotinamide was measured in urine collected during the last 3 days of the experiment. After the feeding period, rats fed the niacin-free and 500 mg nicotinamide diets were placed in metabolic cages, and each rat was given 4 g (dry weight) of diet containing a tracer dose of DL-[7a-14C]tryptophan. Expired CO2 was collected hourly for 10 hours. From rats consuming levels of nicotinamide ranging between 20 and 150 mg/kg of diet, N1-methylnicotinamide excretion increased linearly with increasing nicotinamide intake. From these results and others from this laboratory (4), it was calculated that an additional 10--11 mg of dietary tryptophan above the approximately 20 mg/day essential for growth are needed by the growing rat for the formation of 1 mg of nicotinamide. The addition of 500 mg of nicotinamide per kilogram of diet to a niacin-free diet had no effect on the oxidation of DL-[7a-14C]tryptophan.

Animals↗
PubMed1982

Food intake, growth and tissue amino acid concentrations in lean and obese (ob/ob) mice fed a threonine-imbalanced diet.

Food intake, growth and tissue amino acid concentrations were determined in lean and obese (ob/ob) mice fed a threonine-imbalanced diet. The poorest growth occurred in lean mice fed the imbalanced diet for 7 days; lean mice eating this diet supplemented with the threonine gained three times as much weight as those not receiving the supplement. Weight gains of obese mice consuming the imbalanced diet were not depressed. The obese mice ate more of all but the unsupplemented control diet than did the lean mice. Only lean mice fed a more severely imbalanced diet for 1 day lost weight and decreased their food intake; threonine concentration decreased in blood, brain and muscle of these lean mice but only in brain of the corresponding obese mice. Except for the sum of the concentrations of large neutral amino acids, amino acid levels were low in muscle of control obese mice. When other groups of lean and obese mice were fed a 60% casein diet concentrations of large neutral amino acids in plasma and liver, but not in brain, were 4- and 5-fold greater than in mice fed an 8% casein diet. The results suggest that responses of obese and lean mice to a threonine-imbalanced diet differ.

Amino Acids↗
PubMed1981

Blood and tissue branched-chain amino and alpha-keto acid concentrations: effect of diet, starvation, and disease.

Branched-chain alpha-keto and amino acid (BCKA, BCAA) concentrations were measured in blood, plasma, and tissues of rats fed low protein (8% casein) or high protein (60% casein) diets; and in rats fed a stock diet and subjected to 3 days of starvation of chemically-induced diabetes. Concentrations of these amino and ketoacids were also measured in blood from patients with maple syrup urine disease. Valine, isoleucine, and leucine concentrations in blood from rats fed the stock diet were 124 +/- 7, 58 +/- 4 and 99 +/- 5 microM, respectively. Blood BCAA concentrations of rats fed the high protein diet and diabetic rats were elevated 2- to 3-fold; small increases were observed in blood from starved rats. Changes in blood BCAA concentrations paralleled those in tissues, except in starved rats in which the skeletal muscle free BCAA pool increased proportionately more than the circulating pool. Mean blood BCKA concentrations of rats fed the stock diet were low--7.9 +/- 0.5, 7.1 +/- 0.4 and 12.4 +/- 0.7 microM for alpha-ketoisovaleric, alpha-keto-beta-methylvaleric, and alpha ketoisocaproic acids, respectively. All treatments resulted in increases in blood BCKA concentrations of from 1.4 to 2 fold. In liver and heart, concentrations of BCKA, except for that of alpha-ketoisocaproic acid were near the limits of detection (less than 1 nmole/g). There was significant accumulation of all three BCKA in skeletal muscle which was estimated to contain about 80% of the measured body free BCKA pool. Blood BCKA are well regulated. Only in patients with maple syrup urine disease are plasma concentrations of BCKA useful indicators of altered tissue BCAA metabolism. Skeletal muscle, where oxidation of the BCKA is limited by low BCKA dehydrogenase activity, would seem to be the major source of circulating BCKA.

Amino Acids, Branched-Chain↗