Alfred E. Harper’s research while affiliated with University of Wisconsin–Madison and other places

To assess whether dietary guidelines for Americans are appropriate for young children, the evolution of dietary guidance, the nature of the guidelines, evidence used to support the concept of diet modification to prevent heart disease and the rationale for extending application of the guidelines to children have been examined. As health improved during this century, life expectancy lengthened, and diseases associated with aging became major causes of death. As a consequence, emphasis on dietary advice for selecting a nutritionally adequate diet--the primary need of children--declined, whereas emphasis on dietary advice for preventing chronic and degenerative diseases increased. It is clear from reading the text accompanying the guidelines that they were proposed to prevent diseases of aging by reducing consumption of animal products. Critical evaluation of evidence bearing on the concept of the guidelines reveals that there are grounds for skepticism about claims for the effectiveness of diet modification as a measure for reducing the incidence of heart disease. Also, the rationale for extending the guidelines to young children is based on inferences from observations on adults, not on direct evidence that children will benefit from following them. There is, thus, ample justification for proposing separate dietary guidelines for children.

This study was conducted to determine the effects of different concentrations of leucine on the transport, transamination and oxidation of valine and on incorporation of valine into heart proteins in the isolated perfused rat heart. Valine metabolism was studied in rat hearts perfused with medium containing glucose and graded levels of L-leucine. In transport studies L-phenylalanine was also tested. Uptake of L-[1-14C]valine (0.2 mmol/L) was significantly reduced (-50%) by inclusion of 0.2 mmol/L phenylalanine or leucine, and by -70% by inclusion of 1.0 mmol/L phenylalanine or leucine in the perfusate. Transamination of valine decreased by 37 and 48%, and oxidation of valine by 53 and 71%, respectively, when 0.2 or 1.0 mmol/L leucine was included in the perfusate. Tissue concentrations of valine decreased by 43, 48 and 62% in the presence of 0.2, 0.5 and 1.0 mmol/L leucine, respectively; tissue concentrations of leucine, glutamate and alanine increased approximately 11-fold, 1.2-fold and 0.5-fold, respectively, when 1.0 mmol/L leucine was present in the perfusate. Addition of 0.2-1.0 mmol/L leucine did not affect incorporation of valine into heart proteins. We conclude that 1) competition among large neutral amino acids for transport into heart occurs at physiological concentrations of these amino acids in plasma; 2) inhibition of valine uptake by leucine can limit the rate of valine catabolism in heart; and 3) depletion of tissue valine concentration by an excess of leucine did not affect the rate of protein synthesis.

The effects of sucrose on the neuropsychological test performance of juvenile offenders with low (<50 mg/dl), borderline (50–60 mg/dl), and normal (>60 mg/dl) serum glucose nadirs during an oral sucrose tolerance test were examined using a double-blind crossover challenge design. Subjects ingested a sucrose-loaded (78 g) and a no-sucrose (<1 g) breakfast prior to behavioral assessments. Offenders with atypically low glucose nadirs performed better after ingesting the sucrose-loaded breakfast than after the control meal. A similar effect was observed in offenders with serum glucose nadirs falling in the normal range whereas subjects with borderline nadirs performed comparatively poorly following both breakfasts. These results indicate that the relations among short-term sucrose consumption, biochemistry, and behavior are complex and highlight the need to rigorously test presumptions regarding the effects of sucrose on the behavior of juvenile criminal offenders.

Metabolism of physiological concentrations of valine was studied in mitochondria from mixed skeletal muscle and isolated soleus muscle to extend knowledge of the mechanism by which the leucine-induced branched-chain amino acid antagonism depresses valine and isoleucine concentrations in plasma and tissues.Measurements were made of flux of valine through muscle branched-chain aminotransferase and branched-chain keto acid dehydrogenase (BCKD) and reamination of α-ketoisocaproate (KIC).Concentrations of KIC from 0.05–1.0 mm stimulated transamination of valine. Low concentrations of KIC stimulated valine oxidation in both preparations. However, concentrations above 0.5 mm diminished the rates of CO2 evolution from valine.Inclusion in the assay medium of graded levels of leucine (as a potential source of KIC) depressed valine oxidation through competitive inhibition with valine for transamination in muscle mitochondria. Increasing the BCKD capacity of in vitro preparations by including liver and muscle mitochondria together did not alteviate this inhibition.In contrast, valine oxidation by soleus muscle was stimulated by both leucine and KIC. Addition of [1-14C] KIC in the medium resulted in stimulation of KIC oxidation in both intact and detergent-treated mitochondria. Addition of 0.2 mm valine increased the reamination of KIC to leucine. This can explain in part the high plasma and tissue leucine values, and the decrease in valine, and probably isoleucine, concentrations in animals fed with high leucine diets.

Previous studies have proposed the possibility that erythrocytes (RBC) are involved in the interorgan transport of amino acids; however, this role has not been confirmed. In order to study the likelihood that erythrocytes are involved in the interorgan transport, rates of influx and efflux of glycine, threonine, lysine, histidine and leucine were measured in rat red blood cells. Time course of influx of leucine, a large neutral amino acid, was very rapid (319 mumoles/L RBC. min), and a steady state was reached between 5 to 10 min of incubation, whereas glycine influx was very slow (5.04 mumoles/L RBC. min). Threonine influx was similar to leucine although the rate was slower (41.4 mumoles/L RBC. min); however, the steady state was reached in 30 minutes and its uptake showed less capacity. Histidine and lysine showed a continuous influx, and did not reach a steady state after 60 min of incubation. Efflux of leucine was extremely rapid indicating a rapid equilibration between the incubation medium and the intracellular space of the erythrocytes. Threonine efflux had a half life (t1/2) of between two to three min, independently of the medium used. Histidine showed a t1/2 of around six min, whereas for the small neutral amino acid glycine it was of 14 to 17 min. These results indicate that some large neutral amino acids are not involved in the potential interorgan transport by red blood cells due to the rapid equilibration of the concentration of amino acid between cells and the medium.

Dietary amino acid analogs often strongly and selectively modify rat tissue amino acid profiles. These effects are accompanied by altered activities of several enzymes of amino acid catabolism. In a preliminary study, activities of hepatic serine dehydratase (SDH), glutamate-pyruvate (GPT), GABA and tyrosine (TAT) aminotransferases, and ornithine carbamoyltransferase (OCT) were high in rats fed diets containing a mixture (3%) of analogs (norleucine, norvaline, α-aminophenylacetate, and α-aminooctanoate); pyruvate kinase (PK) was low. Raising the protein content of the diet often lessened the effect. Analog effects on SDH, GPT, and PK occurred within 2 days, but not within 4 hr. After adaptation to a 50% protein diet that raised SDH and GPT and lowered PK, rats were fed a 6% protein diet with or without the analogs; the normal decline in initially high SDH and GPT was slowed within 4 days in rats fed the analogs, whereas the normal increase in PK induced by a low protein diet was strongly blocked by day 1. In rats fed a 6% amino acid diet, dietary norleucine stimulated branched-chain ketoacid dehydrogenase (BCKAD) activity about 290%, had lesser effects on SDH, GPT, and OCT, and did not alter PK, TAT, or branched-chain aminotransferase; norvaline stimulated only BCKAD (85%). In rats fed an 8% amino acid mixture limiting in leucine. SDH activity was stimulated (up to 800%), depending on norleucine level in the diet, and was lessened by added dietary leucine; similar, but less striking patterns occurred for GPT. If all indispensable amino acids were fed in adequate amounts, SDH and GPT were not stimulated by norleucine. Overall, analog effects were usually more prominent in rats fed suboptimal diets.

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.

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 < .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 > .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 > .05) dietary response in egg weight to either Cho or Met. The combination of 427 and 220 ppm of Met and Cho, respectively, with the FS strain resulted in the largest egg weight. However, this was only significantly different (P < .05) from addition of a combination of 73 ppm of Met and 220 ppm Cho. These results indicate strain differences in responses of laying hens to Met and Cho supplementation, and also support the concept that Met and Cho can spare the requirements of each other.