Studies on requirement and excess of isoleucine in laying hens

Three production trials and one nitrogen balance trial were conducted with Lohmann Brown hens to determine the requirement for and effects of an excess of isoleucine in layers at different ages (24 to 32 and 46 to 54 wk of age). The trials were designed as dose-response studies where isoleucine-deficient basal rations with 11.4 MJ metabolizable energy per kilogram were supplemented with varying amounts of L-isoleucine. In the production trials, dietary isoleucine concentrations ranged from 0.37 to 1.05%. In the three production trials, maximum daily egg mass was achieved at dietary isoleucine concentrations of between 0.39 and 0.75% (25 to 32 wk of age, daily egg mass 53 g), 0.40 and 0.57% (24 to 32 wk of age, daily egg mass 57 g), and 0.40 and 0.81% (46 to 54 wk of age, daily egg mass 56 g). The corresponding ranges of daily isoleucine intakes were 412 to 770 mg, 436 to 624 mg, and 431 to 874 mg. In the nitrogen balance trial, maximum total nitrogen retention was achieved at dietary isoleucine concentrations of between 0.43 and 0.57%. Dietary isoleucine concentrations higher than 0.8% caused a reduction in hen BW. Dietary isoleucine concentrations higher than 1.0% additionally caused a reduction in the daily egg mass. The study thus shows that the margin between requirement and excess of isoleucine is narrow in laying hens.

Influence of supplemental lysine, isoleucine, threonine, tryptophan and total sulfur amino acids on egg weight of Hy-line W-36 hens

Four experiments were conducted to determine whether synthetic lysine, isoleucine, threonine, and tryptophan (LITT) or TSAA supplementation to diets formulated based on lysine improved egg weight (EW) and hen performance. In Experiment 1, diets were formulated with three TSAA levels (0.65,0.72, and 0.81%). These diets were fed with and without adding lysine and isoleucine each at 0.055% and threonine and tryptophan each at 0.022%. Treatments were randomly assigned to 960 Hy-Line W-36 hens in eight replicates per treatment (20 birds/replicate). Inclusion of LITT improved (P < 0.05) EW within 2 wk with no TSAA x LITT interaction. Inclusion of LITT also increased average feed consumption (FC) by 1.4 g/d (P < 0.01). However, no effect (P > 0.05) of LITT was observed on egg production (EP), egg specific gravity (SG), or BW. The EW, EP, and FC increased linearly (P < 0.05) as dietary TSAA increased. The TSAA had no effect on SG or BW. In Experiment 2, supplemental LITT were removed to determine how rapidly hens lose the effect of LITT on performance. Within 2 wk, the effect of LITT on EW was lost. Average EW, EP, and FC of hens fed higher TSAA levels remained higher (P < 0.05) than hens fed 0.65% TSAA. In Experiment 3, all hens were fed a diet containing 0.65% TSAA to determine the time it takes to lose the effect of TSAA supplementation. The TSAA supplementation effect on EW, EP, and FC observed in the previous two experiments was lost within 1 wk. In Experiment 4, hens were again fed diets similar to Experiment 2 to confirm the time required for TSAA supplementation to improve EW. Within 1 wk, hens fed 0.72 or 0.81% TSAA improved (P < 0.05) EW over hens fed 0.65% TSAA. It was concluded that hens fed diets formulated based on lysine were deficient in LITT. Hens responded to the inclusion or removal of supplemental LITT and TSAA within 1 to 2 wk.

Evaluation of isoleucine, leucine, and valine as a second-limiting amino acid for milk production in dairy cows fed grass silage diet

Five Finnish ruminally cannulated Ayrshire cows were used in a 5 x 5 Latin square trial with 14-d periods to determine whether branched-chain amino acids (AA) are the second- or colimiting AA for milk protein synthesis on grass silage-cereal based diet. Mammary metabolism of AA as well as AA supply from the basal diet were also studied. Grass silage (17.5% crude protein) was given ad libitum with 9 kg/d as a cereal-based concentrate (13.8% crude protein). Treatments were basal diet without AA infusion (Control), abomasal infusion of AA mixture of His, Ile, Leu, and Val at 8.5, 14.9,27.9, and 18.3 g/d, respectively, AA mixture minus Ile, AA mixture minus Leu, and AA mixture minus Val. Glucose was infused on all treatments at 250 g/d. Amino acid infusions had no effect on dry matter intake (mean 19.2 kg/d), yields of milk (mean 25.3 kg/d), energy-corrected milk (mean 25.9 kg/d), milk protein (mean 807 g/d), lactose (mean 1261 g/d), or fat (mean 1056 g/d). Milk composition was not affected by the treatments. Plasma concentrations of His and Val responded to AA infusions but concentration of Ile increased only on treatment AA mixture minus Leu, and concentration of Leu only on treatment AA mixture minus Ile. Infusion of AA mixture of His, Ile, Leu, and Val decreased plasma concentrations of Arg, Lys, Met, Phe, and Tyr. Amino acid infusions did not affect concentrations of plasma urea and energy metabolites or AA utilization by the mammary gland. Based on unchanged production parameters, the supply of His or branched-chain AA seemed not to be limiting under the current dietary conditions. Changes in plasma AA concentrations suggest either antagonism between individual AA in absorption or increased partitioning of AA into the muscle tissues. About 75% of omasal canal nonammonia nitrogen flow (427 g/d) was of microbial origin, and AA profiles of microbial protein and omasal canal digesta were fairly similar. Postruminal AA supply seems to be dependent on the basal diet, but variation may exist even within the similar basal diets.

Transfer ribonucleic acid charging in rat brain after consumption of amino acid-imbalanced diets

Recognition of an amino acid-imbalanced diet (IMB) is thought to occur in the anterior piriform cortex (APC) of the brain in response to a decrease in the limiting amino acid. We hypothesized that tRNA charging is decreased after ingestion of IMB and that this is part of the mechanism by which a decrease in the limiting amino acid is recognized. We investigated this question by determining levels of charged and uncharged tRNA using the periodate oxidation method and also by using high performance liquid chromatography (HPLC) analysis of amino acids acylated to brain tRNA. Using the periodate method, we found that isoleucyl-tRNA in both whole brain and APC of rats fed an isoleucine-IMB was increased, rather than decreased, in comparison to the basal diet and the corrected diet. Using HPLC analysis, we found that the absolute amount of tRNA charged with the limiting amino acid was not altered by dietary treatment. These two experimental approaches measure different aspects of tRNA charging, but the results clearly indicate that a reduction in tRNA charging is unlikely to be the signal by which a limiting amino acid is recognized in the brain 2 h after ingestion of IMB.

BCAA intake affects protein metabolism in muscle after but not during exercise in humans

Branched-chain amino acids (BCAA) or a placebo was given to seven subjects during 1 h of ergometer cycle exercise and a 2-h recovery period. Intake of BCAA did not influence the rate of exchange of the aromatic amino acids, tyrosine and phenylalanine, in the legs during exercise or the increase in their concentration in muscle. The increase was approximately 30% in both conditions. On the other hand, in the recovery period after exercise, a faster decrease in the muscle concentration of aromatic amino acids was found in the BCAA experiment (46% compared with 25% in the placebo condition). There was also a tendency to a smaller release (an average of 32%) of these amino acids from the legs during the 2-h recovery. The results suggest that BCAA have a protein-sparing effect during the recovery after exercise, either that protein synthesis has been stimulated and/or protein degradation has decreased, but the data during exercise are too variable to make any conclusions about the effects during exercise. The effect in the recovery period does not seem to be mediated by insulin.

Isoleucine imbalance using selected mixtures of imbalancing amino acids in diets of the broiler chick

Three experiments were conducted to determine the isoleucine requirement of a broiler from the time of hatch to 16 d of age. Chicks in the experiments were fed an isoleucine-limiting diet composed of wheat and peanut meal as the primary protein sources; this diet was used to investigate various mixtures of amino acids as imbalancing agents for isoleucine. The isoleucine requirement for maximum weight gain and feed efficiency was determined on the basis of broken-line regression analysis to be 0.63 to 0.65% of the diet or 3.28 to 3.38% of dietary protein. A similar diet, marginally limiting in isoleucine, was used to investigate the response of chicks to the addition of various mixtures of amino acids to the diet. Chicks that received a 5% dietary addition of 11 amino acids consisting of equimolar concentrations of leucine, valine, histidine, methionine, phenylalanine, tryptophan, tyrosine, alanine, glycine, serine, and threonine had significantly lower weight gain and feed consumption and a higher feed conversion ratio than did chicks fed the basal diet. These adverse effects were only partly prevented by an isoleucine supplement. The large neutral amino acids, histidine, methionine, phenylalanine, tryptophan, and tyrosine, accounted for most of the effect of the mixture. No effect of a mixture of leucine and valine or a mixture of the small neutral amino acids (alanine, glycine, serine, and threonine) at the same concentrations as those in the mixture of the 11 amino acids was observed. Lysine and arginine were the only two indispensable amino acids not present in the mixture of 11 amino acids. A subsequent experiment demonstrated that these amino acids did not become co-limiting with isoleucine when the diet was imbalanced with the amino acid mixture. These results indicate that an isoleucine imbalance in chicks is readily precipitated by excessive dietary concentrations of large neutral amino acids in diets that are otherwise marginally adequate in isoleucine.

Effects of branched-chain amino acid supplementation on serum creatine kinase and lactate dehydrogenase after prolonged exercise

BACKGROUND

The aim of this study was to examine the effects of branched-chain amino acid (BCAA) supplementation on serum indicators of muscle damage after prolonged exercise. We hypothesized that BCAA supplementation would reduce the serum activities of intramuscular enzymes associated with muscle damage.

METHODS

To test this hypothesis, sixteen male subjects were assigned to one of two groups: the supplemental group (consuming 12 g x d(-1) BCAA for 14 d in addition to their normal diet) or the control group (normal diet only). Baseline serum creatine kinase (CK) and lactate dehydrogenase (LDH), shown to be accurate indicators of muscle damage, were determined during the week before the exercise test. The exercise test was administered on day seven and required the subjects to cycle for 120 min on an ergometer at approximately 70% VO2max. Blood samples were taken prior to and immediately following exercise and at 1 hr, 2 hrs, 3 hrs, 4 hrs, 1 d, 3 d, 5 d and 7 d postexercise. All subjects were required have their diets analyzed daily during the 14 d.

RESULTS

Dietary analyses indicated that all subjects consumed the recommended daily intake of BCAA (0.64 g x kg(-1)) in their normal diets. Baseline serum values for CK and LDH were not different between groups in the 7 d prior to the test (p>0.05). However there were significant increases (p<0.05) between the pre-exercise and postexercise values for LDH and CK until 5 d postexercise test. Importantly, the BCAA supplementation significantly reduced this change in LDH from 2hrs to 5 d posttest, and CK from 4 hrs to 5 d post-test (p<0.05).

CONCLUSIONS

These results indicate that supplementary BCAA decreased serum concentrations of the intramuscular enzymes CK and LDH following prolonged exercise, even when the recommended intake of BCAA was being consumed. This observation suggests that BCAA supplementation may reduce the muscle damage associated with endurance exercise.

Evaluation of the isoleucine requirement of the commercial layer in a corn-soybean meal diet

An experiment was conducted with Hy-Line W36 hens to evaluate their Ile requirement in a corn-soybean meal diet. Five experimental diets were fed with Ile levels of 0.61, 0.58, 0.55, 0.52, and 0.49%. Supplemental amino acids (AA) were added to ensure that Ile was the first-limiting AA. Two diets with 0.55 and 0.52% Ile were also fed with higher levels of supplemental AA. A positive control (0.67% Ile) with only Met supplementation was fed, which had previously been shown to support maximum performance. All levels of Ile addition significantly increased egg production (EP), egg weight (EW), and egg contents (EC). Broken-line regression indicated a daily Ile requirement of 589.2, 601.2, and 601.4 mg per day for EP, EW, and EC, respectively, which indicated a requirement of 12.6 mg Ile per gram of EC.

Significance of L-alloisoleucine in plasma for diagnosis of maple syrup urine disease

BACKGROUND

The significance of plasma L-alloisoleucine, which is derived from L-isoleucine in vivo, for diagnosis of maple syrup urine disease (MSUD) was examined.

METHODS

Branched-chain L-amino acids were measured by automatic amino acid analysis.

RESULTS

Alloisoleucine reference values in plasma were established in healthy adults [1.9 +/- 0.6 micromol/L (mean +/- SD); n = 35], children 3-11 years (1.6 +/- 0.4 micromol/L; n = 17), and infants <3 years (1.3 +/- 0.5 micromol/L; n = 37). The effect of dietary isoleucine was assessed in oral loading tests. In controls receiving 38 micromol (n = 6; low dose) and 1527 micromol (n = 3; high dose) of L-isoleucine per kilogram of body weight, peak increases of plasma isoleucine were 78 +/- 24 and 1763 +/- 133 micromol/L, respectively; the peak increase of alloisoleucine, however, was negligible for low-dose (<0.3 micromol/L) and minor for high-dose (5. 5 +/- 2.1 micromol/L) load. In patients with diabetes mellitus, ketotic hypoglycemia, phenylketonuria, and obligate heterozygous parents of MSUD patients, alloisoleucine was not significantly different from healthy subjects. Therefore, a plasma concentration of 5 micromol/L was used as a cutoff value. In patients with classical MSUD (n = 7), alloisoleucine was beyond the cutoff value in 2451 of 2453 unselected samples. In patients with variant MSUD (n = 9), alloisoleucine was >5 micromol/L in all samples taken for establishment of diagnosis and in 94% of the samples taken for treatment control (n = 624). With the other branched-chain amino acids, the frequency of diagnostically significant increases was <45%.

CONCLUSIONS

The present findings indicate that plasma L-alloisoleucine above the cutoff value of 5 micromol/L is the most specific and most sensitive diagnostic marker for all forms of MSUD.

Attenuation of the protein wasting associated with bed rest by branched-chain amino acids

Bed rest is generally accepted as being an appropriate ground-based model for human spaceflight. The objectives of this study were to test the hypothesis that increasing the amount of branched-chain amino acids (BCAAs) in the diet could attenuate the protein loss associated with bed rest. Nineteen healthy subjects were randomized into two groups according to diet. During the 6 d of bed rest, the diets were supplemented with either 30 mmol/d each of three non-essential amino acids, glycine, serine, and alanine (control group), or with 30 mmol/d each of the BCAAs, leucine, isoleucine, and valine (BCAA group). Nutrition was supplied as a commercially available defined formula diet at a rate of 1.3 x REE. Nitrogen (N) balance and urinary 3-MeH excretion were determined for the 6 d. In our results, the urine-based estimate of N balance was 22.2 +/- 14.4 (n = 9) mg N.kg-1.d-1 and 60.5 +/- 10.1 mg (n = 8) N.kg-1.d-1 for the control and BCAA-supplemented groups, respectively (P < 0.05). Urinary 3-MeH excretion was unchanged in both groups with bed rest. We conclude that BCAA supplementation attenuates the N loss during short-term bed rest.

Ethylmalonic and methylsuccinic aciduria in ethylmalonic encephalopathy arise from abnormal isoleucine metabolism

Ethylmalonic encephalopathy (EE), an organic aciduria of unknown etiology characterized by developmental delay, hypotonia, and vascular instability associated with lactic acidemia and urinary excretion of ethylmalonic acid (EMA) and methylsuccinic acid (MSA), has been described in 11 patients. To test the possibility that the underlying biochemical defect involves isoleucine catabolism, we determined the response to oral L-isoleucine (IIe) load (150 mg/kg) in a 5-year-old girl with EE and in three healthy, age- and sex-matched controls. Following IIe load in the patient, there was accumulation of 2-methylbutyrylglycine (2-MBG) and a delayed and lower peak urinary excretion of tiglylglycine (TGL), suggesting a partial defect in 2-methyl-branched chain acylcoenzyme A dehydrogenase (2M-BCAD). In vitro measurements 2M-BCAD activity in cultured skin fibroblasts from patients with EE have been reported to be normal. Our results show that isoleucine is a source for the elevated EMA and MSA in patients with EE, and suggest a functional, possibly secondary, deficiency of activity of 2M-BCAD in vivo.

4-Hydroxyisoleucine: a novel amino acid potentiator of insulin secretion

We report the characterization of a new insulinotropic compound, 4-hydroxyisoleucine. This amino acid has been extracted and purified from fenugreek seeds, which are known in traditional medicine for their antidiabetic properties. 4-Hydroxyisoleucine increases glucose-induced insulin release, in the concentration range of 100 micromol/l to 1 mmol/l, through a direct effect on isolated islets of Langerhans from both rats and humans. The stimulating effect of 4-hydroxyisoleucine was strictly glucose dependent; indeed, ineffective at low (3 mmol/l) or basal (5 mmol/l) glucose concentrations, the amino acid potentiated the insulin secretion induced by supranormal (6.6-16.7 mmol/l) concentrations of glucose. In addition, in the isolated perfused rat pancreas, we could show 1) that the pattern of insulin secretion induced by 4-hydroxyisoleucine was biphasic, 2) that this effect occurred in the absence of any change in pancreatic alpha- and delta-cell activity, and 3) that the more glucose concentration was increased, the more insulin response was amplified. Moreover, 4-hydroxyisoleucine did not interact with other agonists of insulin secretion (leucine, arginine, tolbutamide, glyceraldehyde). Therefore, we conclude that 4-hydroxyisoleucine insulinotropic activity might, at least in part, account for fenugreek seeds' antidiabetic properties. This secretagogue may be considered as a novel drug with potential interest for the treatment of NIDDM.

Quick responses of plasma amino acid concentration to changes in dietary amino acid levels in rats

In order to evaluate the availability of plasma amino acid (AA) concentration as a parameter to determine AA requirements of rats within a short period, the response of the plasma AA concentration to changes in dietary AA levels was studied. In Experiment 1, to clarify whether the plasma AA concentration responded to changes in dietary AA levels and how long the response of the plasma AA concentration was maintained, 10 male rats were fed a casein diet for a 7 day period, and then the food was changed to AA diets. The serine (Ser), glycine (Gly) and threonine (Thr) levels were decreased from 120, 90 to 60% of the casein diet at 7-day intervals successively. Blood samples were taken at 2, 4 and 7 days after changing the diet, from the vena caudalis by vein puncture. In all cases, the plasma AA concentration responded to changes in dietary AA within 2 days, and the response was maintained until the 7th day. Experiment 2 was conducted to confirm that the plasma concentration of each AA responded to the changes in dietary AA levels at the first day and the responses of the plasma concentration of AA were maintained until the 4th day after changing the dietary AA levels, when the combination of metabolically unrelated AA was added. Five rats in A groups were fed diets with added arginine + Thr, histidine + methionine, lysine or isoleucine + Ser, and five rats in B groups were fed diets with added Gly + valine, leucine + phenylalanine or Thr + tyrosine + valine for a 4-day period successively. Blood samples were taken at 1 and 4 days after changing diets. Although the plasma concentrations of histidine, leucine, methionine, phenylalanine and Ser did not respond to changes in dietary AA levels, those of other AA responded at 1 day and the responses were maintained until the 4th day.

Rebalancing essential amino acids intake by self-selection in the rat

The purpose of the present study was to assess whether rats are capable of selecting the right proportions of two diets that are individually inappropriate in terms of essential amino acid composition to satisfy their amino acid requirements. Rats were offered a choice of one protein-free regimen and another devoid of only one essential amino acid (either threonine or isoleucine) set up in such a way as to provide amino acid balance if they were consumed in 1/3 and 2/3 proportions respectively. Preliminary experiments had established that all our diets were aversive by themselves except for the 60 g casein/kg diet. Rats did reach almost the necessary proportion with, according to published standards (National Research Council, 1978), some excess in isoleucine intake. In addition, given access to two aversive diets that were each nutritionally inadequate, rats showed no aversion and gained body weight when they had the opportunity to consume both of them. Beyond the capacity that rats have of rebalancing their micronutrient intake, the present experiment brings out the idea that the imbalance-induced aversion:preference ratio may be completely upset when this omnivore has access to more than one feed.

Subchronic toxicity study of L-isoleucine in F344 rats

A subchronic toxicity study with L-isoleucine was conducted using F344 rats. Groups of 10 rats of each sex were given diet containing 0, 1.25, 2.5, 5.0, or 8.0% L-isoleucine for 13 wk. No treatment-related effects were observed in terms of body weight change, food consumption or hematology. In both sexes given 8.0% L-isoleucine, increased or a tendency for increased urine volume and relative kidney weights were observed. Furthermore, the high-dose L-isoleucine treatment brought about an elevation of urinary pH and variations in serum electrolytes. However, histopathological alterations related to these changes were not observed in any organs of either sex. In conclusion, the present study demonstrated that L-isoleucine possessed minimal toxicity at dietary levels of 5.0% and 8.0%, while it did not exert any adverse affects at a dietary level of 2.5% or less.

Oral branched-chain amino acids decrease whole-body proteolysis

BACKGROUND

This study reports the effects of ingesting branched-chain amino acids (leucine, valine, and isoleucine) on protein metabolism in four men.

METHODS

To calculate leg protein synthesis and breakdown, we used a new model that utilized the infusion of L-[ring-13C6]phenylalanine and the sampling of the leg arterial-venous difference and muscle biopsies. In addition, protein-bound enrichments provided for the direct calculation of muscle fractional synthetic rate. Four control subjects ingested an equivalent amount of essential amino acids (threonine, methionine, and histidine) to discern the effects of branched-chain amino acid nitrogen vs the effects of essential amino acid nitrogen. Each drink also included 50 g of carbohydrate.

RESULTS

Consumption of the branched-chain and the essential amino acid solutions produced significant threefold and fourfold elevations in their respective arterial concentrations. Protein synthesis and breakdown were unaffected by branched-chain amino acids, but they increased by 43% (p < .05) and 36% (p < .03), respectively, in the group consuming the essential amino acids. However, net leg balance of phenylalanine was unchanged by either drink. Direct measurement of protein synthesis by tracer incorporation into muscle protein (fractional synthetic rate) revealed no changes within or between drinks. Whole-body phenylalanine flux was significantly suppressed by each solution but to a greater extent by the branched-chain amino acids (15% and 20%, respectively) (p < .001).

CONCLUSIONS

These results suggest that branched-chain amino acid ingestion suppresses whole-body proteolysis in tissues other than skeletal muscle in normal men.

Anorectic responses to dietary amino acid imbalance: effects of vagotomy and tropisetron

We investigated the roles of the vagus nerve and the serotonin3 (5-HT3) receptor in mediating the food intake depression associated with amino acid deficiency. The food intake of sham-operated (sham) rats given an isoleucine-imbalanced (IMB) diet was reduced to < 40% of control basal (BAS) diet intake (P = 0.0009), and pretreatment with the 5-HT3 antagonist tropisetron (Trop) increased IMB intake by twofold over the vehicle (VEH)-treated group (P < or = 0.0001), as we have reported before. However, after subdiaphragmatic vagotomy (VAGX), IMB intake was increased to a level intermediate between the sham-VEH and sham-Trop groups, while administration of Trop did not increase IMB intake over VAGX alone. By the end of day 1, the VAGX-Trop group had eaten only 1 g more of IMB than the VAGX-VEH group (NS). We conclude that 1) the vagus is among the physiological systems involved in the anorectic responses to IMB and 2) intact vagal function is necessary for the full effect of 5-HT3 antagonists in alleviating the anorectic responses to IMB.

Kittens choose a high leucine diet even when isoleucine and valine are the limiting amino acids

This study was conducted to determine the effect of excess leucine on the dietary choice of kittens. The basal diets contained 16% (low nitrogen) or 24% (adequate nitrogen) amino acids and were limiting in isoleucine and valine. The addition of leucine to either of these basal diets has been shown to cause a transitory adverse effect on the growth and food intake of kittens. In separate experiments each basal diet was used to test three sets of choices: basal vs. basal + 10% leucine; basal + alanine vs. basal + leucine (isonitrogenous) and basal vs. basal + alanine. When offered basal vs. basal + excess leucine, the kittens chose significantly more of the excess leucine diet regardless of the level of nitrogen in the basal diet. When offered an isonitrogenous choice of excess alanine vs. excess leucine, the kittens selected somewhat more of the excess leucine diets over the excess alanine diets; this selection was sustained longer in kittens fed low nitrogen. In the third choice experiment (basal vs. basal + alanine), the group offered the low nitrogen diets exhibited no preferences, and the group offered adequate-nitrogen diets selected significantly more of the excess alanine diet. These results for kittens are opposite to those for rats, a species that will select a low protein basal or even a protein-free diet over a diet containing excess leucine.

Effects of valine, leucine, isoleucine, and a balanced amino acid solution on the seizure threshold to picrotoxin in rats

During infusion of branched-chain amino acids (BCAAs) in humans, changes in ventilatory drive, sleeping pattern, and appetite have been reported. The mechanism by which BCAA exerts their effects on CNS remains unclear. An infusion of a BCAA solution (300 mg/kg) has previously been found to increase the seizure threshold in rats to the proconvulsant drug picrotoxin, an antagonist on the GABA-benzodiazepine receptor complex. In this study, each of the BCAAs given separately (valine, leucine, isoleucine; 300 mg/kg) (n = 10) increased the mean latency time to onset of seizures vs. placebo as an indication of an increased seizure threshold. A balanced amino acid solution (Vamin-Glucose) had no effect on the seizure threshold. Thus, these CNS effects are specific for BCAAs and occur with all three.

Effects of intraperitoneal L-leucine, L-isoleucine, L-valine, and L-arginine on milk fat depression in early lactation cows

Eight Holstein cows were assigned following calving to two groups, balanced for parity, using a continuous completely randomized block design. Cows were fed a diet with 13.5% CP and 22.4% ADF from 35 to 55 DIM and then 13.8% CP and 15% ADF from 56 to 92 DIM. Alfalfa grass hay was the forage source, and concentrate mixtures contained primarily corn and soybean meal. Cows were given daily intraperitoneal infusions of a solution of L-Leu (46.1 g, 84.2 mM), L-Ile (31.4 g, 57.3 mM), L-Val (38.3 g, 78.2 mM), and L-Arg (25.0 g, 34.4 mM) or physiological saline following the a.m. milking from 42 through 84 DIM. Infusion of AA significantly increased plasma concentrations of Leu, Ile, Val, and Arg. Effects of AA infusion occurred during the low fiber period. Cows receiving AA maintained daily milk fat yield, increased p.m. milk fat yield, decreased less in p.m. milk fat percentage, and increased daily and p.m. yields of C16 fatty acids in milk. During the posttreatment period, cows previously receiving AA declined in daily milk fat yield, milk fat percentage, and total daily C4 to C16 milk fatty acid yield. Results suggest that the infused AA may have increased de novo synthesis of C16 milk fatty acids.

Protein and energy relationships in the broiler chicken. Effects of protein quantity and quality on metabolism

Male broiler chickens growing from 7 to 35 d were fed on a diet containing 150 g crude protein (N x 6.25)/kg diet supplemented with lysine to equal that in diets containing 166, 183 and 200 g crude protein/kg diet (Expt 1). A second group of male broiler chickens growing over the same period were fed on a diet containing 120 g crude protein/kg supplemented with lysine, arginine, tryptophan, threonine and isoleucine equal to that in diets containing 144, 172 and 200 g crude protein/kg diet (Expt 2). Growth was improved by lysine supplementation but not to the level attained by feeding 200 g crude protein/kg (Expt 1). Lysine, arginine, tryptophan, threonine and isoleucine supplementation of a low-protein diet also improved growth, but growth again fell short of that attained by feeding a diet containing 200 g crude protein/kg. Plasma insulin-like growth factor-1 and thyroxine concentrations increased and triiodothyronine decreased as the crude protein level increased from 150 to 200 g/kg diet. Supplemental lysine did not affect plasma levels of these hormones. Although dietary crude protein levels noticeably changed rates of in vitro lipogenesis, changing either the level of a single limiting amino acid or the levels of several limiting amino acids did not change lipogenesis.

Dermatitis in treated maple syrup urine disease

Two children who had classic maple syrup urine disease developed an eruptive dermatitis when plasma isoleucine levels, leucine levels, or both fell below normal during periods of protein restriction. The dermatitis was resistant to topical corticosteroid therapy. Rapid resolution occurred after treatment with isoleucine and leucine dietary supplements.

Amino acid supplementation of low-protein sorghum-soybean meal diets for 5- to 20-kilogram swine

Four growth experiments were conducted to determine the value of added threonine (Thr), methionine (Met), tryptophan (Trp), and isoleucine (Ile) in low-protein, lysine (Lys)-fortified, sorghum-soybean meal diets for starting pigs weaned at 28 d. Trials lasted 28 d and average initial weight was approximately 6.5 kg. A 21% CP (1.15% total and .95% digestible Lys) diet was included in all trials. Basal 15, 17, and 19% CP diets were formulated to contain .95% digestible Lys by adding .38, .26, and .13% Lys, respectively. In Exp. 1, the additions of either Thr (.27%) or Met (.08%) to the 15% CP diet improved (P < .05) ADG and gain/feed (G/F); Trp (.04%) and Ile (.05%) additions had no effect. None of the 15% CP diets resulted in performance comparable to that obtained on the 21% CP diet. In Exp. 2, 19 and 17% CP diets fortified with Thr, Met, and Trp to obtain the digestible contents of the 21% CP diet produced performance equal to performance on the 21% CP diet. Results of Exp. 3 indicate that Thr (.11%) and Met (.08%) supplementation of the 17% CP diet were needed to maximize performance; Trp and Ile additions were not beneficial. Results of the final experiment suggested that Thr and Met additions to the 17% CP diet could be reduced to .05 and .04%, respectively, without lowering performance. These data indicate that a 17% CP, sorghum-soybean meal diet fortified with Lys, Met, and Thr can produce performance equal to that obtained by pigs fed a 21% CP diet.

Branched-chain amino acid supplementation during trekking at high altitude. The effects on loss of body mass, body composition, and muscle power

To investigate the influence of a branched-chain amino acid (BCAA) supplementation on chronic hypoxia-related loss of body mass and muscle loss, 16 subjects [age 35.8 (SD 5.6) years] participating in a 21-day trek at a mean altitude of 3,255 (SD 458) m, were divided in two age-, sex- and fitness-matched groups and took either a dietary supplementation of BCAA (5.76, 2.88 and 2.88 g per day of leucine, isoleucine and valine, respectively) or a placebo (PLAC) in a controlled double-blind manner. Daily energy intake at altitude decreased by 4% in both groups compared with sea level. After altitude exposure both groups showed a significant loss of body mass, 1.7% and 2.8% for BCAA and PLAC, respectively. Fat mass had decreased significantly by 11.7% for BCAA and 10.3% for PLAC, whereas BCAA showed a significantly increased lean mass of 1.5%, as opposed to no change in PLAC. Arm muscle cross-sectional area tended to increase in BCAA, whereas there was a significant decrease of 6.8% in PLAC (P < 0.05 between groups). The same tendency, although not significant, was observed for the thigh muscle cross-sectional area. On the whole it seemed that PLAC had been catabolizing whereas BCAA had been synthesizing muscle tissue. Single jump height from a squatted position showed a similar tendency to increase in both groups. Lower limb maximal power decreased less in BCAA than in PLAC (2.4% vs 7.8%, P < 0.05). We concluded that BCAA supplementation may prevent muscle loss during chronic hypobaric hypoxia.

Isoleucine requirement of broiler chicks as affected by the concentrations of leucine and valine in practical diets

1. Chicks were fed on an isoleucine-deficient diet, with 6 added concentrations of isoleucine to determine their isoleucine requirement and an additional 6 treatments were devised to determine their isoleucine requirement when dietary leucine and valine contents were increased. 2. The diet deficient in isoleucine contained 5.6 g/kg isoleucine with leucine and valine contents of 20.1 and 10.3 g/kg, respectively. Supplementation with leucine and valine increased these to 24.7 and 12.6 g/kg, respectively. 3. The isoleucine requirement was not affected by dietary leucine and valine contents in a diet with 13.4 MJ of ME per kg. Analysis of variance and Least Significant Difference of means indicated an isoleucine requirement of 7.2 g/kg. Non-linear regression of the same data indicated an isoleucine requirement of 8.44 g/kg, based on weight gain, or 8.19 g/kg based on food efficiency. 4. Reasons for the failure to find an imbalancing effect of branched chain amino acids in practical diets are discussed.

Serum methylmalonic acid before and after oral L-isoleucine loading in cobalamin-deficient patients

Over a 1 1/2-year period, we measured concentrations of methylmalonic acid in serum before and after a standardized loading with oral L-isoleucine (100 mmol) in 13 patients admitted for evaluation of cobalamin deficiency. All patients had serum cobalamin values below 100 pmol l-1, but only 12 of the 13 patients were clinically confirmed cobalamin deficient. The clinically non-cobalamin-deficient patient had folate deficiency and was excluded. The serum methylmalonic acid concentrations before loading with isoleucine were above the upper reference limit (0.37 mumol l-1) in all the patients and L-isoleucine caused an increase in serum methylmalonic acid of more than 1.00 mumol l-1 in 11 of the 12 deficient patients. In the remaining patient the increase was 0.35 mumol l-1. The results show that a significant increase of an initially elevated serum methylmalonic acid concentration after isoleucine loading is a general finding in tissue cobalamin deficiency which strongly supports the diagnosis.

Isoleucine requirements of the chicken: requirement for maintenance

1. The maintenance requirement of adult male cockerels for isoleucine was measured by nitrogen balance. Measured amounts of a diet first-limiting in isoleucine were fed by tube each day for 6 d to give a range of intakes of from 0 to 100 mg isoleucine/kg body weight. A nitrogen-free diet containing energy, vitamins and both major and trace minerals was offered ad libitum during that time. Two series of diets were used, an unbalanced series, as described above, and a balanced series, in which synthetic L-isoleucine was added to each diet in the unbalanced series. Excreta were collected in bags during the last 3 d of the balance period and the N content of the excreta was analysed on wet, homogenised samples. 2. The resultant linear regressions were not statistically different for the unbalanced and the balanced series indicating that the response measured was to isoleucine. The pooled regression equation was: N retention = -144.14 (+/- 8.5) + 2.421 (+/- 0.19)I where I is the intake of isoleucine in mg/kg body weight day. The isoleucine required to maintain the body at zero N retention was therefore calculated to be 60 (+/- 3.2) mg/kg body weight day. 3. A case has been made for the expression of the amino acids required for maintenance to be in terms not of body weight but scaled according to the degree of maturity of the animal, and on this basis the amount of isoleucine required for maintenance was calculated to be 300 mg per unit of maintenance protein (Pm 0.73 mu) per day.

Isoleucine requirements of the chicken: the effect of excess leucine and valine on the response to isoleucine

1. Three experiments were designed to determine the response of broiler chickens to dietary isoleucine, and to quantify the antagonistic effects of excess leucine and valine on this response. 2. A dilution technique was used to measure the responses in growth rate and food intake to a range of diets differing in their isoleucine concentrations. A summit diet was formulated to contain isoleucine at 1.14 times the requirement and with leucine (1.76 times the requirement) and valine (1.87 times the requirement) at the minimum possible concentrations, given the ingredients available. A dilution mixture, devoid of protein, was formulated to correspond in all respects, other than in amino acid content, to the summit diet. These two basal diets were blended in different proportions to give a range of diets of decreasing isoleucine and protein content. 3. In experiment 1 the response was measured to isoleucine with leucine and valine remaining in the same proportion to isoleucine throughout the range of diets fed. In experiments 2 and 3, however, L-leucine and L-valine were added to the diets either singly or in combination to give 6 isoleucine concentrations and 3 ratios of each of leucine and valine to isoleucine. 4. Weight gain decreased as the isoleucine content of the diet was reduced, whereas food intake of broilers fed on the marginally deficient diets increased to a maximum and then decreased. FCE decreased curvilinearly as the isoleucine concentration in the food decreased, reflecting a concomitant change in the fat content of the broilers. 5. It is possible that the amount of dietary isoleucine assumed to be available to the broilers in these experiments was overestimated by hydrolysing the food samples for 72 h, and the doubt thus created makes an estimate of the efficiency of retention of isoleucine suspect. 6. Excess valine had no effect on the response to isoleucine, whereas an increase in the leucine to isoleucine ratio depressed food intake and hence weight gain, but only at the lowest concentrations of isoleucine. 7. If the food content of isoleucine is sufficient to meet the requirements of the broiler, relatively large excesses of leucine, of valine, or of both will not depress growth.

Modification of the effects of blood on amino acid metabolism by intravenous isoleucine

The absence of isoleucine in the hemoglobin molecule has been suggested to contribute to increased urea production after a blood meal. To unravel the underlying mechanism, the effects of isoleucine infusion after blood ingestion in the healthy pig were studied. The isoleucine dose was chosen to induce an arterial isoleucine increase comparable to those observed for leucine or valine after blood ingestion. For the experiments, 10 female overnight-fasted pigs (20-25 kg) received 250 mL bovine erythrocytes intragastrically 1 week after catheter implantation for measuring hepatic, splanchnic, portal-drained viscera, and hindquarter fluxes of amino acids, urea, and ammonia. After the administration of erythrocytes, isoleucine or saline was administered i.v. for 6 hours. The data obtained show that the increase in arterial levels of urea and almost all amino acids was significantly greater in the control group (P less than 0.001) than in the isoleucine group. The net efflux of nearly all amino acids by the portal-drained viscera increased significantly less (P less than 0.001) in the isoleucine group. The liver uptake of amino acids increased after the blood meal, but the difference was not significant except for glutamine (P less than 0.001). Hindquarter amino acid net influx increased marginally. Splanchnic urea production increased more in the control group than in the isoleucine group (P less than 0.05). The data strongly suggest that i.v. administration of isoleucine enhanced the biological value of a blood meal, possibly by promoting amino acid retention in the portal drained viscera.

Oral L-alloisoleucine loading studies in healthy subjects and in patients with maple syrup urine disease

Total body and renal elimination of L-alloisoleucine was assessed after oral loads (0.57 mmol/kg body wt) in four healthy subjects and in five patients with maple syrup urine disease (MSUD) of different degrees of severity. As judged from the fictive initial concentration, L-alloisoleucine is distributed evenly in the total body water space. In the controls, estimated half-time of total elimination was 9.2 +/- 2.2 h (n = 4). In the MSUD patients, it ranged from 26 h (mild variant) to about 8 d (classical type). Because of its low renal clearance rate, L-alloisoleucine was cleared through ketomethylvalerate to greater than 99% in normals and to at least 73% in the MSUD patients. Assuming small variation in the losses of ketomethylvalerate through L-isoleucine formation and through renal excretion, this test allows ranking of MSUD patients with regard to their residual in vivo branched-chain oxo-acid dehydrogenase activity.

Branched-chain amino acid interactions with reference to amino acid requirements in adult men: leucine metabolism at different valine and isoleucine intakes

Recent estimates of the leucine requirement of adult men based on 13C-tracer studies are substantially higher than those proposed by FAO/WHO/UNU (1985). To explore whether leucine oxidation and requirements are affected by the dietary amount of valine. 11 healthy young adult men received, in random order, for 5 d, one of four L-amino acid diets providing 40 or 15 mg leucine.kg-1.d-1 together with variable amounts mg.kg-1.d-1 of valine and isoleucine in the following combinations (Val:Ile): 80:62 and 20:62 (six subjects; phase 1); 20:62 and 20:20 (five subjects, phase 2). On the morning of day 6, a continuous intravenous infusion of L-[1-13C]leucine was given for 7-8 h; the subject was in the fasting state for the initial 2.5 or 3 h and in the fed state for the remainder of the time. Also, [2H3]leucine was added to the diet. Leucine oxidation was similar for all diet groups in the fasted state. During the fed state, leucine oxidation was not affected by the Val:Ile pattern. Thus, changes in the pattern of branched-chain amino acid intake within a physiological range do not affect isotopically derived estimates of the leucine requirement.

Optimum isoleucine requirement of laying hens and the effect of age

1. Medium weight laying hens were used for an assay to determine their isoleucine requirement between 26 and 36 weeks of age and again between 46 and 56 weeks of age. 2. Two isoleucine-limiting mixtures were formulated with similar amino acid profiles, one containing 198 g and the other 110 g crude protein per kg diet. These mixtures were blended to give a series of 11 diets with isoleucine contents ranging from 7.6 to 3.8 g/kg. The lowest protein diet was also fed with a supplement of L-isoleucine. Each of the 12 diets was given to 5 groups of 24 laying hens. 3. The daily isoleucine requirement of individual laying hens was estimated to be 9.48 mg/g egg output plus 44.47 mg/kg body weight per day for the 1st period and 12.11 mg/g egg output plus 6.86 mg/kg body weight per day for the 2nd period. Calculated optimum intakes of isoleucine for various ratios of cost of input to value of output are tabulated. For example, for a flock of medium weight hens producing an average of 50 g daily egg mass, the optimum isoleucine intake (mg/hen d) varied between 760 and 890 varying for ratios of costs to egg prices. 4. It is concluded that the isoleucine required per day does not decrease during the first laying year despite a decrease in rate of egg output.

Methylmalonic acid metabolism and nervous-system fatty acids in cobalamin-deficient fruit bats receiving supplements of methionine, valine and isoleucine

Cobalamin neuropathy was produced in Cape fruit bats (Rousettus aegyptiacus) by a cobalamin-free diet combined with intermittent exposure to nitrous oxide, which inactivates cobalamin. Cobalamin-deficient bats had low hepatic methylmalonyl-CoA mutase holoenzyme activity, with elevated plasma and urinary methylmalonic acid levels. No significant changes could be demonstrated in the concentration of odd- or branched-chain fatty acids in the nervous system. Supplementation of the cobalamin-free diet with methionine, valine or isoleucine delayed the onset of neuropathy, despite persistence of methylmalonic acid accumulation. Supplementation with any of the three amino acids was associated with elevation of hepatic methionine concentration. The action of valine and isoleucine in delaying the onset of neuropathy can be explained by their methionine-sparing effect. These results emphasize the central role of methionine in the cobalamin neuropathy and do not support the hypothesis that the neuropathy is related to an effect of cobalamin deficiency on the propionic acid pathway.

Adrenal hormones and the anorectic response and adaptation of rats to amino acid imbalance

The role of adrenal function in the anorectic response and adaptation of rats to a diet with an isoleucine (Ile) imbalance was investigated. In the first of four experiments, rats were fed a mildly Ile-imbalanced diet after treatment with metyrapone, and inhibitor of glucocorticoid synthesis. In two separate experiments, rats were presented with either a mildly or severely Ile-imbalanced diet (4.93 and 9.86% imbalanced amino acid mixture, respectively) after bilateral adrenalectomy. Finally, the effects of ICS 205-930, a serotonin-3 receptor antagonist, on the intake of mildly Ile-imbalanced diet were tested in adrenalectomized animals. In each experiment a 2 X 2 factorial design was used. Neither metyrapone nor adrenalectomy altered the initial depression in the intake of an imbalanced diet. The adaptation phase in the response of adrenalectomized rats fed a mildly Ile-imbalanced diet was not different from that of controls, but adrenalectomized rats fed severely Ile-imbalanced diets were unable to adapt. Adrenalectomy did not alter the anti-anoretic activity of ICS 205-930 in this model. These results suggest that adrenal hormones are not necessary for the initial anoretic response or adaptation of rats to an Ile-imbalanced diet, nor are they implicated in the anti-anorectic effect of serotonin-3 blockade.

Effect of dietary limiting amino acid in prepyriform cortex on food intake

The mechanisms underlying the reduced intake of an amino acid-imbalanced diet (imbalanced diet) appears to involve a decrease in the content of the dietary limiting amino acid (DLAA) in the prepyriform cortex (PPC). Intake of imbalanced diet was increased from 45-50 to 70-75% of baseline after bilateral injection of the DLAA directly into the PPC, following an inverted U-shaped dose-response curve. Injections had no effect on intake of basal diets. Injection of the DLAA into the PPC reversed the aversion to imbalanced diet in choice studies, as rats selected an imbalanced diet over protein-free diet after such injections. Intake of imbalanced diet did not increase after a nonlimiting amino acid was injected into the PPC or after injections of the DLAA into other brain areas. Results were similar when either threonine or isoleucine was the DLAA. These results confirm that the decrease in the concentration of the DLAA in the PPC is involved in the reduction in intake of imbalanced diets.

Effect of dietary limiting amino acid in prepyriform cortex on meal patterns

Microinjection of the dietary limiting essential amino acid (DLAA) into the prepyriform cortex (PPC) increased intake of a diet having an imbalance among the essential amino acids (imbalanced diet) from 50-55% of baseline, when artificial cerebrospinal fluid (aCSF) was injected, to 70-75% of baseline. The increase in intake of the imbalanced diet by DLAA injection became apparent after 3-6 h and was maintained throughout the dark period. Meal size, meal duration, and the number of meals returned to normal after bilateral injections of the DLAA into the PPC of rats fed the imbalanced diet. Injection of the DLAA 30 min before the onset of the dark phase increased intake of imbalanced diet to 70% of baseline intake. When injections of threonine or isoleucine were made 6 and 3 h, respectively, prior to onset of the dark phase, intake of imbalanced diet increased to 85% of baseline intake. Results suggest that some form of processing of the injected DLAA within the PPC is necessary to increase the intake of imbalanced diets.

Serotonin3 receptor antagonists block anorectic responses to amino acid imbalance

The role of serotonin3 (5-HT3) receptors in the initial food intake depression of rats ingesting amino acid imbalanced or high-protein diets was investigated. The 5-HT antagonists metergoline, pirenpirone, ICS 205-930, and MDL 72222, the dopamine antagonist pimozide, or the alpha-adrenergic antagonist phentolamine were injected 15-45 min before presentation of test diets. Food intake was measured at intervals for 3 days. The 5-HT3 antagonists, ICS 205-930 and MDL 72222, restored feeding of a mild isoleucine (Ile)-imbalanced diet to control levels, although MDL 72222 had a longer time course of action. ICS 205-930 also increased intake of a severe Ile-imbalanced diet and Thr-imbalanced diet but not a high-protein (44% casein) diet. Treatment with metergoline, which blocks 5-HT1, 5-HT2, and dopamine receptor sites but not 5-HT3 sites, increased intake of the basal diet at 3 and 6 h but did not significantly alter intake of the mild Ile-imbalanced diet. Although pimozide tended to increase intake of the mild imbalanced diet, neither dopamine nor alpha-adrenergic receptor antagonism significantly affected imbalanced diet intake. Thus 5-HT3 receptors may mediate the anorexigenic activity of 5-HT associated with feeding an amino acid-imbalanced diet.

Dietary requirements of leucine, isoleucine, and valine in male broilers during the starter period

Growth studies were conducted with 3-wk-old, male broiler chicks to determine their requirements for the branched-chain amino acids (BCAA) leucine, isoleucine, and valine during the starter period. The central-composite, rotatable design was applied. The data were analyzed using regression methodology. The results showed that the linear term of Leu and the cross-product terms of Leu with Ile or Val were nonsignificant (P greater than .05). Second-order equations described the relationship between the BCAA, weight gain (WG), and feed conversion (FC). The coefficient of determination values indicated that 80% or more of the variation in WG and FC was explained by the polynomial equations. The results suggested that the Leu requirement does not exceed 1.16% of a diet calculated to contain 3,200 kcal of metabolizable energy per kilogram. The optimum response, maximum in the case of WG (444 g) and minimum for FC (1.40), would be obtained by feeding a diet containing 1.16, .80, and .90% of Leu, Ile, and Val, respectively. The values of Ile and Val are the actual values obtained when the diets were hydrolyzed for 72 hours. For Leu, however, the hydrolysis time was 24 hours.

Studies on methylmalonic acid in humans. I. Concentrations in serum and urinary excretion in normal subjects after feeding and during fasting, and after loading with protein, fat, sugar, isoleucine, and valine

Determination of methylmalonic acid (MMA) in serum or urine for evaluation of tissue cobalamin (vitamin B12) deficiency is becoming an important diagnostic procedure. Here I present the first investigation of dietary influence on concentrations of MMA in serum and urine. Everyday meals caused an increase in urinary excretion, whereas the concentration in serum was not increased significantly. It is difficult to prime the accumulation of MMA in normal subjects by stressing the metabolic pathway; after loading subjects with 100 mmol of isoleucine or valine, the absolute amount of MMA excreted increased by only about 3 mumol. Its concentration in serum tended to decrease and its urinary excretion declined after lack of protein intake for more than 15 h. Although a linear relationship was demonstrated, for the first time, between concentrations in serum and urinary excretion, my results indicate that patients with early evidence of cobalamin deficiency and normal subjects may best be differentiated by measurements in serum, especially in the case of nonfasting (i.e., ambulatory) patients.

[A clinical study of amino acid metabolism in cancerous hypoproteinemia--the role of branched chain amino acids (BCAA) and appropriate compositions of BCAA in parenteral nutrition]

In order to determine the nutritional effects of BCAA compositions in the treatment of cancerous hypoproteinemia, the appropriate ratio of I-leu: Leu: Val and the proportion of BCAA to Total Amino Acids were investigated. As for results, indices such as the serum albumin, the RBP and N-balance quickly recovered to normal levels when the ratio of I-leu: Leu: Val was 1.0:1.8:1.0 and the proportion o BCAA to TAA was 31%. These composition thus may be suitable for the treatment of cancerous hypoproteinemia.

[The growth of rats in renal compensatory adaptation in feeding with a supplemented diet of hydroxy-analogs of essential amino acids]

Rats were fed protein-restricted after unilateral nephrectomy (6.7% casein). Comparatively other animals were fed with experimental diets, at which 20% of the casein have been replaced by Ketosteril or a mixture of hydroxy acid. The constituents of this mixture are in accordance with the molar relation of all Ketosteril components. However, sodium solts of hydroxy acids of leucine, isoleucine and valin replace the corresponding keto acids of Ketosteril. The other components of the mixture consist of free amino acids. The efficiency of protein utilisation was judged by the relation of increased body weight and nitrogen intake. The efficiency of protein utilisation of both supplemented diets is 2.5 times higher compared with the casein diet.

Pilot trial of branched-chain aminoacids in amyotrophic lateral sclerosis

22 patients with amyotrophic lateral sclerosis were entered into a double-blind, randomised, placebo-controlled trial of treatment with branched-chain aminoacids. 11 received daily 12 g L-leucine, 8 g L-isoleucine, and 6.4 g L-valine, by mouth, and the remainder received placebo. During the one-year trial, patients in the placebo group showed a linear decline in functional status consistent with the natural history of the disease. Those treated with aminoacids showed significant benefit in terms of maintenance of extremity muscle strength and continued ability to walk.

Serotonin and feeding responses of rats to amino acid imbalance: initial phase

The role of serotonin in the anorexic response of rats to an amino acid-imbalanced diet was investigated. After chronic depletion of serotonin with parachlorophenylalanine (PCPA, 300 mg/kg) or 5,7-dihydroxytryptamine (DHT, 200 micrograms/rat, intracisternally), initial intake of a mild isoleucine-imbalanced diet was reduced by 60% vs. a 17% reduction after saline injection. After acute treatment with the agonist, quipazine (quip, 5 mg/kg ip) or the precursor, tryptophan (TRP, 1% added to the diet), imbalanced diet intake was also exacerbated. PCPA and DHT may have caused receptor supersensitivity, such that the food intake depression after serotonin depletion was similar to that seen with the quip and TRP treatments. Injection of the autoreceptor agonist, 8-hydroxy-2(di-n-propylamino)tetralin (8-OH-DPAT, 500 micrograms/kg sc), to reduce transmission in the serotonergic systems resulted in an attenuation of the usual food intake depression of the amino acid-imbalanced diet (only a 7%, nonsignificant reduction). Also measurements made in the absence of pharmacological treatment showed that the ratio 5-hydroxyindole acetic acid-to-serotonin, a putative index of serotonin turnover, was increased 155% in the raphe nuclei and 140% in the hippocampus 3.5 h after ingestion of the mild isoleucine-imbalanced diet. Therefore increased serotonergic activity in some brain areas may be associated with the initial depression of food intake in rats fed an imbalanced amino acid diet.

Effect of dietary energy concentration on the response of laying hens to amino acids

1. A hypothesis, that the optimum amino acid concentration in the diet is not directly proportional to the dietary energy concentration, but changes in inverse proportion to the change in food intake resulting from a change in energy concentration, was tested in three experiments. 2. Response experiments involving the amino acids methionine, lysine and isoleucine were conducted, in each case at three dietary energy concentrations, using a diet dilution and blending technique, thereby ensuring a constant ratio between background amino acids and the first-limiting amino acid in all diets, and also keeping the ratio of amino acids to energy constant as energy varied. 3. A common response curve relating egg output (g/bird d) to amino acid intake (mg/bird d) for each amino acid, fitted by means of the Reading Model, adequately described the response at each of the dietary energy contents. This implies that energy does not influence egg output directly, but only indirectly through its effect on food intake and hence on amino acid intake. 4. Both amino acid and energy concentration significantly influenced food intake. Energy intake was not constant over all dietary energy concentrations, being lower at low energy levels and higher at high energy concentrations. 5. It is concluded that amino acid requirements should not be stated either as percentages or as ratios with energy. Optimum amino acid intakes and energy concentrations should be calculated; the expected food intake should then be predicted, after which the appropriate concentration of nutrients in the diet can be determined.

Utilization of the L- and DL-isomers of alpha-keto-beta-methylvaleric acid by rats and comparative efficacy of the keto analogs of branched-chain amino acids provided as ornithine, lysine and histidine salts

Three experiments were conducted to quantitatively evaluate the growth-promoting capacity of alpha-keto analogs of the branched-chain amino acids (BCAA). Basal chemically defined diets were formulated to be singly deficient in the BCAA under study; analogs therefore were evaluated as sources of supplemental amino acid activity. Analogs of isoleucine tested included alpha-keto-beta-L-methylvalerate (L-KMV) as the Na salt (L-KMV-Na) and alpha-keto-beta-DL-methylvalerate (DL-KMV) as the Na (DL-KMV-Na), ornithine (DL-KMV-Orn) and lysine (DL-KMV-Lys) salts. Slope-ratio efficacy values were L-KMV-Na, 65%; DL-KMV-Na, 44%; DL-KMV-Orn, 41%; DL-KMV-Lys, 43%. Alloisoleucine accumulated in the plasma of rats fed all sources of KMV, but its concentration was three times greater when DL-KMV was fed than when L-KMV was fed. The analog of valine tested was alpha-ketoisovalerate as the ornithine (KIV-Orn) or lysine (KIV-Lys) salts. There was no significant difference in efficacy between salts (47 versus 44%, respectively). The analog of leucine, alpha-ketoisocaproate, was given as the ornithine (KIC-Orn), lysine (KIC-Lys) and histidine (KIC-His) salts with resulting efficacies of 50, 38 and 49%, respectively. Slope-ratio efficacies of KIC-Orn and KIC-His were statistically similar and efficacy of KIC-Lys was inferior to both KIC-Orn and KIC-His.

Isoleucine requirement of young growing male guinea pigs

The isoleucine requirement of young, growing male guinea pigs was investigated by use of crystalline amino acid diets containing 3.65% nitrogen. Three-week-old guinea pigs were fed one of eight crystalline amino acid diets ranging from 0.2 to 1.2% isoleucine for 22 d. Diets were evaluated on the basis of body weight changes, nitrogen retention, carcass weight, liver weight, hematocrit, hemoglobin and carcass and liver weights expressed as percentages of live body weight. A 0.5% level of dietary isoleucine (2.2% of total nitrogen X 6.25) was the lowest level fed that did not have a response significantly lower than the higher levels fed, and that generally promoted a thrifty and well-groomed appearance of the animals.

Protein and amino acid requirements of fishes

Tentative qualitative and quantitative amino acid requirements have been reported for the major species of fish reared for market or as replacement stocks for natural waters. Most work has concentrated upon juvenile fish or upon rapidly growing young market fish; these have high protein dietary requirements (30-50%) that are in direct contrast to the homothermic terrestial animals. Net protein utilization from the diet is similar or slightly better than that found in avian species, but energy needs are much lower in fish and as a result the body protein deposition in fish is larger (about 5 g protein/MJ for the chick versus about 10 g protein/MJ for young fish). Qualitative amino acid requirements appear identical for all fish species examined; arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine are all required for normal growth and metabolism. Quantitative requirements differ only slightly among species that have been tested. Salmon have higher arginine requirements than other fish examined. Catfish appear to have a lower requirement for histidine and threonine, and the Japanese eel seems to need more tryptophan in the diet. However, when the quantitative requirements for indispensable amino acids are expressed as a percentage of the protein fed, then a remarkable harmony appears between values needed for maximal growth for most species examined. A review of Tables 3 and 4 will disclose the paucity of information available considering the large number of fish species reared commercially over the world. Most commercial diet formulations have relied upon the work done on salmon, catfish, and carp, and their amino acid and protein requirement values have been used. Remarkably, these diets have produced other species of fish economically. Sparing effects of one amino acid on another have only been studied with cystine-methionine and tyrosine-phenylalanine. Arginine and analogues of methionine have been used as good nitrogen sources for salmon. Isoleucine-leucine ratios have been measured and experiments indicate some growth inhibition when the isoleucine-leucine ratio was greater than 2/1. Valine at abnormally high levels also inhibited growth. Much more work needs to be done on the effects of subtle differences in amino acid ratios in the diet, and major emphasis should be placed on the important role of the dispensable amino acids in fish nutrition.(ABSTRACT TRUNCATED AT 400 WORDS)

Norepinephrine and amino acids in prepyriform cortex of rats fed imbalanced amino acid diets

Monoamines and amino acids were measured in anterior prepyriform cortex (PPC) and anterior cingulate cortex (CC) of male Sprague-Dawley rats after they were offered basal, imbalanced (IMB) or corrected amino acid diets, limited in threonine (THR) or isoleucine (ILE). In the THR study, brains were taken after 2.5 hr of feeding, when intake of THR-IMB was just depressed. In the ILE study the brains were taken after 3.5 hr on ILE-IMB, a less severely imbalanced ration, before the onset of food intake depression. The PPC has been shown to be involved in the acute response of animals to imbalanced amino acid diets. In the PPC from the IMB diet groups, NE was reduced by 30%, but the other monoamines were unchanged. In CC, an area involved in the adaptive, but not the acute feeding response to imbalanced diets, the monoamines were unchanged in the IMB diet groups. In both studies, in both tissues, the limiting amino acids were decreased in the IMB groups, although the decrease of ILE in the CC failed to reach significance. The remaining indispensable amino acids, added to create the imbalance, were slightly reduced in the THR-IMB group, but not in the ILE-IMB group in both tissues. Thus, the amino acid patterns were altered in the PPC and CC, as they are in whole brains from animals fed imbalanced amino acid diets. These results also suggest that the concentration of NE in the PPC may be associated with the initial food intake response of animals to imbalanced amino acid diets.

[Comparison of casein utilization limited by different amino acids]

Experiments of Wistar rats were made to compare the utilization of proteins limited by sulfur-containing amino acids or isoleucine. The score of the limiting amino acid of the proteins under study was identical (0.65). The diets included 2, 5, 10, 15, 20, 25, 30, 40 and 50 g protein per 100 g diet. Depending on the protein content in the diet, the following values of net protein utilization (NPU) were obtained for protein limited by sulfur-containing amino acids: 0.680, 0.647, 0.616, 0.600, 0.562, 0.460, 0.315, 0.240, 0.210. Meanwhile, the values for protein limited by isoleucine were 0.700, 0.697, 0.600, 0.560, 0.524, 0.450, 0.340, 0.260, 0.200. Despite insignificant differences in feed consumption and weight gains in the animals, the above cited values of the NPU did not differ essentially in terms of test protein concentration under comparison. The data obtained indicate that the biological value of proteins limited by sulfur-containing amino acids does not differ from that of proteins limited by isoleucine.