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.