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PubMed1998

Mechanism of compound- and species-specific food effects of structurally related antiarrhythmic drugs, disopyramide and bidisomide.

PURPOSE: To determine mechanism of food effects observed with bidisomide but not with the structurally similar drug, disopyramide. METHODS: Food effect studies of bidisomide and disopyramide were conducted with and without a standardized high fat meal in healthy subjects and in the dog. Intestinal metabolism of disopyramide and absorption of the metabolites were examined after oral administration of the drug to the dogs with portal vein canula implanted. Effects of food or a mixture of amino acids on metabolism of [14C]disopyramide were examined after intraportal infusion of the drug with and without high fat meal and after drug infusion into portal vein with the amino acid mixture, respectively. RESULTS: The systemic availability of bidisomide was markedly reduced with food in humans, whereas the systemic availability of disopyramide did not change notably. In the dog, the systemic availability of bidisomide was also reduced with food. The systemic availability of disopyramide did not change with food. This was due to the fact that reduction in absorption was compensated by reduction of metabolism. There was no evidence for reduction in hepatic and intestinal metabolism with food. CONCLUSIONS: The apparent reduction in disopyramide metabolism with food may be due to an increase in colonal and/or lymphatic absorption. Food effects on the apparent systemic availability of bidisomide and disopyramide in the dog were similar to those in the rat. However, there was substantial species difference in the mechanism of food effects.

Adult↗

PubMed1984

Response of rat pancreatic proteases to dietary proteins, their hydrolysates and soybean trypsin inhibitor.

The present study was designed to determine whether the adaptation of pancreatic trypsin and chymotrypsin activities to dietary protein level can be attributed to the presence in the diet of the specific peptide bonds that are substrates for these enzymes. In addition, the effect of feeding soybean trypsin inhibitor (SBTI) was tested since this compound is known to stimulate synthesis of pancreatic proteases. For 3 weeks, rats were fed a diet containing 10, 20 or 30% protein as lactalbumin (control); lactalbumin predigested by trypsin, chymotrypsin or pancreatin; a mixture of amino acids; or lactalbumin supplemented with SBTI. At the end of the experiment, the activities of trypsin, chymotrypsin and amylase were determined in the rats' pancreatic homogenates. Trypsin and chymotrypsin activities at each protein level were exactly the same whether predigested lactalbumin or lactalbumin was fed. The 20 and 30% amino acid mixtures, however, produced a decrease in activities of both proteases. SBTI doubled the activities of both proteases at all three levels of protein. Amylase activity was maximal at 20% level of protein. It is concluded that adaptation of pancreatic proteases to dietary protein level is induced by small peptides that are digestion products of dietary protein. Induction of pancreatic trypsin or chymotrypsin therefore does not require the presence of substrate for these enzymes in the intestine. Dietary SBTI produced a considerable increase in pancreatic proteases compared to that produced by proteins or peptides. It is suggested that the increases in pancreatic proteases caused either by protein-rich diets or SBTI are mediated by two distinct mechanisms.

Amylases↗

PubMed2000

Choline is required by tilapia when methionine is not in excess.

Choline is essential in diets fed to most young vertebrates, but previous studies did not confirm the essentiality of choline in diets fed to tilapia. Two experiments were conducted to evaluate the essentiality of dietary choline in such diets. The basal diet used in both experiments contained 32 g crude protein/100 g diet (10.1 g crude protein from casein and gelatin, and 21.9 g from a crystalline L-amino acid mixture). The total sulfur amino acid (TSAA) concentration of the basal diet was 0.28 g/100 g diet, Met:Cys 89:11. In Experiment 1, a 4x2 design was used in which crystalline L-methionine was added to the basal diet resulting in four levels of TSAA (0.28, 0.50, 0.75 or 1.0 g/100 g diet, Met:Cys 89:11, 94:6, 96:4, or 97:3, respectively). At each level of TSAA, diets also contained either 0 or 1 g choline/kg diet supplied as choline chloride. Weight gain, feed efficiency (FE) and serum methionine concentrations were significantly affected by dietary TSAA concentration, but not by dietary choline concentration or the interaction between TSAA and choline. Weight gain, feed efficiency and serum methionine concentrations indicated that the TSAA requirement was 0.5 g/100 g diet. In the second experiment, diets were formulated to contain either 0.28 or 0.5 g TSAA/100 g diet, Met:Cys 89:11 or 94:6, respectively, and graded levels of choline ranging from 1 to 4 g/kg diet in gradations of 1 g/kg. Dietary methionine significantly affected weight gain and FE, whereas dietary choline significantly affected weight gain, FE and survival, and the interaction of methionine and choline significantly affected weight gain. Fish fed diets containing 0.5 g TSAA/100 g diet and 3 g choline chloride/kg diet exhibited the highest weight gain, feed efficiency and survival. On the basis of these data, it seems clear that juvenile tilapia require choline in certain dietary formulations.

Analysis of Variance↗

PubMed2002

Stimulation of protein synthesis by both insulin and amino acids is unique to skeletal muscle in neonatal pigs.

In neonatal pigs, the feeding-induced stimulation of protein synthesis in skeletal muscle, but not liver, can be reproduced by insulin infusion when essential amino acids and glucose are maintained at fasting levels. In the present study, 7- and 26-day-old pigs were studied during 1) fasting, 2) hyperinsulinemic-euglycemic-euaminoacidemic clamps, 3) euinsulinemic-euglycemic-hyperaminoacidemic clamps, and 4) hyperinsulinemic-euglycemic-hyperaminoacidemic clamps. Amino acids were clamped using a new amino acid mixture enriched in nonessential amino acids. Tissue protein synthesis was measured using a flooding dose of L-[4-(3)H]phenylalanine. In 7-day-old pigs, insulin infusion alone increased protein synthesis in various skeletal muscles (from +35 to +64%), with equivalent contribution of myofibrillar and sarcoplasmic proteins, as well as cardiac muscle (+50%), skin (+34%), and spleen (+26%). Amino acid infusion alone increased protein synthesis in skeletal muscles (from +28 to +50%), also with equivalent contribution of myofibrillar and sarcoplasmic proteins, as well as liver (+27%), pancreas (+28%), and kidney (+10%). An elevation of both insulin and amino acids did not have an additive effect. Similar qualitative results were obtained in 26-day-old pigs, but the magnitude of the stimulation of protein synthesis by insulin and/or amino acids was lower. The results suggest that, in the neonate, the stimulation of protein synthesis by feeding is mediated by either amino acids or insulin in most tissues; however, the feeding-induced stimulation of protein synthesis in skeletal muscle is uniquely regulated by both insulin and amino acids.

Amino Acids↗

PubMed1998

Exogenous amino acids stimulate net muscle protein synthesis in the elderly.

We have investigated the response of amino acid transport and protein synthesis in healthy elderly individuals (age 71+/-2 yr) to the stimulatory effect of increased amino acid availability. Muscle protein synthesis and breakdown, and amino acid transport were measured in the postabsorptive state and during the intravenous infusion of an amino acid mixture. Muscle-free amino acid kinetics were calculated by means of a three compartment model using data obtained by femoral arterio-venous catheterization and muscle biopsies from the vastus lateralis during the infusion of stable isotope tracers of amino acids. In addition, muscle protein fractional synthetic rate (FSR) was measured. Peripheral amino acid infusion significantly increased amino acid delivery to the leg, amino acid transport, and muscle protein synthesis when measured either with the three compartment model (P < 0.05) or with the traditional precursor-product approach (FSR increased from 0. 0474+/-0.0054 to 0.0940+/-0.0143%/h, P < 0.05). Because protein breakdown did not change during amino acid infusion, a positive net balance of amino acids across the muscle was achieved. We conclude that, although muscle mass is decreased in the elderly, muscle protein anabolism can nonetheless be stimulated by increased amino acid availability. We thus hypothesize that muscle mass could be better maintained with an increased intake of protein or amino acids.

Aged↗

PubMed1989

Circulating amino acids and pancreatic endocrine function after ingestion of a protein-rich meal in obese subjects.

We measured plasma amino acid together with insulin, glucagon, pancreatic polypeptide (PP), and glucose concentrations after the ingestion of a protein meal in lean and obese subjects. The basal plasma amino acid levels were similar in both groups. The postprandial increase in the plasma amino acid levels in the obese subjects was only 15-50% of that in the lean subjects. The mean basal and peak postprandial plasma insulin levels were significantly higher (72 and 165 pmol/L) in the obese group than in the lean group (36 and 115 pmol/L; P less than 0.05-0.01). The postprandial rise in plasma glucagon was largely attenuated in the obese subjects, and there was no difference in plasma PP and glucose levels in the 2 groups. To further evaluate the role of circulating amino acids on pancreatic endocrine function in obese and lean subjects, an amino acid mixture consisting of 15 amino acids was infused iv. During the infusion the plasma amino acid levels were comparable in both groups. Plasma insulin rose by 36 +/- 7 (+/- SE) pmol/L (5 +/- 1 microU/mL) in the lean and 129 +/- 22 pmol/L (18 +/- 3 microU/mL) in the obese subjects, whereas plasma glucagon, PP, and glucose levels were similar in both groups. In view of the 3.6-fold greater insulin responses in the obese subjects, it is likely that circulating amino acids contribute to their hyperinsulinemia in spite of the reduced postprandial rise of amino acids in this group (50-85%). Thus, under physiological conditions amino acids have to be considered as an important regulatory component of postprandial insulin release in obese subjects.

Adult↗

PubMed1996

Efficiency of D- vs L-methionine utilization by growing steers.

Five ruminally cannulated Holstein steers (180 kg) were used in a 5 x 5 Latin square design experiment to evaluate the efficiency of D- vs L-methionine (Met) utilization in growing steers. Treatments were continuous abomasal infusions of water or water with 2 or 4 g.steer-1.d-1 L-Met or 2 or 4 g.steer-1.d-1 D-Met. All steers were fed 2.7 kg/d (DM basis) of a soyhull-based diet to minimize basal Met flow to the small intestine to create a paradigm by which responses to Met supplementation could be measured easily. To ensure that amino acids other than Met did not limit animal performance, an essential amino acid mixture simulating the nonsulfur amino acid profile of ruminal bacteria was infused abomasally. Energy supply to the steers was increased by continuously infusing acetate, propionate, and butyrate into the rumen at rates of 150, 150, and 37.5 g.steer-1.d-1, respectively. Abomasal infusions of dextrose (300 g/d) also provided an additional energy source. Nitrogen retention increased linearly (P < .05) in response to both L-Met and D-Met infusions, with responses being similar between the two Met isomers. Regression of N retention against Met supplementation yielded: Nitrogen retention (g/d) = 19.2 + 1.81 D-Met (g/d) + 1.90 L-Met (g/d). By slope ratio analysis, the efficiency of D-Met utilization relative to L-Met was 95.5%. In a concurrent study using intestinally cannulated steers, both D- and L-Met were absorbed essentially completely from the small intestine. These results show that D-Met can be utilized efficiently as a Met source by cattle.

Acetates↗

PubMedDate not supplied

[Role of tryptophan in the physiological regulation of brain serotonin synthesis (author's transl)].

Tryptophan hydroilase in brain, normally is not saturated by its substrate; therefore the rate of tryptophan hydroxilation in brain is controlled by the concentration of tryptophan. In the other hand, brain tryptophan content is controlled by the ratio of the concentration of free tryptophan (i.e. not bound to serum proteins) to that of the other circulating amino acids, wich compete for the same transport mechanism from blood to brain. The administration of an amino acid mixture, containing all essential amino acids but not tryptophan, caused a parallel depletion of total and free serum tryptophan and of tryptophan and serotonin in brain. The mechanism of the observed fall in serum tryptophan is a rapid removed of endogenous tryptophan from circulation, secondary to an increased incorporation of tryptophan into proteins by the liver. These results suggest the hypothesis that brain serotonin synthesis is controlled by a perpherical mechanism.

Amino Acids↗

PubMed1991

Enhanced GFR response to oral versus intravenous arginine administration in normal adults.

Both oral protein ingestion and intravenous amino acid infusions have been shown to increase glomerular filtration rate (GFR) and renal plasma flow (RPF) in normal subjects. Although the mechanism of this effect is not known, the renal responses to these loads have been associated with increases in peripheral glucagon concentrations. Conflicting data exist concerning the role of glucagon in the hyperfiltration response after an oral protein meal or administration of an intravenous amino acid mixture. Using a single amino acid as the stimulus for hyperfiltration, we compared the renal responses in six normal subjects to 30 gm oral arginine-HCl, intravenous arginine-HCl, and intravenous glucagon infused at the rate of 10 ng/kg/min. GFR, RPF, and glucagon concentration, as well as levels of plasma amino acids and selected gastrointestinal hormones, were measured for six 30-minute clearance periods after each load. Significant rises in mean peak GFR were noted after both oral arginine (104 +/- 5 ml/min x 1.73 m2 to 145 +/- 9 ml/min x 1.73 m2, p less than 0.02) and intravenous arginine (118 +/- 10 ml/min x 1.73 m2 to 134 +/- 11 ml/min x 1.73 m2, p = 0.02) administration. Mean peak RPF rose significantly after oral arginine (510 +/- 26 ml/min x 1.73 m2 to 710 +/- 32 ml/min x 1.73 m2, p less than 0.01) but not after intravenous arginine (616 +/- 60 ml/min x 1.73 m2 to 687 +/- 64 ml/min x 1.73 m2, p = 0.18). Intravenous glucagon infusion also increased both mean peak GFR (99 +/- 9 ml/min x 1.73 m2 to 149 +/- 10 ml/min x 1.73 m2, p less than 0.01) and RPF (514 +/- 48 ml/min x 1.73 m2 to 771 +/- 38 ml/min x 1.73 m2, p less than 0.01) significantly. We found the mean peak percent rise in GFR (43% +/- 13%) and RPF (42% +/- 12%) after oral arginine to be notably greater than that after intravenous arginine (14% +/- 5% and 13% +/- 9%, respectively). However, the mean peak percent rise in glucagon concentration after oral arginine was significantly lower than that after intravenous arginine (62% +/- 25% versus 479% +/- 176%, respectively, p = 0.04). Infusion of glucagon increased GFR (54% +/- 13%) and RPF (55% +/- 12%) to a degree similar to that seen after oral arginine, but again with a significantly higher mean peak percent rise in peripheral glucagon concentrations when compared with the rise after oral arginine (798% +/- 348% vs 62% +/- 25%, p less than 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)

Administration, Oral↗

PubMed1967

Amino acids and the spikes from the retinal ganglion cells.

The effects of amino acids or mixtures of amino acids on the spike discharges from the optic ganglion cells were studied. Mixtures of amino acids have different effects than single amino acids. Proper composition of excitatory and inhibitory amino acids can enhance only the light-induced spikes without giving rise to any spontaneous discharges. It is implied that amino acids may play an important role in the regulation of the general sensitivity of cells in the central nervous system.

Alanine↗

PubMed1988

Amino acid infusion increases the sensitivity of muscle protein synthesis in vivo to insulin. Effect of branched-chain amino acids.

Rates of muscle protein synthesis were measured in vivo in tissues of post-absorptive young rats that were given intravenous infusions of various combinations of insulin and amino acids. In the absence of amino acid infusion, there was a steady rise in muscle protein synthesis with plasma insulin concentration up to 158 mu units/ml, but when a complete amino acids mixtures was included maximal rates were obtained at 20 mu units/ml. The effect of the complete mixture could be reproduced by a mixture of essential amino acids or of branched-chain amino acids, but not by a non-essential mixture, alanine, methionine or glutamine. It is concluded that amino acids, particularly the branched-chain ones, increase the sensitivity of muscle protein synthesis to insulin.

Amino Acids↗

PubMed1984

The effect of amino acid excess on utilization by the rat of the limiting amino acid--lysine and threonine at equalized food intakes.

The effect of excess amino acids on utilization of the most limiting amino acid was investigated via restricted feeding. Lysine- and threonine-deficient amino acid mixtures were incorporated into diets for young growing rats to provide 75 or 85% of the NRC requirement of the limiting amino acid in combination with zero or 50% of relative excess of the nonlimiting amino acids. The amount of food offered was equalized within treatment groups and increased according to the intake of the group with the lowest rate of consumption. Because of differences in the amount of diet refused, total food intakes were not identical. At equal percentage of the NRC requirement, threonine- and lysine-deficient amino acid mixtures supported equal body weight, dry matter, lipid and ash gains. However, crude protein retention was greater when the threonine-deficient amino acid mixture was fed. The maximum depression in performance due to 50% of amino acid excess with restricted feeding was much less than the maximum decrease previously observed in the ad libitum feeding situation. This supports the conclusion that changes in voluntary food intake are the major effectors of depressed growth due to excess amino acids. These results raise serious concern over the usefulness of amino acid requirements and the applicability of the current system of chemical scores to evaluate protein quality.

Amino Acids↗

PubMed2001

Tyrosine depletion attenuates the behavioural stimulant effects of amphetamine and cocaine in rats.

Neurochemical studies show that a tyrosine-free amino acid mixture depletes brain tyrosine and decreases dopamine synthesis and release. Here, we tested whether such a mixture would reduce the behavioural effects of amphetamine and other psychostimulants. A tyrosine-free amino acid mixture decreased the behavioural activation induced by both D-amphetamine (2 mg/kg s.c.) and cocaine (2 mg/kg s.c.). In contrast, the activation induced by the dopamine agonist, apomorphine (0.75 and 5 mg/kg s.c.), or the 5-hydroxytryptamine releasing agent, p-chloroamphetamine (2 mg/kg s.c.) was not altered. These findings provide behavioural evidence that tyrosine-free amino acid mixtures reduce presynaptic dopamine function in the brain.

Amino Acids↗

PubMedDate not supplied

Amniotic fluid endocrine changes during maternal hyperalimentation.

Ten women with low estriol excretion received hyperalimentation prior to induction of labor. Six received an amino acid mixture (5% Aminofusin) and 25% dextrose, two received the amino acid mixture, and two received 25% dextrose. Amniotic fluid obtained before and after hyperalimentation was assayed for fetal surfactant production, thyroid, pituitary, and carbohydrate regulating hormones. In the combined amino acid/dextrose infusion group the amniotic fluid palmitic acid levels increased significantly post infusion; rT3 also increased significantly but T3 and T4 showed no significant change. The pituitary hormones growth hormone, prolactin, and ACTH showed no significant change, but beta-endorphin-like activity was significantly elevated. No thyroid-stimulating hormone was detected in any of the samples. All the carbohydrate regulating hormones, insulin, cortisol, and cAMP, showed significant increases but cGMP showed a significant decrease. The amino acid and dextrose only groups gave similar results. Seven of the infants showed some degree of intrauterine growth retardation but no neonatal complications attributable to the hyperalimentation.

Amino Acids↗

PubMed2001

Consumption of hypoallergenic flour prevents gluten-induced airway inflammation in Brown Norway rats.

Brown Norway rats were immunized with gluten, and then fed a diet containing hypoallergenic flour or an amino acid mixture. The rats were then made to inhale a solubilized gluten to induce gluten-specific bronchial asthma. The antibody levels in the serum of rats were measured by ELISA, and cell counts were done on cytospin preparations of bronchoalveolar lavage fluid. Body weight was decreased after allergen challenge in rats fed the amino acid mixture but not in rats fed the hypoallergenic flour. Antibody levels in the serum were significantly lower in rats fed hypoallergenic flour than in those fed the amino acid mixture. Differential cell counts in the bronchoalveolar lavage fluid showed that the numbers of eosinophils, lymphocytes, and neutrophils were significantly lower in rats fed the hypoallergenic flour than in those fed the amino acid mixture. These results suggest that hypoallergenic flour actively suppresses the allergic reactions, probably by inducing oral tolerance.

Animals↗

PubMed1979

Protein nutrition of Tenebrio molitor L. XX. Growth response of larvae to graded levels of amino acids.

Larvae of Tenebrio molitor L;, Gembloux strain, race F, having an average initial weight of 10 mg were reared for 4 weeks at 27 +/- 0.25 degrees C and 65 +/- 5% relative humidity on diets containing an amino-acid mixture resembling the composition of larval tissues; Each of 14 amino acids was tested individually at levels of 0, 10, 20, 50, 100 and 200% of the amount found in larval tissues, while the concentration of other amino acids remained constant. Diets were maintained isonitrogenous at 1.6% nitrogen with supplementary glutamic acid, glycine, serine and tyrosine; Maximum fresh weight gains and dry weights were achieved by larvae fed reference levels of all essential amino acids except phenylalanine, threonine and tryptophan. Maximum growth was achieved by larvae fed 50% of the phenylalanine level found in larval tissues, Threonine and tryptophan were the limiting amino acids in this study and are probably required in the diet in excess of twice the concentration occuring in larval tissues, Probable ranges for quantitative amino-acid requirements of T. molitor were determined and suggestions were made for improving the nutritional adequacy of the amino-acid mixture.

Amino Acids↗

PubMed1985

[Comparative study of the absorption of enzymatic protein hydrolysates in the small intestine of the rat. 2. The absorption of tryptic, thermitatic and tryptic-thermitatic casein hydrolysates compared with the equimolar composition of free amino acids].

Tryptic, thermitatic, and tryptic-thermitatic casein hydrolyzates as well as their equimolar amino-acid mixture were perfused through proximal and distal parts of the intestine (10 cm length) of nonanaesthesized rats. The total amino-acid concentration of the perfused solution was 50 mM. The absorption of nitrogen and total amino acids respectively did not reveal significant absorption advantages in favour of the hydrolyzates. In contrast to this, some peptidic bound amino acids of these hydrolyzates show a significantly better absorption as compared to free amino acids. At this, dependences of the kind of hydrolyzate and the part of the intestine are evident. Glutamic acid, e.g. is generally more rapidly absorbed when peptidic bound; methionine is more rapidly absorbed only from the thermitatic and tryptic-thermitatic hydrolyzates, and alanine and glycin only in the distal part of the intestine. Independent of the amino acid or peptide substrate the total absorption of all the amino acids is higher in the distal part of the intestine. The comparison concerning the ranking order of the single amino-acid absorption rates shows in the two parts of the intestine distinct differences between the amino-acid mixtures and the enzymatic hydrolyzates. The lowest differences were found between the thermitatic and the tryptic-thermitatic hydrolyzate. Both of them have approximately the same degrees of hydrolysis (30 and 35%, respectively). The variability of the amino-acid absorption from the three casein hydrolyzates is lower in comparison with the amino-acid mixture. The tryptic-thermitatic hydrolyzates have the lowest coefficients of variability.

Amino Acids↗

PubMedDate not supplied

Dependence of apparent viscosity on mycelial morphology of Streptomyces fradiae culture in various nitrogen sources.

To examine what causes increased viscosity in culture broth in Streptomyces fradiae culture, various natural nitrogen sources were investigated. Extracellular protease activity increased with culture time and decomposed the natural nitrogen source into amino acids. In the case of gluten meal, after a culture time of 5 d, concentrations of glutamic acid and aspartic acid had increased to 600 and 200 mg/L, respectively, which were about 3- and 2-fold as high as levels in cultures under similar conditions using Pharmamedia. For various amino acids tested, the addition of glutamic acid or aspartic acid mixture to the culture medium raised the apparent viscosity to its highest demonstrated value, 260 mPa.s after 5 d of culture, which was 3-fold higher than without amino acids. Consumption of the decomposed glutamic acid and aspartic acid was dependent on the activities of glutamate dehydrogenase and aspartate aminotransferase, respectively. When ammonium ion was used as the nitrogen source, cell concentration reached 1.75 g/L measured as an intracellular nucleic acid concentration, which was about 2.3-fold higher than that with any other natural nitrogen source. However, apparent viscosity was only 75 mPa.s, a value one-third that of the amino acid mixture, and 70% of the pellets were bigger than 1.2 x 10(4) microm(2). In the case of gluten meal or the amino acid mixture, pellets bigger than 1.2 x 10(4) microm(2) comprised only 8%. This demonstrates that consumption of some amino acids affected the formation of filamentous morphology, which caused an increase in the apparent viscosity of the culture broth, and the apparent viscosity was not caused by the mycelial concentration but the mycelial morphology.

Amino Acid Oxidoreductases↗