Dietary amino acids fed in free form or as protein do differently affect amino acid absorption in a rat everted sac model

In the present study, the effect of free amino acid (FAA) diets on the intestinal absorption rate of methionine and leucine was studied ‘ex vivo’ with rats adapted for different periods of time to the diets, using the everted sac method. The adaptation period to the 21% FAA diet with an amino acid content based on casein was either, 0 (no adaptation, N‐ADA), 5 (short‐term adaptation, ST‐ADA), or 26–33 days (long‐term adaptation, LT‐ADA). Within the ST‐ADA and the LT‐ADA groups, three different levels of methionine were included: 50%, 100% and 200% of the level normally present in casein. All diets were iso‐nitrogenous and iso‐caloric. After the adaptation period (0, 5, or 26–33 days), intestinal everted sacs were prepared. Methionine or leucine was added to the medium as transport substrate. The methionine absorption rate of the rats of the LT‐ADA groups was higher than that of the N‐ADA groups. Furthermore, adaptation to 200% dietary methionine levels caused a significantly slower leucine absorption compared to the 100%, and 50% group. Methionine absorption was similar in the 100% and 200% groups, but the absorption of methionine in the 50% group was enhanced in the distal part of the intestines. We concluded that in response diets with 21% FAAs as only amino acid source, amino acid absorption is decreased to avoid toxic effects of high levels of methionine in the circulation.     

Dietary levels of protein and free amino acids affect pancreatic proteases activities,amino acids transporters expression and serum amino acid concentrations in starter pigs

The dietary contents of crude protein and free amino acids (AA) may affect the protein digestion and AA absorption in pigs. Trypsin and chymotrypsin activities, AA serum concentrations and expression of AA transporters in the small intestine of pigs fed a low protein, AA‐supplemented (19.2%, LPAA) or a high protein (28.1%, HP), wheat‐soybean meal diet were measured in two 14‐d trials. The LPAA diet contained free L‐Lys, L‐Thr, DL‐Met, L‐Leu, L‐Ile, L‐Val, L‐His, L‐Trp and L‐Phe. All pigs were fed the same amount of feed (890 and 800 g/d for trial 1 and 2 respectively). In trial 1, samples of mucosa (duodenum, jejunum and ileum) and digesta (duodenum and jejunum) were collected from 14 pigs (17.2 ± 0.4 kg); in trial 2, blood samples were collected from 12 pigs (12.7 ± 0.3 kg). The trypsin and chymotrypsin activities in both intestinal segments were higher in pigs fed the HP diet (p < 0.01). Trypsin activity was higher in jejunum than in duodenum regardless the dietary treatment (p < 0.05). Pigs fed the LPAA diet expressed more b^0,+AT in duodenum, B⁰AT1 in ileum (p < 0.05), and tended to express more y⁺LAT1 in duodenum (p = 0.10). In pigs fed the LPAA diet, the expression of b^0,+AT was higher in duodenum than in jejunum and ileum (p < 0.01), but no difference was observed in pigs fed the HP diet. Ileum had the lowest b^0,+AT expression regardless the diet. The serum concentrations of Lys, Thr and Met were higher in LPAA pigs while serum Arg was higher in HP pigs (p < 0.05). Serum concentrations of AA appear to reflect the AA absorption. In conclusion, these data indicate that the dietary protein contents affect the extent of protein digestion and that supplemental free AA may influence the intestinal site of AA release and absorption, which may impact their availability for growth of young pigs.     

Muscle growth and plasma concentrations of amino acids, insulin-like growth factor-I, and insulin in growing pigs fed reduced-protein diets

Twenty barrows were used to determine if partial replacement of protein-bound AA with crystalline AA (CAA) reduces AA use for muscle tissue and whole-body growth. Barrows (44.2 +/- 1.3 kg of BW) were assigned to 4 diets in a randomized complete block design. Diets consisted of 16.1% CP with no CAA, and 12.8, 10.1, and 7.8% CP containing CAA. As the CP concentration decreased, CAA were gradually increased to meet requirements on a true ileal digestibility basis. Barrows were weighed on d 0 and 13. Blood samples were collected before the morning feeding on d 0, 6, and 12 (prefeeding), and 2 h after the morning feeding on d 13 (postfeeding). Pigs were euthanized on d 13, and liver and right LM were removed and weighed. The reduction in the dietary CP concentration linearly decreased (P < 0.01) ADG, G:F, LM weight, and the CP content of LM. Reducing the CP concentration decreased pre- and postfeeding plasma concentrations of IGF-I (linear, P < 0.01) and insulin (linear, P < 0.10). The reduction in the dietary CP concentration increased prefeeding plasma concentrations of Ala, Gln, Gly, and total AA but decreased Arg, Asn, His, Ile, Phe, Trp, and Tyr (linear, P < 0.05). Plasma concentration of total indispensable AA decreased initially and increased thereafter as the dietary CP concentration decreased from 16.1 to 7.8% (quadratic, P < 0.01). The reduction in the dietary CP concentration increased postfeeding plasma concentrations of Ala, Lys, Met (linear, P < 0.01), and Gly (linear, P = 0.073) and decreased Asn, Ser, Tyr, Arg, His, and Leu (linear, P < 0.05). Plasma concentrations of Ile, Phe, Thr, Trp, and Val decreased initially and increased thereafter as the dietary CP concentration decreased from 16.1 to 7.8% (quadratic, P < 0.05). In muscle tissue, concentrations of free Ala, Asp, Glu, Gln, Gly, and Lys increased (linear, P < 0.05) as the dietary CP concentration decreased. Concentrations of free His, Ile, Phe, Thr, Trp, and Val in muscle tissue decreased initially and increased thereafter as the dietary CP concentration decreased from 16.1 to 7.8% (quadratic, P < 0.05). In summary, the reduction in the dietary protein-bound AA decreased whole-body and LM growth, altered the free AA pool profile in muscle tissue, and decreased plasma insulin and IGF-I. As the replacement of protein-bound AA with CAA increased, 1) free Ala and Gln in muscle tissue increased, indicating an increase of muscle tissue protein breakdown; and 2) utilization of indispensable AA in muscle tissue decreased.     

Pituitary hormone and insulin responses to infusion of amino acids and N-methyl-D,L-aspartate in horses

Thirty-nine adult light horse mares, geldings, and stallions were used in two experiments to assess the pituitary hormone and insulin responses to infusions of arginine, aspartic acid, lysine, glutamic acid, and N-methyl-D,L-aspartate (NMA). In Exp. 1, 27 horses were assigned to one of three infusion treatments: 1) physiological saline (1 L); 2) 2.855 mmol of arginine/kg BW in 1 L of water; or 3) 2.855 mmol of aspartic acid/kg BW in 1 L of water. In Exp. 2, 12 horses were assigned, in a multiple-square 4 x 4 Latin square design, to one of four infusion treatments: 1) 2 mL of saline/kg BW; 2) 2.855 mmol of lysine/kg BW in water; 3) 2.855 mmol of glutamic acid/kg BW in water; or 4) 1 mg of NMA/kg BW in water. In Exp. 1, an acute (within 20 min) release of growth hormone (GH) was induced (P = 0.002) by aspartic acid. In contrast, acute release of prolactin (P = 0.001) and insulin (P = 0.002) was induced only by arginine; moreover, the arginine effect on insulin was present only in mares (P = 0.011). In Exp. 2, an acute release of GH was induced (P = 0.001) by glutamic acid and NMA. In males, the glutamic acid-induced GH release was greater than that of NMA; in mares, the NMA-induced GH release was greater than that of glutamic acid (P = 0.069). Both lysine and glutamic acid induced (P = 0.001) acute release of prolactin, whereas an acute release of insulin was elicited (P = 0.002) only by lysine. The NMA-induced LH response was due almost entirely to the response in mares and stallions (P = 0.016), and the NMA-induced FSH release was due almost entirely to the response in mares (reproductive status effect; P = 0.004). In the horse, aspartic acid, glutamic acid, and NMA seem to stimulate GH release; arginine and lysine seem to stimulate prolactin and insulin release; and NMA seems to stimulate LH and FSH release. It seems that N-methyl-D-aspartate glutamate receptors are involved in controlling GH, LH, and FSH secretion, whereas other mechanisms are involved with prolactin secretion. These results also indicate that gonadal steroids interact with amino acid-induced pituitary hormone release in adult horses.     

High dietary phytase levels maximize phytate-phosphorus utilization but do not affect protein utilization in chicks fed phosphorus- or amino acid-deficient diets

Four trials investigated the effect of high levels of three phytase enzymes on P and protein utilization in chicks. The three phytases were derived from Aspergillus (Fungal Phytase 1), Peniophora (Fungal Phytase 2), and E. coli. Within each assay, 8-d-old male chicks were given ad libitum access to their experimental diet for 10 to 14 d. For Trials 1, 2, and 3, the basal diet was a corn-soybean meal diet deficient in P that was analyzed to contain 23% CP and 0.38% total P (0.10% estimated available P, as-fed basis). Phytase supplementation levels were based on the assessment of phytase premix activity (i.e., P release from Na phytate at pH 5.5 and 37 degrees C). In Trial 1, supplementation of inorganic P from KH2PO4 (0 to 0.20%) resulted in a quadratic (P < 0.05) response in weight gain, gain:feed, and tibia ash concentration but a linear (P < 0.01) increase in tibia ash weight. Tibia ash was higher (P < 0.01) for chicks fed E. coli phytase than for those fed Fungal Phytase 1 at 500, 1,000, and 5,000 phytase units (FTU)/kg, but did not differ between these two phytases at 10,000 FTU/kg. In Trial 2, E. coli phytase supplementation at 1,000 FTU/kg maximized growth and bone responses, whereas addition of either of the two fungal phytases resulted in increasing responses up to 5,000 and 10,000 FTU/kg. Dietary addition of Fungal Phytase 2 resulted in the poorest (P < 0.01) responses among the three phytases. Escherichia coli phytase supplementation at 10,000 FTU/kg in Trial 3 resulted in tibia ash (millligrams) responses that were greater (P < 0.05) than those resulting from either 0.35% inorganic P supplementation or 10,000 FTU/kg of Fungal Phytase 1 or 2. Trial 4 showed that E. coli phytase supplementation at either 500 or 10,000 FTU/ kg did not improve protein efficiency ratio (gain per unit of protein intake) of chicks fed low-protein soybean meal or corn gluten meal diets that were first-limiting in either methionine or lysine, respectively. These results demonstrate that high dietary levels of efficacious phytase enzymes can release most of the P from phytate, but they do not improve protein utilization.     

Interactions of amino acids and hormones regulate the balance between growth and milk protein synthesis in lactating rats fed diets differing in protein content

Insulin-like growth factor-I (IGF-I), growth hormone (GH), and prolactin (PRL) play important roles in milk protein synthesis, and their plasma concentrations were reported to be affected by dietary protein intake. To investigate the relationship between circulating amino acid (AA) and concentrations of these hormones, 18 Wistar rats aged 14 wk were assigned to a low (LP; 9% protein), standard (SP; 21% protein), or high-protein (HP; 35% protein) diet from parturition through day 15 of lactation. Plasma, liver, pituitary gland, skeletal muscle, and mammary gland samples were collected at the end of treatment. Circulating and hepatic IGF-I concentrations increased linearly with elevated dietary protein concentrations (P < 0.0001). Rats receiving the HP diet had higher circulating GH (P < 0.01) and pituitary PRL concentrations (P < 0.0001) but lower pituitary GH concentration (P < 0.0001) relative to those in rats receiving the LP and SP diets. Pearson correlation test performed on composed data across treatments showed that several circulating AAs were correlated with circulating and tissue concentrations of IGF-I, GH, and PRL. Multiple linear regression analyses identified Leu, Gln, Ala, Gly, and Arg as the main AAs associated with hormone responses (R² = 0.37 ~ 0.80; P < 0.05). Rats fed the LP and HP diets had greater Igf1 and Ghr gene expression in skeletal muscle than those fed the SP diets (P < 0.01). However, LP treatment decreased Prlr mRNA abundance in mammary glands as compared with the SP and HP treatments (P < 0.05). The HP diets increased AA transporter expression (P < 0.01) but decreased mammalian target of rapamycin (P < 0.05) and 70 kDa ribosomal protein S6 kinase 1 (P < 0.01) phosphorylation in mammary glands as compared with the LP and SP diets. The results of the present study suggested that several circulating AAs mediated the effects of dietary protein supply on concentrations of IGF-I, GH, and PRL, which in turn altered the metabolism status in peripheral tissues including the lactating mammary glands.     

Relation of soya bean meal level to the concentration of plasma free amino acids and body growth in white rats

Amino acid (AA) levels in plasma and body growth were determined in rats (n20) fed diets with different soya bean meal levels. Free AA in plasma was determined by reversed-phase high-pressure liquid chromatography. We have used four levels of protein diets like 8%, 15%, 23% and 35% in this trial. Rats which were fed the low-protein (8%) diet with low percentage of soya bean meal were found to be growth-retarded. The body weight gain of high protein group (35%) was lower than that of the 23% groups. In the rats fed with the low-soya bean meal diet, some nonessential AA (NEAA) in plasma like asparagine, aspartic acid, cysteine, glutamic acid and serine increased, whereas the essential AA (EAA), with the exception of arginine, methionine and valine decreased. Here, plasma EAA-to-NEAA ratios were not correlated to growth and experimental diet. We hypothesize that AA metabolism is associated to changes in growth in rats on different protein intake. This study has showed the sensitivity of body mass gain, feed intake, feed conversion rate of rats to four levels of protein in the diet under controlled experimental conditions.     

Effect of octreotide on plasma concentrations of glucose, insulin, glucagon, growth hormone, and cortisol in healthy dogs and dogs with insulinoma

The inhibitory effect of the somatostatin analogue octreotide on the secretion of insulin could be used in the treatment of insulinoma. However, current information on the effectiveness of octreotide in dogs is conflicting. Therefore, the endocrine effects of a single subcutaneous dose of 50 microg octreotide were studied in healthy dogs in the fasting state (n=7) and in dogs with insulinoma (n=12). Octreotide did not cause any adverse effects. In healthy dogs in the fasting state, both plasma insulin and glucagon concentrations declined significantly. Basal (non-pulse related) GH and ACTH concentrations were not affected. A slight but significant decrease in the plasma glucose concentrations occurred. Dogs with insulinoma had significantly higher baseline insulin concentrations and lower baseline glucose concentrations than healthy dogs in the fasting state. Plasma glucagon, GH, ACTH, and cortisol concentrations did not differ from those in healthy dogs. Baseline plasma insulin concentrations decreased significantly in dogs with insulinoma after octreotide administration, whereas plasma concentrations of glucagon, GH, ACTH, and cortisol did not change. In contrast to the effects in the healthy dogs, in the dogs with insulinoma plasma glucose concentrations increased. Thus, the consistent suppression of plasma insulin concentrations in dogs with insulinoma, in the absence of an suppressive effect on counter-regulatory hormones, suggests that further studies on the effectiveness of slow-release preparations in the long-term medical treatment of dogs with insulinoma are warranted.     

Effect of glycine supplementation in low protein diets with amino acids from soy protein isolate or free amino acids on broiler growth and nitrogen utilisation

1. Here, it was investigated whether substitution of amino acids (AA) from soy protein isolate with free AA in low crude protein diets influences the growth performance and N utilisation in broilers, and whether interactions with dietary glycine equivalent (Gly_equi) concentration exist.

2. Birds were distributed in two 2 × 2 factorial arrangements of 48 floor pens containing 10 birds each, plus 48 metabolism cages containing two birds each. Experimental feed was provided for ad libitum consumption from d 7 to 22. Diets contained either a soy protein isolate at 79 g/kg or a mix of free AA, which supplied the same amount of 18 proteinogenic AA. A mix of free glycine and l-serine was used to obtain low and high (12.0 and 20.5 g/kg dry matter) levels of dietary Gly_equi.

3. Substitution of soy protein isolate with free AA reduced the average daily gain and feed efficiency, mainly due to reduced feed intake. Efficiency of N accretion was not influenced by the AA source or Gly_equi concentration on d 21, possibly due to the lower AA digestibility of soy protein isolate and higher urinary excretion of nitrogenous substances in the treatments with the AA mix.

4. The average daily weight gain of the treatments with high Gly_equi concentration was higher for both AA sources. This increase was due to higher average daily feed intake by broilers in the treatments with soy protein isolate and due to the increased feed efficiency in the treatments with the AA mix. Broilers exhibited different growth responses to dietary Gly_equi between the AA sources; however, these responses could not be attributed to the different utilisation of Gly_equi for uric acid synthesis.

     

Apelin is involved in postprandial responses and stimulates secretion of arginine-vasopressin, adrenocorticotropic hormone, and growth hormone in the ruminant

Apelin and its mRNA are expressed in several tissues, including the supraoptic and paraventricular nuclei in the hypothalamus. Although apelin is reported to be involved in the regulation of fluid homeostasis, little is known about the postprandial dynamics of apelin in plasma and its regulatory effects on the anterior pituitary hormones of ruminants. Therefore, the aims of this study were to investigate the following: (1) changes in plasma apelin concentrations in response to food intake under conditions of hydration (free access to water) or dehydration (water restriction), and (2) the effects of intravenous administration of apelin on plasma concentrations of arginine-vasopressin (AVP), ACTH, GH, and insulin. In Experiment 1 with the use of goats, the postprandial plasma apelin concentration was significantly increased under the dehydration condition compared with the hydration condition, and this increase was accompanied by increased plasma concentrations of AVP and ACTH after 24 h of dehydration. In Experiment 2 with the use of sheep and hydration conditions, the intravenous administration of apelin ([Pyr(1)]-apelin-13; 0.5 mg/head) caused a tendency to increase or caused a significant increase in plasma concentrations of AVP, ACTH, GH, insulin, and glucose. On the basis of these findings, we concluded that apelin is involved in the feeding process, and it regulates endocrine functions in the anterior pituitary gland via AVP in ruminant animals.     

Luteinizing hormone,growth hormone,insulin-like growth factor-i,insulin and metabolites before puberty in heifers fed to gain at two rates

Fall born Angus x Hereford heifers were allotted to treatments at 9 mo of age to achieve the following growth rates: 1) fed to gain 1.36 kg/d (n = 10; HGAIN); and 2) fed to gain 0.23 kg/d for 16 wk, then fed to gain 1.36 kg/d (n = 9; LHGAIN). Growth hormone (GH), insulin-like growth factor-1 (IGF-I), insulin, glucose, nonesterified fatty acids (NEFA), and progesterone were quantified in twice weekly blood samples until onset of puberty. Body weight, hip height, and pelvic area were recorded every 28 d. Frequent blood samples (n = 8 heifers/treatment) were collected every 14 d, commencing on day 29 of treatment until onset of puberty to evaluate secretion of luteinizing hormone (LH) and GH. The HGAIN heifers were younger (369 d; P < 0.001), were shorter at the hip (115 cm; P < 0.05) and had smaller pelvic area (140 cm²; P < 0.10), but body weight (321 kg) did not differ at puberty compared with LHGAIN heifers (460 d; 119 cm; 155 cm²; 347 kg, respectively). The HGAIN heifers had greater (P < 0.05) concentrations of LH, IGF-I, and insulin in serum and glucose in plasma during the first 84 d of treatment than LHGAIN heifers, whereas LHGAIN heifers had greater (P < 0.05) concentrations of GH in serum and NEFA in plasma than HGAIN heifers. On Day 68 of treatment, HGAIN heifers had less mean GH (P < 0.01) and greater (P < 0.05) LH pulse frequency than LHGAIN heifers, whereas LH pulse amplitude and mean LH did not differ (P > 0.10) between treatments. Treatment did not influence secretion of LH and GH at 1 and 3 wk before puberty. Mean GH concentrations in serum and GH pulse amplitude in all heifers were greater (P < 0.05) 2 to 9 d (12.9 and 40.7 ng/ml, respectively) than 16 to 23 d (10.4 and 20.0 ng/ml, respectively) before puberty. Nutrient restriction decreased LH pulse frequency and delayed puberty in beef heifers. Furthermore, dramatic changes in mean concentration and amplitude of GH pulses just before puberty in beef heifers may have a role in pubertal development.     

High glycemic and insulinemic responses to meals affect plasma growth hormone secretory characteristics in Quarter Horse weanlings

Growth hormone is a key component of the somatotropic axis and is critical for the interplay between nutrition, regulation of metabolic functions, and subsequent processes of growth. The objective of this study was to investigate potential relations between meal feeding concentrates differing in the glycemic responses they elicit and GH secretory patterns in young growing horses. Twelve Quarter Horse weanlings (5.4 ± 0.4 mo of age) were used in a crossover design, consisting of two 21-d periods and two treatments, a high-glycemic (HG) or low-glycemic (LG) concentrate meal, fed twice daily. Horses were individually housed and fed hay ad libitum. On the final day of each period, quarter-hourly blood samples were drawn for 24 h to measure plasma glucose, insulin, non-esterified fatty acids, and GH. Growth hormone secretory characteristics were estimated with deconvolution analysis. After a meal, HG-fed horses exhibited a longer inhibition until the first pulse of GH secretion (P = 0.012). During late night hours (1:00 AM to 6:45 AM), HG horses secreted a greater amount of pulsatile GH than LG horses (P = 0.002). These differences highlight the potential relations between glycemic and insulinemic responses to meals and GH secretion. Dietary energy source and metabolic perturbations associated with feeding HG meals to young, growing horses have the potential to alter GH secretory patterns compared with LG meals. This may potentially affect the developmental pattern of various tissues in the young growing horse.     

Changes in plasma bile acids,plasma amino acids,and hepatic enzyme pools as indices of functional impairment in liver-damaged sheep

Plasma bile acids, plasma amino acids, and the total hepatic pools of aspartate aminotransferase, gamma glutamyltransferase, glutamate dehydrogenase, and sorbitol dehydrogenase were compared in control sheep (Group 1), sheep with subclinical pyrrolizidine alkaloid toxicosis (Group 2), and in sheep with acute hepatocellular necrosis associated with the hemolytic phase of chronic copper poisoning (Group 3). Subclinical pyrrolizidine alkaloid toxicosis was not associated with any changes in bile acid or amino acid status but was associated with a significant decline in the hepatic pools of sorbitol dehydrogenase and aspartate aminotransferase. This observation could not be explained in terms of enzyme leakage from damaged hepatocytes and suggested that pyrrolizidine alkaloids might specifically inhibit hepatocellular enzyme synthesis. Group 3 sheep also had reduced hepatic enzyme pools which were at least partly referable to enzyme leakage from damaged hepatocytes. In these sheep, increases in plasma bile acids were a more sensitive index of hepatic function than were either increased aromatic amino acid concentration or the ratio between branched chain and aromatic amino acids.     

Effect of GABA on oxidative stress in the skeletal muscles and plasma free amino acids in mice fed high‐fat diet

Increased levels of plasma free amino acids (pFAAs) can disturb the blood glucose levels in patients with obesity, diabetes mellitus and metabolic syndrome (MS) and are associated with enhanced protein oxidation. Oxidation of proteins, especially in the muscles, can promote protein degradation and elevate the levels of pFAAs. Gamma‐aminobutyric acid (GABA), a food additive, can reduce high‐fat diet (HFD)‐induced hyperglycaemia; however, the mechanisms remain unclear. The aim of this study was to evaluate the effects of GABA on protein oxidation and pFAAs changes. One hundred male C57BL/6 mice were randomly divided into five groups that were fed with control diet, HFD and HFD supplied with 0.2%, 0.12% and 0.06% GABA in drinking water for 20 weeks respectively. HFD feeding led to muscular oxidative stress, protein oxidation, pFAA disorders, hyperglycaemia and augmented plasma GABA levels. Treatment with GABA restored normally fasting blood glucose level and dose‐dependently inhibited body weight gains, muscular oxidation and protein degradation. While medium and low doses of GABA mitigated HFD‐induced pFAA disorders, the high dose of GABA deteriorated the pFAA disorders. Medium dose of GABA increased the levels of GABA, but high dose of GABA reduced the levels of plasma GABA and increased the activity of succinic semialdehyde dehydrogenase in the liver. Therefore, treatment with GABA mitigated HFD‐induced hyperglycaemia probably by repairing HFD‐induced muscular oxidative stress and pFAA disorders in mice. Our data also suggest that an optimal dose of GABA is crucial for the prevention of excess GABA‐related decrease in the levels of pFAA and GABA as well as obesity.