Effect of Quality and Quantity of Dietary Protein on 4E-BP1 and S6K1 Phosphorylation of Brains in Aged Rats

Abiko

et al. 2012

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SummaryThe purpose of this study was to determine whether the regulation of brain protein synthesis is mediated through changes in the plasma concentration of growth hormone (GH) when dietary ornithine treatment is manipulated in the hypophysectomized or sham-operated aged rats. Experiments were done on four groups of hypophysectomized and sham-operated (24-wk-old) male rats given 0% or 0.7% ornithine-HCl added to a 20% casein diet. The concentrations of plasma GH and fractional rates of protein synthesis in the brains increased signifi cantly with the 20% caseinϩ0.7% ornithine compared with the 20% casein diet alone in the sham-operated rats. However ornithine supplementation to the basal diet did not affect the rates of protein synthesis in the hypophysectomized rats. In the cerebral cortex and cerebellum, the RNA activity [g protein synthesized/(g RNA·d)] signifi cantly correlated with the fractional rate of protein synthesis. The RNA concentration (mg RNA/g protein) was also related to the fractional rate of protein synthesis in these organs. The results suggest that the treatment with ornithine is likely to increase the concentration of GH and the rate of brain protein synthesis in the sham-operated rats only, not in the hypophysectomized rats, and that the ornithine-induced increase in the concentration of GH may be primarily responsible for changes in the brain protein synthesis. The RNA activity is at least partly related to the fractional rate of brain protein synthesis.

Section: Discussionmentioning

confidence: 79%

Effect of Dietary Ornithine on the Brain Protein Synthesis Rate in Hypophysectomized Aged Rats

Abiko

et al. 2012

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“…In both liver and muscle, the stimulation of protein synthe-sis caused by amino acids and hormonal factors is mediated by the increase in the initiation of mRNA translation (32)(33)(34). We reported that the ingestion of a higher quantity of dietary protein and the dietary addition of GABA enhanced brain protein synthesis through the activation of the mRNA binding to the 40S ribosomal subunit (35,36). Kato (11) suggested that GH stimulated the translational phase of tissue protein synthesis.…”

Section: Discussionmentioning

confidence: 99%

Changes in Thyroid Hormone Are Not Involved in Regulating Brain Protein Synthesis in Adults Rats Fed Ornithine

Yokogoshi

et al. 2017

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SummaryBrain protein synthesis and the plasma concentration of growth hormone (GH) are sensitive to dietary ornithine. However, dietary ornithine does not increase brain protein synthesis in hypophysectomized rats. Because hypophysectomy may decrease the secretion of thyroid stimulated hormone (TSH), we assessed whether the regulation of brain protein synthesis was mediated by changes in the plasma concentrations of thyroid hormone and ghrelin in the 6-propyl-2-thiouracil (PTU, thyroid inhibitor)-treated or control adult rats fed ornithine. The four experimental groups consisted of PTU-treated and control (24-wk-old) male rats given 0% or 0.7% ornithine-HCl added to a 20% casein diet. The plasma concentrations of GH and ghrelin, and the fractional rates of protein synthesis and RNA activity [g protein synthesized/(g RNA·d)] in the brains were significantly increased after treatment with the 20% casein 1 0.7% ornithine compared with the 20% casein diet alone in both the PTU-treated and control groups. Ornithine supplementation to the basal diet did not affect the plasma concentration of T3. The RNA concentration (mg RNA/g protein) was not related to the fractional rate of protein synthesis in the brain regions. The results suggest that dietary ornithine likely increases the rate of brain protein synthesis in control and PTU-treated rats, and that the ornithine-induced increase in the GH concentration may stimulate mainly brain protein synthesis via ghrelin. RNA activity is at least partly related to the fractional rate of brain protein synthesis.

“…In liver, muscle and brain, the stimulation of protein synthesis caused by amino acids and proteins is reported to be mediated by an increase in the initiation of mRNA translation (23 -26). We reported that the ingestion of a higher quality or quantity of dietary protein enhanced protein synthesis through the activation of the binding of mRNA to the 40S ribosomal subunit in the brain (26). The most studied example of the regulation of protein synthesis occurring at the mRNA binding to 40S ribosomal subunit is the reversible sequestration of eIF4E into an inactive complex with the eIF4E binding protein (4E-BP1) (23,24).…”

Section: Resultsmentioning

confidence: 99%

Dietary Ornithine Affects the Tissue Protein Synthesis Rate in Young Rats

Aoki³

et al. 2012

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297The metabolic response to dietary proteins, age and hormonal factors includes marked changes in protein synthesis, especially in the liver, muscles and intestines (1)(2)(3)(4)(5). Protein synthesis in the brain is also sensitive to the alteration of dietary amino acid composition in young rats (6,7). Growth hormone (GH) is well known as the anabolic hormone in protein metabolism. Several investigators have demonstrated that the protein synthesis in visceral organs and skeletal muscle was increased by growth hormone in rats (8).Ornithine is a kind of amino acid widely distributed in the liver of mammals and various foods such as Corbicula (Asian clam). Ornithine is also a urea cycle intermediate and the substrate of citrulline synthesis. Urea formation has been shown to be stimulated by adding ornithine in perfused liver (9, 10) and in isolated hepatocytes (11). Recently, ornithine has been attracting attention in functional foods for improvement of hepatic function and GH release (12). Bucci et al. (12) confi rmed that the plasma concentration of GH increased with ornithine ingestion in bodybuilders. Ohsumi et al. (13) demonstrated that hypophysectomy has been shown to decrease the rate of protein synthesis in the brain regions of rats, whereas treatment with GH reversed the effect of hypophysectomy. However, the role of ornithine treatment in maintaining the rate of brain protein synthesis remains unknown in young male rats. Therefore, the possible effects of dietary addition of ornithine on the brain protein synthesis and plasma GH in young male rats are of nutritional importance in understanding the role of nutrition on the brain function in mammals.The purpose of our study was to determine whether ornithine affects the rate of brain protein synthesis in young male rats. In our previous report (7,14), a positive correlation between the rate of protein synthesis and RNA activity was found in the brain when the quality or quantity of dietary protein was manipulated in young and aged rats. However, the reduction with age in protein synthesis in the brain was related to a fall in the RNA concentration (15). Three questions were considered in the present study: 1) whether the dietary addition of ornithine to the basal diet might increase the plasma concentration of GH in young male rats, Igaya-cho, Kariya, Aichi 448-8542, Japan (Received March 28, 2012) Summary The purpose of this study was to determine whether ornithine affects the rate of tissue protein synthesis in male rats. Two experiments were done on fi ve or two groups of young rats (5 wk) given diets containing 0.15, 0.3, 0.5 or 0.7% ornithine-HCl added to a 20% casein diet for 1 d (only one 3 h period) (Experiment 1), and given a diet containing 0 or 0.7% ornithine-HCl added to a 20% casein diet for 10 d (Experiment 2). The plasma concentration of growth hormone (GH) was the highest in rats fed 0.5 and 0.7% ornithine added to the 20% casein diet. The fractional rates of protein synthesis in brain regions, liver and gastrocnemius muscle increa...