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The aim of the present study was to examine the effect of high glucose alone and in combination with high insulin on insulin-stimulated protein synthesis and the activation of insulin signaling pathways in mouse C2C12 myogenic cells. The experiments were performed on mouse C2C12 myoblasts subjected to differentiation under normal glucose (5 mmol/l), high glucose alone (15 mmol/l), or in combination with high insulin (50 nmol/l). Six-day differentiation under high glucose alone or in combination with high insulin resulted in insulin resistance, manifested by the abolition of the stimulatory effect on protein synthesis. High glucose concentration in the culture medium did not affect the protein kinase B (PKB) cellular content in C2C12 myogenic cells, whereas in cells preincubated with a combination of high glucose and high insulin a slight but significant increase (of 19%) in PKB protein content was determined. Insulin caused the activation of protein kinase B (PKB) in control C2C12 myogenic cells. Pretreatment with high glucose did not affect PKB phosphorylation whereas in cells differentiated under high glucose and high insulin PKB activation by insulin was markedly attenuated as compared with the control (differentiation under normal glucose). Neither the p70S6k protein content nor the pattern of insulin-mediated kinase activation was affected by pretreatment with high glucose, however high glucose and high insulin in combination caused an impairment in the p70S6k phosphorylation when compared to the control. High glucose exerted no significant changes in MAP kinase protein content, however concomitant treatment with high glucose and high insulin resulted in the decrease in p42MAPK and p44MAPK proteins (by 20%). During the whole period of observation, p42MAPK exhibited basal phosphorylation that was not modified in the presence of insulin. However, the phosphorylation of p42MAPK was profoundly impaired in cells preincubated with high glucose alone or in combination with high insulin. In conclusion: 1) high glucose abolishes the stimulatory action of insulin on protein synthesis without changes in PKB and p70S6k activation; 2) high glucose and high insulin in combination abolish the stimulatory effect of insulin dependent on PKB- and p70S6k; 3) the stimulatory action of insulin on protein synthesis in C2C12 myogenic cells depends on basal phosphorylation of p42MAPK.
Białka są niezbędne do utrzymania życia każdego żywego organizmu. Synteza białek w ustroju człowieka odbywa się tylko przy prawidłowej dostępności aminokwasów, natomiast brak właściwej podaży białka powoduje rozwój niedożywienia: marasmus, kwashiorkor i niedożywienie mieszane. Interwencja żywieniowa, w skład której wchodzi podaż stosownej ilości białka i kalorii, w zależności od rodzaju zaburzenia jest oparta na żywieniu do- i pozajelitowym.
This paper compares several models of protein synthesis in the mammary gland of cows developed by using various statistical models. According to these models, it is possible to predict an increase in the amount of proteins in milk as a result of the addition of proteins or amino acids (AA) to dairy cows’ diet. It is difficult to increase the amount of proteins in milk via nutritional manipulation. In the case of dairy cows, the extra-ruminal addition of AA increases their intake, but an increase in the amount of proteins in milk is not always achieved, since the AA dose often does not include limiting essential amino acids (EAA). An additional factor that complicates protein transformations is AA metabolism in the small intestine and liver, which to a large degree influences the amount and profile of AA transferred to the mammary gland. The utilization rate of AA in the mammary gland depends on their concentration in arterial blood, the rate of blood flow through the udder, the transport process through cellular membranes and the level of amino acid metabolism in the gland. All these processes may be described mathematically by Michaelis-Menten kinetic equations. Nevertheless, the ideal model of protein synthesis in the mammary gland is yet to be developed. Also the role of the most important amino acids for that synthesis is not fully known. Among non-essential amino acids (NEAA), considerable importance is attributed to glutamine and asparagine.
Four rams (body weight 50 kg) fitted with ruminal and simple duodenal oannulae were fed at random, in six 14-day periods, rations in a loose (S) and pelleted (G) form, containing 70% of dehydrated maize plant and 0, 1.25 and 2.5% of urea (respectively rations SO, SI, SII and GO, GI, GII). The urea doses were assumed to cover 100 and 200% of the deficiency of rumen degradable N /ARC, 1980/. The duodenal flow of microbial protein N (NBM) was in groups S 8.17, 13,8 and 14.6 g and in G 10.8, 13.7 and 16.1 g/24h. The yield of NBM/100 g O.M. apparently digested in the rumen was, respectively, 1.16, 2.18, 2.00 and 1.66, 2.24, 2.86 g. The effect of physical form on NBM flow and yield was significant (P ˂ 0.05). N-NH₃ level in the rumen fluid was lower in groups S than G, being probably a reason for higher NBM synsynthesis in groups G. Better utilization of urea at its highest level (2.5%) from the pelleted ration can be caused by the decreased degradation in the rumen of feed protein due to pelleting process.
Studies have been carried out on 4 fattening steers with permanent rumen fistulas . Corn silage, green alfalfa, pasture lichen and sugar beet top silage were applied. They were supplemented with different forages and concentrates. Samples of rumen content were analysed for pH, N-NH3, total VFA, acetic, propionic and butyric acids, soluble and bacterial N. Using nylon bags in situ, the degradation of nitrogen compounds and dry matter of the feeds examined, was evaluated during 24 hours. High pH values of rumen content / 7 , 5 / was found when green grass and green alfalfa forages were fed. VFA levels for silages and soilages were in the range of 10-11 mmol/and 6,2 - 8,8 mmol/100 ml of rumen content, respectively. The highest concent rations of N-NH3 exceeded 20 - 30 mg/100 mg /urea, green alfalfa, pea/ whereas with green forages they were the lowest /11 mg/100 ml on average/. Bacterial protein synthesis was the most intensive with concentrates in the diets. Degradation of dry matter in bags, after 24 hours varied from 61% /hay/ to 89% /barley meal/ whereas that of crude protein varied from 9% /hay/ to 93% /CJ mixture/.
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