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This study was undertaken to determine whether a pulse protein feeding pattern was more efficient than a spread pattern to improve protein anabolism in young women as was already shown in elderly women. After a 15-d adaptive period [1.2 g protein/(kg fat-free mass. d)], 16 young women (age 26 +/- 1 y) were given a 14-d diet providing 1.7 g protein/(kg fat-free mass. d), using either a pulse pattern (protein consumed mainly in one meal, n = 8), or a spread pattern (spreading daily protein intake over four meals, n = 8). Nitrogen balance was determined at the end of both the 15-d adaptive and the 14-d experimental periods. Whole-body protein turnover was determined at the end of the 14-d experimental period using [(15)N]glycine as an oral tracer. Nitrogen balance was 17 +/- 5 mg N/(kg fat-free mass. d) during the adaptive period. It was higher during the experimental period, but not significantly different in the women fed the spread or the pulse patterns [59 +/- 12 and 36 +/- 8 mg N/(kg fat-free mass. d) respectively]. No significant effects of the protein feeding pattern were detected on either whole-body protein turnover [5.5 +/- 0.2 vs. 6.1 +/- 0.3 g protein/(kg fat-free mass. d) for spread and pulse pattern, respectively] or whole-body protein synthesis and protein breakdown. Thus, in young women, these protein feeding patterns did not have significantly different effects on protein retention. [ABSTRACT FROM AUTHOR]

The aim of this study was to determine whether exogenous glucose metabolism influences the pH in superfused EDL muscle from growing rats fed or starved for 48 h (body weight 55 and 45 g, respectively). Energy state and intracellular pH of muscle were repeatedly monitored by 31P-nuclear magnetic resonance spectroscopy (31P-NMRS); glycogen and other energy metabolites were assayed enzymatically in muscle extracts at the end of the experiment. In EDL muscles from starved rats superfused with glucose for 4 h, intracellular pH was elevated (7-7.3), lactate concentration low, glycogen repletion very intense and citrate synthase activity high. We conclude that glucose was routed mainly toward both oxidative phosphorylation and glycogen synthesis in EDL muscles after food deprivation of rats. In contrast, the major pathway in muscles from fed rats may be glycolysis because the glycogen pool remained constant throughout the experiment. The additional and minor pH component (in the range of 6.5 to 6.8) seen in muscles from fed rats, even in the presence of exogenous glucose, might be due to impaired glucose utilization because this component appears also in muscles from starved rats superfused without glucose or with a nonmetabolizable analog of glucose. Consequently, direct pH measurement by 31P-NMR may be considered to be a precise criterion for evaluation of differences in metabolic potentialities of muscle studied ex vivo in relation to the nutritional state of rats. [ABSTRACT FROM AUTHOR]

We recently demonstrated that a high protein intake partially prevented the decrease in protein synthesis in the atrophied dark soleus muscle of rats that were hindlimb suspended (HS) for 21 d. To study the possible role of protein intake in a muscle more representative of the whole musculature, we measured the effect of a high protein (HP) (30%) and a medium protein (MP) (15%) diet on protein synthesis in the pale fast-twitch tibialis anterior muscle of HS rats. The HS animals were suspended by the tail for 21 d so that only their front legs were able to rest on the floor. The fractional rate of protein synthesis (Ks) was determined in vivo using a flooding dose method. A significantly lower Ks (24-25%) was found in both HS-MP and HS-HP rats compared with their pair-fed control groups. Reduced Ks in HS-MP rats relative to their pair-fed controls resulted from a decrease in the translational efficiency (KRNA, 23%, P < 0.01), while the ratio of RNA to protein (Cs) was unaffected. In contrast, the decrease in KRNA was prevented in the HS-HP animals compared with their pair-fed controls (P < 0.05). Hindlimb suspension did not alter fiber type distribution in the tibialis anterior muscle. However, a higher proportion of intermediate and Type I fibers with a concomitant decrease in Type II fibers was observed in both CT and HS animals fed the HP diet compared with those fed the MP diet (P < 0.05). These data clearly establish that depressed protein synthesis contributes to altered protein accretion in fast-twitch muscles during long-term hindlimb suspension. Although the HP diet prevented the decrease in translational efficiency in muscles from HS rats, it neither sustained protein synthesis nor prevented the reduction in muscle growth. Thus, it seems very unlikely that a high protein diet had any beneficial effect on the overall musculature during weightlessness in rats.

We determined the effect of a 4-h leucine infusion, leading to 15-fold elevated plasma leucine concentrations, on skeletal muscle and whole-body protein synthesis in suckling lambs during the postprandial period. The [3H]phenylalanine large dose method was validated and used to quantify the fractional rates of protein synthesis (Ks in %/d) at the end of the leucine infusion. In the first experiment leucine infusion lowered plasma amino acid concentrations but did not change the Ks, the capacity for protein synthesis (Cs, mg RNA/g protein) or the efficiency of translation [g protein synthesized/(d-g RNA)] in any muscles studied or the whole body. In the second experiment the leucine-induced decreases in plasma amino acid concentrations were compensated by the simultaneous infusion of substantial amounts of amino acids. Again leucine excess did not significantly change Ks, Cs and efficiency of protein synthesis. These results indicated that leucine excess in suckling lambs during the postprandial period lowered aminoacidemia without any change of the protein synthesis rates in skeletal muscles or the whole body.

This study assessed whole-body and tissue protein metabolism and the contribution of skin to whole-body protein synthesis during the post-weaning development of rats. Protein fractional synthesis rate was measured in muscle, skin and the whole body of 70-, 160-, 315- and 586-g rats by use of a continuous infusion of L-[U-14C]lysine. Rates of protein synthesis were then calculated, based on the tissue free and protein-bound lysine specific radioactivity at the end of the infusion. The fractional protein synthesis rate declined progressively in the skin (from 19.6 to 8.0%/d), in muscle (from 18.9 to 4.8%/d) and in whole body (from 25.0 to 8.5%/d) throughout post-weaning development. Absolute synthesis rates [g/(d.100 g body wt)] of whole-body and muscle proteins decreased by 54 and 50%, respectively. On the other hand, the amount of skin protein synthesized per 100 g body wt was 35% greater in 160-g and 315-g rats than in 70-g and 586-g rats. The absolute synthesis rate of muscle proteins as a percentage of whole-body protein synthesis remained fairly constant at a value close to 24%, whereas the skin contribution to whole-body protein synthesis increased from 12% in 70-g rats to 26% in 586-g rats.

We studied whole-body amino acid kinetics in rats of approximately 70, 160, 315 and 586 g body weight. The animals were infused simultaneously with L-[U-14C]lysine, L-[1-14C]leucine, L-[U-14C]tyrosine, L-[U-14C]threonine and L-[U-14C]histidine. The plasma flux of each amino acid was estimated from its plasma specific radioactivity at the end of the infusion. Indirect estimates of whole-body protein turnover were calculated, based on the plasma flux of each amino acid. Body protein synthesis was determined from the ratio of the specific radioactivities of the protein-bound and free lysine in tissue homogenate (direct method). Amino acid oxidation was calculated from the difference between the alimentary intake of each amino acid and the amount of each retained in protein. Whatever the amino acid, the plasma flux decreased progressively during growth. Positive correlations were obtained between the plasma flux of the various amino acids. The difference in indirect estimates of whole-body protein turnover obtained with different amino acids was relatively small and did not exceed 40%. At each age, the plasma flux of the various amino acids was related to their content in whole-body protein. The alimentary intake accounted for 25 to 40% of the flux for all amino acids except tyrosine (16 to 28%). The amount of each amino acid that was oxidized generally accounted for 17% of the flux.(ABSTRACT TRUNCATED AT 250 WORDS)

Whole-body methionine flux (rate of irreversible loss from plasma) and tissue protein synthesis were estimated in dry and early lactating goats (10-14 d postpartum) by intravenous infusion of L-[35S]methionine. Tissue protein mass was significantly (p less than 0.05) higher for mammary gland and liver but lower for carcass in lactating animals. The plasma methionine flux was higher during lactation (8.5 vs. 5.1 g/d). The fractional synthesis rates of tissue proteins (Ksp: %/d) were lower during lactation for some muscles, especially the masseter muscle (1.46 vs. 2.15), and for skin (0.59 vs. 1.22) and the pooled head plus feet fraction (1.64 vs. 2.31), but the rates were greatly increased in mammary gland (42 vs. 3). The non-mammary methionine flux (plasma flux minus the flux corresponding to milk methionine output and methionine utilization for mammary protein synthesis) was significantly (p less than 0.05) lower for the lactating goats than for the dry group (93 vs. 131 mg.d-1.kg empty body weight-1). This is in agreement with the lower rates of protein synthesis in carcass (542 vs. 948 mg.d-1.kg empty body weight-1) and skin (93 vs. 189) for lactating compared to dry goats. It can be inferred from these data that in early lactation, when nutrient requirements of animals are not adequately met, an adaptative mechanism occurs that allows amino acids to be available for the mammary gland by a decrease of their utilization in some extramammary tissues.

The effects of excess leucine intake on food intake, branched-chain amino acid and branched-chain alpha-keto acid concentrations in plasma and nitrogen retention were investigated in the preruminant lamb. Lambs were fed leucine in excess in either an adequate protein diet [24% of dry matter (DM)] or a low protein diet (15% DM) for 2 d. Increasing the dietary leucine content of 2.3 to 10.6 or 12.6% DM led to a significant decrease in food intake. This depressing effect was not influenced by dietary protein content. Increasing the dietary leucine content from 2.3 to 6.4% DM in an adequate protein diet for a week did not significantly improve nitrogen retention in the preruminant lamb. Plasma leucine and its alpha-keto acid concentrations increased with leucine intake. Plasma valine and isoleucine concentrations were significantly decreased only in lambs fed the highest excess leucine diet. Surprisingly, a maximal 50% decrease of their plasma alpha-keto acid concentrations occurred even in the group fed the lowest excess leucine diet. Our results might be explained by an inhibition of the rate of transamination of valine and isoleucine by high leucine concentration.

In vivo pancreatic protein synthesis rates were obtained from the uptake of L-[3,4(n)-3H]valine co-injected with a flooding dose of unlabeled valine into 1-, 5-, and 8-wk-old suckling lambs, and 8-wk-old weaned animals. Protein fractional synthesis rate was 184%/d at 1 wk of age and 153%/d in 5-wk-old animals (P greater than 0.05). This lack of developmental change resulted from constant (P greater than 0.05) ribosomal capacities (total RNA/protein ratios) and efficiencies of protein synthesis (synthetic rates relative to RNA). No further alteration for protein fractional synthesis rate (144%/d) occurred in 8-wk-old suckling animals (P greater than 0.05). In contrast, 8-wk-old ruminants exhibited higher protein fractional synthesis rate (244%/d) than 8-wk-old suckling animals, although ribosomal capacity was markedly higher in both 8-wk-old groups than in youngest animals (P less than 0.05). The present findings clearly indicate that in vivo protein synthesis in the developing ovine pancreas depends primarily on age. Potentialities for increased rates of pancreatic protein synthesis, i.e., increases in total RNA content and ribosomal capacity appear between 5 and 8 wk of age in this species. At 8 wk of age, however, when lambs are generally weaned, solid food ingestion resulted in a rise for both fractional and absolute rates of protein synthesis, essentially because ruminants maintained a higher efficiency of protein synthesis than milk-fed animals (P less than 0.005). Finally, there was a relationship between pancreatic protein synthesis and protein intake in only ruminant lambs.