Relative fat oxidation is higher in children than adults.

BACKGROUND: Prepubescent children may oxidize fatty acids more readily than adults. Therefore, dietary fat needs would be higher for children compared with adults. The dietary fat recommendations are higher for children 4 to 18 yrs (i.e., 25 to 35% of energy) compared with adults (i.e., 20 to 35% of energy). Despite this, many parents and children restrict dietary fat for health reasons. METHODS: This study assessed whether rates of fat oxidation are similar between prepubescent children and adults. Ten children (8.7 +/- 1.4 yr, 33 +/- 13 kg mean +/- SD) in Tanner stage 1 and 10 adults (41.6 +/- 8 yr, 74 +/- 13 kg) were fed a weight maintenance diet for three days to maintain body weight and to establish a consistent background for metabolic rate measurements (all foods provided). Metabolic rate was measured on three separate occasions before and immediately after breakfast and for 9 hrs using a hood system (twice) or a room calorimeter (once) where continuous metabolic measurements were taken. RESULTS: During all three sessions whole body fat oxidation was higher in children (lower RQ) compared to adults (mean RQ= 0.84 +/- .016 for children and 0.87 +/- .02, for adults, p < 0.02). Although, total grams of fat oxidized was similar in children (62.7 +/- 20 g/24 hrs) compared to adults (51.4 +/- 19 g/24 hrs), the grams of fat oxidized relative to calorie expenditure was higher in children (0.047 +/- .01 g/kcal, compared to adults (0.032 +/- .01 p < 0.02). Females oxidized more fat relative to calorie expenditure than males of a similar age. A two way ANOVA showed no interaction between gender and age in terms of fat oxidation. CONCLUSION: These data suggest that fat oxidation relative to total calorie expenditure is higher in prepubescent children than in adults. Consistent with current dietary guidelines, a moderate fat diet is appropriate for children within the context of a diet that meets their energy and nutrient needs.

Resistance exercise increases muscle protein synthesis and translation of eukaryotic initiation factor 2Bepsilon mRNA in a mammalian target of rapamycin-dependent manner.

The contribution of mammalian target of rapamycin (mTOR) signaling to the resistance exercise-induced stimulation of skeletal muscle protein synthesis was assessed by administering rapamycin to Sprague-Dawley rats 2 h prior to a bout of resistance exercise. Animals were sacrificed 16 h postexercise, and gastrocnemius protein synthesis, mTOR signaling, and biomarkers of translation initiation were assessed. Exercise stimulated the rate of protein synthesis; however, this effect was prevented by pretreatment with rapamycin. The stimulation of protein synthesis was mediated by an increase in translation initiation, since exercise caused an increase in polysome aggregation that was abrogated by rapamycin administration. Taken together, the data suggest that the effect of rapamycin was not mediated by reduced phosphorylation of eukaryotic initiation factor 4E (eIF4E) binding protein 1 (BP1), because exercise did not cause a significant change in 4E-BP1(Thr-70) phosphorylation, 4E-BP1-eIF4E association, or eIF4F complex assembly concomitant with increased protein synthetic rates. Alternatively, there was a rapamycin-sensitive decrease in relative eIF2Bepsilon(Ser-535) phosphorylation that was explained by a significant increase in the expression of eIF2Bepsilon protein. The proportion of eIF2Bepsilon mRNA in polysomes was increased following exercise, an effect that was prevented by rapamycin treatment, suggesting that the increase in eIF2Bepsilon protein expression was mediated by an mTOR-dependent increase in translation of the mRNA encoding the protein. The increase in eIF2Bepsilon mRNA translation and protein abundance occurred independent of similar changes in other eIF2B subunits. These data suggest a novel link between mTOR signaling and eIF2Bepsilon mRNA translation that could contribute to the stimulation of protein synthesis following acute resistance exercise.

Resistive training and chromium picolinate: effects on inositols and liver and kidney functions in older adults.

This study assessed the effects of resistive training (RT) with or without chromium picolinate (Cr-pic) supplementation on the 24-h urinary excretions of myo-inositol, D-chiro-inositol, and pinitol, as well as clinical indices of kidney and liver functions. Thirty-two nondiabetic subjects, age 62 +/- 4 y, performed RT twice weekly for 12 wk and consumed either 924 ug Cr/d as Cr-pic (n = 17) or a placebo (n = 15). Whole-body strength increased in all subjects by 20 % and urinary chromium excretion increased 47-fold in the Cr-pic group. Urinary myo-inositol, D-chiro-inositol, and pinitol were not changed with RT or influenced by Cr-pic. Serum indices of kidney and liver functions were within clinically normal ranges at baseline and the end of the study. These results suggest that RT did not influence the urinary excretions of inositols. High dose Cr-pic did not influence the urinary excretion of inositols and the selected indices of kidney and liver functions in conjunction with RT.

Alterations in the expression of mRNAs and proteins that code for species relevant to eIF2B activity after an acute bout of resistance exercise.

The focus of the study described herein was to examine the relative expression levels of mRNAs and proteins relevant to the regulation of translational initiation, and hence protein synthesis, in the time course after an acute bout of resistance exercise in male Sprague-Dawley rats. Significant increases in the relative abundance of the mRNAs coding for the epsilon (33%) and gamma (26%) subunits of eukaryotic initiation factor (eIF) 2B were observed 48 h after the exercise bout. Furthermore, the mRNA coding for the delta subunit of eIF2B was also significantly increased, both 24 h (46%) and 48 h (44%) postexercise. There was a relative decrease in three eIF2Bepsilon kinase mRNAs, namely sequences coding for glycogen synthase kinase 3beta (49%), casein kinase I (48%), and casein kinase II (42%) 48 h into the recovery period. Additionally, there was a significant decrease in expression of the mRNAs coding for eIF2alpha (28% 24 h postexercise) and one of its regulatory kinases, double-stranded RNA-activated protein kinase (33% 48 h postexercise). Finally, an increase in eIF2B total protein (124%) was observed within 3 h postexercise. These results suggest that there may be rapid translational regulation of mRNAs coding for species relevant to translational initiation after an acute bout of resistance exercise. Furthermore, transcription of these mRNAs is altered further into the recovery period, and this might play a role in protein synthetic capacity on subsequent bouts of resistance exercise.

Immediate response of mammalian target of rapamycin (mTOR)-mediated signalling following acute resistance exercise in rat skeletal muscle.

The purpose of the present investigation was to determine whether mammalian target of rapamycin (mTOR)-mediated signalling and some key regulatory proteins of translation initiation are altered in skeletal muscle during the immediate phase of recovery following acute resistance exercise. Rats were operantly conditioned to reach an illuminated bar located high on a Plexiglass cage, such that the animals completed concentric and eccentric contractions involving the hindlimb musculature. Gastrocnemius muscle was extracted immediately after acute exercise and 5, 10, 15, 30 and 60 min of recovery. Phosphorylation of protein kinase B (PKB) on Ser-473 peaked at 10 min of recovery (282% of control, P < 0.05) with no significant changes noted for mTOR phosphorylation on Ser-2448. Eukaryotic initiation factor (eIF) 4E-binding protein-1 (4E-BP1) and S6 kinase-1 (S6K1), both downstream effectors of mTOR, were altered during recovery as well. 4E-BP1 phosphorylation was significantly elevated at 10 min (292%, P < 0.01) of recovery. S6K1 phosphorylation on Thr-389 demonstrated a trend for peak activation at 10 min following exercise (336%, P = 0.06) with ribosomal protein S6 phosphorylation being maximally activated at 15 min of recovery (647%, P < 0.05). Components of the eIF4F complex were enhanced during recovery as eIF4E association with eIF4G peaked at 10 min (292%, P < 0.05). Events regulating the binding of initiator methionyl-tRNA to the 40S ribosomal subunit were assessed through eIF2B activity and eIF2 alpha phosphorylation on Ser-51. No differences were noted with either eIF2B or eIF2 alpha. Collectively, these results provide strong evidence that mTOR-mediating signalling is transiently upregulated during the immediate period following resistance exercise and this response may constitute the most proximal growth response of the cell.

Invited Review: Role of insulin in translational control of protein synthesis in skeletal muscle by amino acids or exercise.

Protein synthesis in skeletal muscle is modulated in response to a variety of stimuli. Two stimuli receiving a great deal of recent attention are increased amino acid availability and exercise. Both of these effectors stimulate protein synthesis in part through activation of translation initiation. However, the full response of translation initiation and protein synthesis to either effector is not observed in the absence of a minimal concentration of insulin. The combination of insulin and either increased amino acid availability or endurance exercise stimulates translation initiation and protein synthesis in part through activation of the ribosomal protein S6 protein kinase S6K1 as well as through enhanced association of eukaryotic initiation factor eIF4G with eIF4E, an event that promotes binding of mRNA to the ribosome. In contrast, insulin in combination with resistance exercise stimulates translation initiation and protein synthesis through enhanced activity of a guanine nucleotide exchange protein referred to as eIF2B. In both cases, the amount of insulin required for the effects is low, and a concentration of the hormone that approximates that observed in fasting animals is sufficient for maximal stimulation. This review summarizes the results of a number of recent studies that have helped to establish our present understanding of the interactions of insulin, amino acids, and exercise in the regulation of protein synthesis in skeletal muscle.

Developmental decline in components of signal transduction pathways regulating protein synthesis in pig muscle.

Our previous studies showed that the feeding-induced stimulation of protein synthesis in skeletal muscle of neonatal pigs is accompanied by enhanced phosphorylation of the eukaryotic initiation factor (eIF)4E-binding protein (4E-BP1) and the ribosomal protein S6 kinase (S6K1). These effects of feeding are substantially reduced with development. The goal of the present investigation was to delineate the basis for the reduced responsiveness to feeding observed in the older animals. In these studies, the content and activity of protein kinases located upstream of S6K1 and 4E-BP1 in signal transduction pathways activated by amino acids, insulin, and insulin-like growth factor I were examined in 7- and 26-day-old pigs that were either fasted overnight or fed porcine milk after an overnight fast. Feeding stimulated phosphatidylinositol (PI) 3-kinase activity to the same extent in muscle of 7- and 26-day-old pigs, suggesting that PI 3-kinase is not limiting in muscle of older animals. In contrast, protein kinase B (PKB) activity was significantly less in muscle from 26- vs. 7-day-old pigs, regardless of nutritional status, suggesting that its activity is regulated by mechanisms distinct from PI 3-kinase. In part, the reduced PKB responsiveness can be attributed to a developmental decline in PKB content. Likewise, muscle content of the protein kinase termed mammalian target of rapamycin (mTOR) in 26-day-old pigs was <25% of that in 7-day-old animals. Finally, in agreement with our earlier work showing that S6K1 phosphorylation is reduced in older animals, S6K1 activity was stimulated to a lesser extent in 26- compared with 7-day-old pigs. Overall, the results suggest that the blunted protein synthetic response observed in 26- vs. 7-day-old neonatal pigs is due in part to decreased content and/or activity of signaling components downstream of PI 3-kinase, e.g., PKB, mTOR, and S6K1.