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BACKGROUND AND OBJECTIVES The activators of rapid-response (RR) events tasked with recognition of clinical decompensation, initial management, and response activation seldom receive RR training. RR activators often experience negative emotions of “failure to rescue” that can compromise team performance during RRs. We used the logic model framework for development and evaluation of an educational program grounded in self-determination theory for pediatric RR activators. METHODS The program unfolded in a large quaternary pediatric hospital to impart knowledge and skills; foster autonomy, competence, and relatedness; and improve participants’ satisfaction with performance in RRs. Logic model–guided inputs-activities-outputs-outcomes-context for program evaluation. Preintervention-postintervention follow-up surveys and interviews generated data to determine outcomes and impact of the program. The evaluation instruments were tested for validity and internal consistency. RESULTS Over 4 years, 207 multidisciplinary RR activators were trained. Iterative modifications yielded a workshop that incorporated multiple learning modalities, a standardized learner-centered case bank, formalized evaluation tools, and a database to track participation. Significant improvements in RR-related knowledge, self-efficacy, and self- determination were noted. Workshop evaluation yielded a mean score of 4.85 (0.27) on a 5-point scale. At 6-months follow-up survey and interviews, participants reported application of the knowledge and increased confidence with participation in real-life RR events. The workshop gained traction across the hospital, was associated with improved RR clinical outcomes, and contributed to professional advancement of the educators. CONCLUSIONS We successfully implemented a self-determination theory–informed RR training program for pediatric RR activators, and the logic model framework was used to facilitate comprehensive evaluation.

Background Asymptomatic pulmonary nodules may appear at any point after lung transplantation. The differential diagnosis is broad and includes serious life-threatening disease entities. Methods A retrospective case report of a single patient who developed a pulmonary nodule after lung transplantation. Results At 2 years post-transplant, an 11-year-old with cystic fibrosis was asymptomatic and had normal lung function. A single nodule was noted on surveillance chest CT scan. Initial evaluation was negative, but subsequently, he was diagnosed with cryptococcal osteomyelitis in a thoracic rib. He responded well to an extended course of antifungal therapy without loss of allograft function or infectious complications. Conclusion Pulmonary nodules after lung transplantation may be a harbinger of serious complications. A systematic approach to evaluation and follow-up is recommended.

Children with End Stage Lung Disease (ESLD) are part of the growing population of individuals with life-limiting conditions of childhood. These patients present with a diverse set of pulmonary, cardiovascular, neuromuscular, and developmental conditions. This paper first examines five cases of children with cystic fibrosis, bronchopulmonary dysplasia, neuromuscular disease, pulmonary hypertension, and lung transplantation from Texas Children’s Hospital. We discuss the expected clinical course of each condition, then review the integration of primary and specialized palliative care into the management of each diagnosis. This paper then reviews the management of two children with end staged lung disease at Hospital Civil de Guadalajara, providing an additional perspective for approaching palliative care in low-income countries.

Lung transplantation has become an accepted therapeutic option for a select group of children with end-stage lung disease. We evaluated the impact of early extubation in a pediatric lung transplant population and its post-operative outcomes. Single-center retrospective study. PICU within a tertiary academic pediatric hospital. Patients

Background: Orogastric tube feeding is indicated in neonates with an impaired ability to ingest food normally and can be administered with an intermittent bolus or continuous feeding schedule. Objectives: The objectives were to 1) compare the long-term effect of continuous with intermittent feeding on growth using the newborn pig as a model, 2) determine whether feeding frequency alters lean tissue and fat mass gain, and 3) identify the signaling mechanisms by which protein deposition is controlled in skeletal muscle in response to feeding frequency. Design: Neonatal pigs were fed the same amount of a balanced formula by orogastric tube either as an intermittent bolus meal every 4 h (INT) or as a continuous infusion (CON). Body composition was assessed at the start and end of the study by dual-energy X-ray absorptiometry, and hormone and substrate profiles, muscle mass, protein synthesis, and indexes of nutrient and insulin signaling were measured after 21 d. Results: Body weight, lean mass, spine length, and skeletal muscle mass were greater in the INT group than in the CON group. Skeletal muscle fractional protein synthesis rates were greater in the INT group after a meal than in the CON group and were associated with higher circulating branched-chain amino acid and insulin concentrations. Skeletal muscle protein kinase B (PKB) and ribosomal protein S6 kinase phosphorylation and eukaryotic initiation factor (eIF) 4E-eIF4G complex formation were higher, whereas eIF2 alpha phosphorylation was lower in the INT group than in the CON group, indicating enhanced activation of insulin and amino acid signaling to translation initiation. Conclusions: These results suggest that when neonates are fed the same amounts of nutrients as intermittent meals rather than continuously there is greater lean growth. This response can be ascribed, in part, to the pulsatile pattern of amino acids, insulin, or both induced by INT, which enables the responsiveness of anabolic pathways to feeding to be sustained chronically in skeletal muscle. National Institute of Arthritis and Musculoskeletal and Skin Diseases grants [AR044474, AR46308]; National Institute of Child Health and Human Development grants [HD072891, HD085573]; USDA National Institute of Agriculture grant [2013-67015-20438]; USDA-Agricultural Research ServiceUnited States Department of Agriculture (USDA) [6250-510000-055] Supported by National Institute of Arthritis and Musculoskeletal and Skin Diseases grants AR044474 (TAD) and AR46308 (MLF), National Institute of Child Health and Human Development grants HD072891 (TAD) and HD085573 (TAD), USDA National Institute of Agriculture grant 2013-67015-20438 (TAD), and by the USDA-Agricultural Research Service under cooperative agreement 6250-510000-055 (TAD). Public domain – authored by a U.S. government employee

Thrombocytopenia associated multi-organ failure (TAMOF) is a clinical syndrome with features of new onset thrombocytopenia, increased lactate dehydrogenase, and multi-organ failure in critically ill patients. TAMOF can be the initial presentation of an underlying disease process or can develop during the course of illness either during the hospital stay. TAMOF has a high mortality rate if not treated; therefore, early detection is critical. TAMOF has been rarely reported in diabetic ketoacidosis. We are describing the first case of a patient diagnosed with hyperglycemic, hyperosmolar non-ketotic syndrome who developed TAMOF on the third day of his hospital course. In addition to supportive care in the intensive care unit the patient received serial therapeutic plasma exchanges and improved quickly after treatment. Early diagnosis and treatment of TAMOF decreases morbidity and mortality.

Background Despite successes in lung transplantation, with infection as the leading cause of death in the first year following lung transplantation, there remains a lag in survival compared with other solid organ transplants. Infections that occur early after transplantation may impact short- and long-term outcomes in pediatric lung transplant recipients (LTRs). Methods We performed a retrospective review of pediatric LTRs at a large quaternary-care hospital from January 2009 to March 2016 to evaluate both epidemiologic features of infection in the first 30 days post-transplantation and mortality outcomes. The 30 days were divided into early (0–7 days) and late (8–30 days) periods. Results Among the 98 LTRs, there were 51 episodes of infections. Cystic fibrosis (CF) was associated with early bacterial infections (P = .004) while non-CF was associated with late viral (P = .02) infections. Infection after transplantation was associated with worse survival by Kaplan-Meier analysis (P value log rank test = .007). Viral infection in the late period was significantly associated with 3-year mortality after multivariable analysis (P = .02). Conclusions Infections in pediatric LTRs were frequent in the first 30 days after transplant, despite perioperative antimicrobial coverage. The association of 3-year mortality with late viral infections suggests a possible important role in post-transplant lung physiology and graft function. Understanding the epidemiology of early post-lung transplant infections can help guide post-operative management and interventions to reduce their incidence and the early- and long-term impact in this population.

Purpose Antibody mediated rejection (AMR) is difficult to treat and often results in death or graft loss. Therapies targeted at antibodies or B cells are inadequate for decreasing donor specific antibodies (DSA), particularly to MHC class II. Bortezomib, a small molecule proteasome inhibitor targets plasma cells, but has many side effects and unsatisfactory results. Alternatively, we used Daratumumab (DAR), an anti-CD38 monoclonal antibody, in two pediatric transplant (Tx) recipients. Methods Chart review. Results An 18-year-old female with cystic fibrosis had a lung-liver Tx at 12-years-old. Twenty months post-Tx she developed severe AMR and Acute cellular rejection (ACR) treated with ATG, rituximab, TPE, photopheresis, and steroids. She ultimately required redo lung Tx. She did well for three years, but then developed AMR. She again received TPE, ATG, photopheresis, and rituximab. She was not considered a candidate for third lung Tx so all attempts were made to salvage her graft. She had no B cells, but continued to make DSA, so a plasma cell targeted therapy was desired. She received three doses of DAR 16 mg/kg on days 0, 7 and 21 with no infusion reactions. She developed neutropenia 2 months later which resolved with 3 weeks of GCSF. Both total PRA and DSA significantly decreased after DAR and have not returned 7 months later. PRA class I dropped from peak of 96% to 0, class II from peak 34% to 3%. She is maintained on subcutaneous IgG replacement for secondary hypogammaglobulinemia. Her graft function is poor, but has stabilized since DAR. She had one episode of presumed line associated sepsis and MSSA pneumonia without sequalae. A 3-year-old girl two years post heart Tx developed refractory AMR (by C4d and elevated DSA) despite ATG, TPE, IVIG, eculizumab, and ofatumumab. She then received two doses of DAR, 16 mg/kg each on days 0 and 14. She tolerated the infusions without any initial side effects. Not enough time has elapsed to follow up antibody levels or graft function. Conclusion Treatment for AMR remains challenging, especially when due to class II HLA antibodies. We safely administered DAR to two pediatric patients without infusion reactions or significant infectious complications to date. One patient had a decline in antibodies, while the other is too soon to determine. While more studies are needed, DAR may be a promising addition to the AMR toolbox.

Continuous and intermittent bolus orogastric feedings are strategies used in infants unable to tolerate normal feeds.To determine the effects of feeding modality on protein synthesis in different tissues, neonatal pigs received a balanced formula by orogastric tube as an intermittent bolus feed every 4 h or as a continuous infusion, or were fasted overnight.As compared with fasting, protein synthesis in gastrocnemius, masseter, and soleus muscles; left ventricle; liver; pancreas; jejunum; and kidney increased in bolus- and continuously fed pigs, but the greatest increase occurred after a bolus meal. Tuberous sclerosis complex (TSC2), the proline-rich AKT substrate of 40 kDa (PRAS40), eukaryotic initiation factor (eIF) 4E binding protein (4EBP1), and ribosomal protein S6 kinase 1 (S6K1) phosphorylation in all tissues, and the proportion of ribosomal protein S4 in liver polysomes were enhanced 90 min following the bolus meal but not immediately before the meal or during continuous feeding. Eukaryotic elongation factor 2 (eEF2) and eIF2α phosphorylation were unaffected by feeding.These results suggest that intermittent bolus feeding increases protein synthesis in muscles of different fiber types and visceral tissues to a greater extent than continuous feeding by stimulating translation initiation.

Orogastric tube feeding is indicated for neonates with impaired ability to ingest and can be administered by intermittent bolus or continuous schedule. Our aim was to determine whether feeding modalities affect muscle protein deposition and to identify mechanisms involved. Neonatal pigs were overnight fasted (FAS) or fed the same amount of food continuously (CON) or intermittently (INT; 7 × 4 h meals) for 29 h. For 8 h, between hours 20 and 28, pigs were infused with [2H5]phenylalanine and [2H2]tyrosine, and amino acid (AA) net balances were measured across the hindquarters. Insulin, branched-chain AA, phenylalanine, and tyrosine arterial concentrations and whole body phenylalanine and tyrosine fluxes were greater for INT after the meal than for CON or FAS. The activation of signaling proteins leading to initiation of mRNA translation, including eukaryotic initiation factor (eIF)4E·eIF4G complex formation in muscle, was enhanced by INT compared with CON feeding or FAS. Signaling proteins of protein degradation were not affected by feeding modalities except for microtubule-associated protein light chain 3-II, which was highest in the FAS. Across the hindquarters, AA net removal increased for INT but not for CON or FAS, with protein deposition greater for INT. This was because protein synthesis increased following feeding for INT but remained unchanged for CON and FAS, whereas there was no change in protein degradation across any dietary treatment. These results suggest that muscle protein accretion in neonates is enhanced with intermittent bolus to a greater extent than continuous feeding, mainly by increased protein synthesis.

Leucine (Leu) activates mammalian target of rapamycin (mTOR) to upregulate protein synthesis (PS).PS in skeletal muscles, heart, liver, pancreas, and jejunum, but not kidney, were greater in low protein supplemented with Leu (LP+L) than LP, but lower than high protein (HP). In longissimus dorsi muscle, protein kinase B phosphorylation was similar in LP and LP+L, but lower than HP. Although less than HP, p70 ribosomal S6 kinase 1 (S6K1) and eukaryotic initiation factor (eIF) 4E binding protein 1 (4EBP1) association with regulatory associated protein of mammalian target of rapamycin was greater in LP+L than LP, resulting in higher S6K1 and 4EBP1 phosphorylation. Feeding LP+L vs. LP decreased 4EBP1·eIF4E and increased eIF4E·eIF4G formation, but not to HP. Similar results were obtained for S6K1 and 4EBP1 phosphorylation in gastrocnemius, masseter, heart, liver, pancreas, and jejunum, but not kidney. eIF2α and elongation factor 2 phosphorylation was unaffected by treatment. DICUSSION: Our results suggest that enteral Leu supplementation of a low protein diet enhances PS in most tissues through mTOR complex 1 pathways.To examine enteral Leu effects on PS and signaling activation, 5-d-old piglets were fed for 24 h diets containing: (i) LP, (ii) LP+L, or (iii) HP.

Protein synthesis (PS) increases after a meal in neonates, but the time course of the changes in PS in different tissues after a meal is unknown. We aimed to evaluate the changes in tissue PS, mammalian target of rapamycin complex 1 (mTORC1) activation, and proportion of ribosomal protein (rp) mRNAs in polysomes over 4 h following a bolus meal in neonatal pigs (n = 6/group; 5- to 7-d-old). The results show a more sustained increase in PS in glycolytic compared to mixed fiber type muscles, and no changes in oxidative muscles. PS increased in liver, jejunum, and pancreas, but not in kidney and heart. Feeding did not affect AMP-activated protein kinase or RAS-related GTP binding B activation. Phosphorylation of tuberous sclerosis complex 2, proline-rich Akt substrate of 40 kDa, mTOR, eukaryotic initiation factor 4E binding protein, and rp S6 kinase 1 increased in all tissues after feeding. The proportion of mRNAs encoding rp S4 and S8 in liver polysomes increased within 30 min post-feeding. These results suggest that feeding stimulates mTORC1 signaling in muscle and viscera, but mTORC1 activation alone is not sufficient to stimulate PS in all tissues.

In muscle, sepsis reduces protein synthesis (MPS) by restraining translation in neonates and adults. Even though protein accretion decreases with development as neonatal MPS rapidly declines by maturation, the changes imposed by development on the sepsis-associated decrease in MPS have not been described. Pigs at 7 and 26 d of age were infused for 8 h with lipopolysaccharide (LPS, endotoxin, 0 and 10 μg · kg⁻¹ · h⁻¹). Fractional MPS rates and translation eukaryotic initiation factor (eIF) activation in muscle were examined (n = 5-7/group). The LPS-induced decrease in MPS was associated with reduced ribosomal and translational efficiency, whereas the age-induced decrease in MPS occurred by decreasing ribosome number. Abundances of mammalian target of rapamycin (mTOR) and S6 decreased, and that of the repressor eIF4E · 4E-binding protein 1 (4EBP1) association increased in 26-d-old pigs--compared with 7-d-old pigs. LPS decreased the abundance of the active eIF4E ·eIF4G association and the phosphorylation of eIF4G across ages, whereas the abundance of eIF4G declined and eIF2α phosphorylation increased with age. Therefore, when lacking anabolic stimulation, the decrease in MPS induced by LPS is associated with reduced ribosomal efficiency and decreased eIF4E ·eIF4G assembly, whereas that induced by development involves reduced ribosomal number, translation factor abundance, and increased eIF2α phosphorylation.

Although infection is the leading cause of death in the first year following pediatric lung transplantation, there are limited data on risk factors for early infection. Sepsis remains under-recognized and under-reported in the early post-operative period for lung transplant recipients (LTR). We evaluated the incidence of infection and sepsis, and identified risk factors for infection in the early post-operative period in pediatric LTRs. A retrospective review of medical records of LTRs at a large quaternary-care hospital from January 2009 to March 2016 was conducted. Microbiology results on days 0-7 after transplant were obtained. Sepsis was defined using the 2005 International Pediatric Consensus Conferencecriteria. Risk factors included history of recipient and donor infection, history of multi-drug resistant (MDR) infection, nutritional status, and surgical times. Among the 98 LTRs, there were 22 (22%) with post-operative infection. Prolonged donor ischemic time ≥7 hours, cardiopulmonary bypass(CPB) time ≥340 minutes, history of MDR infection and diagnosis of cystic fibrosis were significantly associated with infection. With multivariable regression analysis, only prolonged donor ischemic time remained significant (OR 4.4, 95% CI: 1.34-14.48). Further research is needed to determine whether processes to reduce donor ischemic time could result in decreased post-transplant morbidity.

The postprandial rise in amino acids, particularly leucine, stimulates muscle protein synthesis in neonates. Previously, we showed that a 1-h infusion of leucine increased protein synthesis, but this response was not sustained for 2 h unless the leucine-induced decrease in amino acids was prevented. To determine whether a parenteral leucine infusion can stimulate protein synthesis for a more prolonged, clinically relevant period if baseline amino acid concentrations are maintained, overnight food-deprived neonatal pigs were infused for 24 h with saline, leucine (400 mumol.kg(-1). h(-1)), or leucine with replacement amino acids. Amino acid replacement prevented the leucine-induced decrease in amino acids. Muscle protein synthesis was increased by leucine but only when other amino acids were supplied to maintain euaminoacidemia. Leucine did not affect activators of mammalian target of rapamycin (mTOR), i.e. protein kinase B, AMP-activated protein kinase, tuberous sclerosis complex 2, or eukaryotic elongation factor 2. There was no effect of treatment on the association of mTOR with regulatory associated protein of mammalian target of rapamycin (raptor), G-protein beta subunit-like protein, or rictor or the phosphorylation of raptor or proline-rich Akt substrate of 40 kDa. Phosphorylation of mTOR and its downstream targets, eukaryotic initiation factor (eIF) 4E binding protein and ribosomal protein S6 kinase, and the eIF4E . eIF4G association were increased and eIF2alpha phosphorylation was reduced by leucine and was not further altered by correcting for the leucine-induced hypoaminoacidemia. Thus, prolonged parenteral infusion of leucine activates mTOR and its downstream targets in neonatal skeletal muscle, but the stimulation of protein synthesis also is dependent upon amino acid availability.

Food consumption increases protein synthesis in most tissues by promoting translation initiation, and in the neonate, this increase is greatest in skeletal muscle. In this study, we aimed to identify the currently unknown time course of changes in the rate of protein synthesis and the activation of factors involved in translation in neonatal muscle after a meal. After overnight food deprivation, 36 5- to 7-d-old piglets were administered a nutritionally complete bolus i.g. meal and were killed immediately before or 30, 60, 90, 120, or 240 min later. The increase in skeletal muscle protein synthesis peaked 30 min after the meal and this was sustained through 120 min, returning to baseline thereafter. The relative proportion of polysomes to nonpolysomes was higher only after 30 min. Protein kinase B phosphorylation peaked 30 min after feeding and returned to baseline by 90 min. The phosphorylation of mammalian target of rapamycin, eukaryotic initiation factor (eIF) 4E binding protein (4E-BP1), ribosomal protein S6, and eIF4G was increased within 30 min of feeding and persisted through 120 min, but all had returned to baseline by 240 min. The association of 4E-BP1.eIF4E was reduced and eIF4E.eIF4G increased 30 min after receiving a meal, remaining so for 120 min, before returning to baseline at 240 min. Thus, in neonates, food consumption rapidly increased skeletal muscle protein synthesis by enhancing translation initiation and this increase was sustained for at least 120 min after the meal but returned to baseline by 240 min after the feeding.

Orogastric tube feeding is indicated in neonates with impaired ability to ingest food normally and can be administered by intermittent bolus (INT) or continuous (CON) infusion. Insulin and amino acids play important roles in the regulation of protein synthesis in the neonate. While the sensitivity to insulin is developmentally regulated (Davis et al., 1998) and greatly diminishes with age (Wray-Cahen et al., 1997), amino acids exert a positive effect on muscle protein synthesis throughout life (Denne et al., 1991; Davis et al., 1998; Volpi et al., 1998). In addition to providing amino acids to other organs when dietary supplies are insufficient, high rates of proteolysis are necessary to provide amino acids for ongoing tissue modeling and rapid growth. The two most important proteolytic pathways in skeletal muscle are thought to be the ubiquitin-proteasome and autophagy-lysosome systems (Ventadour and Attaix, 2006). The aim of this study was to determine if these feeding modalities affect growth and lean tissue accretion, and the mechanisms for this response.

Accretion rates of muscle protein are elevated in normal neonates, but this anabolic drive decreases with maturation. As this change occurs, it is not known whether development also influences muscle protein catabolism induced by sepsis. We hypothesize that protein degradation in skeletal muscle induced by endotoxemia becomes more severe as the neonate develops. Fasted 7- and 26-day-old pigs were infused for 8 h with LPS (0 and 10 μg·kg−1·h−1), while plasma amino acids (AA), 3-methylhistidine (3-MH), and α-actin concentrations and muscle protein degradation signal activation were determined ( n = 5–7/group/age). Plasma full-length α-actin was greater in 7- than 26-day-old pigs, suggesting a higher baseline protein turnover in neonatal pigs. LPS increased plasma total AA, 3-MH, and full-length and cleaved α-actin in 26- than in 7-day-old pigs. In muscle of both age groups, LPS increased AMPK and NF-κB phosphorylation, the abundances of activated caspase 3 and E-3 ligases MuRF1 and atrogin1, as well as the abundance of cleaved α-actin, suggesting activation of muscle proteolysis by endotoxin in muscle. LPS decreased Forkhead box 01 (Fox01) and Fox04 phosphorylation and increased procaspase 3 abundance in muscle of 26-day-old pigs despite the lack of effect of LPS on PKB phosphorylation. The results suggest that skeletal muscle in healthy neonatal pigs maintains high baseline degradation signal activation that cannot be enhanced by endotoxin, but as maturation advances, the effect of LPS on muscle protein catabolism manifests its severity.

Orogastric tube feeding, using either continuous or intermittent bolus delivery, is common in infants for whom normal feeding is contraindicated. To compare the impact of different feeding strategies on muscle protein synthesis, after withholding food overnight, neonatal pigs received a complete formula orally as a bolus feed every 4 h or were continuously fed. Protein synthesis rate and translational mechanisms in skeletal muscle were examined after 0, 24, and 25.5 h. Plasma amino acid and insulin concentrations increased minimally and remained constant in continuously fed compared to feed-deprived pigs; however, the pulsatile meal feeding pattern was mimicked in bolus-fed pigs. Muscle protein synthesis was stimulated by feeding and the greatest response occurred after a bolus meal. Bolus but not continuous feeds increased polysome aggregation, the phosphorylation of protein kinase B, tuberous sclerosis complex 2, proline-rich Akt substrate of 40 kDa, eukaryotic initiation factor (eIF) 4E binding protein (4EBP1), and rp S6 kinase and enhanced dissociation of the 4EBP1 ·eIF4E complex and formation of the eIF4E ·eIF4G complex compared to feed deprivation (P < 0.05). Activation of insulin receptor substrate-1, regulatory associated protein of mammalian target of rapamycin, AMP-activated protein kinase, eukaryotic elongation factor 2, and eIF2α phosphorylation were unaffected by either feeding modality. These results suggest that in neonates, intermittent bolus feeding enhances muscle protein synthesis to a greater extent than continuous feeding by eliciting a pulsatile pattern of amino acid- and insulin-induced translation initiation.

Protein synthesis and eukaryotic initiation factor (eIF) activation are increased in skeletal muscle of neonatal pigs parenterally infused with amino acids. Leucine appears to be the most effective single amino acid to trigger these effects. To examine the response to enteral leucine supplementation, overnight food-deprived 5-d-old pigs were gavage fed at 0 and 60 min a: 1) low-protein diet (LP); 2) LP supplemented with leucine (LP+L) to equal leucine in the high-protein diet (HP); or 3) HP diet. Diets were isocaloric and equal in lactose. Fractional protein synthesis rates and translation initiation control mechanisms were examined in skeletal muscles and visceral tissues 90 min after feeding. Protein synthesis rates in longissimus dorsi, gastrocnemius, and masseter muscles, heart, jejunum, kidney, and pancreas, but not liver, were greater in the LP+L group compared with the LP group and did not differ from the HP group. Feeding LP+L and HP diets compared with the LP diet increased phosphorylation of mammalian target of rapamycin (mTOR), 4E-binding protein 1, ribosomal protein S6 kinase-1, and eIF4G and formation of the active eIF4E·eIF4G complex in longissimus dorsi muscle. In all tissues except liver, activation of mTOR effectors increased in pigs fed LP+L and HP vs. LP diets. Our results suggest that leucine supplementation of a low-protein meal stimulates protein synthesis in muscle and most visceral tissues to a rate similar to that achieved by feeding a high-protein meal and this stimulation involves activation of mTOR downstream effectors.

Leucine is unique among the amino acids in its ability to promote protein synthesis by activating translation initiation via the mammalian target of rapamycin (mTOR) pathway. Previously, we showed that leucine infusion acutely stimulates protein synthesis in fast-twitch glycolytic muscle of neonatal pigs but this response cannot be maintained unless the leucine-induced fall in amino acids is prevented. To determine whether leucine can stimulate protein synthesis in muscles of different fiber types and in visceral tissues of the neonate in the long-term if baseline amino acid concentrations are maintained, overnight fasted neonatal pigs were infused for 24 h with saline, leucine (400 micromol kg(-1) h(-1)), or leucine with replacement amino acids to prevent the leucine-induced hypoaminoacidemia. Changes in the fractional rate of protein synthesis and activation of mTOR, as determined by eukaryotic initiation factor 4E binding protein (4E-BP1) and S6 kinase 1 (S6K1) phosphorylation, in the gastrocnemius and masseter muscles, heart, liver, jejunum, kidney, and pancreas were measured. Leucine increased mTOR activation in the gastrocnemius and masseter muscles, liver, and pancreas, in both the absence and presence of amino acid replacement. However, protein synthesis in these tissues was increased only when amino acids were infused to maintain baseline levels. There were no changes in mTOR signaling or protein synthesis in the other tissues we examined. Thus, long-term infusion of leucine stimulates mTOR signaling in skeletal muscle and some visceral tissues but the leucine-induced stimulation of protein synthesis in these tissues requires sustained amino acid availability.

Chronic somatotropin (pST) treatment in pigs increases muscle protein synthesis and circulating insulin, a known promoter of protein synthesis. Previously, we showed that the pST-mediated rise in insulin could not account for the pST-induced increase in muscle protein synthesis when amino acids were maintained at fasting levels. This study aimed to determine whether the pST-induced increase in insulin promotes skeletal muscle protein synthesis when amino acids are provided at fed levels and whether the response is associated with enhanced translation initiation factor activation. Growing pigs were treated with pST (0 or 180 μg·kg−1·day−1) for 7 days, and then pancreatic-glucose-amino acid clamps were performed. Amino acids were raised to fed levels in the presence of either fasted or fed insulin concentrations; glucose was maintained at fasting throughout. Muscle protein synthesis was increased by pST treatment and by amino acids (with or without insulin) ( P < 0.001). In pST-treated pigs, fed, but not fasting, amino acid concentrations further increased muscle protein synthesis rates irrespective of insulin level ( P < 0.02). Fed amino acids, with or without raised insulin concentrations, increased the phosphorylation of S6 kinase (S6K1) and eukaryotic initiation factor (eIF) 4E-binding protein 1 (4EBP1), decreased inactive 4EBP1·eIF4E complex association, and increased active eIF4E·eIF4G complex formation ( P < 0.02). pST treatment did not alter translation initiation factor activation. We conclude that the pST-induced stimulation of muscle protein synthesis requires fed amino acid levels, but not fed insulin levels. However, under the current conditions, the response to amino acids is not mediated by the activation of translation initiation factors that regulate mRNA binding to the ribosomal complex.