Despite over 50 years of research, a comprehensive understanding of how intramuscular triglyceride (IMTG) is stored in skeletal muscle and its contribution as a fuel during exercise is lacking. ...Immunohistochemical techniques provide information on IMTG content and lipid droplet (LD) morphology on a fibre type and subcellular-specific basis, and the lipid dye Oil Red O (ORO) is commonly used to achieve this. BODIPY 493/503 (BODIPY) is an alternative lipid dye with lower background staining and narrower emission spectra. Here we provide the first quantitative comparison of BODIPY and ORO for investigating exercise-induced changes in IMTG content and LD morphology on a fibre type and subcellular-specific basis. Estimates of IMTG content were greater when using BODIPY, which was predominantly due to BODIPY detecting a larger number of LDs, compared to ORO. The subcellular distribution of intramuscular lipid was also dependent on the lipid dye used; ORO detects a greater proportion of IMTG in the periphery (5 μm below cell membrane) of the fibre, whereas IMTG content was higher in the central region using BODIPY. In response to 60 min moderate-intensity cycling exercise, IMTG content was reduced in both the peripheral (− 24%) and central region (− 29%) of type I fibres (
P
< 0.05) using BODIPY, whereas using ORO, IMTG content was only reduced in the peripheral region of type I fibres (− 31%;
P
< 0.05). As well as highlighting some methodological considerations herein, our investigation demonstrates that important differences exist between BODIPY and ORO for detecting and quantifying IMTG on a fibre type and subcellular-specific basis.
Intramuscular triglycerides (IMTG) are a key substrate during prolonged exercise, but little is known about the rate of IMTG resynthesis in the postexercise period. We investigated the hypothesis ...that the distribution of the lipid droplet (LD)-associated perilipin (PLIN) proteins is linked to IMTG storage following exercise. Fourteen elite male triathletes (27 ± 1 yr, 66.5 ± 1.3 mL·kg
·min
) completed 4 h of moderate-intensity cycling. During the first 4 h of recovery, subjects received either carbohydrate or H
O, after which both groups received carbohydrate. Muscle biopsies collected pre- and postexercise and 4 and 24 h postexercise were analyzed using confocal immunofluorescence microscopy for fiber type-specific IMTG content and PLIN distribution with LDs. Exercise reduced IMTG content in type I fibers (-53%,
= 0.002), with no change in type IIa fibers. During the first 4 h of recovery, IMTG content increased in type I fibers (
= 0.014), but was not increased more after 24 h, where it was similar to baseline levels in both conditions. During recovery the number of LDs labeled with PLIN2 (70%), PLIN3 (63%), and PLIN5 (62%; all
< 0.05) all increased in type I fibers. Importantly, the increase in LDs labeled with PLIN proteins only occurred at 24 h postexercise. In conclusion, IMTG resynthesis occurs rapidly in type I fibers following prolonged exercise in highly trained individuals. Furthermore, increases in IMTG content following exercise preceded an increase in the number of LDs labeled with PLIN proteins. These data, therefore, suggest that the PLIN proteins do not play a key role in postexercise IMTG resynthesis.
Key points
Muscle glycogen and intramuscular triglycerides (IMTG, stored in lipid droplets) are important energy substrates during prolonged exercise.
Exercise‐induced changes in lipid droplet (LD) ...morphology (i.e. LD size and number) have not yet been studied under nutritional conditions typically adopted by elite endurance athletes, that is, after carbohydrate (CHO) loading and CHO feeding during exercise.
We report for the first time that exercise reduces IMTG content in both central and peripheral regions of type I and IIa fibres, reflective of decreased LD number in both fibre types whereas reductions in LD size were exclusive to type I fibres.
Additionally, CHO feeding does not alter subcellular IMTG utilisation, LD morphology or muscle glycogen utilisation in type I or IIa/II fibres.
In the absence of alterations to muscle fuel selection, CHO feeding does not attenuate cell signalling pathways with regulatory roles in mitochondrial biogenesis.
We examined the effects of carbohydrate (CHO) feeding on lipid droplet (LD) morphology, muscle glycogen utilisation and exercise‐induced skeletal muscle cell signalling. After a 36 h CHO loading protocol and pre‐exercise meal (12 and 2 g kg–1, respectively), eight trained males ingested 0, 45 or 90 g CHO h–1 during 180 min cycling at lactate threshold followed by an exercise capacity test (150% lactate threshold). Muscle biopsies were obtained pre‐ and post‐completion of submaximal exercise. Exercise decreased (P < 0.01) glycogen concentration to comparable levels (∼700 to 250 mmol kg–1 DW), though utilisation was greater in type I (∼40%) versus type II fibres (∼10%) (P < 0.01). LD content decreased in type I (∼50%) and type IIa fibres (∼30%) (P < 0.01), with greater utilisation in type I fibres (P < 0.01). CHO feeding did not affect glycogen or IMTG utilisation in type I or II fibres (all P > 0.05). Exercise decreased LD number within central and peripheral regions of both type I and IIa fibres, though reduced LD size was exclusive to type I fibres. Exercise induced (all P < 0.05) comparable AMPKThr172 (∼4‐fold), p53Ser15 (∼2‐fold) and CaMKIIThr268 phosphorylation (∼2‐fold) with no effects of CHO feeding (all P > 0.05). CHO increased exercise capacity where 90 g h–1 (233 ± 133 s) > 45 g h–1 (156 ± 66 s; P = 0.06) > 0 g h–1 (108 ± 54 s; P = 0.03). In conditions of high pre‐exercise CHO availability, we conclude CHO feeding does not influence exercise‐induced changes in LD morphology, glycogen utilisation or cell signalling pathways with regulatory roles in mitochondrial biogenesis.
Key points
Muscle glycogen and intramuscular triglycerides (IMTG, stored in lipid droplets) are important energy substrates during prolonged exercise.
Exercise‐induced changes in lipid droplet (LD) morphology (i.e. LD size and number) have not yet been studied under nutritional conditions typically adopted by elite endurance athletes, that is, after carbohydrate (CHO) loading and CHO feeding during exercise.
We report for the first time that exercise reduces IMTG content in both central and peripheral regions of type I and IIa fibres, reflective of decreased LD number in both fibre types whereas reductions in LD size were exclusive to type I fibres.
Additionally, CHO feeding does not alter subcellular IMTG utilisation, LD morphology or muscle glycogen utilisation in type I or IIa/II fibres.
In the absence of alterations to muscle fuel selection, CHO feeding does not attenuate cell signalling pathways with regulatory roles in mitochondrial biogenesis.
PURPOSEThis study aimed to quantify net glycogen utilization in the vastus lateralis (VL) and gastrocnemius (G) of male (n = 11) and female (n = 10) recreationally active runners during three outdoor ...training sessions.
METHODSAfter 2-d standardization of carbohydrate intakes (6 g·kg body mass per day), glycogen was assessed before and after 1) a 10-mile road run (10-mile) at lactate threshold, 2) 8 × 800-m track intervals (8 × 800 m) at velocity at V˙O2max, and 3) 3 × 10-min track intervals (3 × 10 min) at lactate turnpoint.
RESULTSResting glycogen concentration was lower in the G of female compared with males (P < 0.001) runners, although no sex differences were apparent in the VL (P = 0.40). Within the G and VL of male runners, net glycogen utilization differed between training sessions where 10 miles was greater than both track sessions (all comparisons, P < 0.05). In contrast, net glycogen utilization in female runners was not different between training sessions in either muscle (all comparisons, P > 0.05). Net glycogen utilization was greater in male than in female runners in both VL (P = 0.02) and G (P = 0.07) during the 10-mile road run. With the exception of male runners during the 3 × 10-min protocol (P = 0.28), greater absolute glycogen utilization was observed in the G versus the VL muscle in both male and female runners and during all training protocols (all comparisons, P < 0.05).
CONCLUSIONData demonstrate that 1) prolonged steady-state running necessitates a greater glycogen requirement than shorter but higher-intensity track running sessions, 2) female participants display evidence of reduced resting muscle glycogen concentration and net muscle glycogen utilization when compared with male participants, and 3) net glycogen utilization is higher in the G muscle compared with the VL.
Concentrations of telithromycin were measured in plasma, bronchial mucosa (BM), epithelial lining fluid (ELF) and alveolar macrophages (AM) following multiple oral doses. Concentrations were ...determined using a microbiological assay. There were 20 subjects in the study, allocated to three nominal time periods: 2, 12 and 24 h. Mean concentrations in plasma, BM, ELF and AM for 2, 12 and 24 h were as follows: 2 h, 1.86 mg/L, 3.88 mg/kg, 14.89 mg/L and 69.32 mg/L; 12 h, 0.23 mg/L, 1.41 mg/kg, 3.27 mg/L and 318.1 mg/L; and 24 h, 0.08 mg/L, 0.78 mg/kg, 0.97 mg/L and 161.57 mg/L. These concentrations of telithromycin in BM and ELF exceeded for 24 h the mean MIC90s of the common respiratory pathogens Streptococcus pneumoniae (0.12 mg/L) and Moraxella catarrhalis (0.03 mg/L), as well as the atypical microorganism Mycoplasma pneumoniae (0.001 mg/L), and suggest that telithromycin may be effective for the treatment of community-acquired pneumonia and chronic obstructive pulmonary disease.
The nasal carrier status of 3,736 patients was determined throughout their stay in hospital. The carrier rate on admission, which was highest in patients under 20 years of age, did not appear to vary ...with season. The carriage of strains resistant to penicillin increased with the patients' stay in hospital from 13·% on admission to 20·5% on discharge, and the acquisition of these strains was enhanced by the administration of antibiotics. Patients discharged from hospital carrying strains of staphylococci acquired in hospital lost them more readily than patients discharged carrying the strain which they had carried on admission, 31% of those discharged carrying strains resistant to penicillin and tetracycline being readmitted carrying these strains compared with 69% of those discharged carrying strains sensitive to these antibiotics.
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