Exercise training reduces PGE2 levels and induces recovery from steatosis in tumor-bearing rats

The effects of endurance training on PGE (2) levels and upon the maximal activity of hepatic carnitine palmitoyltransferase (CPT) system were studied in rats bearing the Walker 256 carciosarcoma. Animals were randomly assigned to a sedentary control (SC), sedentary tumor-bearing (ST), exercised control (EC), and as an exercised tumor-bearing (ET) group. Trained rats ran on a treadmill (60% VO (2) max) for 60 min/day, 5 days/week, for 8 weeks. We examined the mRNA expression (RT-PCR) and maximal activity (radioassay) of the carnitine palmitoyltransferase system enzymes (CPT I and CPT II), as well as the gene expression of fatty-acid-binding protein (L-FABP) in the liver. PGE (2) content was measured in the serum, in tumor cells, and in the liver (ELISA). CPT I and CPT II maximal activity were decreased (p<0.01) in ST when compared with SC. In contrast, serum PGE (2) was increased (p<0.05) in cachectic animals as compared with SC. In the liver, PGE (2) content was also increased (p<0.05) when compared with SC. Endurance training restored maximal CPT I and CPT II activity in the tumor-bearing animals (p<0.0001). Exercise training induced PGE (2) levels to return to control values in the liver of tumor-bearing training rats (p<0.05) and decreased the eicosanoid content in the tumor (p<0.01). In conclusion, endurance training was capable of reestablishing liver carnitine palmitoyltransferase (CPT) system activity associated with decreased PGE (2) levels in cachectic tumor-bearing animals, preventing steatosis.

Influência do treinamento físico aeróbio no transporte mitocondrial de ácidos graxos de cadeia longa no músculo esquelético: papel do complexo carnitina palmitoil transferase

O ácido graxo (AG) é uma importante fonte de energia para o músculo esquelético. Durante o exercício sua mobilização é aumentada para suprir as necessidades da musculatura ativa. Acredita-se que diversos pontos de regulação atuem no controle da oxidação dos AG, sendo o principal a atividade do complexo carnitina palmitoil transferase (CPT), entre os quais três componentes estão envolvidos: a CPT I, a CPT II e carnitina acilcarnitina translocase. A função da CPT I durante o exercício físico é controlar a entrada de AG para o interior da mitocôndria, para posterior oxidação do AG e produção de energia. Em resposta ao treinamento físico há um aumento na atividade e expressão da CPT I no músculo esquelético. Devido sua grande importância no metabolismo de lipídios, os mecanismos que controlam sua atividade e sua expressão gênica são revisados no presente estudo. Reguladores da expressão gênica de proteínas envolvidas no metabolismo de lipídios no músculo esquelético, os receptores ativados por proliferadores de peroxissomas (PPAR) alfa e beta, são discutidos com um enfoque na resposta ao treinamento físico.

Deleteriuos effects of immobilization upon rat skeletal muscle: role of creatine supplementation

AIM

The aim of the study was to investigate the impact of creatine feeding (5 g kg(-1) body weight day(-1)) upon the deleterious adaptations in skeletal muscle induced by immobilization.

METHODS

Male Wistar rats were submitted to hind limb immobilization together with three dietary manipulations: control, supplemented with creatine for 7 days (along with immobilization) and supplemented with creatine for 14 days (7 days before immobilization and together with immobilization). Muscle weight (wet/dry) was determined in the soleus (SOL) and gastrocnemius (GAS). The analysis of lean mass was performed by DEXA and myosin heavy chain (MHC) distribution by SDS-PAGE.

RESULTS

After 14 days of creatine loading, immobilized SOL and GAS total creatine content were increased by 25% and 18%, respectively. Regardless of dietary manipulation, the immobilization protocol induced a decrease in the weight of SOL and GAS (P < 0.001). However, creatine feeding for 14 days minimized mass loss in the SOL and GAS (P < 0.05). Our findings also indicate that creatine supplementation maximizes the expected slow-to-fast MHC shift driven by immobilization (P < 0.05).

CONCLUSIONS

Previous creatine supplementation attenuates muscle wasting induced by immobilization. This effect is associated with the increment of intramuscular creatine content.