Effect of recombinant human tumour necrosis factor α on protein synthesis in liver, skeletal muscle and skin of rats

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Abstract
Bacterial endotoxins cause enhanced protein metabolism in liver, and protein catabolism in muscle and skin. These effects may be mediated by cytokines such as interleukin 1 (IL1) and tumour necrosis factor (TNF). The study investigates the timing and magnitude of effects of recombinant human TNF alpha on protein synthesis and protein and RNA content of the liver, tibialis muscle and skin of Wistar rats. Intravenous doses of 30 and 300 micrograms/kg of body weight were used and effects examined 8 h and 24 h after injection. Muscle protein content and synthetic rate were reduced at 8 h post-injection by over 18% and 20% respectively. Protein synthesis returned to normal after the lowest dose but remained depressed 24 h after the highest dose due to the accompanying anorexia. Opposite effects were observed in liver. Protein fractional synthetic rate (FSR) was increased by over 26% at 8 h post-injection and remained elevated 24 h after the higher but not lower dose of TNF. Total protein and RNA contents were significantly higher than controls at this time. Skin protein synthesis was unaffected by TNF; however an increase in protein and RNA content was observed at 8 h post-injection with the lower dose of TNF. Liver and muscle respond in a similar but more rapid way to TNF than to endotoxin. The response of skin is however totally different. While muscle may contribute amino acids for enhanced hepatic protein synthesis following exposure to TNF, skin does not.