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Muscle and Liver Protein Synthesis Adapt Efficiently to Food Deprivation and Refeeding in 12-Month-Old Rats^1,2,3,

Laboratoire d'Etude du Métabolisme Azoté, INRA Clermont-Ferrand Theix, 63122 Saint Genès Champanelle, France

Our aim was to analyze mechanisms involved in the adaptation of protein metabolism to food deprivation and refeeding in adult rats. Twelve-month-old rats, which had been food-deprived for 113 h and refed for 6 h, were injected subcutaneously with a flooding dose of valine (with 50% [1¹³C]-L-valine) to measure in vivo protein synthesis in tibialis anterior, soleus and liver. Protein and RNA contents were also measured. In both muscles, protein mass was maintained during food deprivation. Due to a drop in protein synthetic capacity (Cs), total and myofibrillar protein synthesis rates were reduced in food-deprived rats and were not stimulated by a 6-h refeeding. In contrast, protein levels were maintained lower than RNA levels in liver during food deprivation, and Cs was higher than in fed rats. Protein synthesis rates and ribosomal efficiency were reduced in food-deprived rats. Due to maintenance of protein synthetic capacity, there was a rapid stimulation of liver protein synthesis with refeeding, which induced a significant rise in protein mass (also related to an inhibition of protein degradation). In conclusion, coordinated responses of liver and muscles allowed a sparing of muscle proteins during food deprivation and a rapid recovery of liver proteins during refeeding. Control of ribosome quantity could play a critical role in these adaptations in tissue protein synthesis in adult rats.

KEY WORDS: • rats • starvation • recovery • aging • protein

¹ Presented in poster form at the Winter Symposium of the Nutrition Society [Mosoni, L., Malmezat, T., Obled, C. & Patureau Mirand, P. (1995) Coordinated response of liver and muscle protein synthesis to fasting and refeeding in 12-month-old rats]. London, UK.

² Supported by grant no. 92G0478 from the French Ministry of Research.

³ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

⁴ To whom correspondence should be addressed.

Manuscript received 13 January 1995. Revision accepted 16 October 1995.

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