Pulse Protein Feeding Pattern Restores Stimulation of Muscle Protein Synthesis during the Feeding Period in Old Rats

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Abstract
Muscle loss during aging could be related to a lower sensitivity of muscle protein synthesis to feeding. To overcome this decrease without increasing protein intake, we proposed to modulate the daily protein feeding pattern. We showed that consuming 80% of dietary proteins at noon (pulse pattern) improved nitrogen balance in elderly women. The present study was undertaken in rats to determine which tissues are the targets of the pulse pattern and what mechanisms are involved. Male Sprague-Dawley 11- and 23-mo-old rats (n = 32 per age) were fed 4 isoproteic (18% protein) meals/d for 10 d. Then half of the rats at each age were switched to a 11/66/11/11% repartition of daily proteins (pulse pattern) for 21 d. On d 21, rats were injected with a flooding dose of L-13C-valine (50 atom% excess, 150 μmol/100 g body) and protein synthesis rates were measured in liver, small intestine and gastrocnemius muscle in either the postabsorptive or the fed state. Epitrochlearis muscle degradation rates and plasma amino acid concentrations were measured at the same times. The pulse pattern had the following effects: 1) it significantly increased liver protein synthesis response to feeding and postprandial plasma amino acid concentrations at both ages; 2) it restored a significant response to feeding of gastrocnemius muscle protein synthesis in old rats; and 3) it had no effect in small intestine or on muscle breakdown. Thus, using a pulse pattern could be useful in preventing the age-related loss of muscle by increasing feeding-induced stimulation of muscle protein synthesis.