Postprandial leucine deficiency failed to alter muscle protein synthesis in growing and adult rats.
OBJECTIVE
This study examined the effect of a specific acute postprandial leucine deficiency on skeletal muscle protein synthesis in growing and adult rats. Because the anabolic action of dietary leucine supplementation is controversial, except during aging, we hypothesized that the maximum leucine effect might be already achieved for a normal postprandial rise of leucine. Preventing this rise during the 1- to 3-h period after feeding may reveal the leucine regulation.


METHODS
On the day of the experiment, rats were fasted (postabsorptive, PA group) or fed for 1 h a control meal (postprandial, control, PP group) or a leucine-poor meal (postprandial, PP-Leu group). Muscle protein synthesis was assessed in vivo, over the 1- to 3-h period after meal distribution, using the flooding dose method (L-1-(13)C phenylalanine).


RESULTS
As expected, the postprandial increase in plasma free leucine was specifically abolished after feeding the leucine-poor meal, whereas all the other plasma free amino acids were roughly at normal postprandial levels. Plasma insulin increased after feeding in young rats but was constant in adult rats. Plasma insulin was similar whatever dietary leucine levels. Rates of muscle protein synthesis were stimulated by feeding in gastrocnemius and soleus muscles from young rats but only in gastrocnemius muscles from adult rats. The PP-Leu group did not differ from the control PP group regarding muscle protein synthesis.


CONCLUSIONS
The rise in plasma free leucine is not required for the stimulation of muscle protein synthesis during the 1- to 3-h period after feeding young and adult rats, as previously observed in old rats.
Debras
Elisabeth
E
Unité de Nutrition Humaine, UMR1019, Institut National de la Recherche Agronomique, F-63122 Saint Genès Champanelle Centre de Recherche en Nutrition Humaine d'Auvergne, Auvergne, France.
Prod'homme
Magali
M
Rieu
Isabelle
I
Balage
Michèle
M
Dardevet
Dominique
D
Grizard
Jean
J
D000375:Aging / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn / Q000254:growth & development; D002247:Carbon Isotopes; D007328:Insulin / Q000097:blood; D007930:Leucine / Q000008:administration & dosage / Q000172:deficiency*; D008297:Male; D009124:Muscle Proteins / Q000096:biosynthesis*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D019518:Postprandial Period / Q000502:physiology*; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar
D002247:Carbon Isotopes; D007328:Insulin; D009124:Muscle Proteins; D007930:Leucine