|Image 1: AMPK, not mTOR turns out to be the caption of the team|
In their study, Gabriel J. Wilson and his colleagues from the Division of Nutritional Sciences at the University of Illinois investigated the effects of leucine and/or carbohydrate supplementation on postprandial muscle protein synthesis in 34 Mmle Sprague-Dawley rats (Wilson. 2011). The animals were provided with a baseline diet providing 20% protein, 50% carbohydrates and 30% fat. In order to model human eating habits, the animals were trained to consume their food in three meals per day: 4g at "breakfast" (7:00am) and "lunch" (1:00pm) and a large dinner of 6g of their chow at 6:00pm. To reduce body fat accumulation those 12g of chow contained only 80% of the rats ad libitum caloric intake, which according to results from a 1983 study by Glore and Layman does not reduce the development of lean tissue in weanling rats (Glore. 1983).
On the day of the experiments, the rats received their usual 4g "breakfast" after a 12h fast (this was the rats customary food deprivation phase from 7pm to 7am) and 135min later, when the the post-prandial muscle protein synthesis was abating (it returned to normal 180 min after the meal), a 5ml oral gavage of either carbohydrates (CHO; 1.35g glucose + 1.35g succrose = 2x more than "breakfast"), leucine (Leu; 270mg l-leucine = 4x more than "breakfast"), carbohydrates + leucine (LC; 1.18g glucose + 1.18g succrose + 270mg leucine), or water (control). According to the scientists, ...
[t]he amounts and timing of the supplements were based on our previous research that produced maximal leucine- and insulin-induced stimulations of translation initiation and MPS 45 min after oral gavage.Or, in other words, with the 135min delay the increase in muscle protein synthesis (MPS) from the supplement should begin exactly when the initial increase in MPS would otherwise have returned to normal, i.e. at 180min post "breakfast".
|Figure 1: Postprandial changes in muscle protein synthesis (MPS expressed relative to daily MPS) 0min, 90min and 180min post ingestion of a 4g meal and following supplementation with water (control), carbohydrate (CHO), leucine (Leu), or leucine + carbohydrate 135min after the ingestion of the meal (data adapted from Wilson. 2011)|
Eukaryotic elongation factor 2 (eEF2), a new player in the game
The low insulin levels in the leucine only group, and the absence of changes in essential amino acid plasma levels and phosphorylation of p70S6K1, all of which could be responsible for the increase in muscle protein synthesis, raise the question what, if neither of these, could have triggered the renewed increase in muscle protein synthesis. The scientists' answer to this question is called eEF2, one of the eukaryotic elongation factors, which has only recently been implicated by Breen et al. (Breen. 2011) as a downstream factor in muscle protein synthesis (i.e. p70S6K1 would suppress eEF2). The results of Wilson et al. falsify this assumption and and establish eEF2, respectively its degree of phosphorylation as an independent factor in muscle protein synthesis; a factor that showed an inverse relationship (r = -0.5; p < 0.05) with MPS, which means that for every 2% decline in eEF2 there was a 1% increase in muscle protein synthesis across all treatment groups in the Wilson study.
|Figure 2: Postprandial changes in AMPK activity (relative to fasted state) 0min, 90min and 180min post ingestion of a 4g meal and following supplementation with water (control), carbohydrate (CHO), leucine (Leu), or leucine + carbohydrate 135min after the ingestion of the meal (data adapted from Wilson. 2011)|
Now, interestingly, the underlying key determinant of all these processes appears to be the good old AMPK energy-sensing mechanism, you learned about in the last installment of the Intermittent Thoughts Series:
[...] the incongruity between MPS and mTORC1 signaling at 180 min after the meal does not reflect a refractory period or decreased sensitivity to anabolic stimuli, but rather, an increase in AMPK activity and a decrease in translation elongation activity.Or, in other words, it is the decrease in AMPK (cf. figure 2) after supplementation, which "allows" for a reduction in eEF2 phosphorylation and thus another increase in muscle protein synthesis.
If you think that this is all too complicated, never mind - with a huge portion of whey and, if you will, added BCAAs and/or some fast acting carbs, i.e. the tried and proven post-workout nutrition, you cannot fail, no matter which funky proteins and genes are behind the muscle-anabolic effect of this bodybuilding classic ;-)