MS; insulin and protein synthesis

[wilson6]

MS,

Check out this paper. Haven't read the review yet, just printed it out. Here's the abstract. The protein synthesis/r-ALA issue we discussed in the previous thread may not be such as issue after all if only low conc. of insulin are required.

Exercise Effects on Muscle Insulin Signaling and Action
Invited Review: Role of insulin in translational control of protein synthesis in skeletal muscle by amino acids or exercise

JAP 93(3) 1168 - 1180, 2002.

Scot R. Kimball1, Peter A. Farrell2, and Leonard S. Jefferson1
1 Department of Cellular and Molecular Physiology,

Protein synthesis in skeletal muscle is modulated in response to a variety of stimuli. Two stimuli receiving a great deal of recent attention are increased amino acid availability and exercise. Both of these effectors stimulate protein synthesis in part through activation of translation initiation. However, the full response of translation initiation and protein synthesis to either effector is not observed in the absence of a minimal concentration of insulin. The combination of insulin and either increased amino acid availability or endurance exercise stimulates translation initiation and protein synthesis in part through activation of the ribosomal protein S6 protein kinase S6K1 as well as through enhanced association of eukaryotic initiation factor eIF4G with eIF4E, an event that promotes binding of mRNA to the ribosome. In contrast, insulin in combination with resistance exercise stimulates translation initiation and protein synthesis through enhanced activity of a guanine nucleotide exchange protein referred to as eIF2B. In both cases, the amount of insulin required for the effects is low, and a concentration of the hormone that approximates that observed in fasting animals is sufficient for maximal stimulation. This review summarizes the results of a number of recent studies that have helped to establish our present understanding of the interactions of insulin, amino acids, and exercise in the regulation of protein synthesis in skeletal muscle.

 

[Fonz]

Insulin has NO NET effect on protein synthesis if not\
admistered exogeneously.

We have been discussing this at AF.

Only a supraphysiological dose of insulin has an
effect on protein synthesis.

Fonz

 

[wilson6]

"Insulin has NO NET effect on protein synthesis "

Under non-diabetic conditions. There appears to be a very low, but critical concentration that is necessary for a normal response to resistance exercise, and I would agree that from that point on until supraphysiologic concentrations are reached, there won't be any additional effect on protein synthesis.

In fact I recently read an abstract that showed that increasing insulin to levels that reduce exogenously administered GH induced hyperglycemia did not increase muscle protein synthesis.

W6

 

[MS]

Good work Wilson6. So ALA does no harm with a post workout meal (for Spatts, this relates to my concerns on Ulter's R-ALA thread that it might decrease protein synthesis ratse due to decreased insulin excretion). I remain to be convinced that it adds any additional benefit when taken post workout. Seems there's only so many glut4 receptors available to be transported (barring changes in transcription/translation) to the cell surface and heavy weight training prolly mobilizes the majority of them without ALA (judging from the non-diabetic rat data). But it's good to know it won't interfere with nett protein synthesis.

There's still some pieces missing from this puzzle, but I'll ponder them another day.