Regulation of protein synthesis and translation initiation in skeletal muscle by feeding mixed meals containing soy or whey protein after endurance exercise.

Abstract

The purpose of this investigation was to comparatively assess the postexercise recovery of skeletal muscle protein synthesis and translation initiation following ingestion of carbohydrate in combination with different protein sources. Treadmill-acclimated rats (n = 6-8 pergroup) were randomly designated as either nonexercised controls (NEX) or treadmill exercised for 2h at 26 m/min (~75% VO2max) and then fed one of four meals: EC, 100% carbohydrate; ESI, carbohydrate plus 20% soy protein isolate; ESC, carbohydrate plus 20% soy protein concentrate (high isoflavone content); EW, carbohydrate plus 20% whey protein concentrate. One hour later, serum insulin concentrations were highest in rats fed EW; serum concentrations of leucine, isoleucine, valine and threonine were also highest in EW. Nevertheless, meals containing soy were similar to whey in promoting muscle protein synthesis above EC. Likewise, both soy and whey-containing meals stimulated phosphorylation of the translational repressor, 4E-BP1, and formation of the mRNA cap binding complex. On the other hand, phosphorylation of the 70kD ribosomal protein S6 kinase (S6K1) was highest in EW. Thus, short-term recovery of general protein synthesis and the mRNA cap binding step is promoted comparably by soy vs. whey protein in the skeletal muscle of exercised rats. In contrast, acute activation of the S6K1 signaling pathway is greatest in response to whey. This differential response is likely related to variations in the content and/or delivery rate of the branched-chain amino acids to the periphery.