Whey Protein Hydrolysates Accelerate Rat Muscle Protein Synthesis At Lower Doses Than Intact Whey Protein

Abstract

PURPOSE: The intake of whey protein is highly effective for accelerating muscle protein synthesis. Many studies have revealed that a rapid absorption rate and the leucine-rich amino-acid composition of whey protein contribute to the acceleration of muscle protein synthesis. Whey protein hydrolysates (WPH) have amino-acid composition identical to intact whey protein isolate (WPI) and are absorbed more rapidly than WPI. Our hypothesis was that WPH is a more potent accelerator for muscle protein synthesis than WPI. The aim of the present study was to compare the effects of WPH on muscle protein synthesis with WPI. METHODS: Male Sprague-Dawley (SD) rats swam for 2 h. Immediately after exercise, WPI was administered to the rats as a single dose (amounts of protein were 2.0 g/kg BW). Phe-D5 was injected via the tail vein 15 min before euthanasia for the measurement of the protein fractional synthesis rate (FSR). Rats were euthanized at designated postprandial time points (30, 60, 90 or 120 min) and triceps muscle samples were collected (n = 7-9/time point). FSR were measured to find out the time point at which FSR became highest. Subsequently, another group of male SD rats swam for 2 h. Immediately after exercise, WPH, WPI or deionized water (control, n = 8) was administered to the rats as a single dose (amounts of protein were 0.5 or 2.0 g/kg BW, n = 8/treatment/dose). Phe-D5 was injected via the tail vein 15 min before euthanasia. At the time point that the first study revealed postprandial FSR became highest, rats were anesthetized and their triceps muscles were excised to measure FSR. RESULTS: Postprandial FSR became highest at 60 min after WPI was administered (2.68+/-0.25, 3.64+/-0.19, 4.62+/-0.28, 4.19+/-0.21 and 3.99+/-0.19 %/day for 0, 30, 60, 90 and 120 min). 60 min after administration, WPH had significantly higher (p < 0.05) FSR compared to control at a dose of either 0.5 or 2.0 g/kg BW (5.21+/-0.22, 5.22+/-0.18 and 3.74+/-0.24 %/day for 0.5, 2.0 g/kg BW and control, respectively). However, WPI had significantly higher (p < 0.05) FSR compared to control only at a dose of 2.0 g/kg BW (4.51+/-0.10 and 5.09+/-0.20 for 0.5 and 2.0 g/kg BW). WPH had significantly higher (p < 0.05) FSR compared to WPI at 0.5 g/kg BW. CONCLUSIONS: Whey protein hydrolysates stimulate muscle protein synthesis at lower doses compared to intact whey protein.