Abstract
BackgroundWe examined the acute effects of different dietary protein sources (0.19 g, dissolved in 1 ml of water) on skeletal muscle, adipose tissue and hypothalamic satiety-related markers in fasted, male Wistar rats (~250 g).MethodsOral gavage treatments included: a) whey protein concentrate (WPC, n = 15); b) 70:30 hydrolyzed whey-to-hydrolyzed egg albumin (70 W/30E, n = 15); c) 50 W/50E (n = 15); d) 30 W/70E (n = 15); and e) 1 ml of water with no protein as a fasting control (CTL, n = 14).ResultsSkeletal muscle analyses revealed that compared to CTL: a) phosphorylated (p) markers of mTOR signaling [p-mTOR (Ser2481) and p-rps6 (Ser235/236)] were elevated 2–4-fold in all protein groups 90 min post-treatment (p < 0.05); b) WPC and 70 W/30E increased muscle protein synthesis (MPS) 104% and 74% 180 min post-treatment, respectively (p < 0.05); and c) 70 W/30E increased p-AMPKα (Thr172) 90 and 180-min post-treatment as well as PGC-1α mRNA 90 min post-treatment. Subcutaneous (SQ) and omental fat (OMAT) analyses revealed: a) 70 W/30 W increased SQ fat phosphorylated hormone-sensitive lipase [p-HSL (Ser563)] 3.1-fold versus CTL and a 1.9–4.4-fold change versus all other test proteins 180 min post-treatment (p < 0.05); and b) WPC, 70 W/30E and 50 W/50E increased OMAT p-HSL 3.8–6.5-fold 180 min post-treatment versus CTL (p < 0.05). 70 W/30E and 30 W/70E increased hypothalamic POMC mRNA 90 min post-treatment versus CTL rats suggesting a satiety-related response may have occurred in the former groups. However, there was a compensatory increase in orexigenic AGRP mRNA in the 70 W/30E group 90 min post-treatment versus CTL rats, and there was a compensatory increase in orexigenic NPY mRNA in the 30 W/70E group 90 min post-treatment versus CTL rats.ConclusionsHigher amounts of whey versus egg protein stimulate the greatest post-treatment anabolic skeletal muscle response, though test proteins with higher amounts of WPH more favorably affected post-treatment markers related to adipose tissue lipolysis.Electronic supplementary materialThe online version of this article (doi:10.1186/s12970-015-0076-9) contains supplementary material, which is available to authorized users.
Highlights
We examined the acute effects of different dietary protein sources (0.19 g, dissolved in 1 ml of water) on skeletal muscle, adipose tissue and hypothalamic satiety-related markers in fasted, male Wistar rats (~250 g)
Select gastrocnemius mRNAs related to skeletal muscle hypertrophy are differentially affected by protein type While transient gene expression patterns in response to feeding provide limited information, mRNA expression patterns of anabolic genes are a putative index regarding whether or not a particular protein source may have a potential impact on long-term anabolism
Mighty/Akirin-1 mRNA, which is transcriptionally down-regulated by MSTN [31] and is related to muscle hypertrophy [32], was similar between groups 90 min post-treatment but: a) was greater in the WPC and 70 W/30E groups 180 min post-treatment compared to 50 W/50E rats (WPC vs. 50 W/50E p = 0.001, 70 W/30E vs. 50 W/50E p = 0.001; Figure 2b); and b) was greater in the WPC, 70 W/30E and 30 W/70E groups 180 min post-treatment compared to CTL rats (WPC vs. CTL p < 0.001, 70 W/30E vs. CTL p < 0.001, 30 W/70E vs. CTL p = 0.046; Figure 2b). p21Cip mRNA, which is a gene potentially related to skeletal muscle hypertrophy [33], remained similar between CTL and all protein-fed groups 90 min postfeeding (Figure 2c)
Summary
We examined the acute effects of different dietary protein sources (0.19 g, dissolved in 1 ml of water) on skeletal muscle, adipose tissue and hypothalamic satiety-related markers in fasted, male Wistar rats (~250 g). Acute whey protein feeding has been shown to reduce appetite 90–180 min following low-dose ingestion [8,9,10] by potentially affecting anorectic hormone and hypothalamic mRNA expression patterns [11,8,9]. Chronic whey protein supplementation has been shown to reduce adiposity in rodents and humans [12,13,14,5]; an effect which may be explained by an increased expression of adipose tissue lipolysis-related gene expression patterns following chronic supplementation [12], an increase in protein-induced thermogenesis (reviewed in [15]), and/or a consistent reduction in food intake given its satietystimulatory effects as discussed above. It is of interest to further examine how WPH versus WPC ingestion differentially affects various physiological systems
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