β-hydroxy-β-methyl butyrate, but not α-ketoisocaproate and excess leucine, stimulates skeletal muscle protein metabolism in growing pigs fed low-protein diets

This study aimed to investigate the effects of leucine (Leu) and its metabolites (alpha-ketoisocaproate (KIC) and beta-hydroxy-beta-methylbutyrate (HMB)) on muscle protein metabolism in growing pigs fed low-protein diets. 32 pigs (Large White x Landrace, 9.55 +/- 0.19 kg) were divided into four groups (basal diet, L-Leu, KIC-Ca, HMB-Ca). Results showed that compared to the control, dietary supplementation of KIC and excess Leu significantly decreased the weight of soleus muscle (SM, P < 0.05), whereas HMB supplementation increased it, accompanied by elevated rate of protein synthesis and elevated phosphorylation of Akt (P < 0.05). The weight of longissimus dorsi muscle remained unaffected by dietary treatments (P > 0.05). In conclusion, HMB, but not KIC or excess Leu, might act as a nutrient signal to stimulate positive protein balance especially in muscles of oxidative fiber-types of growing pigs fed low-protein diets, and these effects might be associated with the Akt signaling.