Although insulin per se has been shown to stimulate wholebody
protein synthesis in several mammalian species (Davis et al.
2002; O’Connor et al. 2003), insulin sensitivity may also have a
significant role. Recent studies in neonatal piglets (Bergeron et al.
2007) and steers (Gingras et al. 2007) have shown that protein
anabolism is upregulated via enhanced insulin sensitivity in
animals fed dietary long-chain n-3 polyunsaturated fatty acids.
In both studies, the increase in whole-body protein accretion was
suggested to be the result of a decrease in protein breakdown, with
no alteration in its synthesis. In addition, studies in rodents have
shown an amino acid-enhanced sensitivity of skeletal muscle
protein synthesis to insulin, allowing for maximal rates of protein
synthesis to be achieved at lower insulin concentrations when
amino acids are infused concurrently (Garlick and Grant 1988).
Taken together, these above studies suggest a dynamic role for
insulin, insulin sensitivity and amino acids and collectively they
may act synergistically to stimulate protein synthesis.