Contribution of skin to whole-body protein synthesis in rats at different stages of maturity.

This study assessed whole-body and tissue protein metabolism and the contribution of skin to whole-body protein synthesis during the post-weaning development of rats. Protein fractional synthesis rate was measured in muscle, skin and the whole body of 70-, 160-, 315- and 586-g rats by use of a continuous infusion of L-[U-14C]lysine. Rates of protein synthesis were then calculated, based on the tissue free and protein-bound lysine specific radioactivity at the end of the infusion. The fractional protein synthesis rate declined progressively in the skin (from 19.6 to 8.0%/d), in muscle (from 18.9 to 4.8%/d) and in whole body (from 25.0 to 8.5%/d) throughout post-weaning development. Absolute synthesis rates [g/(d.100 g body wt)] of whole-body and muscle proteins decreased by 54 and 50%, respectively. On the other hand, the amount of skin protein synthesized per 100 g body wt was 35% greater in 160-g and 315-g rats than in 70-g and 586-g rats. The absolute synthesis rate of muscle proteins as a percentage of whole-body protein synthesis remained fairly constant at a value close to 24%, whereas the skin contribution to whole-body protein synthesis increased from 12% in 70-g rats to 26% in 586-g rats.