Effect of nutritional state and insulin on hind-limb amino acid metabolism in steers.

The effects of dietary protein level, exogenous insulin and starvation on amino acid (AA) uptake or release from the hindquarters of steers were studied. Irrespective of diet fed, physiologic state or time after feeding there was a net release of alanine and glutamine from hind limbs of steers. Steers from control 1 exhibited a net release of leucine, valine and isoleucine (branched-chain amino acids, BCAA) in the postabsorptive (prefeeding) state, but steers from control group 2 exhibited some BCAA uptake by the hind limb. At 2 and 4 hours postfeeding, there was marked net uptake by hind limbs of BCAA and total AA in steers fed the control (12.8% protein) diets. At 2 and 4 hours after feeding there was slight hind-limb uptake of BCAA and total AA in steers fed the low protein diet, while there was a massive uptake of BCAA and total AA by hind limbs of steers fed the high protein diet. Upon insulin injection to postabsorptive steers, BCAA and total AA uptake by hind limbs was markedly stimulated at 1 and 2 hours, but by 4 hours the AA flux pattern had reverted to that in the postabsorptive state. After 24 and 48 hours of starvation, steer hindquarters released significant quantities of BCAA, essential amino acids and total amino acids.