Effect of systemic hyperinsulinemia on amino acid flux across human legs in postabsorptive state.

The effect of physiological hyperinsulinemia (approximately 110 mU/l) on leg tissue protein balance was investigated in eight weight-stable healthy individuals. A primed constant infusion of L-[U-14C]tyrosine was used to measure the disposal and release of tyrosine across the leg before and during 2 h of euglycemic clamp studies. The leg exchange of 3-methyl-L-histidine (3-MH) and all amino acids in blood were measured before and during insulinization, including the muscle tissue content of amino acids. Hyperinsulinemia decreased whole body tyrosine flux from 52 +/- 2 to 35 +/- 1 mumol/min (P less than 0.0001), whereas neither disposal (53 +/- 9 vs. 45 +/- 9 nmol.min-1.100 g-1) nor release of tyrosine across the leg (76 +/- 11 vs. 66 +/- 10 nmol X min-1 X 100 g-1) was significantly influenced. The arterial concentration and the leg exchange of 3-MH were not significantly affected by 2 h of hyperinsulinemia, but the sum of all amino acids declined significantly. The net leg balance of tyrosine was not affected at all by hyperinsulinemia, whereas the balance of the branched-chain amino acids and methionine were switched from efflux toward influx. Phenylalanine efflux from the leg only showed a trend to a significant effect by insulin. The muscle tissue concentration of six individual amino acids decreased significantly during hyperinsulinemia, particularly the branched-chain amino acids. The leg exchange of glucose, free fatty acids, and glycerol immediately changed significantly, as expected in response to insulinization.(ABSTRACT TRUNCATED AT 250 WORDS)