G. Biolo et al., Insulin action on muscle protein kinetics and amino acid transport during recovery after resistance exercise, DIABETES, 48(5), 1999, pp. 949-957
We have determined the individual and combined effects of insulin and prior
exercise on leg muscle protein synthesis and degradation, amino acid trans
port, glucose uptake, and alanine metabolism. Normal volunteers were studie
d in the postabsorptive state at rest and about 3 h after a heavy leg resis
tance exercise routine. The leg arteriovenous balance technique was used in
combination with stable isotopic tracers of amino acids and biopsies of th
e vastus lateralis muscle. Insulin was infused into a femoral artery to inc
rease the leg insulin concentrations to high physiologic levels without sub
stantively affecting the whole-body level. Protein synthesis and degradatio
n were determined as rates of intramuscular phenylalanine utilization and a
ppearance, and muscle fractional synthetic rate (FSR) was also determined.
Leg blood flow was greater after exercise than at rest (P < 0.05). Insulin
accelerated blood now at rest but not after exercise (P < 0.05). The rates
of protein synthesis and degradation were greater during the postexercise r
ecovery (65 +/- 10 and 74 +/- 10 nmol min(-1) . 100 ml(-1) leg volume, resp
ectively) than at rest (30 +/- 7 and 46 +/- 8 nmol . min(-1) . 100 ml(-1) l
eg volume, respectively; P < 0.05). Insulin infusion increased protein synt
hesis at rest (51 +/- 4 nmol . min(-1) . 100 ml(-1) leg volume) but not dur
ing the postexercise recovery (64 +/- 9 nmol . min(-1) . 100 ml(-1) leg vol
ume; P < 0.05). Insulin infusion at rest did not change the rate of protein
degradation (48 +/- 3 nmol . min(-1) . 100 ml(-1) leg volume). In contrast
, insulin infusion after exercise significantly decreased the rate of prote
in degradation (52 +/- 9 nmol . min(-1) . 100 ml(-1) leg volume). The insul
in stimulatory effects on inward alanine transport and glucose uptake were
three times greater during the postexercise recovery than at rest (P < 0.05
). In contrast, the insulin effects on phenylalanine, leucine, and lysine t
ransport were similar at rest and after exercise. In conclusion, the abilit
y of insulin to stimulate glucose uptake and alanine transport and to suppr
ess protein degradation in skeletal muscle is increased after resistance ex
ercise. Decreased amino acid availability may limit the stimulatory effect
of insulin on muscle protein synthesis after exercise.