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School of Biomedical Sciences, University Medical School, Queen's Medical Centre, Nottingham NG7 2UH, United Kingdom
This
study investigated the effect of insulin on plasma and muscle creatine
accumulation and limb blood flow in humans after creatine
administration. Seven men underwent a 300-min euglycemic insulin clamp
combined with creatine administration on four separate occasions.
Insulin was infused at rates of 5, 30, 55, or 105 mU · m
2 · min
1,
and on each occasion 12.4 g creatine was administered. During infusion
of insulin at rates of 55 and 105 mU · m
2 · min
1,
muscle total creatine concentration increased by 4.5 ± 1.4 (P < 0.05) and 8.3 ± 1.0 mmol/kg
dry mass (P < 0.05), and plasma creatine concentrations were lower at specific time points compared with the 5 mU · m
2 · min
1
infusion rate. The magnitude of increase in calf blood flow
(plethysmography) was the same irrespective of the rate of insulin
infusion, and forearm blood flow increased to the same extent as the
three highest infusion rates. These findings demonstrate that insulin
can enhance muscle creatine accumulation in humans but only when
present at physiologically high or supraphysiological concentrations.
This response is likely to be the result of an insulin-mediated
increase in muscle creatine transport rather than creatine delivery.
phosphocreatine; muscle fatigue; exercise
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