Diabetes, Vol 34, Issue 10 1049-1054, Copyright © 1985 by American Diabetes Association
Time dependence of insulin action in muscle and adipose tissue in the rat in vivo. An increasing response in adipose tissue with time
DE James, KM Burleigh and EW Kraegen
The relative time dependency of enhancement of glucose metabolism by
insulin in individual tissues has not been examined previously in vivo.
Using the glucose clamp technique in the rat combined with radiolabeled
2-deoxyglucose (3H or 14C-2DG) administration, we have estimated a glucose
metabolic index (Rg') in major insulin-sensitive tissues at two different
times (between 40-55 min and 80-95 min) after onset of hyperinsulinemia
(insulin levels of approximately 130 mU/L). At the completion of the clamp
(125 min), eight different skeletal muscles and three different adipose
tissue beds were rapidly removed for estimation of Rg', based on the
accumulation of intracellular tracer 2DG-6-phosphate (2DGP).
Insulin-stimulated Rg' was 60-70% higher at 80-95 min than at 40-55 min
after elevation of insulin levels in all three adipose tissue beds (P less
than 0.01). In contrast, insulin-stimulated whole body glucose utilization
and Rg' in all skeletal muscles were not significantly different at these
two times. The constancy of insulin action in skeletal muscles during the
2-h euglycemic clamp, as determined in these studies, does not support the
concept that the glucose clamp represents an integral of many rapidly
changing individual tissue responses. In conclusion, while the amount of
insulin-stimulated glucose uptake in adipose tissue is low compared with
muscle, the fraction increases with duration of insulin elevation. This
effect may have significant implications in hyperinsulinemic states.