Summary
To elucidate insulin action on hepatic glucose output (glycogenolysis) in the state
exposed to an excess glucocorticoid, the fed rat liver was isolated and cyclically
perfused with a medium containing 5 mM glucose and various concentrations of insulin.
The rat was subcutaneously injected with 1 mg/kg of dexamethasone (Dex) for 7 days.
Dex-treated rats showed marked increases of serum insulin and plasma glucose level
compared with those in control rats. Hepatic glycogen contents in Dex group were markedly
increased compared with those in control (115 ± 5 and 28 ± 4 mg/g, respectively).
Insulin extraction rate in the perfused liver was not different between control and
Dex group.
Perfusate glucose level after 60 min perfusion was much higher in the Dex-treated
rat liver than that of the control at 0 μU/ml insulin (34.5 ± 2.5 vs 23.0 ± 2.0 mM,
P < 0.01), and reduced to the nadir level (19.0 ± 3.0 and 13.0 ± 1.5 mM, respectively)
at 100 μU/ml insulin in both groups, i. e., the decreasing rate in perfusate glucose
level was not different between Dex and control group (43% and 44%, respectively).
These results suggest that Dex-treatment augments hepatic glucose output, but does
not affect the sensitivity and responsiveness of that to insulin.
Key words
Dexamethasone - Insulin - Liver Glycogen
