KINETICS OF DEXAMETHASONE-INDUCED ALTERATIONS OF GLUCOSE-METABOLISM IN HEALTHY HUMANS

Six healthy human subjects were studied during three 75-g oral, [C-13] glucose tolerance tests to assess the kinetics of dexamethasone-induce d impairment of glucose tolerance. On one occasion, they received dexa methasone (4 x 0.5 mg/day) during the previous 2 days. On another occa sion, they received a single dose (0.5 mg) of dexamethasone 150 min be fore ingestion of the glucose load. On the third occasion, they receiv ed a placebo. Postload plasma glucose was significantly increased afte r both 2 days dexamethasone and single dose dexamethasone compared wit h control (P < 0.05). This corresponded to a 20-23% decrease in the me tabolic clearance rate of glucose, whereas total glucose turnover ([6, 6-H-2]glucose), total (indirect calorimetry) and exogenous glucose oxi dation (O-13(2) production), and suppression of endogenous glucose pro duction were unaffected by dexamethasone. Plasma insulin concentration s were increased after 2 days of dexamethasone but not after a single dose of dexamethasone. In a second set of experiments, the effect of a single dose of dexamethasone on insulin sensitivity was assessed in s ix healthy humans during a 2-h euglycemic hyperinsulinemic clamp. Dexa methasone did not significantly alter insulin sensitivity. It is concl uded that acute administration of dexamethasone impairs oral glucose t olerance without significantly decreasing insulin sensitivity.