Dexamethasone treatment fails to increase arginine-induced insulin release in healthy subjects with low insulin response

Summary We have compared insulin responses to L-arginine before and during dexamethasone treatment in healthy subjects, previously classified as subjects with either high or low insulin response according to a standardized glucose infusion test. Arginine stimulation was administered as a 150 mg/kg bolus followed by 10 mg·kg^–1·min^–1 to six subjects with high insulin response and to seven subjects with low insulin response. Before dexamethasone treatment the incremental insulin level during 0–10 min of arginine was higher in subjects with high (36.5±6.8 U/ml) than in subjects with low response (14.5±2.3 U/ml), p<0.01 for difference. Dexamethasone treatment (6 mg/day for 60 h) markedly enhanced the insulin response to arginine in subjects with high response (+99% 0–30 min) but failed to affect the subjects with low response (+4% 0–30 min). The C-peptide response to arginine exhibited similar differences between groups. Decreased responsiveness to arginine in subjects with low insulin response, especially during dexamethasone treatment, suggests a Beta-cell capacity defect although a decreased potentiating-sensing effect of glucose cannot be completely ruled out.