OBJECTIVE To examine the relationship between beta-cell function and the incretin effect.

DESIGN We performed a 180-min hyperglycaemic clamp study with oral glucose administration at 60 min in Korean subjects with normal glucose tolerance (NGT, n = 9), impaired fasting glucose (IFG, n = 6) and type 2 diabetes mellitus (T2DM, n = 6).

MEASUREMENTS First- and second-phase insulin secretions were measured during the first 60 min. The insulin response to intravenous glucose during the 60- to 120-min interval (Insiv) was calculated using a prediction method. The insulin response to oral glucose (Ins(oral)) was calculated by subtracting the Insiv from the overall insulin response during the 60- to 120-min interval (Ins(overall)). The incretin effect under the hyperglycaemic clamp condition (IE(clamp)) was calculated by the equation: 100 × [(Ins(overall) - Insiv)/Ins(overall)].

RESULTS The IE(clamp) was comparable among the three groups (46.3 ± 6.4%, 35.7 ± 8.8% and 51.4 ± 7.4% for the NGT, IFG and T2DM group, respectively, P = 0.327) and was not correlated with the first- and second-phase insulin secretions. However, the Ins(oral) (mU/l 60 min) was significantly different between the NGT, IFG and T2DM groups (5199 ± 1185, 2164 ± 956 and 1034 ± 355, respectively; P = 0.010) and was well correlated with the first- and second-phase insulin secretions.

CONCLUSIONS The incretin effect measured by the hyperglycaemic clamp with oral glucose loading was neither correlated with beta-cell function nor different between NGT, IFG and T2DM groups in Koreans.