Objective: To study the changes of insulin secretion in Chinese individuals with impaired glucose tolerance and diabetes and the relationship between insulin release and overweight/obesity.
Methods: Sixty-four individuals were divided into 6 groups according to glucose tolerance (GT) and body weight: normal weight with normal glucose tolerance (NW-NGT) group, NW with impaired glucose tolerance (NW-IGT) group, NW with diabetes (NW-DM) group, overweight or obese (OW/OB) with NGT (OW/OB-NGT) group, OW/OB with IGT (OW/OB-IGT) group, OW/OB with DM (OW/OB-DM) group. The subjects were required to fast for 12 hours and then underwent oral glucose tolerance test (OGTT) and hyperglycemic clamp.
Results: 1. The first-phase insulin release, the sum of insulin concentrations during the first 10 minutes (at the 2(nd), 4(th), 6(th), 8(th), and 10(th) minutes) were 186 mU/L +/- 38 mU/L in the IGT groups, significantly lower than that of the NGT groups (P = 0.001). The first-phase insulin release of the DM groups was 71 mU/L +/- 10 mU/L, significantly lower than those of the NW-NGT group and IGT group (257 mU/L +/- 22 mU/L and 164 mU/L +/- 47 mU/L respectively, both P < 0.01). The second-phase insulin release, the average insulin concentration during the 20th to 150th minutes of the DM groups was 31 mU/L +/- 4 mU/L, significantly lower than those of the NGT and IGT groups (74 mU/L +/- 5 mU/L and 45 mU/L +/- 19 mU/L, P < 0.01 and P < 0.04). The 2nd-phase insulin release was not significantly different between the NGT and IGT groups (P = 0.13). The maximum insulin release (INS-Max), the average insulin concentration during the last 30 minutes (120th to 150th minutes), of the DM groups was 40 mU/L +/- 6 mU/L, significantly lower than those of the NGT and IGT groups (P < 0.05). The INS-MAX was not significantly different between the NGT and IGT groups (P = 0.12). The first-phase insulin release, second-phase insulin release, and INS-MAX of the NW-IGT group were 164 mU/L +/- 47 mU/L, 45 mU/L +/- 19 mU/L, and 53 mU/L +/- 22 mU/L respectively, all significantly higher than those of the NW-IGT group (61 mU/L +/- 17 mU/L, 27 mU/L +/- 5 mU/L, and 34 mU/L +/- 6 mU/L respectively, P < 0.05) and those of the DM groups (61 mU/L +/- 17 mU/L, 27 mU/L +/- 5 mU/L, and 34 mU/L +/- 6 mU/L respectively, P < 0.05). 3. The first-phase insulin release, second-phase insulin release, and INS-MAX of the OW/OB-NGT group were 546 mU/L +/- 62 mU/L, 138 mU/L +/- 18 mU/L, and 163 mU/L +/- 24 mU/L respectively, all significantly higher than those of the NW-NGT group (257 mU/L +/- 22 mU/L, 74 mU/L +/- 6 mU/L, and 97 mU/L +/- 8 mU/L, respectively, P < 0.05). The first- phase insulin secretion in the OW/OB-IGT group and OW/OB-DM group were 201 mU/L +/- 47 mU/L and 82 mU/L +/- 9 mU/L respectively, both significantly lower than that of the OW/OB- NGT group (P < 0.05).
Conclusion: 1. The insulin release is progressively decreased in Chinese individuals with IGT and DM. The individuals with IGT have lower first phase insulin release. In addition to decreased first phase insulin release, subjects with DM have reduced second-phase and maximum insulin release. 2. Simply overweight/obese individuals have higher insulin secretion, while overweight or obese individuals with IGT and DM have reduced first phase insulin release.