[The relation between fasting plasma glucose concentrations and insulin resistance].

OBJECTIVE: To study whether insulin resistance exists in the Chinese individuals with impaired glucose regulation (IGR) defined by the modified cut-point value (5.6 mmol/L) in 2003 version of ADA criteria for impaired fasting glucose (IFG).

METHODS: We selected 9 persons [aged (44 +/- 5) years, body mass index (BMI) (24.0 +/- 0.8) kg/m(2)] with normal glucose regulation [NGR, fasting plasma glucose (FPG) < 5.6 mmol/L, plasma glucose-2h (PG2h) < 7.8 mmol/L], 9 [aged (49 +/- 3) years, BMI (29.0 +/- 0.8) kg/m(2)] with isolated IFG defined by the new criteria (n-i-IFG, FPG < 5.6 mmol/L, PG2h < 7.8 mmol/L), 20 with combined impaired glucose tolerance (c-IGT) including 10 [aged (45 +/- 4) years, BMI (26.0 +/- 1.3) kg/m(2)] defined by the new criteria (n-c-IGT, FPG 5.6 - 6.0 mmol/L, PG2 h 7.8 - 11.0 mmol/L) and 10 [aged (49 +/- 3) years, BMI (27.0 +/- 1.1) kg/m(2)] defined by the old criteria (o-c-IGT, FPG 6.1 - 6.9 mmol/L, PG2h 7.8 - 11.0 mmol/L), 10 [aged (43 +/- 5) years, BMI (29.0 +/- 2.8) kg/m(2)] with type 2 diabetes mellitus (DM). Insulin resistance of the subjects was measured by using hyperinsulin-euglycemic clamp in which the glucose infusion rate (GIR) was the major index. Beta-cell function was assessed by intravenous glucose tolerance test. The DM patients only underwent the hyperinsulin-euglycemic clamp.

RESULTS: (1) The GIR of n-i-IFG group and n-c-IGT group was significantly lower than that of the NGR group [(7.2 +/- 0.8), (7.0 +/- 1.5) vs (10.3 +/- 0.9) mg.kg(-1).min(-1), P < 0.05]. The GIR of o-c-IGT group was the least [(4.8 +/- 0.4) mg.kg(-1).min(-1)], which was similar to that of the DM group [(5.6 +/- 1.0) mg.kg(-1).min(-1)], the GIR of the two groups was significantly reduced compared with the NGR goup [(4.8 +/- 0.4), (5.6 +/- 1.0) vs (10.3 +/- 0.9) mg.kg(-1).min(-1), P < 0.01]. (2) As compared with the NGR group, the fasting insulin level was increased in all the IGR groups and was decreased in the DM group. (3) The first phase of insulin secretion were similar in NGR and n-i-IFG group [(37.0 +/- 8.6) vs (31.7 +/- 9.2) mU/L, P > 0.05], and the n-i-IFG group had greater amount than the n-c-IGT group [(31.7 +/- 9.2) vs (25.9 +/- 9.8) mU/L, P > 0.05]. But it was the least in the o-c-IGT group that significantly less than the NGR group [(17.2 +/- 4.8) vs (37.0 +/- 8.6) mU/L, P < 0.05]. As compared with the NGR group, the second phase of insulin secretion was slightly increased in the n-i-IFG group [(16.6 +/- 2.9) vs (21.9 +/- 3.6) mU/L, P > 0.05], and was even greater in the n-c-IGT group [(16.6 +/- 2.9) vs (38.7 +/- 13.7) mU/L, P < 0.05]. But it was reduced in the o-c-IGT group [(20.7 +/- 2.9) mU/L].

CONCLUSIONS: (1) The IGR subjects defined by the new cut-point value already has insulin resistance. (2) Deficit in insulin secretion is worsening as the IGR deteriorates.