Pioglitazone improvement of fasting and postprandial hyperglycaemia in Mexican-American patients with Type 2 diabetes: a double tracer OGTT study.

OBJECTIVES: By using tracer techniques, we explored the metabolic mechanisms by which pioglitazone treatment for 16 weeks improves oral glucose tolerance in patients with type 2 diabetes when compared to subjects without diabetes.
METHODS: In all subjects, before and after treatment, we measured rates of tissue glucose clearance (MCR), oral glucose appearance (RaO) and endogenous glucose production (EGP) during a (4-h) double tracer oral glucose tolerance test (OGTT) (1-(14)C-glucose orally and 3-(3)H-glucose intravenously). Basal hepatic insulin resistance index (HepIR) was calculated as EGPxFPI. beta-cell function was assessed as the incremental ratio of insulin to glucose (DeltaI/DeltaG) during the OGTT.
RESULTS: Pioglitazone decreased fasting plasma glucose concentration (10.5 +/- 0.7 to 7.8 +/- 0.6 mM, P < 0.0003) and HbA1c (9.7 +/- 0.7 to 7.5 +/- 0.5%, P < 0.003) despite increased body weight and no change in plasma insulin concentrations. This was determined by a decrease both in fasting EGP (20.0 +/- 1.1 to 17.3 +/- 0.8 micromol/kg(ffm) min, P < 0.005) and HepIR (from 8194 declined by 49% to 3989, P < 0.002). During the OGTT, total glucose Ra during the 0- to 120-min time period following glucose ingestion decreased significantly because of a reduction in EGP. During the 0- to 240-min time period, pioglitazone caused only a modest increase in MCR (P < 0.07) but markedly increased DeltaI/DeltaG (P = 0.003). The decrease in 2h-postprandial hyperglycaemia correlated closely with the increase in DeltaI/DeltaG (r = -0.76, P = 0.004) and tissue clearance (r = -0.74, P = 0.006) and with the decrease in HepIR (r = 0.62, P = 0.006).
CONCLUSIONS: In diabetic subjects with poor glycaemic control, pioglitazone improves oral glucose tolerance mainly by enhancing the suppression of EGP and improving beta-cell function.