The Effect of Pioglitazone on Hepatic Glucose Uptake Measured With Indirect and Direct Methods in Alloxan-Induced Diabetic Dogs

Pioglitazone, a thiazolidinedione derivative, ameliorates hyperglycemia by augmenting peripheral glucose disposal and suppressing hepatic glucose production in diabetic animals. However, the effect of this agent on hepatic glucose uptake has not been explored. To determine this, experiments were conducted in alloxan-induced diabetic dogs with (pioglitazone group, n = 7) or without (control group, n = 5) a 10-day oral treatment with pioglitazone (1 mg · kg⁻¹ · day⁻¹). A euglycemic-hyperinsulinemic (insulin infusion rate 25.2 pmol · kg⁻¹ · min⁻¹) clamp was maintained by adjusting the peripheral glucose infusion rate (GIR). After a 60-min basal period (period I), portal glucose infusion (Pinf, 33.3 μmol · kg⁻¹ · min⁻¹) was administered for 120 min (period II). This was followed by a 60-min recovery period (period III). Arterial insulin levels were kept stable in the supraphysiological range throughout the experiment (1,623 ± 52, pioglitazone group; 1,712 ± 52 pmol/l, C group). There was no significant difference in whole-body glucose utilization determined by [3-³H]glucose between the pioglitazone and C groups in period I (68.4 ± 2.8 vs. 70.1 ± 2.8 μmol · kg⁻¹ · min , respectively) and period III (81.2 ± 5.0 vs. 74.5 ± 3.3 μmol · kg⁻¹ · min⁻¹, respectively). Net hepatic glucose uptake (NHGU) determined by arteriovenous difference method was approximately zero in the basal period (−0.7 ± 1.1, pioglitazone group; 0.1 ± 1.2 μmol · kg⁻¹ · min⁻¹, C group). In period II, hepatic glucose uptake, determined by the changes in GIR, was significantly higher in the pioglitazone group (6.5 ± 0.6 μmol · kg⁻¹ · min) than in the C group (–0.4 ± 0.6 μmol · k⁻¹ · min⁻¹, P < 0.001). This observation was also confirmed by NHGU during portal glucose infusion (6.9 ± 1.4 vs. 2.1 ±1. 8 μmol · kg⁻¹ · min⁻¹, pioglitazone vs. C, respectively; P < 0.025). We conclude that pioglitazone treatment enhances hepatic glucose uptake during portal glucose loading in alloxan-induced diabetic dogs. However, in hyperinsulinemic conditions, pioglitazone does not enhance the already high peripheral glucose uptake.