Figure 5. Glucose metabolism and lipolysis in rat islets in the absence or presence of GLP-1.

Islets were processed as described for insulin secretion (see [Fig. 1]) and after the pre-incubation step they were incubated in 70 µl KRBH/0.25% defatted BSA medium containing 2.8, 8.3 or 16.7 mM glucose plus or minus 20 nM GLP-1 in presence of D-[U-¹⁴C]-glucose (for oxidation) (A) and D-[5-³H]-glucose (for utilization) (B). Incubations were stopped after 90 min as described in Methods. Glucose oxidation was measured as ¹⁴CO₂ released, and glucose utilization was determined by measuring the amount of released ³H₂O. Results are means±SE of 15 determinations in 3 separate experiments. *p<0.05, **p<0.01, ***p<0.001 when compared to the corresponding 2.8 mM glucose group; #p<0.05 when compared to the corresponding ‘minus GLP-1’ group. For lipolysis determinations (C) overnight-cultured rat islets were washed in KRBH/0.07% BSA medium with 2.8 mM glucose and were transferred into 0.2 mL KRBH/0.07% BSA medium with 2.8, 8.3 or 16.7 mM glucose with or without 20 nM GLP-1. After incubation for 3 h at 37°C, glycerol released into the media and the islet protein content were determined. Means±SE from 4 independent experiments with pentaplicates.