Glucose bolus

OGTTs were performed in overnight-fasted rats (16 h in Sprague–Dawley studies and 11 h in ZDF studies). A glucose bolus (1 g/kg for ZDF rats and 2 g/kg for Sprague–Dawley rats) (Sigma-Aldrich, Copenhagen, Denmark) was administered via p.o. gavage at time 0. EDTA blood samples were collected from the tail vein before the glucose challenge (0 min) and then 15, 30, 60, and 120 min post glucose challenge, before being used for insulin measurement. Blood glucose was monitored at time points 0, 15, 30, 60, 120, and 180 min post glucose challenge. S.c. dosing was performed 24 h before all OGTTs. Rats equipped with an infusion pump received continuous dosing throughout the OGTT.

All the blood glucose and lactate measurements were carried out with a StatStrip Xpress (nova biomedical) glucose and lactate meters. Blood was sampled from the tail vein. For glucose tolerance test (GTT), mice were placed in clean cages and fasted for 14–15 hr (overnight) with free access to water. Baseline glucose level (0 time point) was measured and then a glucose bolus (Sigma-Aldrich) of 2 g/kg in PBS was intraperitoneally injected. Glucose was monitored after 15, 30, 60, 90, 120 and 150 min. For insulin tolerance test, mice were fasted for 4 hr and baseline glucose was measured (0 time point). Next, insulin (Roche, Penzberg, Germany) was intraperitoneally injected (0.75 U/kg) and blood glucose content recorded after 15, 30, 60, 90 and 120 min. For lactate tolerance test, mice were injected with a bolus of 2 g/kg of sodium lactate (Sigma-Aldrich) in PBS and blood lactate measured after 15, 30, 60, 90 and 120 min.