To explore whether antioxidant treatment by TEMPOL reverses pseudohypoxia-induced lactate production¹ in early DN in a rat model of insulinopenic diabetes mellitus.Twenty-four ten-week old female Wistar rats were included in this study. The rats were randomly grouped in a diabetic group of 10 untreated animals and a diabetic treated group of 8 animals receiving TEMPOL treatment in the drinking water for 3 weeks and a healthy control group consisting of 6 animals that not receive TEMPOL. Diabetes was induced by an intravenous injection of freshly prepared streptozotocin (STZ; 55 mg/kg body weight; Sigma-Aldrich, St. Louis, USA) dissolved in 10 mmol/L cold citrate buffer (pH 4.5). Blood glucose was measured in tail-capillary blood with a Contour blood glucose meter (Bayer Diabetes Care, Copenhagen, Denmark). Rats were considered diabetic if the blood glucose levels exceeded 15 mmol/L 48 h after administration of STZ. Up to three consecutive examinations was performed 2, 3 and 4 weeks after the induction of diabetes. The rats were anesthetized and hyperpolarized [1-13C]pyruvate polarized in a SpinLab (GE Healthcare) was injected via a catheter in the tail vein. Temperature, arterial oxygen saturation and respiration rate were monitored throughout the experiment. Each examination consisted of one injection of 1.5 mL hyperpolarized [1-13C]pyruvate over 10 s. The experiments were performed in a 3 T clinical MR system (GE Healthcare) equipped with a dual tuned 13C/1H volume rat coil. A slice-selective 13C IDEAL spiral sequence was used for hyperpolarized [1-13C]pyruvate imaging acquiring images every 5 s initiated 20 s after the start of injection. (Scanning) protocol was as follows: Flip angle=10º, 11 IDEAL echoes and one initial spectrum per IDEAL encoding, TR/TE/ΔTE=100 ms/0.9 ms/0.9 ms, FOV=80x80 mm2, 5 x 5 mm real resolution and an axial slice thickness of 15 mm covering both kidneys.All rats receiving STZ developed sustained hyperglycaemia within 48 h. No significant changes were observed in body weight gain over the period and no differences were found in body temperature, arterial oxygen saturation and respiration rate between among the three groups. As previously reported, untreated diabetic rats had increased renal lactate production. However, chronic antioxidant treatment with TEMPOL significantly attenuated the diabetes-induced lactate production (p=0.03 versus untreated diabetics) although still being elevated compared to normoglycemic controls (p=0.04, Figure 1A). No significance effects of diabetes or TEMPOL treatment were observed on alanine or bicarbonate productions (Figure 1B-C).This study demonstrates that the diabetes-induced elevation of the lactate-to-pyruvate ratio can be attenuated by antioxidant treatment, which demonstrates a pivotal role of oxidative stress for the renal metabolic alterations occurring in early diabetes.The clinical impact of reversal of the pseudo-hypoxic condition, is currently unknown, thus further studies are needed to elucidate the importance of reversing the pseudo-hypoxic condition.