Reduced Nitric Oxide Concentration in the Renal Cortex of Streptozotocin-Induced Diabetic Rats

Abstract

Nitric oxide (NO) regulates vascular tone and mitochondrial respiration. We investigated the hypothesis that there is reduced NO concentration in the renal cortex of diabetic rats that mediates reduced renal cortical blood perfusion and oxygen tension (PO 2 ). Streptozotocin-induced diabetic and control rats were injected with L-arginine followed by N-nitro-L-arginine-metyl-ester (L-NAME). NO and PO 2 were measured using microsensors, and local blood flow was recorded by laser-Doppler flowmetry. Plasma arginine and asymmetric dimethylarginine (ADMA) were analyzed by high-performance liquid chromatography. L-Arginine increased cortical NO concentrations more in diabetic animals, whereas changes in blood flow were similar. Cortical PO 2 was unaffected by L-arginine in both groups. L-NAME decreased NO in control animals by 87 ؎ 15 nmol/l compared with 45 ؎ 7 nmol/l in diabetic animals. L-NAME decreased blood perfusion more in diabetic animals, but it only affected PO 2 in control animals. Plasma arginine was significantly lower in diabetic animals (79.7 ؎ 6.7 vs. 127.9 ؎ 3.9 mmol/l), whereas ADMA was unchanged. A larger increase in renal cortical NO concentration after L-arginine injection, a smaller decrease in NO after L-NAME, and reduced plasma arginine suggest substrate limitation for NO formation in the renal cortex of diabetic animals. This demonstrates a new mechanism for diabetesinduced alteration in renal oxygen metabolism and local blood flow regulation. Diabetes 54:3282-3287, 2005 N itric oxide (NO) regulates vascular tone in resistance vessels and thereby blood perfusion in most capillary beds. Systemic inhibition of NO synthase (NOS) decreases renal blood perfusion, both in the cortex and in the medulla (1-3), and increases mean arterial blood pressure (4). Previous investigations in vitro have also shown that NO is a potent competitive inhibitor of oxygen consumption (5) at the level of cytochrome oxidase, the terminal electron acceptor in mitochondria (6). Therefore, the magnitude of the inhibition of oxygen consumption by NO will increase at low PO 2 (7).Long-term hyperglycemia is associated with increased oxidative stress, i.e., increased production of reactive oxygen species (ROS) (8 -11). ROS can react with NO, forming peroxynitrite, and thus decrease the bioavailability of NO (11). The bioavailability of NO and formation of peroxynitrite are also highly dependent on superoxide dismutase, as modeled by Buerk et al. (12). Decreased influence of NO has therefore been suggested to be involved in the increased renal cortical cellular oxygen consumption closely associated with manifest diabetes (10,13,14). Furthermore, involvement of endogenous competitive NOS inhibitor asymmetric dimethylarginine (ADMA) in the development of vascular complications has gained increasing support over the last few decades (15).Because NO regulates the delivery of oxygen to tissue both by setting the level of vascular tone and blood pressure and by inhibiting cellular oxygen consumption, alterations in NO activity might ...

Expression of NG,NG-Dimethylarginine Dimethylaminohydrolase and Protein Arginine N-Methyltransferase Isoforms in Diabetic Rat Kidney

“…These studies have confirmed some reports that have shown that plasma ADMA is elevated in insulinopenia or diabetes (19 -23), although we found normal levels in a Wistar-Furth STZ-induced diabetic model (36). They have shown further that the elevated levels can be normalized by 2 weeks of ARB administration.…”

“…As reported in our previous studies in this STZ-induced diabetic rat model at 4 weeks (31,(33)(34)(35)(36)(37)(38), rats with diabetes had a significant decrease in body weight, an increase in blood glucose to ϳ400 mg/dl, an increase in urinary volume, and an increase in creatinine clearance without changes in mean blood pressure measured under anesthesia (Table 1). These parameters were not changed significantly by 2 weeks of telmisartan administration in both control or diabetic rats (Table 1).…”

“…After 3 days, the induction of diabetes was confirmed by urinary glucose excretion. As in our prior studies (31,(33)(34)(35)(36)(37)(38) no attempt was made to treat the diabetes with insulin, since we wished to study the pathophysiology of insulinopenic diabetes.…”

“…After 2 weeks of treatment and 4 weeks of diabetes, 24-h urine and blood were collected and rats were killed. Rats were allowed free access to food to permit ongoing hyperglycemia and hyperfiltration (31,(33)(34)(35)(36)(37)(38). The animals were anesthetized with pentobarbital (50 mg/kg body wt), the abdominal aorta was cannulated, blood pressure was measured with a pressure transducer, and the kidneys were perfused retrogradely with ice-cold PBS.…”

“…Administration of an ACE inhibitor or an Ang II receptor blocker (ARB) to STZ-induced diabetic rats or patients with type 2 diabetes reduces markers of inflammation, oxidative stress, and albuminuria, independent of blood pressure or creatinine clearance (31,32). We used the STZ-induced model of diabetes, which we had characterized (31,(33)(34)(35)(36)(37) to explore the regulation of DDAH and PRMT expression by Ang II type 1 receptors (AT 1 -Rs) in diabetes.…”