Effect Of Aldose Reductase Inhibitor Research Articles

Aldose reductase inhibitors for the treatment of diabetic polyneuropathy

Polyneuropathy, a common complication of diabetes mellitus, causes pain and sensory and motor deficits in the limbs, and is also an important independent predictor of foot ulceration. Inhibiting the metabolism of glucose by the polyol pathway using aldose reductase inhibitors is a potential mechanism to slow or reverse the neuropathy's progression. To assess the effects of aldose reductase inhibitors on the progression of symptoms, signs or functional disability in diabetic polyneuropathy. We searched the Cochrane Neuromuscular Disease Group Trials Register, MEDLINE (from January 1966 to May 2007), EMBASE (from January 1980 to May 2007) and LILACS (from 1982 to May 2007). We reviewed bibliographies of randomized trials identified, and contacted authors and experts in the field. We included randomized controlled trials comparing an aldose reductase inhibitor with control, and lasting at least six months. The primary outcome measure was change in neurological function, measured in various ways, including strength testing, sensory examination, and composite scores of neurological examination. Secondary outcome measures were nerve conduction studies, neuropathic symptoms, quality of life, occurrence of foot ulcers and adverse effects. Trials included in the review were selected and assessed independently by at least two of us. Methodological criteria and study results were recorded on data extraction forms. Thirty-two randomized controlled trials meeting the inclusion criteria were identified. Many had significant methodological flaws. Change in neurological function, our primary outcome measure, was assessed in 29 trials, but sufficient data for meta-analysis were only available in 13 studies, involving 879 treated participants and 909 controls. There was no overall significant difference between the treated and control groups (SMD -0.25, 95% CI -0.56 to 0.05), although one subgroup analysis (four trials using tolrestat) favored treatment. A benefit for neuropathic symptoms was suggested by a group of trials using a dichotomized endpoint (improvement or not), but this was contradicted by another group of trials which measured symptoms on a continuous scale. There was no overall benefit on nerve conduction parameters (27 studies) or foot ulceration (one study). Quality of life was not assessed in any of the studies. While most adverse events were infrequent and minor, three compounds had dose limiting adverse events that lead to their withdrawal from human use: severe hypersensitivity reactions with sorbinil, elevation of creatinine with zenarestat, and alteration of liver function with tolrestat. We found no statistically significant difference between aldose reductase inhibitors and placebo in the treatment of diabetic polyneuropathy. Any future clinical trials of aldose reductase inhibitors should be restricted to compounds proven to have substantial biological or preclinical advantages over previously tested agents.

Latent addition in human diabetic neuropathy: The effects of aldose reductase inhibition on nodal Na + currents

Latent addition in human diabetic neuropathy: The effects of aldose reductase inhibition on nodal Na + currents

Effect of Aldose Reductase Inhibition on Calcium homeostasis in adult rat ventricular myocytes subjected to stimulated ischemia

Cardiovascular disease represents the major cause of morbidity and mortality in patients with diabetes mellitus. Recently, it has been found that aldose reductase (AR), a key enzyme in the pathogenesis of diabetic complications, is involved in myocardial infarction. The mechanism is assumed to be due to the depletion of ATP level by increasing the cytosolic NADH/NAD+ ratio. Previous studies showed that the activity of cardiac RyR decreased in the presence of NADH and increased with NAD+. We hypothesized that the I/R-induced increase in NADH/NAD+ by the activation of polyol pathway impaired the Ca2+ handling at multiple sites. To test the hypothesis, we therefore determine how the ryanodine receptor (RyR) and sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) handled Ca2+ in rat ventricular myocytes followed by either inhibiting AR or sorbitol dehydrogenase (SDH) with 5uM zopolrestat (CP-83,750) or SDH inhibitor (CP-470,711), and subsequently subjected to stimulated ischemia. We determine the following: Ca2+ transient induced by the electrical stimulation, which provided the overall picture for Ca2+ homeostasis; expression of RyR and SERCA by Western blot analysis in rat ventricular myocytes. We found that inhibition of AR or SDH attenuated the I/R-induced decrease in the activity of RyR and SERCA, but the expression of RyR and SERCA remained unchanged. The results are evidence that AR may contribute to the severity of I/R injury of the rat hearts by impairing Ca2+ homeostasis at multiple sites (RyR and SERCA).

Erythrocyte sorbitol level as a predictor of the efficacy of epalrestat treatment for diabetic peripheral polyneuropathy

The relationship between the effect of aldose reductase inhibitors (ARIs) on the activation of the polyol pathway and on diabetic neuropathy has not been fully established. To address this issue, we investigated the effect of epalrestat (150 mg/day), an ARI, on erythrocyte sorbitol levels as an index of polyol activation and on nerve function test results in 43 patients with diabetic peripheral polyneuropathy. After 6 months of epalrestat administration, erythrocyte sorbitol levels did not decrease in patients as a whole. However, a decrease in erythrocyte sorbitol levels during epalrestat administration was significantly correlated with baseline erythrocyte sorbitol levels ( ρ=−.47, P<.01): The higher the level at baseline, the greater the decrease after epalrestat treatment. Moreover, the mean sorbitol level during epalrestat treatment was associated with the beneficial effect of epalrestat on vibration sensitivity as measured with a C-128 tuning fork ( ρ=−.66, P<.01) and/or a pallesthesiometer TM-31A ( ρ=.53, P<.05). On the other hand, erythrocyte sorbitol levels did not reflect the prognosis of nerve conduction velocity. These findings at least partly suggest a causal relationship between polyol activation and the development of diabetic neuropathy. Aldose reductase inhibitor treatment may be clinically useful in the control of polyol activation, especially in patients with excessive accumulation of sorbitol.

Effect of aldose reductase on the abnormality of calcium metabolism in diabetic patients

Bone disease in patients with type 2 diabetes mellitus (DM) is characterized by low bone turnover, resulting from either impaired secretion of parathyroid hormone or osteoblasts dysfunction. We have reported that intracellular sorbitol accumulation via. sorbitol pathway might be involved in the development of osteoblast dysfunction and osteoclast formation, as evidenced by either in vitro or in vivo study. The importance of metabolic pathway is further supported by the protective effect of aldose reductase inhibitor against the development of galactose-induced bone diseases in vivo and of functional impairments of human osteoblasts-like MG-63 cells. In conclusion, sorbotol pathway might be important in the development of low bone turnover disease in DM patients, and thus aldose reductase inhibitor might be clinically useful in the protection against the development of bone diseases in DM patients.

Aldose reductase inhibitory effect by tectorigenin derivatives from Viola hondoensis

Aldose reductase (AR), the key enzyme of the polyol pathway, is known to play important roles in the diabetic complication. The inhibitors of AR, therefore, would be potential agents for the prevention of diabetic complication. The AR inhibition activity of several isoflavonoids was evaluated in vitro against rat lens. Tectoridin-4′- O-β- d-glucoside exhibited strong AR inhibition activity on rat lens with an IC 50 of 0.54 μM. Similar activities were recorded for the natural tectorigenin and tectoridin. In contrast, tectoridin-4′- O-β- d-glucoside showed a stronger inhibitory activity than tectorigenin and tectoridin. Our results indicate that glucose conjugation position in this type of isoflavonoids may be required for the activity.

Phosphorylation of c-Jun N-terminal kinase (JNK) in sensory neurones of diabetic rats, with possible effects on nerve conduction and neuropathic pain: prevention with an aldose reductase inhibitor

This study was designed to determine whether diabetes in rats is associated with phosphorylation of c-Jun N-terminal kinase (JNK) and one of its transcription factors, c-Jun, in sensory neurones innervating the lower limb. We also sought to determine which neuronal phenotypes are affected and to examine the effect of aldose reductase inhibition on JNK and c-Jun phosphorylation. Diabetes was induced in rats using streptozotocin. Phosphorylation of JNK and c-Jun in lumbar dorsal root ganglia was determined by binding of phospho-specific antibodies using western blots and immunocytochemistry. Neuronal phenotypes were characterised by binding of N52 (an antibody that recognises the heavy neurofilament protein; for large-diameter mechanoceptors) and of calcitonin gene-related peptide and the plant glycoprotein lectin IB4 (for nociceptors). The efficacy of the aldose reductase inhibitor fidarestat was determined by measuring polyol pathway metabolites in sciatic nerve, and functionally by measuring the conduction velocity of motor and sensory nerves. In control rats, activated JNK and c-Jun were primarily associated with mechanoceptors; in diabetes this was increased, but a greater increase was seen in nociceptors. Phosphorylation was prevented in all cells by fidarestat, which normalised polyol pathway metabolites as well as motor nerve and sensory nerve conduction velocity. Fidarestat-sensitive phosphorylation of JNK and c-Jun occurs in fast-conduction mechanoceptors-the same class of neurones that registers the changes in sensory nerve conduction velocity-and in nociceptors. This supports the notion that mitogen-activated protein kinase phosphorylation, via the polyol pathway, may convert the direct effects of raised glucose into impaired nerve conduction and neuropathic pain. For proof of this we await the availability of specific JNK antagonists formulated for in vivo use.

Aldose Reductase Inhibition Counteracts Oxidative-Nitrosative Stress and Poly(ADP-Ribose) Polymerase Activation in Tissue Sites for Diabetes Complications

This study evaluated the effects of aldose reductase inhibition on diabetes-induced oxidative-nitrosative stress and poly(ADP-ribose) polymerase (PARP) activation. In animal experiments, control and streptozotocin-induced diabetic rats were treated with or without the aldose reductase inhibitor (ARI) fidarestat (16 mg . kg(-1) . day(-1)) for 6 weeks starting from induction of diabetes. Sorbitol pathway intermediate, but not glucose, accumulation in sciatic nerve and retina was completely prevented in diabetic rats treated with fidarestat. Sciatic motor nerve conduction velocity, hindlimb digital sensory nerve conduction velocity, and sciatic nerve concentrations of two major nonenzymatic antioxidants, glutathione and ascorbate, were reduced in diabetic versus control rats, and these changes were prevented in diabetic rats treated with fidarestat. Fidarestat prevented the diabetes-induced increase in nitrotyrosine (a marker of peroxynitrite-induced injury) and poly(ADP-ribose) immunoreactivities in sciatic nerve and retina. Fidarestat counteracted increased superoxide formation in aorta and epineurial vessels and in in vitro studies using hyperglycemia-exposed endothelial cells, and the DCF test/flow cytometry confirmed the endothelial origin of this phenomenon. Fidarestat did not cause direct inhibition of PARP activity in a cell-free system containing PARP and NAD(+) but did counteract high-glucose-induced PARP activation in Schwann cells. In conclusion, aldose reductase inhibition counteracts diabetes-induced nitrosative stress and PARP activation in sciatic nerve and retina. These findings reveal the new beneficial properties of fidarestat, thus further justifying the ongoing clinical trials of this specific, potent, and low-toxic ARI.

The Inhibitory Effect of Aldose Reductase Inhibitor on Proliferation in the Lens Epithelial Cells of Rat Sugar Cataract

To evaluate the inhibitory effect of aldose reductase inhibitor (ARI) for the accumulation of sugar alcohol and the enhanced proliferation of lens epithelial cells of rats fed a galactose diet. Sprague-Dawley rats were fed a diet containing 50% galactose with or without ARI (SNK-860). Histological changes in the lenses were observed by light microscopy, and the amount of galactitol accumulated in the lens epithelium was measured by liquid-gas chromatography. Immuno-histochemical staining of proliferating cell nuclear antigen (PCNA) in whole-mount preparations was performed to assay the proliferative ability of the lens epithelial cells. The amount of galactitol in the lens epithelium and the number of PCNA positive cells in rats administered ARI were less than in rats fed the galactose diet. Multi-layered epithelium was observed in advanced cataract of rats fed the galactose diet, but not in the rats given ARI. The administration of ARI can prevent cataractous changes and aberrant proliferation of lens epithelial cells.

The effect of aldose reductase inhibitor on heterogeneous MIBG accumulation in diabetes; implication for norepinephrine transporter expression

Cardiac scintigraphic studies using [ 123I]MIBG have demonstrated a heterogeneous myocardial accumulation of radioactivity in diabetes. Recently, we have shown that this accumulation of MIBG was correlated with a heterogeneous decrease in the level of norepinephrine transporter (NET). In diabetes, an aldose reductase (AR) is activated in the peripheral nerve tissue, and the sorbitol that accumulates causes nerve dysfunction and degeneration. Therefore, to assess the influence of AR on the reduction in NET, we investigated changes in the myocardial expression of NET and distribution of [ 12 5I]MIBG in a streptozotocin (STZ)-induced animal model of diabetes, the STZ rats, treated with AR inhibitor (ARI). NET expression levels were investigated and were lower in the inferior wall than anterior wall in STZ rats. On the other hand, there was no significant difference between the anterior and inferior walls in control or ARI rats. Regarding the distribution of [ 125I]MIBG, in STZ rats, there was significantly less uptake in the inferior than anterior wall. Conversely, there was no significant difference between the anterior and inferior walls in ARI and control rats. In conclusion, ARI suppressed the regional reduction of NET expression in diabetic rats, and this suppression prevented the heterogeneous accumulation of MIBG.

Effects of aldose reductase inhibitors and galactose withdrawal on fluorescein angiographic lesions in galactose-fed dogs.

To assess the effect of aldose reductase inhibitor (ARI) M79175 (2-methyl-6-fluoro-spiro-chroman-4-5'-imidazolidine-2',4'-dione) administration and galactose withdrawal on the progression of retinal changes using fluorescein angiography in galactose-fed dogs. Thirty male beagles were randomized into 4 groups. Three dogs were fed a normal control diet containing 30% nonnutritive fiber for 74 months (control group), 11 dogs a 30% galactose diet for 74 months (continuous galactose group), 8 dogs a 30% galactose diet for 36 months followed by replacement with a normal diet for 36 months (galactose withdrawal group), and 8 dogs a 30% galactose diet supplemented with M79175 for 34 months followed by replacement with a normal diet and removal of M79175 treatment for 38 months (ARI-treated galactose withdrawal group). Stereoscopic color fundus photography and fluorescein angiography, performed at baseline and follow-up, were assessed for the clinical development of retinopathy, including the first appearance of hyperfluorescence, varying severity of retinal nonperfusion, and retinal neovascularization. Histopathologic features were examined in selected dogs. All dogs in the 3 groups fed the 30% galactose diet developed areas of hyperfluorescence and nonperfusion. Of these dogs, only those supplemented with the ARI did not develop areas of nonperfusion greater than or equal to half the field and retinal neovascularization. Parametric survival analysis showed significant differences (galactose withdrawal group vs ARI-treated galactose withdrawal group) in the median times to the development of nonperfusion greater than or equal to half the field (P =.003) and retinal neovascularization (P =.03). Normalization of glycemic control with galactose withdrawal and ARI treatment may delay the onset and progression of retinal lesions in galactose-fed dogs. Clinical Relevance Perfect glycemic control after a period of poor control does not completely prevent the progression of retinal lesions. Therapy with ARIs may potentially be important in the prevention of retinal lesions associated with diabetic eye disease.

Lens aldose reductase inhibiting potential of some indigenous plants

Cataract is the leading cause of blindness worldover. Diabetes is one of the major risk factors for cataractogenesis and aldose reductase (AR) has been reported to play an important role in sugar-induced cataract. In the present study, the AR inhibitory activity of Ocimum sanctum (OS), Withania somnifera (WS), Curcuma longa (CL), Azadirachta indica (AI) were studied together with their effect on sugar-induced cataractogenic changes in rat lenses in vitro. Aqueous extracts of the plants, procured from Dabur, India, were reconstituted with double distilled water to make various dilutions. AR inhibitory activity of these extracts and their anticataract potentials were evaluated in vitro in rat lenses. AR inhibitory activity of the aqueous extract of different plants was calculated considering the AR activity of normal rat lenses as 100%. The concentration of the plant extract that showed maximum AR inhibitory activity was selected to further study its effect on galactose-induced lens swelling and polyol accumulation in vitro. All the four plants were found to inhibit lens AR activity but to different extent. From dose–response curve, OS was found to be the most effective AR inhibitor followed by CL, AI and WS. The IC 50 values of OS, CL, AI and WS were calculated to be 20, 55, 57 and 89 μg/ml, respectively. OS showed a significant inhibition (38.05%) in polyol accumulation followed by CL and AI (28.4 and 25.04%, respectively). WS did not show any effect on polyol level in rat lenses. None of the plant extracts showed any significant effect on lens water content. OS possesses a significant anticataract activity in vitro and its anticataract potential could be related with its AR inhibitory effect.

Minalrestat, an Aldose Reductase Inhibitor, Corrects the Impaired Microvascular Reactivity in Diabetes

We demonstrated that aldose reductase inhibition corrects the impaired microvascular responses to inflammatory mediators in diabetic rats. To study the mechanism involved in the restoring effect of aldose reductase inhibition, we examined the effects of minalrestat, another aldose reductase inhibitor, on the responses of mesenteric microvessels studied in vivo to permeability-increasing agents in diabetic and galactosemic rats. The diabetic group was treated from 3 days after the alloxan injection with minalrestat (10 mg/kg/day) for 30 days and the minalrestat treatment (10 mg/kg/day/7 days) of galactosemic rats started concomitantly with the induction of galactosemia. The mesenteric microvessel reactivity was studied using intravital microscopy and changes in vessel diameters were estimated after the topical application of vasoactive agents. The impaired responses to bradykinin, histamine, and platelet-activating factor of arterioles and venules observed in diabetic and galactosemic rats were completely prevented by minalrestat. Neither diabetes nor galactosemia affected responses to acetylcholine and sodium nitroprusside. Responses to these agents were not modified by aldose reductase inhibition. The restoring effect of minalrestat was reversed by inhibition of nitric oxide (NO) synthesis with N(omega)-nitro-L-arginine methyl ester, by blocking K(+) channel with tetraethylammonium but not by cyclooxygenase inhibition with diclofenac. Therefore, we concluded that NO, membrane hyperpolarization, but not cyclooxygenase products are involved in the beneficial effect of minalrestat on the microvascular reactivity in diabetes. Together, these findings led us to suggest that aldose reductase inhibition might ameliorate diabetic complications through the correction of the altered microvascular reactivity by a mechanism that involves NO and membrane hyperpolarization.

How does glucose generate oxidative stress in peripheral nerve?

Diabetes-associated oxidative stress is clearly manifest in peripheral nerve, dorsal root, and sympathetic ganglia of the peripheral nervous system and endothelial cells and is implicated in nerve blood flow and conduction deficits, impaired neurotrophic support, changes in signal transduction and metabolism, and morphological abnormalities characteristic of peripheral diabetic neuropathy (diabetic peripheral neuropathy). Hyperglycemia has a key role in oxidative stress in diabetic nerve, whereas the contribution of other factors, such as endoneurial hypoxia, transition metal imbalance, and hyperlipidemia, has not been rigorously proven. It has been suggested that oxidative stress, particularly mitochondrial superoxide production, is responsible for sorbitol pathway hyperactivity, nonenzymatic glycation/glycooxidation, and activation of protein kinase C. However, this concept is not supported by in vivo studies demonstrating the lack of any inhibition of the sorbitol pathway activity in peripheral nerve, retina, and lens by antioxidants, including potent superoxide scavengers. Its has been also hypothesized that aldose reductase (AR) detoxifies lipid peroxidation products, and therefore, the enzyme inhibition in diabetes is detrimental rather than benefical. However, the role for AR in lipid peroxdation product metabolism has never been demonstrated in vivo, and the effects of aldose reductase inhibitors and antioxidants on diabetic peripheral neuropathy are unidirectional, i.e., both classes of agents prevent and correct functional, metabolic, neurotrophic, and morphological changes in diabetic nerve. Growing evidence indicates that AR has a key role in oxidative stress in the peripheral nerve and contributes to superoxide production by the vascular endothelium. The potential mechanisms of this phenonmenon are discussed.

Neuropathy in diabetic mice overexpressing human aldose reductase and effects of aldose reductase inhibitor.

The present study was designed to examine the effect of aldose reductase (AR) overexpression on the development of diabetic neuropathy by using mice transgenic for human AR. At 8 weeks of age, transgenic mice (Tg) and non-transgenic littermates (Lm) were made diabetic with streptozotocin. After 8 weeks of untreated diabetes, plasma glucose levels and the reduction in body weight were similar between the groups of diabetic animals. Despite the comparable levels of hyperglycaemia, levels of sorbitol and fructose were significantly greater in the peripheral nerve of diabetic Tg than in diabetic Lm (both P < 0.01). Ouabain sensitive Na(+),K(+)-ATPase activity was similarly decreased in both diabetic Tg and Lm. Protein kinase C activity in the sciatic nerve membrane fraction was unaffected by diabetes in Lm, but was reduced by nearly 40% in the diabetic Tg. Although both groups of diabetic animals exhibited a significant decrease in tibial nerve motor nerve conduction velocity (MNCV), this decrease was significantly more severe (P < 0.01) in diabetic Tg than in diabetic Lm. Consistent with these findings, nerve fibre atrophy was significantly more severe in diabetic Tg than in diabetic Lm (P < 0.01). These findings implicate increased polyol pathway activity in the pathogenesis of diabetic neuropathy. In support of this hypothesis, treating diabetic Tg with an aldose reductase inhibitor (WAY121-509, 4 mg/kg/day) for 8 weeks significantly prevented the accumulation of sorbitol, the decrease in MNCV and the increased myelinated fibre atrophy in diabetic Tg.

Effect of Aldose Reductase Inhibition on Interleukin‐1β‐Induced Nitric Oxide (NO) Synthesis in Vascular Tissue

Glucose metabolism via sorbitol pathway has been implicated as a possible contributor to the diabetes-related vascular changes. Nitric oxide plays a major regulatory role in the vascular dilatatory and constricted response. Also it has been observed that diabetes causes vascular changes leading to a decrease in nitric oxide production. Additionally the accumulation of sorbitol is also related to decreased nitric oxide production. In the present study we investigated the effect of normal and high glucose in the presence or absence of both interleukin-1β or an aldose reductase inhibitor on nitric oxide production in rat aortic rings in vitro. Aortic rings from normal male Wistar rats were dissected and incubated for 24 to 48 hrs in the presence of glucose (5.0 mM or 20 mM) or with or without interleukin (20 ng/ml). Other rings were incubated in the above media with the addition of the aldose reductase inhibitor (WAY 121509). Interleukin-1β stimulated the 24 hr nitric oxide production and WAY 121509 decreased it under both low and high glucose culture conditions. The interleukin-1β stimulation was continued for 72 hrs. Nitric oxide production in response to interleukin-1β was greater at all time points when compared to the incubation in media without interleukin-1β. In media containing WAY 121509 the nitric oxide production was decreased. Interleukin-1β stimulated a greater increase in nitric oxide production from aortic rings when incubated in high glucose when compared to normal glucose. The inhibitory effect of aldose reductase inhibition was reversible after 24 hr inhibition under both normal and high glucose conditions. We conclude that high glucose enhances the interleukin- 1β-induced nitric oxide synthesis and the cytokine-induced nitric oxide production was inhibited by aldose reductase inhibition. Nitric oxide production may be linked to redox influences caused by the polyol pathway.

Effect of aldose reductase inhibition on nerve conduction and morphometry in diabetic neuropathy

Effect of aldose reductase inhibition on nerve conduction and morphometry in diabetic neuropathy

The role of aldose reductase inhibitors in diabetic complications: recent trends.

Pharmacological intervention of hyperglycemia-induced diabetic complications would be of great clinical significance since it is very difficult to maintain normoglycemia by any means in patients with diabetes mellitus. Several factors and pathways are involved in diabetic complications. One of the major contributory factors is aldose reductase. The beneficial effects of aldose reductase inhibitors in animal models have been reported. The clinical efficacy of these agents, however, is far from satisfactory and the reasons for this may vary. Recent advances in understanding the structure-based functioning, physiological and pathophysiological role of aldose reductase, the use of transgenic animal models and the abundant availability of human aldose reductase have greatly influenced the design and development of its inhibitors, which are highly selective, specific, potent and less toxic. Concurrently, other mechanisms involved in diabetic complications are being explored as targets for better therapeutic agents.

Effect of aldose reductase inhibition on glucose-induced proliferation of cultured rat aortic smooth muscle cells

Effect of aldose reductase inhibition on glucose-induced proliferation of cultured rat aortic smooth muscle cells

Effects of aldose reductase inhibition on responses of the corpus cavernosum and mesenteric vascular bed of diabetic rats.

We examined the effects of 2 months of streptozotocin-induced diabetes mellitus in rats on relaxation and contraction of corpus cavernosum and the mesenteric vascular bed in vitro. A further diabetic group was treated from diabetes induction with 10 mg/kg/day of the aldose reductase inhibitor, WAY121509. For corpus cavernosum, maximal acetylcholine-induced relaxation was 35.5% reduced (p < 0.001) by diabetes, and this deficit was completely prevented by WAY121509 treatment. Neither diabetes nor treatment affected contractile responses to field stimulation of noradrenergic nerves; however, nonadrenergic noncholinergic nerve relaxation responses were 32.9% decreased by diabetes and WAY 121509 attenuated this by 84% (p < 0.001). For the mesenteric vascular bed, diabetes depressed maximal endothelium-dependent vasodilation to acetylcholine by 25.2% (p < 0.001), and this was partially (50.6%; p < 0.01) prevented by WAY121509. Nitric oxide synthase blockade revealed endothelium-derived hyperpolarising factor-mediated vasodilation to acetylcholine that was 73.5% (p < 0.001) depressed by diabetes; WAY121509 provided partial (43.4%; p < 0.001) protection. Neither diabetes nor treatment affected endothelium-independent vasorelaxation to the nitric oxide donor, sodium nitroprusside, in corpus cavernosum or mesenteric vessels. Thus the data show protective effects of WAY121509 on nitric oxide-mediated cavernosal vasorelaxation responses and on mesenteric endothelium-derived hyperpolarising factor responses. Together these findings could account for the beneficial effects of aldose reductase inhibition on diabetic complications in experimental models.