Vasa nervorum in rat major pelvic ganglion are innervated by nitrergic nerve fibers.

INTRODUCTION: The vasa nervorum comprises a network of small diameter blood vessels that provide blood supply to nerves and ganglia. The cell bodies of autonomic nerves innervating the urogenital organs are housed in the major pelvic ganglia (MPG) in rats. The vasa nervorum of rat MPG have not been characterized previously, and it is not known whether these blood vessels are innervated by neuronal nitric oxide synthase (nNOS) containing nitrergic nerves. AIM: To characterize the blood vessels in and around the rat MPG and to assess their nitrergic innervation. MAIN OUTCOME MEASURES: Characterization of small blood vessels in and around the rat MPG and expression of nNOS in nerve fibers around those blood vessels. METHODS: MPG were obtained from healthy Sprague Dawley rats, fixed in paraformaldehyde, frozen and sectioned using a cryostat. The blood vessels and their nitrergic innervation were assessed with immunohistochemistry using antibodies against alpha-smooth muscle actin (smooth muscle marker), CD31 (endothelial marker), collagen IV (basal membrane marker) and nNOS. The immunofluorescence was imaged using a laser scanning confocal microscope. RESULTS: The neuronal cell bodies were contained within a capsule in the MPG. Blood vessels were observed within the capsule of the MPG as well as outside the capsule. The blood vessels inside the capsule were CD31-positive capillaries with no smooth muscle staining. Outside the capsule capillaries, arterioles and venules were observed. The extra-capsular arterioles and venules, but not the capillaries were innervated by nNOS-positive nerve fibers. CONCLUSIONS: This study, to our knowledge, is the first to demonstrate the blood vessel distribution pattern and their nitrergic innervation in the rat MPG. While similar studies in human pelvic plexus are warranted, these results suggest that the blood flow in the MPG may be regulated by nitrergic nerve fibers and reveal a reciprocal relationship between nerves and blood vessels.

Poly(ADP-ribose) polymerase inhibition reverses nitrergic neurovascular dysfunctions in penile erectile tissue from streptozotocin-diabetic mice.

INTRODUCTION: Activation of the DNA repair enzyme, poly(adenosine diphosphate [ADP]-ribose) polymerase (PARP), in response to hyperglycemia-driven oxidative/nitrosative stress, may be an important mechanism in the development of vascular and neural complications in diabetes mellitus. However, a role for PARP in diabetic erectile dysfunction (ED) has not been demonstrated. AIM: To assess whether treatment with a novel PARP-1 inhibitor, GPI 15427, could improve neurovascular dysfunction in corpus cavernosum (CC) from diabetic mice. METHODS: Diabetes was induced by streptozotocin in male MF1 mice; duration was 6 weeks. Intervention GPI 15427 treatment (20mg/kg/day intraperitoneal [i.p.]) was given for 2 weeks following 4 weeks of untreated diabetes. CC strips were mounted in aerated organ baths for measurement of pharmacological or electrical stimulation-evoked changes in smooth muscle tension. MAIN OUTCOME MEASURES: Contractile responses to noradrenergic stimulation and to pharmacological agents stimulating endothelium-dependent and -independent relaxation, and nerve-mediated relaxations against a background precontraction. RESULTS: Contractions in response to phenylephrine or activation of noradrenergic nerves were not significantly altered by diabetes. In contrast, maximum nitrergic nerve-mediated relaxation of phenylephrine-precontracted CC was approximately 28% reduced by diabetes: GPI 15427 treatment completely corrected this diabetic deficit. Similarly, maximal nitric oxide (NO)-mediated endothelium-dependent and -independent relaxations to acetylcholine and sodium nitroprusside, against phenylephrine precontraction, were attenuated approximately 37% and 23% by diabetes, respectively. These deficits were completely reversed by PARP-1 inhibition. Furthermore, GPI 15427 corrected a modest diabetic deficit in sensitivity to nitroprusside (EC(50) reduced by 0.14 log units); a similar trend was observed for acetylcholine-induced relaxation. CONCLUSIONS: GPI 15427 treatment provides marked benefits for NO-dependent neurovascular function in diabetic mouse CC. Therefore, PARP-1 inhibition may be worthy of further investigation for diabetes-associated ED.

Treatment with the xanthine oxidase inhibitor, allopurinol, improves nerve and vascular function in diabetic rats.

Several putative sources of reactive oxygen species could potentially contribute to diabetic neuropathy and vasculopathy. The aim was to assess the involvement of elevated xanthine oxidase activity. After 6 weeks of streptozotocin-diabetes, groups of rats were given 2 weeks of high-dose allopurinol treatment (50 and 250 mg/kg) to gauge the effect of maximal blockade of xanthine oxidase. In the final experiments, rats were subjected to sensory testing and, under butabarbital anaesthesia, measurements were made on nerve conduction velocities and neural tissue blood flow estimated by hydrogen clearance microelectrode polarography. Further groups were used to study detailed responses of the isolated mesenteric vascular bed after 4 weeks of diabetes and allopurinol (150 mg/kg) treatment. Diabetes caused 20% and 14% reduction in motor and sensory conduction velocity, which were 78% and 81% corrected by allopurinol treatment respectively, both doses giving similar results. Diabetic rats showed tactile allodynia and thermal hyperalgesia, which were completely corrected by allopurinol, whereas mechanical hyperalgesia was only 45% ameliorated. Sciatic nerve and superior cervical ganglion blood flow was halved by diabetes and allopurinol corrected this by approximately 63%. Mesenteric endothelium-dependent vascular responses to acetylcholine, which depend upon nitric oxide and endothelium derived hyperpolarizing factor, were attenuated by diabetes. Allopurinol treatment gave approximately 50% protection for both components. Thus, xanthine oxidase is an important source of reactive oxygen species that contributes to neurovascular dysfunction in experimental diabetes. Inhibition of xanthine oxidase could be a potential therapeutic approach to diabetic neuropathy and vasculopathy.

Neutrophils Infiltrate the Spinal Cord Parenchyma of Rats with Experimental Diabetic Neuropathy.

Spinal glial cell activation and cytokine secretion have been implicated in the etiology of neuropathic pain in a number of experimental models, including diabetic neuropathy. In this study, streptozotocin- (STZ-) induced diabetic rats were either untreated or treated with gabapentin (50 mg/kg/day by gavage for 2 weeks, from 6 weeks after STZ). At 8 weeks after STZ, hypersensitivity was confirmed in the untreated diabetic rats as a reduced response threshold to touch, whilst mechanical thresholds in gabapentin-treated diabetic rats were no different from controls. Diabetes-associated thermal hypersensitivity was also ameliorated by gabapentin. We performed a cytokine profiling array in lumbar spinal cord samples from control and diabetic rats. This revealed an increase in L-selectin, an adhesion molecule important for neutrophil transmigration, in the spinal cord of diabetic rats but not diabetic rats treated with gabapentin. Furthermore, we found an increase in the number of neutrophils present in the parenchyma of the spinal cord, which was again ameliorated in gabapentin-treated diabetic rats. Therefore, we suggest that dysregulated spinal L-selectin and neutrophil infiltration into the spinal cord could contribute to the pathogenesis of painful diabetic neuropathy.

The calpain inhibitor, A-705253, corrects penile nitrergic nerve dysfunction in diabetic mice.

Calpains, a superfamily of Ca(2+)-activated proteases, are associated with an array of physiological and pathological events, including susceptibility to diabetes. Recently, increased calpain activity has been linked to reduced endothelium-derived nitric oxide-mediated vasodilatation in diabetes. However, a similar mechanism for neuronal-derived nitric oxide has not been examined. Thus, the aim was to investigate effects of the calpain inhibitor A-705253, N-(1-benzyl-2-carbamoyl-2-oxoethyl)-2-[E-2-(4-diethyl-aminomethylphenyl)ethen-1-yl]benzamide, on nitrergic neurovascular function in diabetic mice. Diabetes was induced by streptozotocin; duration was 6 weeks. Intervention A-705253 treatment (30 mg/kg/day) was given for 2 weeks following 4 weeks of untreated diabetes. After 6 weeks of diabetes, corpus cavernosa were isolated in organ baths for measurement of agonist- and electrical stimulation-evoked smooth muscle tensions. Adrenergic nerve- and phenylephrine-mediated contractions were not altered by diabetes or calpain inhibition. In contrast, maximum nitrergic nerve-mediated relaxation of phenylephrine-precontracted cavernosum was approximately 29% reduced by diabetes (P<0.001). This neurological deficit was 66% corrected by A-705253 treatment (P<0.05). Maximum nitric oxide-mediated endothelium-dependent relaxation to acetylcholine was attenuated approximately 39% by diabetes (P<0.01). Similarly, maximum endothelium-independent relaxation to the nitric oxide donor, sodium nitroprusside, was blunted approximately 23% by diabetes (P<0.001). A-705253 treatment partially improved endothelium-dependent relaxation to acetylcholine but had no effect on the deficit in response to nitroprusside. The data suggest that calpain contributes to the aetiology of diabetic nitrergic autonomic neuropathy and endothelial dysfunction, which may provide a novel therapeutic target for neurovascular complications.

Alteration of aortic function from streptozotocin-diabetic rats with Kilham's virus is associated with inducible nitric oxide synthase.

Kilham's rat virus (KRV) is a parvovirus commonly known to affect laboratory rats. Qualitative immunohistochemical analysis revealed that aorta isolated from KRV-infected streptozotocin (STZ)-induced diabetic adult rats expressed markedly greater levels of inducible nitric oxide synthase (iNOS) than aorta from KRV-infected controls. In contrast with the prevailing literature, nitric oxide-mediated endothelium-dependent relaxation to acetylcholine was not blunted by STZ-diabetes, but was comparable to relaxations of aorta from controls. However, with increasing ex vivo duration, a decreased response to acetylcholine was observed in the STZ-diabetic aorta. In addition, whereas contraction responses to phenylephrine were not significantly altered over time in control tissue, aorta from STZ-diabetic rats developed increased tensions. The data suggest that increased iNOS-derived nitric oxide masks expected acetylcholine-mediated relaxation deficits as a result of KRV-infection, and that the deficit is unmasked by iNOS turnover ex vivo.

Effects of rosuvastatin on nitric oxide-dependent function in aorta and corpus cavernosum of diabetic mice: relationship to cholesterol biosynthesis pathway inhibition and lipid lowering.

Elevated plasma lipids contribute to neurovascular dysfunction in diabetes. Statins have lipid-lowering properties and can modulate endothelial nitric oxide (NO) bioavailability. The aim was to assess the impact of these factors on autonomic nitrergic nerve and endothelial function. Thus, the effects of diabetes and treatment with the HMG-CoA reductase inhibitor rosuvastatin (RSV) were examined on corpus cavernosum and aorta from streptozotocin-induced diabetic mice in a 4-week prevention study and a 2-week intervention study, following 4 weeks of untreated diabetes. Cotreatment with mevalonate was used to assess the dependence of RSV's effects on HMG-CoA reductase blockade. Diabetes caused a 25% reduction in NO-mediated endothelium-dependent relaxation to acetylcholine for aorta and cavernosum. Relaxations of cavernosum were in the nondiabetic range following prevention or reversal treatment. The aortic deficit was completely prevented and 60% reversed by RSV. Maximum NO-dependent nonadrenergic, noncholinergic nerve-mediated relaxations of cavernosum were reduced 25-33% by diabetes. RSV treatment prevented 75% and reversed 71% of this diabetic deficit. Cotreatment with mevalonate inhibited the beneficial actions of RSV on aorta and cavernosum. Total plasma cholesterol was unaltered by diabetes or treatment. Thus, RSV corrected defective NO-mediated nerve and vascular function in diabetic mice independent of cholesterol lowering but via effects dependent on cholesterol biosynthesis pathway inhibition.

Effects of proinsulin C-peptide in experimental diabetic neuropathy: vascular actions and modulation by nitric oxide synthase inhibition.

Proinsulin C-peptide treatment can partially prevent nerve dysfunction in type 1 diabetic rats and patients. This could be due to a direct action on nerve fibers or via vascular mechanisms as C-peptide stimulates the nitric oxide (NO) system and NO-mediated vasodilation could potentially account for any beneficial C-peptide effects. To assess this further, we examined neurovascular function in streptozotocin-induced diabetic rats. After 6 weeks of diabetes, rats were treated for 2 weeks with C-peptide to restore circulating levels to those of nondiabetic controls. Additional diabetic groups were given C-peptide with NO synthase inhibitor N(G)-nitro-L-arginine (L-NNA) co-treatment or scrambled C-peptide. Diabetes caused 20 and 16% reductions in sciatic motor and saphenous sensory nerve conduction velocity, which were 62 and 78% corrected, respectively, by C-peptide. L-NNA abolished C-peptide effects on nerve conduction. Sciatic blood flow and vascular conductance were 52 and 41%, respectively, reduced by diabetes (P < 0.001). C-peptide partially (57-66%) corrected these defects, an effect markedly attenuated by L-NNA co-treatment. Scrambled C-peptide was without effect on nerve conduction or perfusion. Thus, C-peptide replacement improves nerve function in experimental diabetes, and the data are compatible with the notion that this is mediated by a NO-sensitive vascular mechanism.

Inhibitors of advanced glycation end product formation and neurovascular dysfunction in experimental diabetes.

Advanced glycation and lipoxidation end products (AGEs/ALEs) have been implicated in the pathogenesis of the major microvascular complications of diabetes mellitus: nephropathy, neuropathy, and retinopathy. This article reviews the evidence regarding the peripheral nerve and its vascular supply. Most investigations done to assess the role of AGEs/ALEs in animal models of diabetic neuropathy have used aminoguanidine as a prototypic inhibitor. Preventive or intervention experiments have shown treatment benefits for motor and sensory nerve conduction velocity, autonomic nitrergic neurotransmission, nerve morphometry, and nerve blood flow. The latter depends on improvements in nitric oxide-mediated endothelium-dependent vasodilation and is responsible for conduction velocity improvements. A mechanistic interpretation of aminoguanidine's action in terms of AGE/ALE inhibition is made problematic by the relative lack of specificity. However, other unrelated compounds, such as pyridoxamine and pyridoxamine analogues, have recently been shown to have beneficial effects similar to aminoguanidine, as well as to improve pain-related measures of thermal hyperalgesia and tactile allodynia. These data also stress the importance of redox metal ion-catalyzed AGE/ALE formation. A further approach is to decrease substrate availability by reducing the elevated levels of hexose and triose phosphates found in diabetes. Benfotiamine is a transketolase activator that directs these substrates to the pentose phosphate pathway, thus reducing tissue AGEs. A similar spectrum of improvements in nerve and vascular function were noted when using benfotiamine in diabetic rats. Taken together, the data provide strong support for an important role for AGEs/ALEs in the etiology of diabetic neuropathy.

Effects of alpha-lipoic acid on impaired gastric fundus innervation in diabetic rats.

Diabetes mellitus is a major cause of neuropathy, leading to adverse effects including autonomic gastrointestinal dysfunction. Oxidative stress contributes to the etiology of diabetic neuropathy. The aim was to examine whether treatment with the antioxidant, alpha-lipoic acid (LA), could prevent or correct diabetic functional defects in the gastric fundus non-adrenergic, non-cholinergic (NANC) nerves, which use nitric oxide as their major neurotransmitter. LA (100 mg/kg/d) was given in a prevention study for 8 weeks following streptozotocin-diabetes induction, and in an intervention study for 4 weeks after 4 weeks of untreated diabetes. Fundus strips were studied in vitro after precontraction with 5-hydroxytryptamine in the presence of guanethidine and atropine to isolate NANC relaxation to electrical field stimulation. After 4 and 8 weeks of diabetes, there were 26% and 48% deficits in maximum relaxation, respectively. Prevention LA treatment gave 83% protection; intervention LA prevented the deterioration between 4 and 8 weeks of diabetes and corrected the initial 4 week deficit by 56%. Diabetes also resulted in a failure to maintain relaxation for prolonged stimulation, which was prevented by LA. Thus, LA prevented and reversed the development of impaired gastric fundus NANC responses in diabetic rats, which has potential therapeutic implications for gastrointestinal autonomic neuropathy.

The effect of cannabinoids on capsaicin-evoked calcitonin gene-related peptide (CGRP) release from the isolated paw skin of diabetic and non-diabetic rats.

Sensory neural dysfunction is common in patients with peripheral neuropathy, a major complication of diabetes mellitus. In animal models of inflammatory and neuropathic pain cannabinoids potently attenuate pain behaviour, cannabinoid (CB) receptors located on nociceptive primary afferent neurones being important in their anti-hyperalgesic actions. A key measure of sensory neurone function is stimulus-evoked neuropeptide release. We investigated the effect of cannabinoid on capsaicin-evoked release of calcitonin gene-related peptide (CGRP) from the rat paw skin in vitro, comparing non-diabetic and streptozotocin-induced diabetic animals. Diabetes caused a greater than two-fold increase in basal and capsaicin-evoked CGRP release. The synthetic CB(1)/CB(2) receptor agonist, CP55940 (100 nM), inhibited capsaicin-evoked CGRP release in both non-diabetic (30.92+/-7.69%, P<0.05) and diabetic animals (37.82+/-9.85%, P<0.05). The CB(1) receptor antagonist SR141716A (100 nM), but not the CB(2) receptor antagonist SR144528 (100 nM), significantly attenuated the inhibitory action of CP55940. The endogenous cannabinoid, anandamide (100 nM) inhibited capsaicin-evoked CGRP release in non-diabetic animals (28.88+/-7.12%, P<0.05) but neither the CB(1) nor the CB(2) receptor antagonist attenuated this action of anandamide. Anandamide (100 nM) did not significantly inhibit capsaicin-evoked CGRP release from the paw skin of diabetic animals, but it did produce a small stimulation of CGRP release at high concentrations (10 microM). These data suggest that peripheral CB(1) receptors mediate inhibition of capsaicin-evoked neuropeptide release from the paw skin of both non-diabetic and diabetic animals. However, pathological changes in the diabetic animals appear to preclude the non-CB(1) receptor mediated inhibitory action of the endogenous cannabinoid, anandamide.

Angiotensin converting enzyme inhibition partially prevents deficits in water maze performance, hippocampal synaptic plasticity and cerebral blood flow in streptozotocin-diabetic rats.

Vascular dysfunction is important in the pathogenesis of peripheral complications of diabetes. However, the effects of diabetes on cerebral blood flow and the role of vascular deficits in the pathogenesis of diabetic encephalopathy are still unknown. The present study examined whether experimental diabetes is associated with reduced cerebral blood flow and whether treatment with enalapril can improve cerebral perfusion and function (blood flow and functional cerebral deficits). Streptozotocin-diabetic rats were treated with the ACE inhibitor enalapril (24 mg/kg) from onset of diabetes. After 14 weeks of diabetes, 12 enalapril treated and 12 untreated diabetic rats, and 12 nondiabetic age-matched control rats were tested in a spatial version of the Morris water maze. After 16 weeks of diabetes, in the same groups, blood flow in the hippocampus and thalamus was measured by hydrogen clearance microelectrode polarography. In a separate study, hippocampal long-term potentiation was measured after 26 weeks of diabetes. Water maze performance and hippocampal long-term potentiation were impaired in diabetic rats. Furthermore, blood flow in diabetic rats was reduced by 30% (P<0.001) in the hippocampus and by 37% (P<0.005) in the thalamus compared to nondiabetic controls. Enalapril treatment significantly improved water maze performance (P<0.05), hippocampal long term potentiation (P<0.05) and hippocampal blood flow (P<0.05). Cerebral perfusion is reduced in diabetic rats compared to controls. Treatment aimed at the vasculature can improve cerebral blood flow, deficits in Morris maze performance and long term potentiation. These findings suggest that vasculopathy plays a role in the development of cerebral dysfunction in diabetic rats.

Effects of the peroxynitrite decomposition catalyst, FeTMPyP, on function of corpus cavernosum from diabetic mice.

Peroxynitrite, the reaction product of nitric oxide and superoxide, may contribute to vascular tissue oxidant stress in diabetes mellitus. The aim was to establish whether the peroxynitrite decomposition catalyst 5,10,15,20-tetrakis(N-methyl-4'-pyridyl)porphyrinato iron III (FeTMPyP) could improve nitric oxide-dependent autonomic nerve and microvascular penile function in the diabetic mouse. Diabetes was induced by streptozotocin; duration was 6 weeks. Intervention FeTMPyP treatment (25 mg kg(-1) day(-1)) was given for 2 weeks following 4 weeks untreated diabetes. Corpus cavernosum were isolated in organ baths for measurement of agonist or electrical stimulation-evoked nerve-mediated tension responses. Maximum nitrergic nerve-mediated relaxation of phenylephrine-precontracted cavernosum was approximately 35% reduced by diabetes; FeTMPyP treatment reversed this deficit by 45%. The concentration response-curve for nitric oxide-mediated endothelium-dependent relaxation to acetylcholine was attenuated by diabetes; FeTMPyP restored the deficit to the nondiabetic range. Sensitivity (EC50) to the nitric oxide donor, sodium nitroprusside, was reduced by approximately 0.56 log10 M units in diabetes; however, FeTMPyP treatment failed to significantly reverse this deficit. Therefore, the peroxynitrite mechanism contributes to nitric oxide-dependent diabetic autonomic neuropathy and vasculopathy and may be a potential target for clinical trials using peroxynitrite decomposition catalysts.

Protein kinase C beta inhibition and aorta and corpus cavernosum function in streptozotocin-diabetic mice.

Increased activity of the beta-isoform of protein kinase C (PKC) has been linked to the vascular and neural complications of diabetes mellitus. Treatment with the PKCbeta inhibitor, (s)-13-[(dimethylamino)methyl]-10,11,14,15-tetrahydro-4,9:16,21-dimetheno-1H,13H-dibenzo[e,k]pyrrolo[3,4-h][1,4,13]oxadiazacyclohexadecene-1,3(2H)-dione, (LY333531), improves somatic nerve function and blood flow in diabetic rats. The aim was to assess whether LY333531 treatment could prevent nitric oxide-dependent autonomic nerve and vascular dysfunction in a diabetic mouse model. Diabetes was induced by streptozotocin; duration was 4 weeks. Aorta and corpus cavernosum were isolated and mounted in organ baths and agonist or electrical stimulation-evoked nerve-mediated tension responses were examined. Maximum nitric oxide-mediated endothelium-dependent relaxation of phenylephrine-precontracted aorta and cavernosum to acetylcholine were more than 30% reduced by diabetes. LY333531 treatment (10 mg kg(-1) day(-1)) completely prevented the diabetic deficit in cavernosum, and 75% prevented the deficit in aorta. Maximum nitric oxide-dependent non-adrenergic, non-cholinergic (NANC) nerve-mediated relaxation of phenylephrine-precontracted cavernosum was approximately 43% reduced by diabetes; LY333531 attenuated the deficit by 44%. For diabetic aorta, but not cavernosum, sensitivity (EC50) to phenylephrine-mediated contraction was increased by approximately 0.85 log10 M units; LY333531 treatment completely prevented this effect. Thus, PKCbeta activation contributes to nitric oxide-dependent vascular and autonomic nerve dysfunction in diabetic mice and could prove suitable for further study in clinical trials of diabetic autonomic neuropathy and vasculopathy.

Effects of trientine, a metal chelator, on defective endothelium-dependent relaxation in the mesenteric vasculature of diabetic rats.

Diabetes mellitus compromises endothelium-dependent relaxation of blood vessels. This has been linked to the generation of reactive oxygen species (ROS), which neutralise nitric oxide (NO) and interfere with vasodilator function. Experiments using chelators have emphasised the importance of ROS produced by transition metal catalysed reactions. However, particularly for the small arteries and arterioles that control microcirculatory blood flow, NO is not the only endothelium-derived mediator; endothelium-derived hyperpolarizing factor (EDHF) has a major role. EDHF-mediated vasodilation is severely curtailed by diabetes; however, little information exists on the underlying pathophysiology. Deficits in the EDHF system, alone or in combination with the NO system, are crucial for the development of diabetic microvascular complications. To further elucidate the mechanisms involved, the aim was to examine the effects of diabetes and preventive and intervention chelator therapy with trientine on a preparation that has well-defined NO and EDHF-mediated responses, the rat mesenteric vascular bed. In phenylephrine-preconstricted preparations, maximum vasodilation to acetylcholine was reduced by 35 and 44% after 4 and 8 weeks of streptozotocin-induced diabetes, respectively. Trientine treatment over the first 4 weeks gave 72% protection; intervention therapy over the final 4 weeks prevented deterioration and corrected the initial deficit by 68%. These responses depend on both NO and EDHF. When the latter mechanism was isolated by NO synthase inhibition, diabetic deficits of 53.4 (4 weeks) and 65.4% (8 weeks) were revealed, that were 65% prevented and 50% corrected by trientine treatment. Neither diabetes nor trientine altered vascular smooth muscle responses to the NO donor, sodium nitroprusside (SNP). Thus, the data suggest that metal catalysed ROS production makes a substantial contribution to defects in both the EDHF and NO endothelial mechanisms in diabetes, which has therapeutic implications for microvascular complications.

The effects of 5-hydroxytryptamine 5-HT2 receptor antagonists on nerve conduction velocity and endoneurial perfusion in diabetic rats.

Reduced peripheral nerve perfusion participates in the aetiology of diabetic neuropathy. 5-Hydroxtryptamine causes vasa nervorum vasoconstriction and platelet aggregation, which are enhanced by diabetes. To assess whether these mechanisms could contribute to neuropathy, the effects of 5-hydroxytryptamine 5-HT2 receptor antagonist treatment were examined in streptozotocin-induced diabetic rats. One study determined the dose-response relationship for AT1015 (N-[2-[4-(5H-dibenzo[a,d]cyclohepten-5-ylidene)piperidino]ethyl]-1-formyl-4-piperidinecarboxamide monohydrochloride monohydrate). Two weeks AT1015 treatment after 6 weeks of diabetes dose-dependently corrected 19.7%, 54.1%, and 15.7% deficits in sciatic nerve motor conduction velocity and blood flow, and saphenous nerve sensory conduction: ED50 values were 0.52, 0.74 and 0.15 mg/kg(-1)/day(-1), respectively. In a second study, high-dose AT1015 (3 mg/kg(-1)/day(-1)) actions were compared with those of the 5HT2 receptor antagonists, ritanserin (10 mg/kg(-1)/day(-1)) and sarpogrelate (100 mg/kg(-1)/day(-1)), and the anti-platelet phosphodiesterase III inhibitor, cilostazol (100 mg/kg(-1)/day(-1)). Two weeks treatment with these drugs produced a marked correction (82.6-99.7%) of a 19.8% sciatic motor conduction deficit in diabetic rats. Similarly, 44.7% and 14.9% reductions in sciatic endoneurial blood flow and saphenous sensory conduction velocity were completely reversed. Thus, 5-HT2 receptor antagonists had marked beneficial effects in experimental diabetic neuropathy, and AT1015 appears suitable for further evaluation in clinical trials.

Effects of diabetes and evening primrose oil treatment on responses of aorta, corpus cavernosum and mesenteric vasculature in rats.

Diabetes causes endothelial dysfunction, with deleterious effects on nitric oxide (NO) mediated vasodilatation. However, in many vessels other local vasodilators such as endothelium-derived hyperpolarizing factor (EDHF), prostacyclin, epoxides or endocannabinoids are also important. Several of these factors may be derived from omega-6 essential fatty acids via arachidonate metabolism. Diabetes inhibits this pathway, a defect that may be bypassed by diets enriched with omega-6 gamma-linolenic acid-containing oils such as evening primrose oil (EPO). The aim was to examine the effects of preventive EPO treatment on endothelium-dependent and neurally mediated vasorelaxation. Diabetes was induced by streptozotocin in rats; duration was 8 weeks. Vascular responses were examined in vitro on thoracic aorta, corpus cavernosum and perfused mesenteric bed preparations. Diabetes caused 25% and 35% deficits, respectively, in aorta and corpus cavernosum NO-mediated endothelium-dependent relaxation to acetylcholine that were largely unaffected by EPO treatment. Moreover, a 44% reduction in maximum corpus cavernosum vasorelaxation to nitrergic nerve stimulation was not prevented by EPO. However, for the mesenteric vascular bed, a 29% diminution of responses to acetylcholine, mediated by both NO and EDHF, was 84% attenuated by EPO treatment. When the EDHF component was isolated during NO synthase inhibition, a 76% diabetic deficit was noted. This was completely prevented by EPO treatment, which also caused supernormal EDHF responses in nondiabetic rats. EPO treatment prevented the development of deficits in endothelium-dependent relaxation in diabetic rats. Effects were particularly marked on the resistance vessel EDHF system, which may have potential therapeutic relevance for diabetic microvascular complications.

Microvascular dysfunction and efficacy of PDE5 inhibitors in BPH-LUTS.

Benign prostatic hyperplasia (BPH)-related lower urinary tract symptoms (LUTS) and erectile dysfunction commonly coexist, and both respond to phosphodiesterase (PDE) 5 inhibitors, suggesting a shared pathophysiological mechanism. We propose that both BPH-LUTS and erectile dysfunction are caused by microvascular dysfunction within the pelvic organs, and we present an overview of preclinical and clinical studies supporting the hypothesis that, within both the penis and the lower urinary tract, a combination of endothelial and neural dysfunction leads to a vicious cycle of hypoxia, vasoconstriction, altered smooth muscle contractility, and degeneration of autonomic neurons and ganglia. This hypothesis explains much of the preclinical and clinical research relating to these two conditions, and provides a rationale for further investigation into the effects of PDE5 inhibitors on the pathophysiology and symptoms of BPH-LUTS.