Exercise training enhances insulin-stimulated nerve arterial vasodilation in rats with insulin-treated experimental diabetes.

Insulin stimulates nerve arterial vasodilation through a nitric oxide (NO) synthase (NOS) mechanism. Experimental diabetes reduces vasa nervorum NO reactivity. Studies investigating hyperglycemia and nerve arterial vasodilation typically omit insulin treatment and use sedentary rats resulting in severe hyperglycemia. We tested the hypotheses that 1) insulin-treated experimental diabetes and inactivity (DS rats) will attenuate insulin-mediated nerve arterial vasodilation, and 2) deficits in vasodilation in DS rats will be overcome by concurrent exercise training (DX rats; 75-85% VO2 max, 1 h/day, 5 days/wk, for 10 wk). The baseline index of vascular conductance values (VCi = nerve blood flow velocity/mean arterial blood pressure) were similar (P ≥ 0.68), but peak VCi and the area under the curve (AUCi) for the VCi during a euglycemic hyperinsulinemic clamp (EHC; 10 mU·kg(-1)·min(-1)) were lower in DS rats versus control sedentary (CS) rats and DX rats (P ≤ 0.01). Motor nerve conduction velocity (MNCV) was lower in DS rats versus CS rats and DX rats (P ≤ 0.01). When compared with DS rats, DX rats expressed greater nerve endothelial NOS (eNOS) protein content (P = 0.04). In a separate analysis, we examined the impact of diabetes in exercise-trained rats alone. When compared with exercise-trained control rats (CX), DX rats had a lower AUCi during the EHC, lower MNCV values, and lower sciatic nerve eNOS protein content (P ≤ 0.03). Therefore, vasa nervorum and motor nerve function are impaired in DS rats. Such deficits in rats with diabetes can be overcome by concurrent exercise training. However, in exercise-trained rats (CX and DX groups), moderate hyperglycemia lowers vasa nervorum and nerve function.

Synergistic vasculogenic effects of AMD3100 and stromal-cell-derived factor-1α in vasa nervorum of the sciatic nerve of mice with diabetic peripheral neuropathy.

Autologous endothelial progenitor cell (EPC) transplantation has been suggested as a potential therapeutic approach in diabetic neuropathy (DN). However, such treatment might be limited by safety concerns regarding possible unwanted proliferation or differentiation of the transplanted stem cells. An alternative approach is the stimulation of endogenous bone-marrow-derived EPC (BM-EPC) recruitment into ischemic lesions by the administration of stem cell mobilization agents or chemokines. We first tested the EPC mobilization effect of vascular endothelial growth factor (VEGF) and AMD3100 in a mouse model of diabetes and found that AMD3100 was effective as an EPC mobilization agent, whereas VEGF did not increase circulating EPCs in these animals. Because recent studies have suggested that deceased local expression of stromal-cell-derived factor (SDF)-1α in diabetes is the main cause of defective EPC migration, AMD3100 was administrated systemically to stimulate EPC mobilization and SDF-1α was injected locally to enhance its migration into the streptozotocin-induced DN mice model. This combined therapy increased local expression levels of vasculogenesis-associated factors and newly formed endothelial cells in the sciatic nerve, resulting in the restoration of the sciatic vasa nervorum. The treatment also improved the impaired conduction velocity of the sciatic nerve in DN mice. Thus, AMD3100 might be an effective EPC mobilization agent in diabetes, with local SDF-1α injection synergistically increasing vascularity in diabetic nerves. This represents a novel potential therapeutic option for DN patients.

Therapeutic angiogenesis inhibits or rescues chemotherapy-induced peripheral neuropathy: taxol- and thalidomide-induced injury of vasa nervorum is ameliorated by VEGF.

Toxic neuropathy represents an important clinical problem in the use of the chemotherapeutic substances Taxol and thalidomide. Sensory neuropathy has a high incidence, lacks an effective treatment and is the dose-limiting factor for these drugs. The pathogenic basis of these neuropathies is unknown. We investigated the hypothesis that the experimental toxic neuropathies from Taxol and thalidomide results from destruction of vasa nervorum and can be reversed by the administration of an angiogenic cytokine. In animal models of Taxol- and thalidomide-induced neuropathy, nerve blood flow has been attenuated and the number of vasa nervorum has been reduced. Intramuscular gene transfer of naked plasmid DNA encoding VEGF-1 administered in parallel with Taxol injections completely inhibited deterioration of nerve function and diminution of the peripheral nerve vasculature. Gene therapy in animals with established Taxol- or thalidomide-induced neuropathies resulted in recovery of vascularity and improved nerve electrophysiology. These findings implicate microvascular damage as the basis for toxic neuropathy and suggest that angiogenic growth factors may constitute a novel treatment for this disorder.

Differences in direct effects of adrenergic stimuli on coronary, cutaneous, and muscular vessels.

Direct effects of adrenergic stimuli on coronary vessels in dogs were compared with effects on vessels to skin (hind paw) and skeletal muscle (gracilis muscle) after intravenous administration of practolol (2 mg/kg), a selective myocardial beta receptor blocker which minimized indirect effects of myocardial stimulation on coronary vascular resistance. The left circumflex coronary, cranial tibial, and gracilis arteries were perfused separately but simultaneously at constant flow. Perfusion pressures, left ventricular pressure and dP/dt. and heart rate were recorded. Changes in perfusion pressure to each bed reflected changes in vascular resistance. The direct constrictor effects of sympathetic nerve stimulation, norepinephrine and phenylephrine on coronary vessels were minimal compared with effects on cutaneous and muscular vessels. Subsequent blockade of vascular beta receptors did not augment the constrictor responses. Angiotensin, a nonadrenergic stimulus, produced striking coronary vasoconstriction which exceeded that in skin and approximated that in muscle. These results suggests that there is a paucity of alpha adrenergic receptors in coronary vessels compared to cutaneous and muscular vessels. Direct dilator responses to isoproterenol were similar in coronary and cutaneous vessels, but were greater in muscular vessels. Responses to glyceryl trinitrate, a nonadrenergic dilator, also were greater in skeletal muscle. Therefore, differences in effects of isoproterenol on the three beds may reflect differences in reactivity to dilator stimuli rather than differences in the density of beta receptors. In contrast to norepinephrine, the predominant direct effect of epinephrine on coronary vessels was dilatation mediated through activation of vascular beta receptors. A constrictor effect caused by stimulation of alpha receptors was unmasked by propranolol.Finally, the order of potency of agonists in stimulating coronary vascular beta receptors and the demonstration of selective beta receptor blockade with practolol suggest that beta receptors in coronary vessels resemble those in peripheral vessels more than those in myocardium.

Neuronal nitric oxide synthase mediates statin-induced restoration of vasa nervorum and reversal of diabetic neuropathy.

BACKGROUND: Peripheral neuropathy is a frequent and major complication of diabetes. METHODS AND RESULTS: Severe peripheral neuropathy developed in type II diabetic mice, characterized by significant slowing of motor and sensory nerve conduction velocities. Rosuvastatin restored nerve vascularity, including vessel size, and nerve function also recovered to the levels of nondiabetic mice. Neuronal nitric oxide synthase expression in sciatic nerves was reduced in diabetic mice but was preserved by rosuvastatin. Coadministration of a nitric oxide synthase inhibitor with rosuvastatin attenuated the beneficial effects of rosuvastatin on nerve function and limited the recovery of vasa nervorum and nerve function. In vitro, rosuvastatin inhibited downregulation of neuronal nitric oxide synthase expression induced by high-glucose conditions in cultured Schwann cells. Furthermore, Akt phosphorylation in Schwann cells, downregulated by high-glucose conditions, was also restored by rosuvastatin, consistent with the change of neuronal nitric oxide synthase expression. Akt inhibition independently reduced neuronal nitric oxide synthase expression in Schwann cells in low-glucose cultures. CONCLUSIONS: These data indicate that the HMG-CoA reductase inhibitor rosuvastatin has a favorable effect on diabetic neuropathy independent of its cholesterol-lowering effect. Our data provide evidence that this effect may be mediated in part via neuronal nitric oxide synthase/nitric oxide and phosphatidylinositol 3-kinase/Akt-signaling pathways and also suggest that restoration or preservation of the microcirculation of the sciatic nerve may be involved.

Antiangiogenesis mediates cisplatin-induced peripheral neuropathy: attenuation or reversal by local vascular endothelial growth factor gene therapy without augmenting tumor growth.

BACKGROUND: Toxic neuropathies induced by cisplatin and other chemotherapeutic agents are important clinical problems because of their high incidence, their lack of effective treatment, and the fact that neuropathy represents a dose-limiting factor for these therapies. The pathogenic basis for toxic neuropathies induced by chemotherapeutic agents has not been completely elucidated. METHODS AND RESULTS: We investigated the hypothesis that experimental toxic neuropathy results from an antiangiogenic effect of these drugs, resulting in destruction of the vasa nervorum, and accordingly that the neuropathy could be prevented or reversed by locally administered VEGF gene transfer without augmenting tumor growth. In an animal model of cisplatin-induced neuropathy, nerve blood flow was markedly attenuated, and there was a profound reduction in the number of vasa nervorum associated with marked endothelial cell apoptosis, resulting in a severe peripheral neuropathy with focal axonal degeneration characteristic of ischemic neuropathy. After intramuscular gene transfer of naked plasmid DNA encoding VEGF-1 in animals with an established neuropathy, vascularity and blood flow returned to levels similar to those of control rats, peripheral nerve function was restored, and histological nerve architecture was normalized. Gene therapy administered in parallel with cisplatin chemotherapy completely attenuated endothelial cell apoptosis and inhibited destruction of nerve vasculature, deterioration of nerve function, and axonal degeneration. In a rat tumor model, VEGF gene transfer administered locally did not alter tumor growth or vascularity. CONCLUSIONS: These findings implicate microvascular damage as the basis for toxic neuropathy induced by cisplatin and suggest that local angiogenic gene therapy may constitute a novel prevention or treatment for this disorder without augmenting tumor growth or vascularization.

Sonic hedgehog induces arteriogenesis in diabetic vasa nervorum and restores function in diabetic neuropathy.

OBJECTIVE: The embryonic morphogen sonic hedgehog (SHh) has been shown to induce neovascularization of ischemic tissue but has not been shown to play a role in regulating vascular nerve supply. Accordingly, we investigated the hypothesis that systemic injection of SHh protein could improve nerve blood flow and function in diabetic neuropathy (DN). METHODS AND RESULTS: Twelve weeks after induction of diabetes with streptozotocin, motor and sensory nerve conduction velocities (MCV and SCV) of the sciatic nerves were significantly reduced in diabetic rats. SHh-treated diabetic rats demonstrated marked improvement of both MCV and SCV (P<0.05). Laser Doppler perfusion imaging showed that nerve blood flow was significantly reduced in the diabetic rats but was restored in SHh-treated diabetic rats (P<0.05 versus diabetic saline-treated rats) to levels similar to those achieved with vascular endothelial growth factor-2 (VEGF-2) gene therapy. In vivo perfusion of Bandeuraea simplicifolia (BS)-1 lectin showed marked reduction in the vasa nervora in diabetic sciatic nerves but restoration of nerve vasculature to nondiabetic levels in the SHh-treated and plasmid DNA encoding human VEGF-2 (phVEGF-2)-treated diabetic nerves. Interestingly, the SHh-induced vasculature was characterized by larger diameter and more smooth muscle cell-containing vessels, compared with VEGF-2 gene-treated diabetic rats. CONCLUSIONS: These data indicate that Shh induces arteriogenesis and restores nerve function in DN.

Vasa nervorum constriction from substance P and calcitonin gene-related peptide antagonists: sensitivity to phentolamine and nimodipine.

Previous work has suggested that vasa nervorum are 'tonically' vasodilated by substance P (SP) and calcitonin gene-related peptide (CGRP) arising from perivascular afferent nerve fibers. Local application of specific receptor antagonists of SP or CGRP results in constriction of vasa nervorum. In this work, we examined the responsiveness of vasa nervorum to epineurial spantide and spantide II (SP antagonists) and hCGRP (8-37) (CGRP antagonist) using serial hydrogen clearance curves in the rat sciatic nerve. Vasoconstriction from spantide and hCGRP (8-37) was dose-dependent, and was slightly greater with spantide than hCGRP (8-37). Spantide II induced vasoconstriction comparable to that of spantide. The vasoconstrictive effects of both spantide and hCGRP (8-37) were eliminated by concurrent systemic treatment with with either phentolamine or nimodipine. The findings support the hypothesis that SP or CGRP blockade interrupts 'tonic' peptide vasodilatation and permits vasoconstriction, perhaps by unopposed adrenergic action mediated through calcium channels. The findings however do not exclude a unique direct vasoconstrictive action of the peptide antagonists.

Effects of nimodipine on sciatic nerve blood flow and vasa nervorum responsiveness in the diabetic rat.

Evidence is accumulating that impairment of nerve blood flow is a key factor in the pathogenesis of diabetic neuropathy. Nimodipine, a 1,4-dihydropyridine type Ca2+ channel antagonist, has been shown to ameliorate an existing neuropathy in the streptozotocin-induced diabetic rat. In the present study the effect of diabetes mellitus itself and the effect of chronic nimodipine treatment on the sciatic nerve blood flow of streptozotocin-induced diabetic rats were investigated. Nerve blood flow was assessed using laser-Doppler flowmetry. Nerve blood flow gradually decreased during the first 10 weeks of diabetes mellitus and remained relatively stable thereafter. Intervention with nimodipine significantly improved the flow deficit observed in the diabetic rats. Vasa nervorum adrenergic responsiveness was also investigated. Diabetic rats showed a postsynaptic adrenergic hyporesponsiveness. Treatment with nimodipine restored the reduced presynaptic responsiveness independent of the postsynaptic adrenergic hyporesponsiveness. It was concluded that, in addition to direct neuroprotective effects, nimodipine exerts beneficial effects on disturbed nerve blood flow and on reduced presynaptic adrenergic responsiveness of the vasa nervorum in experimental diabetic neuropathy.

Direct intraoperative confirmation of penetration of ethylene vinyl alcohol copolymer (Onyx) into the vasa nervosa of the facial nerve.

The case history is described of a patient referred to our institution with facial nerve palsy following embolization of a middle cranial fossa dural arteriovenous fistula using ethylene vinyl alcohol copolymer (EVOH). Facial nerve decompression was performed which showed evidence of extensive penetration of EVOH into the vasa nervosa of the facial nerve. Facial nerve palsy is a debilitating complication that can be avoided by attention to the lower cranial nerve arterial supply during careful procedural planning and consideration of alternative strategies for fistula obliteration in cases where eloquent feeders are involved.

Vasoreactivity to prostaglandins of rat peripheral nerve.

1. We evaluated the effect of the local superfusion of prostaglandins E1, I2 and F2 alpha (PGE1, PGI2 and PGF2 alpha, respectively) on rat sciatic nerve blood flow and microvascular resistance. 2. PGE1 increased nerve blood flow (NBF) in a dose-dependent fashion with an EC50 of 10(-6.7) M and an asymptote of 20.1 ml (100 g)-1 min-1. 3. PGI2 increased NBF in a linear dose-dependent fashion, with an EC50 of 10(-5.1) M. PGI2 appeared to be about 1.5 orders of magnitude less potent than PGE1. 4. PGF2 alpha also increased NBF in a dose-dependent fashion. The threshold dose appeared to be identical with PGI2 but may have a reduced capacity of response. The EC50 of 10(-5.8) M was slightly lower than that of PGI2.

Evidence that capsaicin hyperaemia of rat sciatic vasa nervorum is local, opiate-sensitive and involves mast cells.

1. In previous work, we identified a prolonged and intense hyperaemic response of rat sciatic endoneurial vasa nervorum produced by epineurial application of capsaicin. We postulated that this response, which was blocked by substance P (SP) or calcitonin gene-related peptide (CGRP) antagonists, was a result of local release of neuropeptides on the 'feeding' epineurial vascular plexus. 2. In the present study, we evaluated factors that might influence capsaicin-induced hyperaemia of the rat sciatic endoneurium as measured by hydrogen clearance: central afferent connections, the epineurial vascular plexus, the release of histamine and administration of opiates. 3. Interruption of central afferent connections by proximal nerve section or removal of the epineurial vascular plexus did not influence baseline endoneurial perfusion. Plexus removal, but not proximal section, prevented capsaicin hyperaemia. 4. The epineurial vascular plexus was desensitized to the effect of capsaicin by prior application of capsaicin. Capsaicin hyperaemia was also prevented by: topical treatment with Spantide II ((D-NicLys1,3-Pal3,D-Cl2Phe5,Asn6,D-Trp7,9,Nl e11) substance P) an SP antagonist, systemic pretreatment with a combination of H1 and H2 histamine receptor antagonists, systemic pretreatment with cromolyn sodium or systemic pretreatment with morphine. None of these pretreatments influenced baseline perfusion. When systemic morphine was given together with systemic naloxone, an opiate antagonist, capsaicin-induced hyperaemia was restored. 5. These findings indicate that the capsaicin hyperaemia of vasa nervorum is locally mediated, is independent of central afferent connections and is sensitive to a variety of interventions. It requires an intact epineurial plexus that 'feeds' endoneurial microvessels and the release of histamine by mast cells. Its inhibition by morphine suggests that there are local opiate receptors on epineurial perivascular peptidergic fibres.