Outcome Measures of New Technologies in Uveal Melanoma: Review from the European Vision Institute Special Interest Focus Group Meeting.

Uveal Melanoma (UM) is the most common primary intra-ocular tumor in adults. New diagnostic procedures and basic science discoveries continue to change our patient management paradigms. A recent meeting of the European Vision Institute (EVI) special interest focus group was held on "Outcome Measures of New Technologies in Uveal Melanoma", addressing the latest advances in UM, starting with genetic developments, then moving on to imaging and treatment of the primary tumor, as well as to investigating the most recent developments in treating metastases, and eventually taking care of the patient's wellbeing. This review highlights the meeting's presentations in the context of the published literature.

Blue-Light Fundus Autofluorescence Imaging following Ruthenium-106 Brachytherapy for Choroidal Melanoma.

PURPOSE: To describe changes in blue-light fundus autofluorescence (FAF) and corresponding alterations in optical coherence tomography (OCT) within the irradiation field after ruthenium-106 brachytherapy (RBT) for choroidal melanoma. METHODS: Consecutive patients with choroidal melanoma were included in a retrospective case series. Patients were treated with RBT at a single institution. As part of their routine examination patients underwent multimodal imaging including ultrasonography, fundus photography, OCT, and FAF imaging (excitation = 488 nm). FAF images were analysed for changes within the irradiation field. RESULTS: 31 patients (mean age 65.7 years) were treated with RBT for unilateral choroidal melanoma. Mean tumour height before therapy was 2.7 mm (SD 1.0). Mean follow-up time was 23.3 months (SD 13.3). Main FAF characteristics attributable to RBT emerged as increased FAF with speckled decreased FAF (FAF mottling) within the irradiation field and a rim of increased FAF at its border. OCT scans demonstrated loss of the ellipsoid zone and the external limiting membrane, thinning of the neurosensory retina, and alterations of the retinal pigment epithelium like clumping, migration, and atrophy. CONCLUSIONS: FAF changes in the irradiation field after RBT of choroidal melanomas follow a characteristic pattern that correlates with distinct OCT alterations. FAF and OCT imaging give additional information to monitor effects of RBT and, therefore, complement multimodal imaging techniques after plaque therapy.

Fundus Autofluorescence Imaging in Patients with Choroidal Melanoma.

Choroidal melanocytic lesions require reliable and precise clinical examination and diagnosis to differentiate benign choroidal nevi from choroidal melanoma, as the latter may become life-threatening through metastatic disease. To come to an accurate diagnosis, as well as for monitoring, and to assess the efficacy of therapy, various imaging modalities may be used, one of which is non-invasive fundus autofluorescence (FAF) imaging using novel high-resolution digital imaging technology. FAF imaging is based on the visualization of intrinsic fluorophores in the ocular fundus. Lipofuscin and melanolipofuscin within the postmitotic retinal pigment epithelium (RPE) cells represent the major fluorophores that contribute to the FAF signal. In addition, the presence or loss of absorbing molecular constituents may have an impact on the FAF signal. A choroidal melanoma can cause secondary retinal and RPE alterations that affect the FAF signal (e.g., occurrence of orange pigment). Therefore, FAF imaging supports multimodal imaging and gives additional information over and above conventional imaging modalities regarding retinal metabolism and RPE health status. This article summarises the features of FAF imaging and the role of FAF imaging in the context of choroidal melanoma, both before and following therapeutic intervention.

Ifosfamide or trofosfamide in patients with intraocular lymphoma.

We evaluated response, progression-free survival (PFS), overall survival (OS), relapse patterns and long-term toxicity of intraocular lymphoma (IOL) patients treated with ifosfamide (IFO) or trofosfamide (TRO). In a prospective single center study, IFO or TRO were given to 10 patients with IOL. The median patient age was 73 (range 46-83) years. Six patients were pretreated with up to four treatment regimens for ocular or cerebral lymphoma, and four were therapy-naive. All patients responded, including nine complete remissions and one partial remission, with a median PFS of 18 (7-36) months. Seven patients relapsed: five in the eye and two in the brain. Median OS was 32 (7-37+) months. No long-term toxicity was observed in patients treated with IFO or TRO alone. IFO or TRO were active and well tolerated in this study. Thus, they may represent suitable combination partners for other cytostatics used for PCNSL and IOL treatment.

Neoadjuvant proton beam irradiation followed by transscleral resection of uveal melanoma in 106 cases.

AIMS: To describe results after neoadjuvant proton beam irradiation followed by transscleral resection of large uveal melanoma. METHODS: Retrospective interventional case series, including 106 consecutive patients. Local tumour control, enucleation and metastasis development were assessed with survival curves. Predictors of local recurrence and metastasis were investigated with log-rank testing. RESULTS: Mean follow-up was 3.2 years. Local recurrence occurred in five cases with an estimated risk of 4.2% and 10.4% at 3 and 5 years after treatment, respectively. Enucleation was performed in 10 cases with an estimated risk of 9.2% and 18.4% at 3 and 5 years, respectively. Significant risk factors for local recurrence were not evident. Metastasis was estimated to occur in 28.4% at 3 years and 40.3% at 5 years, correlating with patient's age only (p=0.01). Seventy four patients (69.8%) underwent vitreoretinal surgery for complications after tumour resection. Median visual acuity (VA) was 20/50 at diagnosis and 20/400 in the third year after treatment. VA preservation of 20/200 or better was achieved in 33 patients (31.1%). CONCLUSION: Neoadjuvant proton beam irradiation may help to prevent local recurrence after transscleral resection. Additional vitreoretinal surgery was frequently needed in the presented series. The majority of patients avoided enucleation and functional blindness.

The Development of Orange Pigment Overlying Choroidal Metastasis.

AIMS: The aim of this study was to correlate the ophthalmoscopic and histopathological findings of orange pigment overlying a choroidal metastasis. METHODS: This is a single case report with clinical follow-up and histopathological examination. RESULTS: Histopathology revealed a choroidal metastasis with subretinal CD68-positive macrophages showing autofluorescent deposits in fluorescence microscopy. CONCLUSION: The development of orange pigment is not pathognomonic for choroidal melanoma but may be seen in other lesions such as carcinoma metastasis.

Magnetic resonance imaging based morphologic evaluation of the pineal gland for suspected pineoblastoma in retinoblastoma patients and age-matched controls.

PURPOSE: The purpose of this study was to evaluate the morphologic magnetic resonance imaging (MRI) characteristics of the pineal gland in retinoblastoma (Rb) patients without and with pineoblastoma in comparison to age-matched controls to improve early identification of pineoblastomas (trilateral retinoblastoma, TRb). METHODS AND MATERIALS: 80 patients with retinoblastoma and 80 age-matched controls who had undergone brain MRI were included in this retrospective institutional review board approved cohort study. Two readers analyzed the following MR characteristics of the pineal gland: signal intensity on T1- and T2-weighted images, enhancement pattern, delineation of the gland, presence of cystic component, size of pineal gland and size of pineal cysts, respectively. A third reader assessed all images for the presence or absence of pineoblastoma. RESULTS: 3 patients were positive (TRb cohort) and 77 negative for pineoblastoma (non-TRb cohort). The mean maximum diameter of the pineal gland was 6.4mm in Rb patients and 6.3mm in age-matched controls. The mean volume of the pineal gland in Rb patients was 93.1mm(3) and was 87.6mm(3) in age-matched controls. Considering all available MRI scans the mean maximum diameter of the pineal gland in TRb patients was 11.2mm and the mean volume in TRb patients was 453.3mm(3). The third reader identified pineoblastomas with a sensitivity of 100% (3 of 3) and a specificity of 94% (72 of 77). CONCLUSION: Our non-TRb patients did not show significant differences in the size of the pineal gland and pineal gland cysts compared to age-matched controls. The presented data can serve as a reference for the volume of normal pineal glands and pineal cysts in the diagnostic work-up of Rb patients with suspected pineoblastoma.

Proton beam radiotherapy of diffuse iris melanoma in 54 patients.

BACKGROUND: Treatment modalities in iris melanoma include excision, plaque radiotherapy, photon or proton beam therapy and enucleation. In extensive tumours and diffuse seeding, radiotherapy remains as an alternative to enucleation. METHODS: This study is a retrospective, consecutive, interventional, single-institutional case series. 54 patients with a diffuse and non-resectable iris melanoma diagnosed from September 1998 to June 2012 were included. A 68-megaelectron volt proton beam was used to treat the anterior segment with a total dose of 4×12.5 cobalt grey equivalent. The cases were evaluated for local tumour control, eye retention, functional outcome and local complications after treatment. RESULTS: During a mean follow-up of 62.7 months (median 54.8 months, range 5.5-159.6 months), local tumour control was achieved in 96.3% of the patients. Cataract and glaucoma were the main complications developing after irradiation in 42.6% and 55.6%, respectively. In 34 of 44 patients (77.3%) who underwent cataract removal, a visual acuity of 20/40 or better following surgery was preserved. Enucleation was performed in three patients. The reason was suspected tumour recurrence in one and glaucoma in two. Hepatic metastasis occurred in one patient. CONCLUSIONS: As an alternative to enucleation, whole anterior segment fractionated proton beam radiotherapy offered excellent local tumour control in diffuse iris melanoma. Given the limited alternatives, the rate of complications appears acceptable and visual function could be preserved in the majority of the patients during follow-up.

Dynamic contrast-enhanced MRI of ocular melanoma.

Dynamic contrast-enhanced MRI is used for the assessment of microvasculature in several tumours. We aimed to assess the contrast signal enhancement characteristics of ocular melanoma. Forty patients with ocular melanoma were prospectively investigated with ocular MRI including dynamic contrast-enhanced sequences over a 13-month period. A region-of-interest analysis of the images was carried out to calculate signal enhancement characteristics after a contrast injection. Clinical follow-up data such as extraocular spread and development of liver metastasis were compared with the signal enhancement characteristics of the ocular melanoma. In 39 patients (98%), the ocular melanomas showed an early strong signal enhancement after contrast injection, resulting in a mean time of maximum enhancement of 49 s. Clinical follow-up was available in 28 patients (70%) and indicated that the peak signal intensity was significantly increased (P=0.039) in patients who developed extraocular spread or liver metastasis at a later stage. Ocular melanoma shows signal enhancement characteristics of hypervascular neoplasms. This study provides baseline curve pattern data that may be useful for assessing changes in vascularity, for example during therapy response. Furthermore, the study showed that a strong signal enhancement of the ocular melanoma might be linked to a less favourable prognosis.

The specificity of the histochemical NADPH diaphorase reaction for nitric oxide synthase-1 in skeletal muscles is increased in the presence of urea.

Nitric oxide synthase-1 (NOS-1) can be demonstrated in the sarcolemma region of myofibers in rodent skeletal muscles with the use of NADPH diaphorase histochemistry. Since other, especially intrafibrar enzymes also exhibit NADPH diaphorase activity, we tried to increase the specificity of the histochemical reaction for NOS-1. A qualitative and quantitative analysis was performed on cryostat sections of fast-twitch oxidative myofiber-rich tongue and fast-twitch glycolytic myofibers-rich tibialis anterior muscle derived from C57 mice and NOS-1 deficient knockout mice. All myofibers of both C57 mice and NOS-1 knockout mice contained significant intrafibrar NADPH diaphorase activity which was inhibited to almost background levels when 2 M urea was added to the incubation medium. On the other hand, myofibers of C57 mice but not of NOS-1-deficient knockout mice exhibited NADPH diaphorase activity in their sarcolemma region which was only weakly reduced in the presence of 2 M urea as was demonstrated by image analysis. Quantitative data on the activity of NADPH diaphorase(s) were obtained in situ by photometric analysis of formazan extracted from cryostat sections. The catalytic activity in tongue and tibialis anterior muscle was reduced in presence of 2 M urea to approximately 27% in C57 mice and to 7-17% in NOS-1 knockout mice, respectively. An in vitro NADPH diaphorase assay performed on homogenates of skeletal muscles also revealed an inhibitory effect of 2 M urea in both mouse strains and, additionally, indicated an upregulation of NADPH diaphorase activity in NOS-1 knockout mice. Finally, an immunodepletion analysis demonstrated that NOS-1 comprises 38% of the total NADPH diaphorase activity in tongue and approximately 59% in tibialis anterior muscle in C57 mice. In conclusion, we recommend the addition of 2 M urea to the incubation medium to increase the specificity of the NADPH diaphorase reaction to localise NOS-1 with the use of catalytic histochemistry.

Endodrainage, Tumor Photocoagulation, and Silicone Oil Tamponade for Primary Exudative Retinal Detachment due to Choroidal Melanoma Persisting after Proton Beam Therapy.

BACKGROUND: Choroidal melanoma is frequently accompanied by an exudative retinal detachment that can persist after proton beam therapy. This study investigates whether vitrectomy without tumor resection improves the clinical outcome. METHODS: This is a retrospective interventional case series. Twenty patients with choroidal melanoma with exudative retinal detachment involving the macula were treated by vitrectomy, endodrainage, photocoagulation, and silicone oil tamponade after proton beam therapy. RESULTS: The mean follow-up was 38.4 months (median 21.5, range 12.0-122.0). The mean time between proton beam therapy and surgery was 4.5 months (range 0.1-9.2). Reattachment was achieved in 95% of the patients after one vitrectomy. One patient was lost to follow-up because enucleation was performed after 45.9 months due to a secondary glaucoma. Mean visual acuity decreased from 1.1 to 1.8 logMAR before vitrectomy and after 4 years, respectively. No patient showed local tumor recurrence. Metastatic disease was present in 1 patient after 15.2 months, and this patient died after 19.2 months. CONCLUSION: Vitrectomy is indicated after therapeutic proton beam irradiation in patients who present with persisting exudative retinal detachment involving the macula and high local or systemic risk factors for hemorrhagic complications, thus excluding endoresection.

Proton beam therapy leads to excellent local control rates in choroidal melanoma in the intermediate fundus zone.

PURPOSE: To evaluate long-term outcomes of proton beam radiotherapy in the treatment of choroidal melanoma of the intermediate zone of the fundus. DESIGN: Retrospective interventional single-center study. METHODS: The study was a retrospective analysis with long-term follow-up of 62 patients with a minimum tumor-to-disc and tumor-to-fovea distance of 2 mm of choroidal melanoma in the intermediate zone of the fundus. Mean values of tumor prominence, largest basal diameter, and tumor distances to the optic disc and fovea were 7.6, 12.8, 5.2, and 4.6 mm, respectively. All patients were irradiated with a total proton dose of 60 cobalt gray equivalents. RESULTS: After proton beam radiotherapy, 71.0% of the patients received subsequent endoresection of the tumor. Only 18 patients (29.0%) did not require additional tumor resection and were analyzed as a separate group. For the total of patients, the median follow-up time was 70.3 months. The 5-year Kaplan-Meier rates of local tumor relapse, enucleation, and distant metastasis were 3.9%, 3.7%, and 13.4%, respectively. Cataract surgery was the most frequent secondary treatment in our cohort. CONCLUSIONS: In this study we demonstrate the effectiveness of proton beam irradiation in tumor control and preservation of the globe in the analyzed patients. The rate of metastasis was not higher than previously described. Nevertheless, consecutive tumor surgery is frequently required to maintain the eye in patients with large-sized choroidal melanomas. In conclusion, proton beam radiotherapy allows preservation of the eye in mid-zone choroidal melanomas.

Proton beam therapy of parapapillary choroidal melanoma.

PURPOSE: To analyze the functional outcome with regard to the development of visual acuity and radiation-induced optic neuropathy of patients with parapapillary choroidal melanoma treated with proton beam therapy. DESIGN: Clinical case series, retrospective study. METHODS: We evaluated 147 consecutive patients with parapapillary choroidal melanoma who received proton beam therapy as primary tumor treatment at the Helmholtz Center in Berlin from 1998 to 2005. A cumulative dose of 60 Cobalt Gray Equivalents (CGE) was delivered to the tumor and the optic disc received a minimum of 50 CGE. Kaplan-Meier analysis was used to assess ocular outcome and survival rates. For trend analysis of functional development, Wilcoxon-Mann-Whitney U test was used to compare the medians of 2 groups and Kruskal-Wallis test was used in the case of more than 2 groups. RESULTS: The mean follow-up time was 6.5 years (range 0.3-11.7 years). The most common side effects were radiation-induced optic neuropathy, retinopathy, and cataract. The median visual acuity before and within the first year after therapy was 0.4 logMAR (20/50), lapsing to 1.3 logMAR (20/400) after 3 years and 1.4 logMAR (20/500) after 5 years. During follow-up, no light perception developed in 17 cases (11.6%), mostly attributed to radiation-induced retinopathy, optic neuropathy, and secondary glaucoma. Enucleation was carried out in 14 patients (9.5%) because of local recurrence or severe side effects. CONCLUSION: Radiation-induced optic neuropathy is an expected issue after proton beam therapy of parapapillary choroidal melanoma, and visual impairment is common during long-term follow-up, but some useful vision can be preserved in a considerable number of patients.

Diffusion-weighted imaging of ocular melanoma.

OBJECTIVES: Diffusion-weighted imaging (DWI) allows characterization of masses on the basis of their cellular density. We hypothesized that ocular melanoma has a marked diffusion restriction as seen in other malignant tumors. Furthermore, we aimed to assess whether DWI is useful to differentiate ocular melanoma from retinal detachment. MATERIALS AND METHODS: The institutional review board approved the prospective study on 44 patients investigated with ocular magnetic resonance imaging including DWI during a 9-month period. A region-of-interest analysis of diffusion-weighted images with b values of 0 and 1000 s/mm was performed to calculate the apparent diffusion coefficient (ADC) of the ocular melanoma and the retinal detachment. Three patients were excluded because DWI was nondiagnostic owing to severe artifacts; in 1 patient, the melanoma was too small for ADC calculation. Therefore, 40 patients were included in the final analysis. Ocular melanomas and detachments were compared with respect to their ADC values. The image quality of DWI was qualitatively scored by 2 readers in consensus on a 3-point scale from 1 (minor artifacts) to 3 (major artifacts). RESULTS: Ocular melanomas showed a marked diffusion restriction, and the mean (SD) ADC was 891 (172) × 10 mm/s. Twenty-nine patients (66%) had retinal detachment. The mean ADC of the ocular melanoma differed significantly (P < 0.001) from the mean ADC of the retinal detachment (1986 [375] × 10 mm/s). The image quality of DWI was rated 1 in 38 patients, 2 in 3 patients, and 3 in 3 patients. CONCLUSIONS: Ocular melanoma shows a marked diffusion restriction with an ADC of less than 1000 mm/s, which is in concordance with other malignant tumor entities. Diffusion-weighted imaging helps differentiating ocular tumors from retinal detachment and should therefore be included in the ocular magnetic resonance imaging protocol if an ocular mass is suspected.

Phosphorylated pVEGFR2/KDR receptor expression in uveal melanomas: relation with HIF2α and survival.

Hypoxia and its down-stream activated pathways are commonly involved in tumor progression. Genes involved in angiogenesis and glycolysis, i.e. vascular endothelial growth factor (VEGF) and lactase dehydrogenase A (LDHA), respectively, are transcriptionally controlled by the hypoxia inducible factors 1α and 2α (HIF1α and HIF2α). A series of 60 uveal melanomas were immunohistochemically assessed for the expression of VEGF and the phosphorylated/activated form of VEGF receptor 2 (pVEGFR2/KDR), after binding to VEGF. The expression of HIF1α, HIF2α and LDH5 was also investigated. Uveal melanomas overexpressing HIF2α (but not that of HIF1α) were significantly associated with high VEGF (P = 0.005), pVEGFR2/KDR (P < 0.0001) and LDH5 (P ≤ 0.0001). High LDH5 was linked with tumor necrosis (P = 0.01) and increased tumor size (P = 0.03). High VEGF was linked with phosphorylated pVEGFR2/KDR receptors. In univariate analysis high pVEGFR2/KDR receptor expression was significantly related with poor prognosis (P = 0.02). It is concluded that HIF2α plays an important role in the progression of uveal melanomas possibly by promoting the autocrine loop VEGF-pVEGFR2/KDR, and by enhancing the expression of LDHA gene, conferring thus a growth advantage. As pVEGFR2/KDR expression was significantly related with poor prognosis, inhibitors of this receptor may improve the clinical outcome of patients with pVEGFR2/KDR overexpressing uveal melanomas.

Results and complications after implantation of a black iris-lens diaphragm in patients with traumatically induced aphakia and aniridia.

PURPOSE: The black iris-lens diaphragm (ILD) can be used in the treatment of traumatic aniridia and aphakia. The aim of our study was to show postoperative functional and anatomic results and complications in a small case series. METHODS: We retrospectively analyzed the files of 16 patients managed with a black ILD or a sole iris diaphragm in the period 1994-2007. Four of them were female and 12 were male. The mean age of the group was 50±17 years. At the time of the implantation, all of the eyes had already undergone primary surgical repair. RESULTS: The preoperative best-corrected visual acuity in half of the patients was =0.1 and remained stable after the first postoperative year. During the follow-up years, one eye developed a subluxation of the implant and one eye an anterior chamber hemorrhage. At the same time, out of 8 eyes carrying a silicone tamponade in the vitreous cavity, silicone oil entered the anterior chamber in 3 cases. In one case, enucleation was undertaken due to phthisis. CONCLUSIONS: In the case of severely traumatized eyes with aniridia and aphakia, the implantation of a black ILD can have a positive effect on functional and anatomic stabilization.

Ten-year results of transscleral resection of large uveal melanomas: local tumour control and metastatic rate.

AIMS: To describe the long-term tumour control and metastatic rate after transscleral resection (TSR) of large uveal melanomas in a single-centre study. METHODS: The sample included 210 patients with large uveal melanomas. Univariate analysis of local tumour control and metastatic risk by Kaplan-Meier survival curves and log-rank testing. Cox proportional HR analysis with forward and backward selection was used to identify independent prognostic factors in patients submitted to TSR of a large uveal melanoma. RESULTS: A residual tumour was diagnosed in 6% of the patients. The 5- and 10-year local tumour recurrence rates were 24% and 32%, respectively. Older age, a large basal tumour diameter, the lack of adjuvant ruthenium brachytherapy and retinal detachment led to a 2.6, 2.4, 4.4 and 7.8 times higher risk of melanoma recurrence, respectively. The 5- and 10-year metastatic rates were 28% and 44%, respectively, and were statistical significantly affected by extraocular spread, tumour thickness and local tumour recurrence. CONCLUSIONS: TSR is an alternative to enucleation for the treatment of large uveal melanomas. Results should improve with better patient selection and more effective methods of adjuvant radiotherapy.

Intraocular surgery under systemic interferon-alpha therapy in ocular Adamantiades-Behçet's disease.

BACKGROUND: Adamantiades-Behçet's disease (ABD) is a multi-system disorder with recurrent oral and/or genital ulcerations, skin lesions and ocular involvement. Eye involvement is a common manifestation that affects the patients' quality of life more than any other. Left untreated, it leads to blindness and often to loss of the eye through secondary complications like phthisis or painful glaucoma. In some cases, such as tractional retinal detachment, secondary glaucoma or secondary cataract formation, intraocular surgery is required. METHODS: A prospective study of patients with ocular ABD who underwent intraocular surgery under systemic treatment with interferon-alpha was conducted. From 1999 to 2005, we treated eight eyes from five patients with pars plana vitrectomy (n = 1), phacoemulsification (n = 6) and trabeculectomy (n = 1). The mean follow-up was 49 months (range 5-94 months). RESULTS: Seven out of eight eyes had better visual acuity following surgery. One eye did not benefit from cataract surgery because of optic nerve atrophy. Only one eye showed prolonged inflammation following phacoemulsification. None of the patients showed a recurrence during follow-up. The failure of conservative glaucoma treatment necessitated trabeculectomy in one eye; the patient has had no further recurrence for 6 years under monotherapy with interferon-alpha. CONCLUSION: Interferon-alpha is a potent therapy for Adamantiades-Behçet's disease with ocular involvement. It also provides a basis for safe and reliable surgical interventions. In seven of eight eyes, there was no intra- or peri-operative recurrence of inflammation, which is a common complication after these procedures. Only one eye showed acute and prolonged inflammation following cataract surgery.

Endothelial NOS is main mediator for shear stress-dependent angiogenesis in skeletal muscle after prazosin administration.

The increase of wall shear stress in capillaries by oral administration of the alpha1-adrenergic receptor antagonist prazosin induces angiogenesis in skeletal muscles. Because endothelial nitric oxide synthase (eNOS) is upregulated in response to elevated wall shear stress, we investigated the relevance of eNOS for prazosin-induced angiogenesis in skeletal muscles. Prazosin and/or the NOS inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME) were given to C57BL/6 wild-type mice and eNOS-knockout mice for 14 days. The capillary-to-fiber (C/F) ratio and capillary density (CD; no. of capillaries/mm2) were determined in frozen sections from extensor digitorum longus (EDL) muscles of these mice. Immunoblotting was performed to quantify eNOS expression in endothelial cells isolated from skeletal muscles, whereas VEGF (after precipitation with heparin-agarose) and neuronal NOS (nNOS) concentrations were determined in EDL solubilizates. In EDL muscles of C57BL/6 mice treated for 14 days, the C/F ratio was 28% higher after prazosin administration and 11% higher after prazosin and L-NAME feeding, whereas the CD increased by 21 and 13%, respectively. The C/F ratio was highest after day 4 of prazosin treatment and decreased gradually to almost constant values after day 8. Prazosin administration led to elevation of eNOS expression. VEGF levels were lowest at day 4, whereas nNOS values decreased after day 8. In EDL muscles of eNOS-knockout mice, no significant changes in C/F ratio, CD, or VEGF and nNOS expression were observed in response to prazosin administration. Our data suggest that the presence of eNOS is essential for prazosin-induced angiogenesis in skeletal muscle, albeit other signaling molecules might partially compensate for or contribute to this angiogenic activity. Furthermore, subsequent remodeling of the capillary system accompanied by sequential downregulation of VEGF and nNOS in skeletal muscle fibers characterizes shear stress-dependent angiogenesis.