Expression of thrombospondin-1 in ischemia-induced retinal neovascularization.
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Thrombospondin-1 is an extracellular matrix protein that inhibits endothelial cell proliferation, migration, and angiogenesis. This study was performed to investigate the role of thrombospondin-1 in ischemic retinal neovascularization. In a murine model of retinal neovascularization, thrombospondin-1 mRNA was increased from postnatal day 13 (P13), with a threefold peak response observed on P15, corresponding to the time of development of retinal neovascularization. Prominent expression of thrombospondin-1 was observed in neovascular cells, specifically, cells adjacent to the area of nonperfusion. It has been suggested that vascular endothelial growth factor (VEGF) plays a major role in ischemia-induced retinal neovascularization of this model, so we studied the effects of VEGF on thrombospondin-1 expression. In bovine retinal microcapillary endothelial cells, VEGF induced a biphasic response of thrombospondin-1 expression; VEGF decreased thrombospondin-1 mRNA 0.41-fold after 4 hours, whereas it increased, with a threefold peak response, after 24 hours. VEGF-induced endothelial cell proliferation was completely inhibited by exogenous thrombospondin-1 and increased by 37.5% with anti-thrombospondin-1 antibody. The present findings suggest that, in the ischemic retina, retinal neovascular cells increase thrombospondin-1 expression, and VEGF may stimulate endogenous thrombospondin-1 induction, which inhibits endothelial cell growth. VEGF-mediated thrombospondin-1 induction in ischemia-induced angiogenesis may be a negative feedback mechanism. (+info)
Rescue of diabetes-related impairment of angiogenesis by intramuscular gene therapy with adeno-VEGF.
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Diabetes is a major risk factor for coronary and peripheral artery diseases. Although diabetic patients often present with advanced forms of these diseases, it is not known whether the compensatory mechanisms to vascular ischemia are affected in this condition. Accordingly, we sought to determine whether diabetes could: 1) impair the development of new collateral vessel formation in response to tissue ischemia and 2) inhibit cytokine-induced therapeutic neovascularization. Hindlimb ischemia was created by femoral artery ligation in nonobese diabetic mice (NOD mice, n = 20) and in control C57 mice (n = 20). Hindlimb perfusion was evaluated by serial laser Doppler studies after the surgery. In NOD mice, measurement of the Doppler flow ratio between the ischemic and the normal limb indicated that restoration of perfusion in the ischemic hindlimb was significantly impaired. At day 14 after surgery, Doppler flow ratio in the NOD mice was 0.49+/-0.04 versus 0.73+/-0.06 for the C57 mice (P< or =0.005). This impairment in blood flow recovery persisted throughout the duration of the study with Doppler flow ratio values at day 35 of 0.50+/-0.05 versus 0.90+/-0.07 in the NOD and C57 mice, respectively (P< or =0.001). CD31 immunostaining confirmed the laser Doppler data by showing a significant reduction in capillary density in the NOD mice at 35 days after surgery (302+/-4 capillaries/mm2 versus 782+/-78 in C57 mice (P< or =0.005). The reduction in neovascularization in the NOD mice was the result of a lower level of vascular endothelial growth factor (VEGF) in the ischemic tissues, as assessed by Northern blot, Western blot and immunohistochemistry. The central role of VEGF was confirmed by showing that normal levels of neovascularization (compared with C57) could be achieved in NOD mice that had been supplemented for this growth factor via intramuscular injection of an adenoviral vector encoding for VEGF. We conclude that 1) diabetes impairs endogenous neovascularization of ischemic tissues; 2) the impairment in new blood vessel formation results from reduced expression of VEGF; and 3) cytokine supplementation achieved by intramuscular adeno-VEGF gene transfer restores neovascularization in a mouse model of diabetes. (+info)
Modulation of the thermoregulatory sweating response to mild hyperthermia during activation of the muscle metaboreflex in humans.
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1. To investigate the effect of the muscle metaboreflex on the thermoregulatory sweating response in humans, eight healthy male subjects performed sustained isometric handgrip exercise in an environmental chamber (35 C and 50 % relative humidity) at 30 or 45 % maximal voluntary contraction (MVC), at the end of which the blood circulation to the forearm was occluded for 120 s. The environmental conditions were such as to produce sweating by increase in skin temperature without a marked change in oesophageal temperature. 2. During circulatory occlusion after handgrip exercise at 30 % MVC for 120 s or at 45 % MVC for 60 s, the sweating rate (SR) on the chest and forearm (hairy regions), and the mean arterial blood pressure were significantly above baseline values (P < 0.05). There were no changes from baseline values in the oesophageal temperature, mean skin temperature, or SR on the palm (hairless regions). 3. During the occlusion after handgrip exercise at 30 % MVC for 60 s and during the occlusion alone, none of the measured parameters differed from baseline values. 4. It is concluded that, under mildly hyperthermic conditions, the thermoregulatory sweating response on the hairy regions is modulated by afferent signals from muscle metaboreceptors. (+info)
Hypothermic neuroprotection of peripheral nerve of rats from ischaemia-reperfusion injury.
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Although there is much information on experimental ischaemic neuropathy, there are only scant data on neuroprotection. We evaluated the effectiveness of hypothermia in protecting peripheral nerve from ischaemia-reperfusion injury using the model of experimental nerve ischaemia. Forty-eight male Sprague-Dawley rats were divided into six groups. We used a ligation-reperfusion model of nerve ischaemia where each of the supplying arteries to the sciatic-tibial nerves of the right hind limb was ligated and the ligatures were released after a predetermined period of ischaemia. The right hind limbs of one group (24 rats) were made ischaemic for 5 h and those of the other group (24 rats) for 3 h. Each group was further divided into three and the limbs were maintained at 37 degrees C (36 degrees C for 5 h of ischaemia) in one, 32 degrees C in the second and 28 degrees C in the third of these groups for the final 2 h of the ischaemic period and an additional 2 h of the reperfusion period. A behavioural score was recorded and nerve electrophysiology of motor and sensory nerves was undertaken 1 week after surgical procedures. At that time, entire sciatic-tibial nerves were harvested and fixed in situ. Four portions of each nerve were examined: proximal sciatic nerve, distal sciatic nerve, mid-tibial nerve and distal tibial nerve. To determine the degree of fibre degeneration, each section was studied by light microscopy, and we estimated an oedema index and a fibre degeneration index. The groups treated at 36-37 degrees C underwent marked fibre degeneration, associated with a reduction in action potential and impairment in behavioural score. The groups treated at 28 degrees C (for both 3 and 5 h) showed significantly less (P < 0.01; ANOVA, Bonferoni post hoc test) reperfusion injury for all indices (behavioural score, electrophysiology and neuropathology), and the groups treated at 32 degrees C had scores intermediate between the groups treated at 36-37 degrees C and 28 degrees C. Our results showed that cooling the limbs dramatically protects the peripheral nerve from ischaemia-reperfusion injury. (+info)
Age-related outcome for peripheral thrombolysis.
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OBJECTIVES: To investigate the age-related outcome of peripheral thrombolysis and determine for which patient group this treatment is worthwhile. DESIGN AND METHODS: A combined retrospective and prospective analysis of consecutive patients undergoing thrombolysis for acute lower-limb ischaemia was made with respect to age-related outcome and other risk factors. RESULTS: One hundred and two patients underwent thrombolysis for acute limb ischaemia. In the under 60 age group there was a 40% amputation rate. Seventy-three per cent of this group smoked. In the over 80 age group, the amputation rate was 15% and only 8% were smokers. CONCLUSION: Advancing age is not an adverse risk factor for thrombolysis which appears to be safe and effective in this patient group. There is a high incidence of smoking in the younger age group (< 60 years), in whom failed thrombolysis frequently leads to amputation. (+info)
Accumulation of N-acyl-ethanolamine phospholipids in rat brains during post-decapitative ischemia: a 31p NMR study.
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Phosphorus-31 nuclear magnetic resonance (31P NMR) spectroscopy has been used to study accumulation of N-acyl-ethanolamine phospholipids in rat brains during post-decapitative ischemia. Lipids were extracted from rat brain homogenates and the extracts were thoroughly washed with aq. potassium ethylenediaminetetraacetic acid (EDTA). The lower organic phases were isolated and evaporated to dryness under a stream of nitrogen and the lipids were redissolved in CDCl3-CH3OH-H2O 100.0:29.9:5.2 (v/v/v) for NMR analysis. Increasing the period of post-decapitative ischemia resulted in an accumulation of two signals in the NMR spectra at 0.18 and 0.22 ppm (relative to the chemical shift of 1,2-diacyl-sn-glycero-3-phosphocholine (PCDIACYL) at -0.84 ppm). These signals were identified as originating from 1,2-diacyl-sn-glycero-3-phospho-(N-acyl)-ethanolamine (NAPEDIACYL) and 1-(1'-alkenyl)-2-acyl-sn -glycero-3-phospho-(N-acyl)-ethanolamine (NAPEPLAS), respectively, by spiking with authentic materials. Additionally, the identification was verified by thin-layer chromatography, which also showed the accumulation of N-acyl-ethanolamine phospholipids. The use of K-EDTA instead of the commonly used Cs-EDTA in the preparation of the NMR samples allowed the separation of the chemical shifts of N-acyl-ethanolamine phospholipids from those of the ethanolamine phospholipids. Moreover, the chemical shift of cardiolipin was moved from 0.15 ppm observed with Cs-EDTA to about 0.31 ppm with K-EDTA. The present study demonstrates that it is possible to detect and quantify post-decapitative accumulation of NAPE subclasses (NAPEDIACYL and NAPEPLAS) in rat brains by the use of 31P NMR spectroscopy. (+info)
Heart rate during exercise with leg vascular occlusion in spinal cord-injured humans.
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Feed-forward and feedback mechanisms are both important for control of the heart rate response to muscular exercise, but their origin and relative importance remain inadequately understood. To evaluate whether humoral mechanisms are of importance, the heart rate response to electrically induced cycling was studied in participants with spinal cord injury (SCI) and compared with that elicited during volitional cycling in able-bodied persons (C). During voluntary exercise at an oxygen uptake of approximately 1 l/min, heart rate increased from 66 +/- 4 to 86 +/- 4 (SE) beats/min in seven C, and during electrically induced exercise at a similar oxygen uptake in SCI it increased from 73 +/- 3 to 110 +/- 8 beats/min. In contrast, blood pressure increased only in C (from 88 +/- 3 to 99 +/- 4 mmHg), confirming that, during exercise, blood pressure control is dominated by peripheral neural feedback mechanisms. With vascular occlusion of the legs, the exercise-induced increase in heart rate was reduced or even eliminated in the electrically stimulated SCI. For C, heart rate tended to be lower than during exercise with free circulation to the legs. Release of the cuff elevated heart rate only in SCI. These data suggest that humoral feedback is of importance for the heart rate response to exercise and especially so when influence from the central nervous system and peripheral neural feedback from the working muscles are impaired or eliminated during electrically induced exercise in individuals with SCI. (+info)
CT angiography and Doppler sonography for emergency assessment in acute basilar artery ischemia.
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BACKGROUND AND PURPOSE: Both Doppler sonography (DS) and spiral CT angiography (CTA) are noninvasive vascular assessment tools with a high potential for application in acute cerebral ischemia. The usefulness of CTA for vascular diagnosis in acute basilar artery (BA) ischemia has not yet been studied. METHODS: We prospectively studied 19 patients (mean+/-SD age, 58+/-11 years) with clinically suspected acute BA occlusion by DS and CTA. Prior extracranial and transcranial DS was performed in all but 1 patient, with DS 4 hours after CTA. In 6 of 19 patients, we performed digital subtraction angiography. RESULTS: CTA was diagnostic in all but 1 patient. CTA revealed complete BA occlusion in 9 patients and incomplete BA occlusion with some residual flow in 2 patients. A patent BA was shown in 7 patients. Because of severe BA calcification, CTA results were inconclusive in 1 patient. DS was diagnostic in only 7 of 19 patients, indicating certain BA occlusion in 3 patients and BA patency in 4 patients. In an additional 9 patients, the results of DS were inconclusive. DS was false-negative in 2 patients with distal BA occlusion shown by CTA and digital subtraction angiography. In 1 patient with DS performed after CTA, recanalization was demonstrated. In addition to the diagnosis or exclusion of BA occlusion, CTA provided information on the exact site and length of BA occlusion and collateral pathways. In our series, CTA results prompted indication for intra-arterial thrombolysis in 5 patients. CONCLUSIONS: CTA was superior to DS in the assessment of BA patency in patients with the syndrome of acute BA ischemia in terms of feasibility and conclusiveness, particularly in cases with distal BA occlusion. Our study confirmed the usefulness of combined extracranial and transcranial DS in the diagnosis and exclusion of proximal BA occlusion. (+info)