Training increases muscle blood flow in rats with peripheral arterial insufficiency

This study investigated the effect of physical training on muscle blood flow (BF) in rats with peripheral arterial insufficiency during treadmill running. Bilateral stenosis of the femoral artery of adult rats (300-350 g) was performed to reduce exercise hyperemia in the hindlimb but not limit resting muscle BF. Rats were divided into normal sedentary, acute stenosed (stenosed 3 days before the experiment), stenosed sedentary (limited to cage activity), and stenosed trained (run on a treadmill by a progressively intense program, up to 50-60 min/day, 5 days/wk for 6-8 wk). Hindlimb BF was determined with 85Sr- and 141Ce-labeled microspheres at a low (20 m/min) and high treadmill speed (30-40 m/min depending on ability). Maximal hindlimb BF was reduced to approximately 50% normal in the acute stenosed group. Total hindlimb BF (81 +/- 5 ml.min-1.100 g-1) did not change in stenosed sedentary animals with 6-8 wk of cage activity, but a redistribution of BF occurred within the hindlimb. Two factors contributed to a higher BF to the distal limb muscle of the trained animals. A redistribution BF within the hindlimb occurred in stenosed trained animals; distal limb BF increased to approximately 80% (P less than 0.001) of the proximal tissue. In addition, an increase in total hindlimb BF with training indicates that collateral BF has been enhanced (P less than 0.025). The associated increase in oxygen delivery to the relatively ischemic muscle probably contributed to the markedly improved exercise tolerance evident in the trained animals.     

bFGF increases collateral blood flow in aged rats with femoral artery ligation

We tested the hypothesis that aged animals are as responsive as the young adult animals in expanding collateral vasculature under a similar treatment of basic fibroblast growth factor (bFGF). Two age groups of male Fischer 344 rats (11 mo old; n = 32, 23 mo old; n = 43) weighing approximately 385 g were subdivided into normal, acute ligation [femoral artery (FA) ligated 3 days before blood flow (BF) measurement] or ligated groups for 16 days and received recombinant human bFGF intra-arterial infusion at doses of 0, 0.5, 5, and 50 microg x kg(-1) x day(-1). BF was determined with (85)Sr- and (141)Ce-labeled microspheres during treadmill running at 15 and 20 m/min at 15% grade. Blood pressure (BP) values were approximately 149 and approximately 163 mmHg (p < 0.05); heart rates were approximately 496 and approximately 512 beats/min in the aged and young adult groups during running, respectively. Maximal collateral BF values were confirmed by no additional BF increase in the calf muscle at the higher speed. Ligation of the FA for 3 days reduced the BF reserve to the calf muscle by approximately 90%. Calf muscle BF was modestly greater (10 ml x min(-1) x 100 g(-1)) by 16 days in the carrier group. bFGF infusion expanded collateral BF in a dose-dependent manner with an increase of 33 and 42 ml x min(-1) x 100 g(-1) (P < 0.001) in the 5 and 50 microg x kg(-1) x day(-1) bFGF groups, respectively. Aged animals showed similar BF improvements as observed with the adult groups in response to ligation surgery and bFGF treatment. Our data indicate that the aged rats (approximately 23 mo old) remain responsive to exogenous bFGF induced in developing collateral-dependent BF as the young adult (approximately 11 mo old) controls. This suggests that the influence of bFGF in expanding collateral BF should not be preempted in the aged group, the population most affected by peripheral arterial insufficiency.     

bFGF enhances the development of the collateral circulation after acute arterial occlusion.

An adequate collateral circulation is crucial to tissue survival subsequent to proximal major arterial occlusion. The precise mechanism of collateral blood vessel development and the biochemical mediators involved in this process are unknown. To evaluate the influence of a number of agents on the development of the collateral circulation, we developed a rat model of severe hind limb ischaemia. The recovery of blood flow after acute arterial occlusion was increased by exogenous basic fibroblast growth factor and heparin, and decreased by protamine. Erucamide (cis-13-docosenamide), an angiogenic lipid, had no effect on collateral blood flow. These results indicate that basic fibroblast growth factor and heparin are potential therapeutic agents in the treatment of peripheral vascular disease.     

Intermittent pneumatic leg compressions enhance muscle performance and blood flow in a model of peripheral arterial insufficiency

Despite the escalating prevalence in the aging population, few therapeutic options exist to treat patients with peripheral arterial disease. Application of intermittent pneumatic leg compressions (IPC) is regarded as a promising noninvasive approach to treat this condition, but the clinical efficacy, as well the mechanistic basis of action of this therapy, remain poorly defined. We tested the hypothesis that 2 wk of daily application of IPC enhances exercise tolerance by improving blood flow and promoting angiogenesis in skeletal muscle in a model of peripheral arterial insufficiency. Male Sprague-Dawley rats were subjected to bilateral ligation of the femoral artery and randomly allocated to treatment or sham groups. Animals were anesthetized daily and exposed to 1-h sessions of bilateral IPC or sham treatment for 14-16 consecutive days. A third group of nonligated rats was also studied. Marked increases in treadmill exercise tolerance (～33%, P < 0.05) and improved muscle performance in situ (～10%, P < 0.05) were observed in IPC-treated animals. Compared with sham-treated controls, blood flow measured with isotope-labeled microspheres during in situ contractions tended to be higher in IPC-treated animals in muscles composed of predominantly fast-twitch white fibers, such as the plantaris (～93%, P = 0.02). Capillary contacts per fiber and citrate synthase activity were not significantly altered by IPC treatment. Collectively, these data indicate that IPC improves exercise tolerance in a model of peripheral arterial insufficiency in part by enhancing blood flow to collateral-dependent tissues.     

The Y2 receptor mediates increases in collateral-dependent blood flow in a model of peripheral arterial insufficiency

We have utilized a rat model of peripheral artery disease (PAD) to examine whether the known angiogenic activity of the Y(2) receptor would translate into a meaningful increase in collateral blood flow. The maximal increase in collateral blood flow capacity of approximately 60% (p<0.001) was obtained with a 10microg/kgday (IA infusion, 14 days) of either PYY or PYY(3-36) and did not differ from that obtained with a maximally angiogenic dose of VEGF(165). Pharmacodynamic modeling based upon single dose pharmacokinetic plasma profiles of both agonists suggests that E(max) is reached when the Y(2) receptor is occupied by >or=50%. Furthermore, for PYY(3-36), occupancy of the Y(2) receptor is sufficient to promote a significant benefit in collateral blood flow.     

Study of the association of adrenomedullin and basic-fibroblast growth factors with the peripheral arterial blood flow and endothelial dysfunction biomarkers in type 2 diabetic patients with peripheral vascular insufficiency

Background

Progressive micro-vascular vaso-degeneration is the major factor in progression of diabetic complications. Adrenomedullin (AM) and basic-Fibroblast growth factor (b-FGF) are strongly correlated with angiogenesis in vascular diseases. This study aims to provide base line data regarding the vascular effects and correlation of AM, and b-FGF with the peripheral blood flow in diabetic patients with peripheral vascular disease (PVD), and their effect on endothelial dysfunction markers. Ninety age- and sex matched females were enrolled in the study: 30 were controls, 30 had diabetes without complications (group II) and 30 had diabetes with PVD (group III) diagnosed by ankle/ brachial index (A/BI). Plasma levels of AM, b-FGF, intercellular adhesion molecule −1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) were measured by indirect enzyme immunoassay (ELISA).

Results

There was a significant increase in plasma AM, VCAM-1and ICAM-1, while a significant decrease in plasma b-FGF in diabetic patients with PVD (p < 0.05). A positive correlation was observed between plasma AM, b-FGF and A/BI and a negative correlation with VCAM −1 and ICAM in diabetic PVD. AM was not a predictor, while b-FG, VCAM-1 and ICAM-1 could be predictors for peripheral blood flow in diabetic PVD.

Conclusion

This study elucidates for the first time that AM and b-FGF are correlated and have a direct impact on the peripheral blood flow, the rise of AM in diabetic PVD may be a consecutive and compensatory vasculo-protective effect as its angiogenic and anti-inflammatory properties act to relief the endothelial insult. Down expression of b-FGF may be a predisposing factor for micro-vascular derangement. It is not clear if the rise of AM and the decline of b- FGF levels may be consequences or predisposing factors for VCAM-1 and ICAM-1 elevation as these endothelial dysfunction biomarkers could reduce peripheral blood flow and vascular integrity. It is optimistic to believe that drug intervention through AM and b-FGF administration together with reversing the endothelial inflammatory process by targeting VCAM and ICAM could reduce the prevalence of diabetic vascular complications, reduce the risk of cerebrovascular and cardiovascular morbidity in diabetes through normalizing vascular endothelium function and peripheral blood flow.     

Radionuclide plethysmography for noninvasive evaluation of peripheral arterial blood flow

We validated a noninvasive radionuclide plethysmography technique to evaluate peripheral arterial blood flow during reactive hyperemia. This method, based on the measurement of blood volume variations during repetitive venous occlusions, was compared with strain-gauge venous impedance plethysmography. The technique uses 99mTc-labeled autologous red blood cells scintigraphy to determine the rate of change of forearm scintigraphic counts during venous occlusion. Thirteen subjects were simultaneously evaluated with radionuclide and impedance plethysmography. Six baseline flow measurements were performed to evaluate the reproducibility of each method. Twenty-seven serial measurements were then made to evaluate flow variation during forearm reactive hyperemia. After 30 min of recovery, resting forearm blood flows were again evaluated. Impedance and radionuclide methods showed excellent reproducibility with intraclass correlation coefficients of 0.96 and 0.93, respectively. There was also good correlation of flows between both methods during reactive hyperemia (r = 0.87). Resting flows at 30 min after reactive hyperemia were slightly lower than at baseline with both methods. We conclude that radionuclide plethysmography could be used for the noninvasive evaluation of forearm blood flow and its dynamic variations during reactive hyperemia.     

Tyrosine phosphatase inhibition augments collateral blood flow in a rat model of peripheral vascular disease

During embryonic development, the growth of blood vessels requires the coordinated activation of endothelial receptor tyrosine kinases (RTKs) such as vascular endothelial growth factor receptor-2 (VEGFR-2) and Tie-2. Similarly, in adulthood, activation of endothelial RTKs has been shown to enhance development of the collateral circulation and improve blood flow to ischemic tissues. Recent evidence suggests that RTK activation is negatively regulated by protein tyrosine phosphatases (PTPs). In this study, we used the nonselective PTP inhibitor bis(maltolato)oxovanadium IV (BMOV) to test the potential efficacy of PTP inhibition as a means to enhance endothelial RTK activation and improve collateral blood flow. In cultured endothelial cells, pretreatment with BMOV augmented VEGFR-2 and Tie-2 tyrosine phosphorylation and enhanced VEGF- and angiopoietin-1-mediated cell survival. In rat aortic ring explants, BMOV enhanced vessel sprouting, a process that can be influenced by both VEGFR-2 and Tie-2 activation. Moreover, 2 wk of BMOV treatment in a rat model of peripheral vascular disease enhanced collateral blood flow similarly to VEGF, and after 4 wk, BMOV was superior to VEGF. Taken together, these studies provide evidence that PTPs are important regulators of endothelial RTK activation and for the first time demonstrate the potential utility of phosphatase inhibition as a means to promote collateral development and enhance collateral blood flow to ischemic tissue.     

Characteristics of development of collateral vessels after experimental ligation of the femoral artery under conditions of venous insufficiency

Isolated ligation of the femoral artery and its combined ligation with the vein was performed in experiments on 62 dogs. Anatomical and physiological methods were used. It was stated that at the combined ligation collaterals developed sooner, number of anastomoses in muscles of the femoral posterior osseous-fascial case was greater, and their lumen was wider than at the isolated ligation of the femoral artery. However, the combined arterio-venous insufficiency was followed by a more severe postoperative course and noticeable biochemical disturbances. Thus, a certain discrepancy between the development of collaterals and the function of the tissue they feed was revealed. Analysing the data obtained it is possible to conclude that venous insufficiency, despite accelerating the transformation of the collaterals as a whole, aggravates conditions for collateral arterial circulation in the extremity.     

Changes in local cerebral blood flow during increased general arterial pressure in animals]

General blood pressure was increased in normal rabbits and in the animals with experimental renal hypertension by intravenous injection of noradrenaline; local cerebral circulation was recorded in two areas of the cortex the white matter of the large hemispheres by the method of hydrogen clearance and also by EEG. A number of successive changes of the local cerebral circulation was observed; these changes could be unitypical or different by duration and character on different electrodes. The appearance of pathological forms of electrical activity was noted on the EEG.     

The pulmonary hemodynamics changes under experimental myocardial ischemia in rabbits following increased arterial pressure

In acute experiments in anesthetized rabbits, changes of the pulmonary hemodynamics following myocardial ischemia in the region of the descendent left coronary artery were studied in control animals and after the infusion of adrenaline and phenylephrine. The pulmonary artery pressure was increased following infusion of these drugs; however, it decreased to normal level in the condition of myocardial ischemia. Meanwhile the pulmonary vascular resistance was elevated to the same level in both cases. Following adrenaline infusion, the pulmonary artery blood flow and venous return increased and, in the condition of myocardial ischemia, they decreased to normal level, but the left atrial pressure was decreased. Following phenylephrine infusion, the pulmonary artery blood flow and venous return did not change and, in the condition of myocardial ischemia, these parameters decreased lower than normal level but the left atrial pressure was elevated. Thus we concluded that equal values of the pulmonary artery pressure in both cases were caused by changes of different character in the left atrial pressure. The differences of the changes character and values of the pulmonary artery flow under experimental myocardial ischemia following the infusion of adrenaline and phenylephrine were caused by different shifts of the venous return.