The Effects Of Drag-reducing Polymers On Hemodynamic Parameters Of Abdominal Aorta And Hindlimb Arteries And Microcirculational Perfusion Of Rat Skeletal Muscle

ObjectiveIn 1948,British scientists BA Toms reported a special class of soluble polymers (average molecular weight>1 000 000 Dalton) can reduce resistance to turbulent flow without influence on the fluid viscosity in the First International Congress on Rheology. These polymers so be called drag-reducing polymers (DRPs) and this drag reducting phenomenon is known as Toms phenomenon. Since discovery of the Toms phenomenon, DRPs has been used in petroleum, fire fighting, irrigation, navigation and other areas widely.In recent years,the prospect of DRPs in the biomedical field has been paid more and more attention. Circulation system is a closed transport system composed of heart, arteries,capillaries and veins.The flow power of this system comes from heart keeping beating. As circulation system has many similarities with the industrial pipe, so the application of DRPs in circulation system can be referred to the industrial theory.Preliminary studies by foreign scientists found that DRPs has very impotant potential value in ischemic cardiovascular diseases, atherosclerosis, hemorrhagic shock and some other circulatory diseases.Foreign studies on the DRPs are mainly on its value of pharmacodynamic characters.As to the dose-response relationship of the drag-reducing phenomenon in vivo study, there is no any report.Normal animal models or arterial stenosis models are mainly used in the potential application of DRPs in circulation system in recent years.It is reported that drag reducing can improve blood flow of normal or stenotic arteries.But to the acute totally obstructed arteries, can DRPs also improve blood perfusion of the ischemic skeletal muscle by collateral ateries?This study was undertook to research the dose-response relationship of DRPs and to estimate the effects of DRPs on improving microcirculation in vivo.Polyethylene oxide (PEO) is a typical polymer widely used in drag-reducing areas, so it is chose as DRPs in this study. Firstly, find a method to purify PEO and observe the effects of PEO solutions on the abdominal aortic blood flow and vascular resistance at different concentrations to find the dose-effect relationship.And then, estimate the effect of PEO on improving microcirculation in both normal skeletal muscle and acute ischemic skeletal muscle of rat hindlimbs.Methods1.Preparation of DRPs and analyze the dose-effect relationship in vivo.1.1.Preparation of DRPs.Polyethylene oxide (PEO) with 5000 kDa molecular weight(Sigma-Aldrich, St Louis, MO, USA) was chose to be the DRPs in current study,which was dissolved in saline at a concentration of 0.1%(1000 ppm) and then dialyzed against saline for 24 h using a membrane with 50 kDa molecular weight (MW) cutoff (Spectrum Laboratories Inc.).After dialysis, PEO solution was diluted to 10ppm and stored at-4 centigrade degrees.1.2.Analyze the dose-effect relationship of DRPs by monitoring hemodynamic parameters of normal ratsThirty-two rats were anesthetized and randomly divided into four groups.An ultrasonic flow probe was placed around the abdominal aorta (5 mm above the common iliac artery) to measure blood flow. Carotid artery pressure,iliac artery pressure, iliac vein pressure, central venous pressure (CVP) and ECG were also monitored during this study. Saline and varying concentrations of PEO (1 ppm,10 ppm and 50 ppm) were separately injected through caudal vein at a constant rate of 5 ml/h for 20 minutes in each group.Vascular resistance was calculated as AP/abdominal aortic flow, where AP= iliac artery pressure-iliac vein pressure.2.Estimate the effects of polyethylene oxide (PEO) solutions on improving microcirculation of normal rat hindlim.2.1.Preparation of DRPs.10ppm PEO solution was chose in this study.2.2.Animals and experimental protocol.10 ppm PEO solution or Saline was separately injected through the caudal vein at a constant rate of 5 ml/h for 20 minutes in each group.Contrast-enhanced ultrasonography (CEU) was performed before and after drug (PEO or Saline) injected. ECG, blood pressure, and central venous pressure (CVP) were also monitored in this study.2.3 CEU data analysis.CEU images were analyzed with Auto-Tracking Contrast Quantification (ACQ) software (Acuson, Siemens).ACQ software depicted Sound Intensity (SI)-time curve and calculated A, (3 automatically.ΔAT versus SI data were fit to the function Y=A(1-e(-β*t)),where Y is SI at the pulsing interval t, A is plateau SI, which is an index of blood volume, and (3 is the rate constant that provides a measure of microvascular blood velocity.A×βused for calculating microvascular blood flow.All the contrasted perfusion images also been colour-coded by an off-line image analysis software (MCE Version 2.7,University of Virginia, West Virginia, US).The software use a map whereby video intensity change for each pixel was coded by gradations of read,orange,yellow, and white,in proportion to increasing contrast enhancement.3.Estimate the effects of polyethylene oxide (PEO) solutions on improving microcirculation of acute ischemic rat hindlimb. 3.1.Preparation of DRPs.10ppm PEO solution was chose in this study.3.2.Animals and experimental protocol.Right femoral artery was exposed and ligated.10 ppm PEO solution or Saline was separately injected through the caudal vein at a constant rate of 5 ml/h for 20 minutes in each group.Contrast-enhanced ultrasonography was performed before and after drug (PEO or Saline) injected.ECG,blood pressure, and central venous pressure (CVP) were also monitored in this study.3.3 CEU data analysis.The same as 2.3.Results1.Preparation of DRPs and analyze the dose-effect relationship in vivo.Abdominal aortic flow was increased significantly in the group treated with 10 ppm PEO (F=18.884,P=0.003), while the vascular resistance was reduced (F=12.597, P=0.009) as compared to the saline control group. There were no any changes in abdominal flow (F=3.973,P=0.088) and vascular resistance (F=4.117, P =0.082) in the group treated with 1 ppm PEO. When treated with 50 ppm PEO abdominal aortic flow increased to a threshold during the first 4 minutes, after which it rapidly decreased towards baseline levels despite continuous infusion. Blood pressure was constant except in the 50 ppm group in which it was reduced by about 10 mmHg (F=11.156, P=0.014) during infusion.Heart rate and CVP were constant in all groups.2.Estimate the effects of polyethylene oxide (PEO) solutions on improving microcirculation of normal rat hindlimb.After giving PEO, microcirculation capillary volume (A) increased from 20.78±2.63 to 22.40±1.94 (t=2.908, P=0.023); red blood cell velocity(β) increased from 0.27±0.08 to 0.35±0.13((t=3.479,P=0.010);capillary blood flow (A×β) increased from5.65±1.81 to 7.91±3.28(t=3.292,P=0.013).As to the control group, there were no significant differences in A, (3 and A×β(all P>0.05)between saline injected before and after. Both PEO and normal saline have no influence on the heart rates, blood pressures and CVP (all P>0.05).3.Estimate the effects of polyethylene oxide (PEO) solutions on improving microcirculation of acute ischemic muscle rat hindlim.After giving PEO, ischemic skeletal muscle capillary volume (A) have no significant change (before injection:21.71±2.41,after injection:21.67±2.58,t= 0.035,P=0.973);while red blood cell velocity(β) and capillary blood flow (A×β) increased significantly(β:0.05±0.01 vs.0.10±0.03,t=7.338,P<0.001;A×β: 1.06±0.35 vs.2.12±0.57,t=6.552,P<0.001).As to the control group, there were no significant differences in A,βand A×β(A:20.28±1.09 vs.20.31±1.37,t= 0.039,P=0.970;p:0.05±0.02 vs.0.06±0.03,t=1.263,P=0.247;A×β:1.00±0.39 vs.1.20±0.56, t=1.287, P=0.239) between saline injected before and after. Both PEO and normal saline have no influence on the heart rates, blood pressures and CVP (all P>0.05).Conclusions1.PEO solution purified by our laboratory can reduce the vascular resistance effectively.2.The drag-reducing effect is closely related to PEO concentration. Compared with lppm, lOppm PEO increased flow and decreased resistance more effectively. The effectiveness and safety were reduced as PEO concentration increased to 50 ppm.3.PEO increased capillary volume, red blood cell velocity and capillary blood flow of normal rat hindlimb skeletal.4.PEO increased both red blood cell velocity and capillary blood flow of acute ischemic rat hindlimb significantly.