Determination of regional myocardial blood flow using fluorescent microspheres.

Determination of blood flow in tissues at risk for infarction is necessary for in vivo studies of the pathologic effects of vascular occlusion. Such blood flow measurements are traditionally carried out using radioactive microspheres. These are expensive and may pose a significant hazard to laboratory personnel. In addition, disposal of radioactive wastes, especially radioactive carcasses, is an increasingly expensive and inconvenient process. To avoid these problems, we have developed a modified procedure using fluorescent microspheres. To measure blood flow, spheres are injected intravenously and a blood sample is taken. Following cardiectomy, appropriate segments of left ventricular myocardium are digested with proteases to release the spheres, which are then purified through sucrose gradients. The spheres may be counted manually using an epifluorescence microscope, or by flow cytometry. Comparison of this method with the traditional radioactive microsphere procedure reveals similar results for the two methods. Fluorescent microspheres should provide a useful and accurate alternative method for measuring blood flow in studies of vascular disease.

Reduction of myocardial infarct size by poloxamer 188 and mannitol in a canine model.

Poloxamer 188 has been reported to inhibit thrombosis, decrease whole blood viscosity, and improve perfusion of damaged tissue. Mannitol has free radical scavenging capabilities that might contribute to myocardial salvage after ischemia. Because these agents appear to work in different ways, we studied their cardioprotective properties when they were used separately and in combination. After 75 minutes of left anterior descending coronary artery (LAD) occlusion, dogs received poloxamer 188 (48 mg/kg), mannitol (0.5 gm/kg), or both intravenously during an additional 15 minutes of LAD occlusion and for 45 minutes of reperfusion, whereas control dogs received an equal volume of saline solution. After surgery the animals were maintained for 24 hours and then killed. Areas of myocardial infarction (MI) and risk of infarction (R) were calculated by means of planimetric analysis of slices of myocardium stained with 1.5% triphenyltetrazolium and 0.5% Evans blue dye. The ratio of MI/R (mean +/- standard error of the mean) were: control, 25.6 +/- 1.8% (n = 10); poloxamer 188, 12.7 +/- 2.0% (n = 10); mannitol, 10.6 +/- 2.5% (n = 11); and poloxamer 188 plus mannitol, 8.0 +/- 4.1% (n = 10). Measurement of microvascular blood flow indicated a similar 86% to 91% reduction of blood flow to the area at risk in all treatment groups. Consequently both poloxamer 188 and mannitol appear to increase salvage of ischemic myocardium and a combination of the two may be more effective than either agent alone.