Chronically instrumented fetal lambs are used extensively in fetal research. We have recently developed a method for measuring regional blood flow by means of fluorescent microspheres (FM) in fetal brain, heart, lung, liver, gut, spleen, kidney, adrenal, brown fat, skin, muscle, bone and placenta. 5 different spheres are used: blue (B), yellow-green (Y), orange (O), red (R), crimson (C). Tissues are digested by 4 M ethanolic KOH. The sedimentation method and dye extraction with Cellosolve acetate, as previously reported by others, is used for sample processing. Bones are cut and directly soaked in Cellosolve to extract the dye. Fluorescence is determined with a Cytofluor 2350 96-well plate reader. The spillover of the fluorescent signals into adjacent colors was experimentally determined to be 4% for O to Y and O to R and 25% for R to C, and these values are used to correct the initial sample readings. We have applied the method to fetal serial flow measurements during labor and delivery and the results agree very well with our previous estimates using radioactive microspheres. Moreover, use of the 96-well plate reader greatly reduces the sample measurement time compared to the latter method. The fluorescent method is thus a viable alternative to the radioactive technique for the measurement of blood flow to all fetal organs and tissues, including the placenta.
Supported by the Medical Research Council of Canada
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