The Radiolabeled Frog Red Blood Cell

The red cell of the bullfrog Bufo vulgaris was used to measure the intrarenal distribution of blood flow in the kidney of the dog. These cells were fixed in 1% glutaraldehyde and labeled with sodium pertechnetate (99MTc); they were 18 × 10μ in size and had a specific gravity of 1.076—a value close to that of the dog red blood cell. These cells had no discernible effect on systemic or renal hemodynamics after injection, did not agglutinate, were well mixed and evenly distributed throughout different areas of the renal cortex, and were completely extracted in one circulation through the kidney. When the renal cortex was divided into four equal zones, the fractional distribution of the frog red blood cells was 39, 33, 20, and 8% going from the outer to the inner cortex. These values were not significantly different from those obtained in the same dogs with radioactive microspheres—particles much denser than the frog red cells. In two other models involving intrarenal acetylcholine administration and hemorrhagic hypotension, there was no difference between the regional blood flow distribution measured with the frog red cell method and that measured with the microsphere method. However, with both acetylcholine infusion and hemorrhage, there was a redistribution of renal cortical blood flow to the inner cortex compared with the distribution determined by either method during hydropenia. Thus, a similar intrarenal distribution of blood flow was found with two indicators of different size, shape, and density. We suggest that the primary rheologic factor affecting a particle such as a frog red blood cell or a microsphere markedly diluted among circulating red cells is its interaction with these normal cells.