Measurement of intrarenal blood-flow distribution in the rabbit using radioactive microspheres

1. Total renal blood flow and its distribution within the renal cortex of the conscious rabbit were studied with radioactive microspheres of 15 and 25 mum diameter. 2. The reliability of the microsphere technique was influenced by microsphere diameter and number (dose). The optimum microsphere diameter for determination of flow distribution in the rabbit kidney was 15 mum and dose 100-150 000 spheres. 3. Spheres of 15 mum nominal diameter were randomly distributed within the renal cortex of adult rabbits. The larger spheres in batches nominally 15 mum in diameter in young rabbits and 25 mum diameter in adult rabbits were preferentially distributed to the superficial cortex. 4. In adult rabbits 15 mum diameter spheres lodged in glomerular capillaries. Larger spheres occasionally lodged in interlobular arteries causing intrarenal haemorrhage. 5. Microspheres of 15 mum caused a decrease in renal clearance of creatinine and of p-amino-hippurate when the total injection dose was about 200 000 spheres. These effects were greater when the injection dose was increased to 500 000 spheres. 6. The reduction in total renal blood flow observed with large doses of spheres largely reflected decreased outer cortical flow, as measured by a second injection of spheres, and confirmed by a decrease in p-aminohippurate extraction. 7. The reproducibility of multiple injection studies was limited by these intrarenal effects of microspheres. 8. Total renal blood flow measured in six rabbits in acute experiments by the microsphere technique was 107 plus or minus 12 (mean plus or minus SD) ml/min and by p-amino-hippurate clearance was 100 plus or minus 10 ml/min. 9. Total renal blood flow in twelve conscious, chronically instrumented rabbits was 125 plus or minus 11 ml/min, of which 92 plus or minus 6 ml/min was distributed to the superficial cortex and 33 plus or minus 4 ml/min to the deep cortex.