Intrarenal Distribution of Nutrient Blood Flow Determined with Krypton 85 in the Unanesthetized Dog.

• The development of the couutercnrrent hypothesis as an explanation for the osmotic gradient from cortex to papilla of the kidney has again stimulated investigation of the intrarenal distribution of blood flow. Theoretical considerations have emphasized the necessity of a relatively low medullary blood flow for the maintenance of this gradient. However, present methods of measuring renal blood flow in the intact animal do not estimate the distx-ibution of flow to the medulla. Trueta and co-workers demonstrated by renal angiography that medullary flow was slower than that of the cortex; these observations have been confirmed by Kramer et al.,'' who found that the medullary transit time of Evans blue dye was much longer than that of the cortex. In the present investigation, a method has been developed for determining distribution of renal blood flow in the unanesthetized dog by monitoring the disappearance of Kr from the kidney after injection of the isotope into the chronically catheterized renal artery; no blood samples are needed for the measurement. .Kr**, an inexpensive and readily available isotope, was used by Brun and coworkers" to measure renal blood flow by the modified ICety technique; they were, at that time, unaware of the gamma emissions from Kr'\ Although Kr is primarily a beta emitter, 0.6% of its disintegrations are gamma