MEASUREMENT OF GLOMERULAR BLOOD-FLOW IN RABBITS AND RATS - ERRONEOUS FINDINGS WITH 15-MU-M MICROSPHERES

Measurement of glomerular blood flow in rabbits and rats: Erroneous findings with 15-μm microspheres. Intrarenal distribution of blood flow was assessed in rabbits and rats with the 15-μm microsphere method. Collection of individual glomeruli after silicone rubber arterial filling of the kidney permitted determination of blood flow rate per glomerulus (GBF) in glomeruli from various cortical depth and with different vascular patterns: G1, most superficial; G4, true juxtamedullary (giving rise to vasa recta); G2 and G3, intermediate. In rabbits, GBFs in G1 and G4 were equal and significantly higher than were GBFs in G2 and G3 (G1 to G4: 198 ± 21 SEM, 101 ± 18, 114 ± 14, and 197 ± 13 nl/min). In rats, GBF in G1 was threefold higher than that of other glomeruli (G1, 308 ± 18; G2-G3, 108 ± 16; G4, 100 ± 10). Mean size and the frequency distribution of the microspheres found in superficial and deep glomeruli in the rabbit, both differed significantly. Larger spheres were preferentially found in superficial glomeruli in both species. This uneven distribution of the microspheres of different sizes throughout the cortex, as well as the unlikely filtration fractions that are derived from the present GBF values and commonly reported values for SNGFR, lead to the conclusion that microsphere distribution in the renal cortex does not reflect intracortical blood flow distribution accurately in rats and rabbits. From the present study, no statement can be made concerning the use of the microsphere technique in the dog.