Diameter of the afferent arteriole in the dog kidney estimated by the microsphere method

Microspheres with diameters of from 10 to 30 mum were injected into the renal arteries of three anesthetized dogs. The six kidneys were studied by light microscopy. The diameters of the spheres trapped in the afferent arterioles and of all spheres recovered in the kidneys were recorded. On the basis of the distribution of diameters in these two populations of spheres, the average diameter of the afferent arteriole and the distribution of the afferent arteriolar diameters were estimated. The average diameter of the afferent arterioles was 16.3 mum (S.D. 2.2 mum), without any difference between three cortical layers of equal thickness. The mean diameter of spheres trapped in the interlobular arteries was 25.7 mum (S.D. 2.6). It is suggested that the pressure drop along some interlobular arteries may be of physiological importance, affecting the autoregulation of blood flow in the renal cortex.