Distribution of SNGFR in the cortex

Kidney posts Nov 11, 2011 Anatomy Autoregulation Filtration Vasculature

Juxta-medullary nephrons are consistently found to have higher filtration rates than superficial nephrons. Is this due to the underlying anatomy of the cortical radial artery, from which the juxta-medullary afferent arterioles branch before the superficial arterioles? Is it due to anatomical differences in the glomeruli, such as length, surface area or permeability? Or is it perhaps a matter of differences in the regulation of glomerular blood flow?

Due in part to the physical difficulty of observing juxta-medullary glomeruli without damaging the kidney, this is not an easy question to answer. And indeed, I have been unable to find any experimental results that directly address this issue. The most relevant papers that I have been able to find detail studies of the filtration rates in superficial and juxta-medullary nephrons, without investigation of the underlying cause(s).

The (non-definitive) answer seems to be that redistribution of SNGFR is rarely and inconsistently observed in adult models, and so the safest modelling assumption is to assume a constant (or near-constant) ratio of juxta-medullary to superficial SNGFR in the range 1.5–2.0.

Other papers that consider the distribution of SNGFR between the superficial and deep cortex include:

On a side note, I'm happy to finally cite two papers by Christian de Rouffignac, which were published in French.