Concentrative transport in human renal biopsy specimens

In vitro concentrative transport to tritiated p-aminohippuric acid (3H-PAH) was evaluated in renal biopsy specimens from human subjects by section freeze-dry autoradiography. Renal cortical tissue obtained by percutaneous needle biopsy (23 of 27 tissue specimens) was incubated in vitro using a modified renal cortical slice technic. Following incubation in medium containing 3H-PAH, the biopsy fragment was snap-frozen, and section freeze-dry autoradiographs were prepared. The autoradiographs demonstrated cellular accumulation of 3H-PAH by proximal tubules of human kidney in vitro and suggest that PAH transport is uphill across the luminal as well as the antiluminal membrane. The number of proximal tubules which accumulate 3H-PAH in vitro diminishes as renal failure progresses. Cellular accumulation of PAH, however, was not impaired by heavy proteinuria, and appeared not to be related to the underlying glomerular histologic diagnosis. The frequency of proximal tubules showing 3H-PAH uptake in the cortex varied directly with the glomerular filtration rate and inversely with the degree of interstitial involvement. Proximal tubules which maintain the ability to accumulate 3H-PAH are clustered in fewer regions of the cortex in patients with reduced glomerular filtration rates. This observation is consistent with the view that residual renal function is renal failure arises from a few relatively normal nephrons rather than from a more uniformly damaged population of nephrons.