The intrarenal distribution of tritiated para-aminohippuric acid determined by a modified technique of section freeze-dry radioautography

Multiorgan crystal deposition following intravenous oxalate infusion in rat

Deposition of calcium oxalate is responsible for the pathologic manifestations of oxalosis and may contribute to multiorgan dysfunction in uremia and to the progression of renal damage after renal failure is established. We have developed a rat model of oxalosis using a single intravenous injection of sodium oxalate, 0.3 mmol./kg. body weight, in rats. Polarized light microscopy and section freeze-dry autoradiography were used to identify 14C-oxalate within the renal parenchyma and in extrarenal organs. 14C-oxalate crystals under three mu in length were identified within one min. of injection in proximal tubule lumens. Section freeze-dry autoradiography showed occasional minute crystals within glomeruli, heart, lung and liver at one hr. In contrast to concentrative cellular uptake demonstrated in rat renal cortical slices in vitro, intracellular accumulation of 14C-oxalate could not be detected in vivo. Within the first 24 hr., renal oxalate retention reached a maximum of 25 +/- 4 per cent of the injected dose/gm. kidney compared to a maximum of only 7 +/- 3 per cent/gm. kidney after intraperitoneal administration. Although less than one per cent dose/gm. kidney remained after one week, crystal fragments were scattered throughout the cortex and medulla, often surrounded by foci of interstitial nephritis. The retention of crystals in kidney and other body organs following i.v. oxalate provides a model of oxalosis which stimulates pathophysiologic events in a variety of clinical situations characterized by transiently or persistently elevated serum oxalate.

Phlorizin stimulation of p-aminohippurate uptake in rat kidney cortex slices

Phlorizin, 0.5 mM, increases the uptake of tritiated p-aminohippuric acid (PAH) in rat kidney cortex slices in vitro. Phlorizin also diminishes the rate of 3H-PAH washout from preloaded slices into PAH-free medium. At higher concentrations, phlorizin (5.0 mM) reduces slice uptake of 3H-PAH following short incubations but increases 3H-PAH accumulation after more prolonged incubations. Section freeze-dry autoradiography demonstrates that phlorizin inhibits secretion of 3H-PAH from cell to lumen in proximal tubules. Consequently, the increased 3H-PAH uptake and delayed washout induced by phlorizin may be attributed to effects at the antiluminal cell membrane. Phlorizin stimulation of PAH uptake occurs despite inhibition of secretion across the luminal membrane. Intracellular accumulation of 3H-phlorizin, demonstrable by autoradiography, provides direct evidence that cellular accumulation affords the glycoside access to both the luminal and antiluminal membrane in proximal tubules. These interactions between phlorizin and PAH suggest shared features of the membrane transport systems for secretion and reabsorption of sugars and organic acids in kidney.

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.

Occupational lead nephropathy

Among eight subjects suspected of excessive occupational exposure to lead, detailed examination of renal function identified abnormalities in four. Glomerular filtration rate was less than 87 ml/mim/1.73 m2 in one subject with asymptomatic renal failure, and in three subjects with preclinical renal dysfunction. In the subject with asymptomatic renal failure, chelation therapy increased the glomerular filtration rate, p-aminohippurate (PAH) extraction, the maximal PAH secretion rate (TmPAH) and improved proximal tubule ultrastructure, despite decreased renal plasma flow. This improvement in PAH transport was associated with correction of a proximal tubule defect in tritiated PAH uptake detected by section freeze-dry autoradiography of renal biopsy specimens. In three subjects, the etiologic diagnosis of lead-induced nephropathy was established by exclusion, but tubular dysfunction did not obviously exceed the reduction in blomerular filtration. Proximal tubule abnormalities were seen in each of the three patients who underwent biopsy. These studies suggest that lead nephropathy may be an important occupational hazard in the United States lead industry.