Dynamics of Renal Proximal Tubular Secretion

Kinetic modeling of the renal excretion of iodopyracet in the dog

In a fundamental study on the kinetics of the urinary excretion of a number of agents secreted by the renal tubules of the mammalian kidney, we measured plasma levels of iodopyracet after intravenous application to male beagle dogs. The animals were anesthetized throughout the experiments with sodium pentobarbital, and provisions were made for the collection of blood and urine samples. In order to obtain a sufficiently high urine flow throughout the experiments, the dogs received a constant infusion of a solution containing 5% mannitol and 0.5% inulin. Inulin was added for measurement of the glomerular filtration rate. Linear plots of the urinary excretion rate against the average plasma concentration of each urine collection period were drawn as an illustrative way to depict the relation between plasma concentration period were excretion rate. For the mathematical description of these so-called tubular titration curves, a dynamic model was conceived to characterize the various renal transport mechanisms. Parameters for the description of the renal handling of iodopyracet were estimated by a simulation procedure with the aid of the computer program CSMP III.

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.

Factors affecting the maturation of renal PAH extraction in the new-born dog

1. The maturation of renal para-amino-hippurate extraction (E(PAH)) was studied in thirty-nine mongrel new-born dogs aged 2-29 days. E(PAH) was also measured in five adult dogs for comparison.2. There was no apparent change of PAH extraction during the first month of life but E(PAH) was lower in the puppy than in the adult. Under mannitol diuresis E(PAH) averaged 0.49 for the puppies and 0.83 for the adult dogs (P < 0.001). E(PAH) averaged 0.48 for the puppies under nondiuretic conditions, a value not significantly different from that observed during mannitol diuresis. There was no correlation of E(PAH) with mean arterial blood pressure.3. Inulin extraction (E(In)) remained constant during the first month of life and was the same in the new-born and adult dog suggesting that preglomerular shunting of plasma away from functioning nephrons was the same for both the puppy and adult dog.4. E(PAH) did not change in the puppy when plasma concentrations varied from trace (using [(3)H]PAH) to 0.25 mM indicating that excessive PAH load is not a factor in the low E(PAH) of the puppy.5. Diffusion of PAH from the red blood cell was excluded as an explanation for the low E(PAH) since diffusion was the same for both the adult and new-born dog.