Lead flux through the kidney and salivary glands of rats

The blood disappearance curve of lead injected intravenously into rats and its appearance curve in the saliva reflect a three-compartment open model. Urinary elimination rate showed many fluctuations in the first 10 days but decreased progressively afterward. In clearance experiments, with low lead infusion (4 micrograms/min), renal reabsorption accounted for nearly all the filtered lead load, and salivary secretion was on the order of 1 ng/min. Experiments with renal and salivary tissue fragments indicated maximal accumulation in both tissues. Contrary to salivary tissue uptake, renal accumulation of lead decreased in the presence of KCN and 2,4-dinitrophenol, and in Na+-deficient media. Renal lead uptake contains, therefore, an important energy-dependent component. In vitro evidence that the lead transport mechanisms of the kidney and salivary glands are fundamentally different is consistent with the results of the pharmacokinetic study. The resemblance between the early profile of salivary lead secretion and its disappearance from the blood indicates that salivary glands represent diffusion barriers for the metal, in contrast to the kidney where lead uptake may be influenced by energy- and metabolism-dependent mechanisms.