Nalidixic acid: intrarenal distribution and its effect upon para-aminohippurate excretion.
Studies performed on the intrarenal distribution of nalidixic acid in dogs show that this weak organic acid is indeed accumulated in the kidney, the highest concentration being attained in the cortex and followed in order by the outer medulla, papillae, and inner cortex. Our results also show that nalidixic acid produces significant changes in the para-aminohippuric concentration and on the filtered load, secretion and clearance of para-aminohippuric acid. Stop-flow experiments confirmed the inhibitory effect of nalidixic acid upon para-aminohippuric acid secretion. It is plausible that nalidixic acid may inhibit the secreted moiety of creatinine. This inhibitory effect is localized in the proximal tubule, where para-aminohippuric acid is known to be secreted. Based on our data it is suggested that nalidixic acid competes with para-aminohippuric acid for the same transport system or that the decreased secretory para-aminohippuric acid activity after nalidixic acid may be caused by a direct inhibition produced by the latter.