Effects of Xanthine Diuretics on Renal Tubular Transport of PAH and Glycine Conjugation of PABA

Abstract

In renal cortical slices, methylated xanthine diuretics caused a reduction of PAH uptake to 50–70% of the control values with a slight increase in O₂ consumption; xanthine, hypoxanthine, guanine and adenine had little effect. Among the three methylated xanthine derivatives studied, 1,3 dimethylxanthine ethylenediamine (Aminophylline) was found to have more inhibitory effect than the others. This inhibitory effect was a function of the concentration of the compound in the medium and cannot be reversed by addition of glutathione as is the case with mercurial diuretics. The potassium exchange between cells and medium and the glycine conjugation of PABA to PAH by the tubular cells were not significantly affected in the presence of aminophylline. The mechanism of the action is discussed and it is postulated that aminophylline or the other methylated xanthine compounds increase the membrane permeability of renal tubular cells, allowing more PAH to leak out.