The competition between p-amino-hippuric acid (PAH) and diodrast for renal excretion and extraction in man.

The competition between two substances for tubular excretion has been demonstrated repeatedly with orthodox clearance techniques. Smith, Goldring, and Chasis (1) found that raising the plasma concentration of diodrast depressed the excretion of phenol red. They concluded that both substances were excreted by the same mechanism. Similarly, it has been reported that intravenously administered diodrast (2) or PAH (3) retard the excretion of penicillin, that hippuric acid depresses the tubular excretion of glucuronic acid derivatives in the chicken (4), and that the amide of methyl-nicotinic acid depresses the tubular excretion of guanidine (5). Recently, it has been demonstrated that PAH in sufficient concentrations excludes phenol red from the cells or lumen of fish tubules suspended in appropriate salt solutions (6). Smith, Finkelstein, Aliminosa, Crawford and Graber (7) found that diodrast and PAH given simultaneously had approximately the same renal clearance in man when the plasma concentration of both was low. They concluded that the two substances were excreted by the same mechanism. In none of these previous studies has the simultaneous renal extraction of the examined substances been investigated by analysis of renal vein blood. In fact, although it has been reported that renal extraction of diodrast is lower than that of PAH (8), there have been no published reports of simultaneous measurements of extraction of the two substances. In the present study, the renal percentage extraction (E) and the tubular excretion (T) of diodrast and PAH in man were simultaneously compared in experiments during which the plasma