Die Bedeutung des Anions f�r den renal tubul�ren Transport von Na+ und die Transporte von Glucose und PAH

Organic acid (or anion) and organic base (or cation) transport by renal tubules of nonmammalian vertebrates

Organic acids (or anions) and organic bases (or cations) are transported by the renal tubules of nonmammalian vertebrates, but until recently the details of the transport processes have been poorly studied. Work with isolated perfused and nonperfused renal tubules and with membrane vesicles has now begun to supply information on the transepithelial transport processes and the transport steps at the individual cell membranes. The current information is reviewed for organic acids (or anions) as a general group, for urate (which generally appears to be transported by a separate system from that for other organic anions), and for organic bases (or cations) as a general group. Tentative cellular models for the transepithelial transport of each of these general categories of compounds are suggested.

Inhibitory effect of 6-aminonicotinamide on the renal transport of para-aminohippurate in the rat

In this study, we investigated the effect of 6-aminonicotinamide (6-AN), a typical potent inhibitor of the pentose phosphate pathway, on the renal transport of para-aminohippurate (PAH) in the rat. The contents of adenosine-triphosphate (ATP) and 6-phosphogluconate (6-PG) in the kidney were measured at intervals of 2 hours after the administration of 6-AN (75 mg/kg body weight, i.p.). It was found that the 6-PG content in the kidney rapidly increased and reached a plateau at the fourth hour after the administration, with this level being maintained up to the eighth hour. In contrast, the ATP content was found to remain normal up to the sixth hour, after which it significantly decreased as time elapsed. Furthermore, additional experiments were carried out by loading the rat with a high concentration of PAH solution at 6 hours after the administration of 6-AN. The renal tubular secretion maximum for PAH was significantly depressed in the 6-AN group in comparison to the control. These results suggest that this depression in renal PAH secretion capacity was partially due to the inhibition of the pentose phosphate pathway in the kidney, but not due to the change of renal ATP level.

Influence of glomerular filtration rate on renal PAH secretion rate in the rat kidney. Dependency of PAH extraction on renal filtration fraction

PAH secretion (TPAH) was studied in rats at spontaneously occurring glomerular filtration rate (GFR). At saturated transport, TPAH was found to be correlated to GFR. This relationship was also observed at unsaturated transport where TPAH depends upon the PAH concentration in arterial plasma. However, no significant correlation between TPAH and renal PAH load or renal plasma flow rate was found when the effects of GFR were removed by partial correlation analysis. A dependency of TPAH on GFR explains the correlations found between filtration fraction (FF) and renal PAH extraction (EPAH) or renal tubular PAH extraction fraction (EPAH--FFPAH). Thus, even at low PAH concentration in a. plasma, renal PAH extraction may only be assumed to be constant if the filtration fraction is constant.