Reabsorption of inorganic sulfate in the frog kidney: saturation of transport mechanism.

1. Clearance experiments were performed to study reabsorption of inorganic sulfate (SO4) in the frog kidney. 2. During stepwise elevation of the SO4 concentration in plasma by i.v. sulfate administration (SO4 titration), the absolute reabsorption of SO4 did not increase but kept constant during mild SO4 loading. 3. The maximal reabsorptive capacity for SO4 (TmSO4) was about 0.37 mumol/30 min in this species. 4. The present results do not indicate renal net secretion of SO4 in the frog.