The Tubular Factor in Renal Hemoglobin Excretion

A drop has been observed in the renal threshold for hemoglobin in dogs, of over 60 per cent, following repeated injections daily. It was not associated with a cessation of tubular reabsorption. Hemoglobin excretion rate curves, obtained initially and after lowering the threshold, have proved to be parallel lines originating at the respective levels. Hemoglobin containing radio-active iron has been used to determine the amount of iron retained by the kidneys 24 hours after injection. The kidneys of normal animals retain slightly less iron than those of animals with lowered thresholds, despite the fact that the former group has a much higher estimated rate of tubular reabsorption. It is suggested that hemoglobin products are more rapidly removed from the kidneys of normal animals, following reabsorption, than from those of animals which have received multiple injections of hemoglobin.