ON THE RENAL TUBULAR EXCRETION OF CREATININE IN NORMAL MAN1

Abstract

[longdash]The process responsible for the renal tubular excretion of creatinine in normal man was reexamined. In order to isolate the tubular process for examination, glomerular filtration rate was measured simultaneously with the observations on creatinine excretion by means of the inulin clearance. 1. The dependent curvilinear relationship between plasma conc. and the tubular excretion of this substance was reaffirmed. 2. After the oral adm. of a dose of creatinine (13 gs.) the initially high clearance falls progressively with time. 3. If, after this fall, a 2d dose of creatinine is administered, tubular excretion is raised to or toward the initial level of activity. 4. When the plasma conc. is maintained by the constant intraven. infusion of creatinine, tubular excretion is usually maintained at a level close to that observed initially. 5. It is tentatively suggested that the phenomena described under 2 and 3 are not due to a change in the renal tubular mechanism itself, but rather that, subsequent to its entry into the body, some of the creatinine undergoes a change which makes it less readily transferable by the tubular mechanism.