Micropuncture study of composition of proximal and distal tubular fluid in rat kidney.

ULLRICH, KARL J., BODIL SCHMIDT-NIELSEN, ROBERTA O’DELL, GUNDULA PEHLING, CARL W. GOTTSCHALK, WILLIAM E. LASSITER, AND MARGARET MYLLE. Micropuncture study of composition of proximal and distal tubular @id in rat kidney. Am. J. Physiol. 204(4) : 527-531. I 963.~Fluid was collected by micropuncture from proximal and distal convolutions of anesthetized rats and analyzed for inulin, sodium, urea, and total osmotically active solute. The proximal fluid/plasma (F/P) sodium ratio was not significantly different from unity in antidiuretic animals, but was as low as 0.78 during mannitol diuresis. The distal F/P sodium ratio averaged 0.62 in antidiuresis, and 0.24 during osmotic diuresis. The data are interpreted to indicate active sodium transport by both proximal and distal convolutions. The F/P ratios for inulin, urea, and total osmotically active solute are in general agreement with previous studies.