Abstract Ammonium (NH3 plus NH4+), produced predominantly in the proximal tubule, is
transferred to the final urine by a process involving countercurrent multiplication of
ammonium which generates an ammonium concentration gradient in the renal medulla. It
was hypothesized that if urinary ammonium excretion rates are controlled in part by the
medullary ammonium gradient, changes in hydration and acid-base state should cause
changes in the medullary ammonium gradient consistent with expected changes in urinary …