AJP - Renal Physiology, Vol 258, Issue 5 1196-F1202, Copyright © 1990 by American Physiological Society
Urea recycling from the renal pelvis in sheep: a study with [14C]urea
A. Cirio and R. Boivin
Laboratoire de Physiologie, Ecole Nationale Veterinaire de Lyon, Marcy l'Etoile, France.
To test the hypothesis that urea can be recycled from the renal pelvis,
[14C]urea diluted in native urine (1 microCi/ml) was perfused (0.5 ml/min)
into one of the pelvises of sheep fed either normal (NP) or low
(LP)-protein diets. Blood samples were obtained from the ipsilateral renal
vein and from the carotid artery throughout the perfusions. 14C activity
determinations in urine and plasma demonstrated a flux of [14C]urea from
the pelvis to renal vein blood (40,000 in NP and 130,000
disintegrations/min in LP sheep, P less than 0.01). The corresponding flux
of native urea was only 1.5 times higher in NP than in LP sheep (6.8 +/-
1.1 vs. 4.7 +/- 2.9 mumol/min, not significant) despite their 8 times
higher urinary concentration of urea. The fraction of filtered urea that
was reabsorbed in the pelvis was larger in LP sheep (7.5 +/- 3.7 vs. 1.9
+/- 0.7% in NP sheep, P less than 0.05). A fraction of urea is thus
actually recycled from the renal pelvis in sheep, and this pelvic retention
is enhanced in LP animals. The importance of this phenomenon in the
nitrogen economy is discussed.
