[The effect of water depletion on renal excretion of urea and electrolytes in sheep].

Experiments were conducted with the sheep of Merino breed given water only at a rate corresponding to 0.5% of their live weight for three days. The animals were given feed ad libitum and during the control measurements water was also available to them ad lib. The fourth day the sheep were given no water and no feed and their renal functions were measured by the standard clearance technique. In the water-depleted sheep the diuresis was naturally reduced and the glomerular filtration rate (GFR) was also observed to have decreased from 77.6 +/- 5.3 to 62.2 +/- 4.2 ml X min-1, P less than 0.05. A small, though significant, decrease was also recorded in plasma urea concentration as a result of the reduced intake of food. The amount of excreted urea decreased by 41% (from 354.0 +/- 41.6 to 208.5 +/- 25.5 mumol X min-1, P less than 0.01) without significant changes in fractional excretion and tubular reabsorption of urea. After three days of water depletion the sheep exhibited a tendency of slight natriuresis whereas the excretion of potassium was reduced. Water depletion was also accompanied by a significant increase in the osmolality of plasma (from 298.0 +/- 1.3 to 317.0 +/- 1.8 mosmol X kg-1 H2O, P less than 0.001) and urine from 789.0 +/- 95.0 to 1547.0 +/- 53.0 mosmol X kg-1 H2O, P less than 0.001), without changes in the clearance of free water. On the other hand, the osmotic clearance was reduced as a result of suppressed excretion of urea and potassium (from 2.33 +/- 0.21 to 1.61 +/- 0.17 ml X min-1, P less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)