The effect of saline water on kidney tubular function and electrolyte excretion in sheep

Abstract

The function of the kidney tubules of sheep which, for periods of 6 months or more, have been confined solely to saline water (1.3% sodium chloride) for drinking, has been compared with that of sheep on identical fodder but receiving drinking water with a low salt content (rain-water). As no consistent difference was observed between the maximal rates of excretion and reabsorption in the kidneys of the two groups, it is probable that prolonged ingestion of sodium chloride by the sheep does not induce an increase in the number of active tubules in its kidneys. The sodium content of the plasma remained unchanged, but slight increases in potassium and chloride were observed in the plasma of those sheep confined to saline water. Urinary excretion of sodium and chloride was greatly increased, and potassium to a lesser extent. Reabsorption of each of these electrolytes, after filtration at the glomerulus, was found to be reduced during transit through the renal tubules. In the sheep which drank saline water, urinary pH was increased and osmolarity reduced. Clearance of total free water, however, was negative, and the osmotic concentration of body fluids was maintained by the production and excretion of urine which was hyperosmotic with blood plasma. The findings illuminate the manner in which renal adjustments assist the sheep to tolerate water relatively high in salt.