INFLUENCE OF PREVIOUS SALT INGESTION ON RENAL FUNCTION OF SHEEP SUBJECTED TO INTRAVENOUS HYPERTONIC SALINE

1. Sheep, which had access to a solution containing 1·3% sodium chloride as their sole source of drinking water for 6 months or more, were infused with a hypertonic solution (10%) of sodium chloride, and their ability to tolerate this salt load was compared with that of a similar group of sheep which drank only rain water. 2. The sheep which drank the rain water were often affected by the infusion and exhibited signs resembling potassium deficit. No such signs were apparent in the animals which consumed saline water. 3. Glomerular filtration rates were increased in all sheep by the hypertonic saline infusion, the increases being greater in the sheep which were maintained on the saline water. Effective renal plasma flow rates, though extremely variable, behaved in a similar manner. 4. Plasma values for sodium and chloride were increased in all sheep, but remained at a higher level for a longer period in the sheep which consumed rain water. The diuresis produced by hypertonic saline appeared to persist for a longer period in the sheep which drank rain water, while the excretion of sodium and chloride tended to be greater in the sheep maintained on saline water. 5. Plasma potassium was reduced in all sheep and urinary excretion of potassium increased. The latter response was more pronounced in the sheep which drank the rain water. 6. Filtered loads of sodium, chloride and potassium were greater in the sheep which were accustomed to drinking saline water. However, the amounts of potassium excreted were greater than those filtered in the rain water sheep and less than those filtered in the sheep which drank saline water. It therefore seems that secretion of potassium into the kidney tubules predominated in the former group and reabsorption prevailed in the latter. 7. Reabsorption of free water in excess of solute was greater in the kidney tubules of the sheep which drank saline water. 8. Increased blood volume and greater dilution of plasma proteins occurred in the sheep which drank rain water. © 1968 The Physiological Society