INFLUENCE OF NEED ON RATS PREFERENCE FOR DILUTE NACL SOLUTIONS

Thirsty rats were given a 24 hr drinking test in which both water and 0.15 M NaCl were available. Rats dehydrated intracellularly, by subcutaneous injection of hypertonic NaCl or sorbitol solutions, decreased their saline preferences during hyperosmolality and consumed sufficient water to rapidly relieve their water deficits. In contrast, rats dehydrated intravascularly, by subcutaneous injection of hyperoncotic polyethylene glycol solution, increased their saline preferences during hypovolemia and more gradually consumed sufficient saline to relieve their plasma deficits. The alterations in fluid selection indicate that the intakes of dehydrated rats were adjusted in accordance with their needs. Differences in drinking rates reflected previously demonstrated differences in the rates of dehydration produced by the treatments. These results suggest that physiological need, in addition to well-known oral and postingestional factors, is an important determinant of saline and water consumption by thirsty rats in a 2-bottle choice situation. The influence of need on fluid selection might result from a learned discrimination between the fluids based on differences in postingestional rehydration. © 1969.