Maximum Sodium Chloride Intake and Thirst in Domesticated and Wild Norway Rats

Abstract

Rats are able to handle very large amts. of salt, 15-20 g./kg. body wt./day, provided they are permitted to ingest sufficiently large amts. of water. Domesticated rats need 50-60 cc. of water/g. of salt ingested to maintain health. No such statement can be made for wild rats since other functions apparently influence their water intake. The ingestion of large amts. of salt over 2-3 mos. time did not produce any visible dietary deficiencies, nor did it produce any detectable pathological changes in the kidneys. When given access to water, rats will freely eat diets containing as much as 35% salt; they will eat fair amts. of a diet containing 50-70% salt. Salt does not produce as much thirst in domesticated Norway rats as in their wild ancestors. A greater secretion of a salt-conserving hormone from the larger and more active adrenals of the latter may account for this difference. On the basis of the results of these expts. it was suggested that difficulties encountered by man in using salt may result from his failure, for cultural and social reasons, to drink adequate amts. of water for excreting the excess of salt ingested.