Control of thirst and salt appetite in rats: early inhibition of water and NaCl ingestion.

Most previous studies on the controls of thirst and salt appetite in rats have focused on systemic factors. Our recent experiments suggest that presystemic factors also are likely to play an important role. For example, dehydrated rats were found to consume similar volumes in an initial drinking bout when given access either to water or 0.05, 0.10, 0.15, or 0.20 M NaCl solution. Thus, cessation of the bouts evidently was not related to the concentration of fluid consumed but to its volume. It occurred despite the continued presence of known systemic stimuli for thirst (i.e. either increased plasma osmolality or decreased plasma volume), and therefore it resulted from inhibition rather than satiation. This inhibition appeared to derive from signals related to the cumulative volume of ingested fluid in the stomach and small intestine. Similar findings were obtained in studies of NaCl solution intake by NaCl-deprived adrenalectomized rats. These and other observations suggest that gastrointestinal fill generates stimuli that inhibit drinking in rats regardless of whether thirst or salt appetite motivates fluid consumption and regardless of whether rats consume water or NaCl solution.