Inhibition of thirst when dehydrated rats drink water or saline

The present experiments sought to identify the physiological signals that inhibit thirst when dehydrated rats drink water or NaCl solution. Rats were deprived of drinking fluid but not food overnight. When allowed to drink again, the dehydrated animals consumed water or saline (0.05 M, 0.10 M, 0.15 M, or 0.20 M NaCl solution) almost continuously for 5-8 min before stopping. The volumes consumed were similar regardless of which fluid they ingested, but blood analyses indicated that increased plasma osmolality and decreased plasma volume, or both, still remained when drinking terminated. These results suggest that the composition of the ingested fluid is less significant than its volume in providing an early signal that inhibits thirst and fluid consumption by dehydrated rats. Analyses of the gastrointestinal tracts revealed that the cumulative volume in the stomach and small intestine correlated highly with the amount consumed regardless of which fluid was ingested. These and other results suggest that the volume of fluid ingested by dehydrated rats is sensed by stretch receptors detecting distension of the stomach and small intestine, which provide an early inhibitory stimulus of thirst.