Stimulation of drinking by bacterial endotoxins in the rat.

We investigated the effects of endotoxins on water balance, rectal temperature, and food intake in male Long-Evans rats with femoral venous catheters. Extracts of Escherichia coli or Salmonella minnesota, in doses ranging from 125 to 500 micrograms/kg IV, stimulated drinking and reduced urinary water loss for several hours. The net gain of 5 ml water 2 h after the lowest dose of E. coli endotoxin was sufficient to reduce plasma osmolality and sodium concentration 2 to 3%. Drinking occurred during the period of hypothermia that frequently precedes the onset of endotoxin-induced fever, so cannot be attributed to increased body temperature. Doses of endotoxin causing drinking inhibited both spontaneous and deprivation-induced feeding. The cause of the drinking is not known, but may involve mechanisms other than the known dehydrational signals controlling thirst.