Examining the effects of lipopolysaccharide and cholecystokinin on water ingestion: comparing intake and palatability.

Lipopolysaccharide (LPS) and cholecystokinin (CCK) have been shown to have anorectic properties in a variety of species. The present study examined the effects of LPS and CCK, both alone and in combination, on two different aspects of water ingestion, water intake and palatability. On test days, animals were first injected intraperitoneally (i.p.) with either LPS (200 microg/kg) or NaCl vehicle, and 2 h later received a second injection of either CCK (8 microg/kg) or NaCl vehicle. In Experiment 1, water intake was monitored for 1 h on 3 separate test days 72 h apart; while in Experiment 2, water palatability was assessed using the taste reactivity test (TRT), on two separate test days 72 h apart. Both LPS and CCK significantly (p<0.05) reduced water intake, with the effects of combined LPS with CCK being more pronounced than either agent injected alone. Rats developed a rapid tolerance to the effects of LPS on water intake on subsequent exposures to LPS. Results from the TRT indicated that LPS enhanced water palatability (p<0.05), as evidenced by a high level of ingestive responding, whereas CCK produced a pattern of responding indicative of satiety. LPS plus CCK reduced ingestive responding on the first test day, but these responses were significantly increased on the second test day (p<0.05). These results demonstrate that although LPS reduces water intake, it enhances water palatability. The results further underscore the necessity for examining palatability changes in addition to intake measures when studying the regulation of feeding and drinking.