The effect of preloads of water and sodium chloride on voluntary water intake of thirsty rats.

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Abstract
The use of predrink stomach-loading techniques makes possible exptl. manipulation and relative isolation of a number of the component circumstances of water ingestion in the dehydrated rat. When varying volumes of water are preloaded and the animal is allowed a 0.5 hr. free drinking period after a 15-min. delay, drinking is affected in the following ways (1) voluntary intake is decreased in approx. direct proportion to the volume of the preload; (2) when the no-preload voluntary intake is used as a reference point, the total intake (preload plus voluntary intake) increases as a direct function of the preload volume. When fixed-volume preloads varying in NaCl concn. through the hypotonic and slightly hypertonic range are placed in the rat''s stomach and it is allowed to drink tap water after a 15-min. delay, the following conclusions appear: (1) hypotonic solns. of 0.5-0.75% increase water intake significantly above that following preloading of the same volume of water or 0.25% solns. of NaCl; (2) hypertonic solns. of 1-3% produce an even greater increase in subsequent voluntary water ingestion. When thirsty rats are given NaCl solns. of varying concns., their drink-ing is affected as follows: (1) any concn. of NaCl from 0.25 to 1.00% produces an increase in fluid ingestion over tap water; (2) no significantly different intakes were noted for concns. within the range from 0.50 to 1.00%, all of which were ingested in significantly greater quantities than were 0.25% solns. or tap water.

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