Extracehlar fluid volume and thirst’)’

STRICKER, EDWARD n/i. Extracellular @id volume and thirstAm. J. Physiol. 2 I I (I) : 232-238. 1966. -Rats which were hyperhydrated by loading the stomach with water, 5% of body wt, did not drink additional water, although osmoreceptor expansion in these animals was inferred to be comparable tO that observed following salt depletion by subcutaneous Formalin injection, which decreased plasma volume and elicited drinking. These results indicate that osmoreceptor expansion does not elicit thirst, and suggest that drinking may only accompany cellular hydration that is achieved at the expense of intravascular fluid volume. In another experiment, drinking was also elicited in rats given subcutaneous injections of polyethylene glycol, which significantly reduced plasma volume without changing intracellular fluid volume. This evidence shows that cellular volume changes are not necessary for the elicitation of drinking, and suggest the importance of decreased intravascular fluid volume. It thus seems likely that osmoreceptors are responsive only to an increased effective osmotic pressure of the extracellular fluid, and that volume receptors, responsive to decreased intravascular fluid volume, are also important in stimulating thirst.