Administration of a single dose of angiotensin II (AII) has been shown to induce a state of hyperhydration in rats that can last from 6-10 h depending upon the route of administration and the dose. The objective of the present study was to determine whether another dipsogenic agent, isoproterenol (ISO), a beta-adrenoceptor agonist, could also induce a state of hyperhydration. The results indicate that a single SC dose of ISO can induce a hyperhydration that lasts from 4-6 h depending upon the dose administered. Administration of graded doses of either AII or ISO induced graded increases both in the time of hyperhydration and change in accumulative mean fluid exchange, (DELTAFE, fluid exchange of treated less fluid exchange of control). These two parameters were related linearly and directly for each drug, although the slopes, but not the intercepts, of the relationship for each drug differed significantly. Because the objective of optimal hyperhydration should be to achieve the longest duration of positive fluid balance with the least amount of ingested fluid (i.e., DELTAFE), the slopes of the two lines provide a convenient way to compare the hyperhydration induced by AII and ISO. By this criterion, it would appear that AII provides a more optimal hyperhydration than ISO.
