Isoproterenol-induced thirst: renal and extrarenal mechanisms

Abstract

When given systemically, isoproterenol will induce water intake in various species. The drug also causes hypotension and renin release from the kidney. Angiotensin II and arterial baroreceptors have been hypothesized to be involved in the mediation of beta-adrenoceptor agonist-induced thirst, but their relative importance has been disputed. In the present series of experiments, isoproterenol was infused intravenously at different rates into nephrectomized and ureteric-ligated rats. Thus, different levels of hypotension could be achieved and maintained while water intake was measured. Also, plasma levels of angiotensin II were determined in ureteric-ligated rats following the intravenous infusion of a dipsogenic dose of isoproterenol. The results indicate that for moderate blood pressure changes a renal-related factor, probably angiotensin II, plays a major role in the mediation of isoproterenol-induced thirst. Under extreme conditions involving a very dramatic drop of arterial blood pressure, extrarenal mechanisms (e.g., arterial baroreceptors) are implicated.

Effects of β-adrenergic receptor agonists on drinking and arterial blood pressure in young and old rats

“…Middle-aged and old rats did not have pronounced surges in drinking after the drugs and had greatly reduced renin levels compared with young rats. A likely explanation for drinking after isoproterenol and salbutamol is that ␤ 2 -adrenoceptor activation by the drugs causes vasodilation and reductions in arterial pressure that stimulate drinking by releasing renal renin (17,21,23,26,31). Signals arising from arterial baroreceptors in response to hypotension are postulated to stimulate drinking after isoproterenol (16,31).…”

“…In conclusion, there are age-related differences in ␤-adrenergic receptor-mediated drinking that can be explained only in part by age-related differences in renin secretion after ␤-adrenergic receptor stimulation. aging; water intake; heart rate; renin activity; hematocrit; aldosterone ISOPROTERENOL IS A MIXED ␤ 1 , ␤ 2 -adrenergic receptor agonist that causes hypotension (6,16,21,31,35), tachycardia (6, 9, 21), renin secretion (21, 26), and water drinking (16, 17, 21, 31) upon administration. The ␤ 1 and ␤ 2 receptor subtypes contribute differently to the effects of isoproterenol.…”

“…Stimulation of vascular ␤ 2 -adrenergic receptors causes vasodilation and reductions in arterial pressure, which reflexively increase HR and renin secretion through baroreceptor mechanisms (21, 26). The water drinking response is a result of isoproterenol-induced hypotension and renin secretion (21,26,31).Several studies have used isoproterenol to examine agerelated declines in drinking by rats (24,25,34,35). However, the relative contributions of the ␤ 1 -and ␤ 2 -adrenergic receptor subtypes to age-related drinking have not been examined.…”

“…Stimulation of vascular ␤ 2 -adrenergic receptors causes vasodilation and reductions in arterial pressure, which reflexively increase HR and renin secretion through baroreceptor mechanisms (21, 26). The water drinking response is a result of isoproterenol-induced hypotension and renin secretion (21,26,31).…”

“…ISOPROTERENOL IS A MIXED ␤ 1 , ␤ 2 -adrenergic receptor agonist that causes hypotension (6,16,21,31,35), tachycardia (6,9,21), renin secretion (21,26), and water drinking (16,17,21,31) upon administration. The ␤ 1 and ␤ 2 receptor subtypes contribute differently to the effects of isoproterenol.…”