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Am J Physiol Regul Integr Comp Physiol 297: R149-R157, 2009. First published May 6, 2009; doi:10.1152/ajpregu.00118.2009
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ARTICLES

Hypotension- and osmotically induced thirst in old Brown Norway rats

Robert L. Thunhorst,1,4 Terry G. Beltz,1 and Alan Kim Johnson1,2,3,4

Departments of 1Psychology, 2Integrative Physiology and 3Pharmacology, and the 4Cardiovascular Center, University of Iowa, Iowa City, Iowa

Submitted 20 February 2009 ; accepted in final form 5 May 2009

Compared to young cohorts, old rats drink less water in response to several thirst-inducing stimuli. In these experiments, we characterized water drinking in response to hypotension and cellular dehydration in young (4 mo), middle-aged adult (12 mo) and old (29–30 mo) male Brown Norway rats. We injected the vasodilator, minoxidil as an intravenous bolus in a range of doses (0–20 mg/kg), so that drinking responses could be compared at equivalent reductions of arterial pressure. Old rats had greatly diminished reflex tachycardia and became significantly more hypotensive after minoxidil compared with young and middle-aged rats. When compared at equivalent reductions of arterial pressure, old rats drank one-third as much as middle-aged rats, and one-fifth as much as young rats. In addition, there were age-related deficits in drinking in response to a range of administered loads of sodium (0.15–2 M NaCl, 2 ml/100 g body wt). Urinary excretion of water and sodium in response to the loads was equivalent across ages. Both middle-aged and old rats were less able than young rats to repair their water deficits after sodium loading, attributable almost entirely to their reduced drinking responses compared with young rats. Lastly, age-related declines in drinking appeared to be more severe in response to hypotension than in response to cellular dehydration.

aging; drinking; diuresis; natriuresis; dehydration; blood pressure; heart rate


Address for reprint requests and other correspondence: R. L. Thunhorst, Dept. of Psychology, Univ. of Iowa, 11 Seashore Hall E., Iowa City, IA 52242-1407 (e-mail: robert-thunhorst{at}uiowa.edu)






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