title: Age-related declines in thirst and salt appetite responses in male Fischer 344×Brown Norway rats.
abstract: The F344×BN strain is the first generational cross between Fischer 344 (F344) and Brown Norway (BN) rats. The F344×BN strain is widely used in aging studies as it is regarded as a model of "healthy" aging (Sprott, 1991). In the present work, male F344×BN rats aged 4mo (young, n=6) and 20mo (old, n=9) received a series of experimental challenges to body fluid homeostasis to determine their thirst and salt appetite responses. Corresponding urinary responses were measured in some of the studies. Following sodium depletion, old rats ingested less saline solution (0.3M NaCl) than young rats on a body weight basis, but both ages drank enough saline solution to completely repair the accrued sodium deficits. Following intracellular dehydration, old rats drank less water than young rats, again on a body weight basis, and were less able than young rats to drink amounts of water proportionate to the osmotic challenge. Compared with young rats, old rats drank less of both water and saline solution after combined food and fluid restriction, and also were refractory to the stimulatory effects of low doses of captopril on water drinking and sodium ingestion. Age differences in urinary water and sodium excretion could not account for the age differences in accumulated water and sodium balances. These results extend observations of diminished behavioral responses of aging animals to the F344×BN rat strain and support the idea that impairments in behavior contribute more to the waning ability of aging animals to respond to body fluid challenges than do declines in kidney function. In addition, the results suggest that behavioral defense of sodium homeostasis is less diminished with age in the F344×BN strain compared to other strains so far studied.
authors: Department of Psychology, University of Iowa, Iowa City, IA 52242-1407, United States; The Cardiovascular Center, University of Iowa, Iowa City, IA 52242-1407, United States. Electronic address: robert-thunhorst@uiowa.edu.
authors: Robert L
authors: RL
authors: Thunhorst
authors: Department of Psychology, University of Iowa, Iowa City, IA 52242-1407, United States.
authors: Terry
authors: T
authors: Beltz
authors: Department of Psychology, University of Iowa, Iowa City, IA 52242-1407, United States; Department of Health and Human Physiology, University of Iowa, Iowa City, IA 52242-1407, United States; Department of Pharmacology, University of Iowa, Iowa City, IA 52242-1407, United States; The Cardiovascular Center, University of Iowa, Iowa City, IA 52242-1407, United States.
authors: Alan Kim
authors: AK
authors: Johnson
mesh_terms: D000367:Age Factors; D000375:Aging / Q000502:physiology*; D000818:Animals; D001066:Appetite / Q000502:physiology*; D003681:Dehydration / Q000503:physiopathology; D005508:Food Deprivation / Q000502:physiology; D008297:Male; D051381:Rats; D011914:Rats, Inbred BN; D011916:Rats, Inbred F344; D012982:Sodium, Dietary; D013894:Thirst / Q000502:physiology*
chemical_list: D012982:Sodium, Dietary
keywords: Aging; Dehydration; Diuresis; Hypovolemia; Natriuresis